Extraocular muscles and their disorders. Eye muscles - structure and functions How the eye muscles work
7-06-2012, 14:35
Description
The muscular apparatus of the eye is represented by 6 muscles: four straight lines - upper, lower, medial, lateral and two oblique - upper and lower. The origin of all of the listed extraocular muscles, except for the inferior oblique, is the apex of the orbit, where the muscles fuse to form a dense tendon ring located around the optic foramen and the medial part of the superior orbital fissure. All rectus muscles in the form of flat wide ribbons are directed anteriorly, to the place of their attachment. Gradually diverging, all four rectus oculi muscles form the so-called muscular funnel. The concept of the muscular funnel plays an important role in the topography of the orbit and in the differential diagnosis of pathological processes in the orbit, especially tumors, which give different symptoms and a different prognosis depending on the location inside or outside the funnel (Figure 2).
Figure 2.
Location of the external eye muscles in the orbit. Muscle funnel. The optic nerve passes between the diverging muscles along the axis of the muscular funnel. 1 - tendon ring of Zinn (annulus tendineus communis Zinnii); 2 - m. obliquus superior; 3 - the place of its passage through the block; 4 - m. rectus superior; 5 - m. obliquus inferior; 6 - m. rectus lateralis; 7 - m. rectus inferior; 8 - m. rectus medialis (no Beninghoff, 1957).
By perforating Tenon's capsule at the level of the equator of the eye, the muscles are attached to the eyeball by wide tendons that intertwine into the sclera.
Superior oblique muscle begins, just like the rectus muscles of the eye, in the depths of the orbit, but outside the ring of Zinn, in the immediate vicinity of it, and is directed along the superomedial wall of the orbit, to the spina trochlearis. The muscle looks like a round cord. Passing through the block, it sharply narrows, upon exiting the block it thickens again and turns posteriorly outward. Passing between the eyeball and the superior rectus muscle, it is attached behind the equator in the superior outer quadrant.
Inferior oblique muscle originates separately from all other muscles, from the inner bony wall of the orbit, goes downward outward, encircling the eyeball between the lower wall of the orbit and the inferior rectus muscle, rises upward and attaches to the sclera behind the equator in the same outer quadrant as the upper one.
According to their function, the muscles of the eyeball are divided into three pairs of antagonists acting in directly opposite directions:
- medial and lateral rectus- turn the eye inward and outward;
- upper and lower straight- raise and lower the eyeball;
- oblique muscles- impart rotational movements to the eye.
However Only the external and internal rectus muscles are pure antagonists, they rotate the eye in a horizontal plane, regardless of the initial position of the eyeball. The remaining muscles act as pure antagonists only in the abduction position, when the orbital axis and the anatomical axis of the eye coincide. In the direct direction of gaze, when the anatomical axis of the orbit and the axis of the eye are at an angle of 25 - 27 degrees, muscle actions are more complex:
- inferior rectus muscle lowers the eyeball downwards, brings it in, tilts its vertical meridian outward.
- superior rectus muscle lifts the eyeball upward, brings it in, tilts the vertical axis of the eye inward.
- inferior oblique muscle raises the eye upward, moves it away, tilts the vertical meridian outward.
- superior oblique muscle lowers the eyeball downwards, retracts it, tilts the vertical axis of the eye inwards.
In addition, the tone of the rectus oculi muscles tends to pull the eyeball posteriorly, and the two oblique muscles anteriorly.
Thus, the entire muscular system of the eye is in a very finely regulated equilibrium.
Upper and lower eyelids protect the eyeball from the front and due to their blinking movements, which promote the uniform distribution of tears, they protect it from drying out.
The eyelids regulate the amount of light entering the eyes. Reflex closure of the eyelids occurs in response to the influence of mechanical, visual or
sound stimuli. The reflex upward movement of the eye (Bell's phenomenon) when closing the eyelids protects the cornea from foreign bodies and drying out of the cornea during sleep.
The edges of the eyelids form palpebral fissure(rima palpebrarum). (Figure 3).
Figure 3. The structure of the eyelids.
Sagittal section through both eyelids, conjunctival sac and anterior eyeball.
1 - supreorbital edge of the frontal bone; 2 - orbital fat; 3 - levator musculus palpebrae superior; bundles of its tendon fibers penetrate from the left through the circular muscle of the eyelids into the skin; 4 - tendon m. rectus superior. Eyeball: 5- sclera; 6 - conjunctiva of the superior fornix - superior transitional fold; 7 - cornea; 8 - conjunctiva of the lower fornix; 9 - tendon m. rectus inferior; 10 - section of the inferior oblique muscle; 11 - lower orbital edge of the upper jaw bone; 12 - orbital fat; 13 - tarsoorbital fascia - septum orbitale; 14 - cartilage of the lower eyelid; 15 - conjunctiva of the cartilage of the lower eyelid; 16 - conjunctiva of the cartilage of the upper eyelid; 17 - cartilage of the upper eyelid; 18 - m. orbicularis palpebrarum (according to M. L. Krasnov, 1952).
The border of the upper eyelid runs along the eyebrow, the lower eyelid along the lower edge of the orbit. Both eyelids are connected at the corners of the palpebral fissure by the internal and external ligaments (l.palpebrale mediale et laterale). The width and shape of the palpebral fissure varies normally: its horizontal length in an adult is 30 mm, its height ranges from 10 to 14 mm, the edge of the lower eyelid does not reach the limbus by 0.5-1 mm, the edge of the upper eyelid covers the limbus by 2 mm. The outer edge of the palpebral fissure is sharp, the inner edge is blunted in the form of a horseshoe bend. The latter limits the space called the lacrimal lake, in which there are the lacrimal caruncle (caruncula lacrimalis) - a small pink tubercle, which has the structure of the skin with sebaceous and sweat glands, and the semilunar fold (plica semilunaris) of thickened mucous membrane, which are the rudiments of the third eyelid. The free edges of the eyelids, about 2 mm thick, fit tightly to each other. They distinguish between anterior, posterior ribs and intermarginal space. On the anterior, more rounded rib, eyelashes grow (75-150 pcs.), into the bulbs of which the excretory ducts of the sebaceous glands of Zeiss open. Between the eyelashes there are modified Moll's sweat glands. The excretory ducts of the meibomian glands open into the intermarginal space, the fatty secretion of which lubricates the edges of the eyelids, helping to seal them. At the inner corner of the eye, i.e. near the tear lake, the intermarginal space narrows and turns into lacrimal papillae(papilli lacrimales). At the top of each of them there is a lacrimal punctum - an opening leading into the lacrimal canaliculus. The diameter of the lacrimal opening with open eyelids is 0.25 - 0.5 mm. The eyelids consist of 2 plates: the outer plate is formed by skin with muscles, the inner one - by cartilage (tarsus) and the cartilage conjunctiva tightly fused with it.
The skin of the eyelids is very thin, tender, poor in fatty tissue, loosely connected to the underlying tissues. On the skin surface of the upper eyelid there is a deep orbital-palpebral upper fold, on the lower - orbitopalpebral lower fold. The first is located just below the superior orbital margin and is caused by the tone of the anterior leg of the levator muscle attached to the posterior surface of the skin. The thinness and easy displacement of the skin of the eyelids relative to the underlying tissues are good conditions for performing plastic surgery. But in this regard, the skin easily swells with local inflammation, venous stasis, a number of general diseases, hemorrhages and subcutaneous emphysema.
Eyelid mobility is ensured by two groups of antagonistic muscles: orbicularis oculi muscle and levator veli to (m. levator palpebrae superior and m. tarsalis inferior).
Circular muscle of the eyelid- m.orbicularis oculi, s. palpebrarum, in which the palpebral, orbital and lacrimal parts are distinguished. The orbicularis muscle is involved in lowering the upper eyelid and closing the palpebral fissure. The palpebral part is located within the eyelids themselves and does not extend beyond their edges. The muscle fibers of both the upper and lower eyelids are woven into a dense medial ligament. Having described a semicircle along each eyelid, they are temporally attached to the external commissure (lateral ligament) of the eyelids. Thus, two crescents on each eyelid. When the palpebral part contracts, blinking and slight closing of the eyelids occurs, as in a dream. The muscle fibers running along the edge of the eyelids between the roots of the eyelashes and the excretory ducts of the meibomian glands constitute the ciliary muscle, or Riolan muscle (m.ciliaris Riolani), the contraction of which promotes the secretion of the meibomian glands, as well as the tight fit of the edges of the eyelids to the eyeball. Orbital part: fibers start from the medial ligament and from the frontal segment of the maxilla and pass along the periphery of the palpebral part of the orbicularis muscle. The muscle has view of a wide layer extending beyond the edges of the orbit and connects to the facial muscles. Having described a full circle, the muscle is attached near its origin. When this muscle contracts, together with the contraction of the palpebral part, the eyelids are tightly closed.
Lacrimal part of the orbicularis oculi muscle(Horner's muscle) is represented by a deep portion of muscle fibers that begin somewhat posterior to the posterior crest of the lacrimal bone (crista lacrimalis posterior os lacrimale). They then pass behind the lacrimal sac and become woven into the palpebral fibers of the orbicularis muscle, coming from the anterior lacrimal crest. As a result, the lacrimal sac is surrounded by a muscle loop, which, when contracting and relaxing during blinking movements, either expands or narrows the lumen of the lacrimal sac. The absorption and movement of tear fluid along the lacrimal ducts is also facilitated by the contraction of those bundles of lacrimal muscle that cover the lacrimal canaliculi.
Participates in raising the upper eyelid and opening the palpebral fissure striated- m.levator palpebrae superior and smooth muscle- superior and inferior tarsal or Müller muscles. In the lower eyelid there is no muscle similar to the levator. The function of raising the lower eyelid is carried out by a weakly expressed muscle (m. tarsalis inferior) and the inferior rectus muscle of the eye, which gives an additional tendon to the thickness of the lower eyelid.
M. levator palpebrae superior - begins in the depths of the orbit, where at the apex it departs from the tendon ring (annulus tendineus communis) together with the rectus muscles of the eyeball, is directed under the roof of the orbit anteriorly and at the level of the supraorbital edge passes into a wide tendon, which diverge fan-shaped and divide into three departments. The anterior part of the tendon in the form of thin bundles of fibers passes through the tarso-orbital fascia and orbicularis muscle, diverges in a fan-shaped manner and merges with the subepithelial layer of the skin of the eyelids. Rear portion penetrates into the upper fornix of the conjunctiva and attaches here. Medium - the most powerful(Müller's muscle) is attached along the upper edge of the cartilage along its entire continuation. In its structure, the Müller muscle is reticulate, only part of its muscle bundles approach perpendicular to the edge of the cartilage, penetrating between the levator fibers and accompanying them in places to the upper edge of the cartilage. In this case, the levator tendon is separated by smooth muscle fibers. The other part of the fibers approaches in an oblique direction. The third forms a well-defined transverse beam, intertwined with the levator aponeurosis. Such contact with the levator aponeurosis provides not only elevation, but also prevents wrinkling of the eyelid. The lateral branches of the levator tendon fix it to the periorbita. Contraction of the muscle leads to upward simultaneous lifting of the skin, tarsal plate and conjunctival fornix. The main muscle is the muscle that lifts the upper eyelid, the auxiliary muscle underlying it is the Müller muscle, and when looking up - the frontal and superior rectus. The Müller muscle is innervated by the sympathetic nerve, and the remaining two portions are innervated by the third pair (oculomotor nerve).
When the palpebral part of the orbicularis oculi muscle contracts blinking and slight squeezing of the eyelids is carried out. Electromyographically it has been established that during voluntary blinking movements the muscle, The levator palpebrae superioris and orbicularis muscles act reciprocally: the activity of one is accompanied by the passivity of the other. If the upper eyelid slowly droops, not only does the activity of the levator muscle decrease, but the antagonist (orbicularis muscle) also remains passive. However, the general mechanism of eyelid closure is more complex due to the combined connection of the orbicular muscle with the facial muscles on the one hand and the epidermis of the facial skin on the other. As a result of these connections, when closed, the eyelids move not only up and down, but also in the horizontal direction - inward, especially the lower one, which plays an important role in the movement of tear fluid. When the eyelids close, the palpebral fissure is shortened by 2 mm. In addition, the leading role in the lacrimal drainage mechanism belongs to the deep part of the palpebral portion of the orbicularis muscle.
Eyelid ligaments
Medial and lateral ligaments serve as the main apparatus that attaches various elements of the eyelid to the bony wall of the orbit: the edges of the eyelids themselves, the orbicularis oculi muscle, the edges of the cartilages and the tarso-orbital fascia. The medial ligament has two legs: front and back. The first, in the form of a powerful collagen cord formed by the tendon of the orbicularis muscle and merging with it by collagen fibers of the medial sections of the cartilage and orbicular fascia, runs horizontally in front of the lacrimal sac from the inner corner of the eyelids to the anterior lacrimal ridge (upper jaw). The cord can be easily palpated and becomes visible when the conjunctiva is pulled downwards, due to tension in the internal ligament. His back leg branches off slightly from the corner of the eyelids in the form of a tendon, bends around the lacrimal sac from the outside and behind and attaches to the posterior lacrimal crest of the lacrimal bone. Thus, the medial ligament covers the lacrimal sac both anteriorly and posteriorly. The lateral ligament of the eyelids, compared to the internal one, is poorly developed and is only a suture with a tendon bridge between the outer parts of the circular muscle of the upper and lower eyelids. The ligament is reinforced by the collagen fibers woven into it from the outer ends of the cartilages and the tarso-orbital fascia. It also runs horizontally from the outer corner of the eyelids to the bony tubercle of the zygomatic bone - tuberculum orbitae, where it is attached 2-3 mm from the edge of the orbit.
Cartilage of the century
It is a semilunar-shaped plate with pointed edges (when performing incision in the intermarginal space, it easily separates into 2 plates). The collagen tissue that forms this plate with an admixture of elastic fibers is distinguished by its special cartilaginous density. Therefore, the name cartilage has taken root, although histologically there are no elements of cartilage here. The pointed ends of the cartilage are firmly connected to each other by an interweaving of collagen fibers. Collagen fibers running from the edges of the cartilage to the medial and lateral ligaments of the eyelids fix the cartilage to the bony walls of the orbit. The density of cartilage determines its protective “skeletal” function. Cartilage follows the convex shape of the eyeball. The length of the cartilage of the upper eyelid is 2 cm, height 1 cm, thickness 1 mm, the cartilage of the lower eyelid is smaller, its height is 5 mm. The anterior surface is bordered by loose connective tissue, the posterior surface is closely connected with the conjunctiva.
The thickness of the cartilage contains modified sebaceous glands - Meibomian(on the upper eyelid - 27-30, on the lower - about 20). They have an alveolar structure and secrete fatty secretions. The very short ducts of the alveoli flow into the long common excretory duct. The glands are parallel to each other and perpendicular to the free edge of the eyelids, occupying the entire height of the cartilage. The openings of the ducts open in front of the posterior edge of the eyelid in the form of pores. The secretion of the meibomian glands serves as a fatty lubricant, protects the edges of the eyelids from maceration, and prevents tears from overflowing over the edge of the eyelids, promoting its proper outflow.
Thus, cartilage is, as it were, direct continuation of the tarsoorbital fascia, firmly connected to the orbital edge. This septum (septum orbitae) completely separates the contents of the orbit from the tissues of the eyelids, preventing the spread of pathological processes deeper. The back surface of the eyelids is covered with the conjunctiva, which is tightly fused with the cartilage, and beyond it forms a mobile arch. Deep upper and shallower and easily accessible lower arch.
The conjunctiva is a thin, transparent mucous tissue, which in the form of a thin shell covers the entire back surface of the eyelids (tunica conjunctiva palpebrarum), forms deep vaults (fornix conjunctivae superior et inferior) and passes to the eyeball (tunica conjunctiva bulbi) ending at the limbus. In the conjunctiva of the eyelids, in turn, there is a tarsal part - tightly fused with the underlying tissue, and a mobile - orbital part, in the form of a fold transitional to the arches.
Conjunctival cartilage covered with a two-layer cylindrical epithelium and contains goblet cells at the edge of the eyelids, and the crypts of Henle at the distal end of the cartilage. Both of them secrete mucin. Under the epithelium there is reticular tissue tightly fused with cartilage. The mucous membrane at the free edge of the eyelids is smooth, but already 2-3 mm from it a roughness appears, due to the presence of papillae here.
Conjunctiva transitional fold smooth and covered with 5-6 layer transitional epithelium, also with a large number of goblet cells secreting mucin. Under the epithelium is loose connective tissue consisting of elastic fibers and containing plasma cells and lymphocytes. The conjunctiva here easily moves and forms folds that facilitate free movements of the eyeball.
On the border between the tarsal and orbital parts in the conjunctiva there are accessory lacrimal glands s, similar in structure and function to the main lacrimal gland: Wolfring - 3 at the upper edge of the upper cartilage and one more below the lower cartilage, and in the area of the vaults - Krause. The number of the latter reaches 6-8 on the lower eyelid and from 15 to 40 on the upper. The blood circulation of the eyelids is carried out by two systems: the system of the internal carotid artery (branch of a.ophthalmica). a.supraorbitalis, a.lacrimalis and the system of the external carotid artery (anastomoses a.facialis and a.maxillaris, a.temporales superfacialis).
From the nasal side, they penetrate into the thickness of both eyelids from the depths of the orbit. medial palpebral arteries of the eyelid- upper and lower (a. palpebralis mediales superiores et inferiores) - terminal branches of a.supraorbitalis. The a.palpebralis lateralis extends from the lateral side of the a.lacrimalis. In the loose connective tissue layer between the musculocutaneous and tarsal-conjunctival plates of the eyelid, these medial and lateral branches of the palpebral arteries are directed towards each other, merge and form transversely located arterial arches: upper and lower (arcus tarseus sup. et inf., or arcus subtarsalis sup.et inf.). Both arterial arches run along the edges of the eyelid, the upper one is 1-2 mm from the edge of the eyelid, the lower one is 1-3 mm. At the level of the upper edge of the cartilage, a second peripheral arc or arcus tarseus sup is formed. It is not always pronounced on the lower eyelid. Between the peripheral and subtarsal arches there are vertical anastomoses with the arteries of the face. The vascularization of the lower eyelid and the surrounding area also involves branches of the infraorbital artery, arising from the maxillary artery (from the external carotid artery system). These arches nourish all the tissues of the eyelids. The veins of the eyelid follow the arteries, forming two networks: superficial and deep. There are significantly more anastomoses - with the veins of the face and the veins of the orbit. Because there are no valves in the veins, blood flows both into the venous network of the face and orbit and through the v.ophthalmica. superior, shedding blood into the cavernous sinus (hence, there is a high probability of infection entering the cranial cavity). On their way into the orbit, the veins that drain blood from the eyelid area also penetrate the orbital muscle. Its spasm in diseases of the eyeball (scrofulosis) can lead to swelling of the eyelids.
The most important anastomoses of the venous network of the eyelids- with the lacrimal vein (v.lacrimalis) and with the superficial temporal vein (v.temporalis superfacialis). Of particular importance are anastomoses with v. angularis, passing from the inner corner of the palpebral fissure and anastomosing with v. ophthalmica superior.
Lymphatic system- a network of widely branched lymphatic vessels in both the deep and subtarsal layers. Both networks anastomose widely with each other. The regional lymph node draining lymph from the upper eyelid is the preauricular one, and from the lower eyelid area is the submandibular one.
Innervation of the eyelids
The third and seventh pairs of cranial nerves take part in the motor innervation of the eyelids.
Orbicularis oculi muscle- a branch of the facial nerve (VII pair), its motor fibers ensure the closure of the eyelids. The facial nerve has a mixed composition: includes motor, sensory and secretory fibers that belong to the intermediate nerve, closely connected with the facial nerve. The motor nucleus of the nerve is located in the lower part of the pons at the bottom of the IV ventricle, bending around the nucleus of the abducens nerve localized above, forms a knee (genu n. facialis) and exits to the base of the brain in the cerebellopontine angle. Then, through the internal auditory opening, it enters the canalis facialis, in which it makes two turns to form the genu and the genu ganglion (geniculum et ganglium gen.). From the ganglion node, the great petrosal nerve (n. petrosus major) originates, carrying secretory fibers to the lacrimal gland, extending from a special lacrimal nucleus, and the facial nerve itself leaves the canal through the foramen stilomastoideum, giving off branches n at this level. auricularis posterior et r. digastricus. Then, with a single trunk, it penetrates the parotid gland and is divided into superior and inferior branches, which give off multiple branches, including to the orbicularis oculi muscle. The muscle that lifts the upper eyelid is innervated by the oculomotor nerve (III pair), only its middle part, i.e. Müller's muscle - sympathetic nerve.
Nucleus of the oculomotor nerve located at the bottom of the Sylvian aqueduct. The oculomotor nerve leaves the skull through the superior orbital fissure, joining sympathetic (from the plexus of the internal carotid artery) and sensory fibers (from the n.ophthalmicus), passes through the cavernous sinus. In the orbit, within the muscular funnel, it is divided into superior and inferior branches. The upper, thinner branch, passing between the superior rectus muscle and the levator palpebral muscle, innervates them.
Sensory nerves to the upper eyelid and skin of the forehead come from the orbital nerve (n.ophthalmicus) of the 1st branch of the trigeminal nerve, which exits through the superior orbital fissure and is divided into three main branches: n.lacrimalis, n.frontalis et n.nasociliaris. The n.frontalis plays a major role in the innervation of the skin of the eyelids., in the medial region of the upper eyelid, its branches n.supraorbitalis et n.supratrochlearis extend under the skin. The orbital nerve supplies sensitive innervation to the skin of the forehead, the anterior surface of the scalp, the upper eyelid, the inner corner of the eye, the back of the nose, the eyeball itself, the mucous membranes of the upper part of the nasal cavity, the frontal and ethmoid sinuses, and the meninges. The lower eyelid receives sensitive innervation from n.infraorbitalis, extending from the 2nd branch of the trigeminal nerve (n.maxillaris). Maxillary nerve exits the cranial cavity through the round foramen and innervates the dura mater, skin, cartilage and conjunctiva of the lower eyelid (except for the innermost and outer corners of the palpebral fissure), the lower half of the lacrimal sac and the upper half of the nasolacrimal duct, the skin of the anterior part of the temporal region, the upper part of the cheek , wings of the nose, as well as the upper lip, the upper jaw (and the teeth on it), the mucous membranes of the back of the nasal cavity and the maxillary sinus.
Article from the book:
The eye must learn to see, just as the tongue learns to speak.
D. Diderot
The oculomotor apparatus is a complex sensorimotor mechanism, the physiological significance of which is determined by its two main functions: motor (motor) and sensory (sensitive).
The motor function of the oculomotor system ensures the guidance of both eyes, their visual axes and the central fossae of the retinas to the object of fixation; the sensory function ensures the merging of two monocular (right and left) images into a single visual image.
The innervation of the extraocular muscles by the cranial nerves determines the close connection between neurological and ocular pathologies, as a result of which an integrated approach to diagnosis is necessary.
18.1. Anatomical and physiological features
Movements of the eyeball are carried out with the help of six extraocular muscles: four straight muscles - external and internal (m. rectus externum, m. rectus internum), upper and lower (m. rectus superior, m. rectus inferior) and two obliques - upper and lower ( m. obliguus superior, m. obliguus inferior).
All straight And superior oblique muscle begin at the tendon ring located around the optic nerve canal at the apex of the orbit and fused with its periosteum (Fig. 18.1). The rectus muscles in the form of ribbons are directed anteriorly to the parallel
along the corresponding walls of the orbit, forming the so-called muscular funnel. At the equator of the eye, they pierce Tenon’s capsule (the vagina of the eyeball) and, before reaching the limbus, they are woven into the superficial layers of the sclera. Tenon's capsule supplies the muscles with a fascial covering that is missing in the proximal region where the muscles begin.
Superior oblique muscle originates from the tendon ring between the superior and internal rectus muscles and goes anteriorly to the cartilaginous block located in the superior internal corner of the orbit at its edge. At the pulley, the muscle turns into a tendon and, passing through the pulley, turns posteriorly and outward. Located under the top line
Rice. 18.1. Muscles of the eye [Broshevsky T.I., Bochkareva A.A., 1983].
muscle, it is attached to the sclera outward from the vertical meridian of the eye. Two-thirds of the entire length of the superior oblique muscle is between the apex of the orbit and the trochlea, and one-third is between the trochlea and its attachment to the eyeball. This part of the superior oblique muscle determines the direction of movement of the eyeball during its contraction.
Unlike the five muscles mentioned inferior oblique muscle begins at the lower inner edge of the orbit (in the area of the entrance of the nasolacrimal canal), goes posteriorly outward between the orbital wall and the inferior rectus muscle towards the external rectus muscle and is fan-shaped attached under it to the sclera in the posteroexternal part of the eyeball, at the level of the horizontal meridian of the eye.
Numerous cords extend from the fascial membrane of the extraocular muscles and Tenon’s capsule to the orbital walls.
The fascial-muscular apparatus ensures a fixed position of the eyeball and gives smoothness to its movements.
The muscles of the eye are innervated by three cranial nerves:
Oculomotor nerve - n. oculomotorius (III pair) - innervates the internal, superior and inferior rectus muscles, as well as the inferior oblique;
Trochlear nerve - n. trochlearis (IV pair) - superior oblique muscle;
Abducens nerve - n. abducens (VI pair) - external rectus muscle.
All these nerves pass into the orbit through the superior orbital fissure.
The oculomotor nerve, after entering the orbit, divides into two branches. The superior branch innervates the superior rectus muscle and the levator palpebrae superioris, the inferior branch innervates the internal and inferior rectus muscles, as well as the inferior oblique.
The nucleus of the oculomotor nerve and the nucleus of the trochlear nerve located behind and next to it (provides the work of the oblique muscles) are located at the bottom of the aqueduct of Sylvius (aqueduct of the brain). The nucleus of the abducens nerve (provides the work of the external rectus muscle) is located in the pons under the bottom of the rhomboid fossa.
The rectus oculomotor muscles are attached to the sclera at a distance of 5-7 mm from the limbus, the oblique muscles - at a distance of 16-19 mm.
The width of the tendons at the muscle attachment site ranges from 6-7 to 8-10 mm. Of the rectus muscles, the widest tendon is the internal rectus muscle, which plays a major role in the function of bringing together the visual axes (convergence).
The line of attachment of the tendons of the internal and external muscles, i.e., their muscular plane, coincides with the plane of the horizontal meridian of the eye and is concentric with the limbus. This causes horizontal eye movements, their casting, turn to the nose - adduction with contraction of the internal rectus muscle and lead, turn to temple - abduction with contraction of the external rectus muscle. Thus, these muscles are antagonistic in nature.
The superior and inferior rectus and oblique muscles perform mainly vertical movements of the eye. The line of attachment of the superior and inferior rectus muscles is located somewhat obliquely, their temporal end is further from the limbus than the nasal end. As a result, the muscular plane of these muscles does not coincide with the plane of the vertical meridian of the eye and forms an angle with it, equal to an average of 20 o and open to the temple.
This attachment ensures rotation of the eyeball during the action of these muscles not only upward (with contraction of the superior rectus
muscles) or downward (with contraction of the inferior straight line), but simultaneously inwardly, i.e. adduction.
The oblique muscles form an angle of about 60° with the plane of the vertical meridian, open to the nose. This determines the complex mechanism of their action: the superior oblique muscle lowers the eye and produces its abduction (abduction), the inferior oblique muscle is an elevator and also an abductor.
In addition to horizontal and vertical movements, these four vertically acting oculomotor muscles perform torsional eye movements clockwise or counterclockwise. In this case, the upper end of the vertical meridian of the eye deviates towards the nose (intrusion) or towards the temple (extortion).
Thus, the extraocular muscles provide the following eye movements:
Adduction (adduction), i.e. its movement towards the nose; this function is performed by the internal rectus muscle, additionally by the superior and inferior rectus muscles; they are called adductors;
Abduction (abduction), i.e. movement of the eye towards the temple; this function is performed by the external rectus muscle, additionally by the superior and inferior oblique muscles; they are called abductors;
Upward movement - under the action of the superior rectus and inferior oblique muscles; they are called lifters;
Downward movement - under the action of the inferior rectus and superior oblique muscles; they are called lowerers.
The complex interactions of the oculomotor muscles are manifested in the fact that when moving in some directions they act as synergists (for example, partial adductors - the superior and inferior rectus muscles, in others - as antagonists).
nists (upper straight line - lifter, lower straight line - lowerer).
The extraocular muscles provide two types of conjugal movements of both eyes:
Unilateral movements (in the same direction - right, left, up, down) - so-called version movements;
Opposite movements (in different directions) are vergent, for example, to the nose - convergence (bringing together the visual axes) or to the temple - divergence (spreading the visual axes), when one eye turns to the right, the other to the left.
Vergence and version movements can also be performed in the vertical and oblique directions.
The functions of the oculomotor muscles described above characterize the motor activity of the oculomotor apparatus, while the sensory one is manifested in the function of binocular vision.
Binocular vision, i.e. vision with two eyes, when an object is perceived as a single image, is possible only with clear conjugal movements of the eyeballs. The eye muscles ensure that the two eyes are positioned on the object of fixation so that its image falls on identical points in the retinas of both eyes. Only in this case does a single perception of the object of fixation occur. Identical, or corresponding, are the central foveae and points of the retina, located at the same distance from the central fovea in the same meridian. The points of the retina, located at different distances from the central fovea, are called disparate, inappropriate (non-identical). They do not have the innate property of single perception. When the image of the object of fixation hits non-identical points of the retina, double vision occurs,
or diplopia (Greek diplos - double, opos - eye) is a very painful condition. This occurs, for example, with strabismus, when one of the visual axes is shifted to one side or the other from the common point of fixation.
The two eyes are located in the same frontal plane at a certain distance from each other, so in each of them not quite identical images of objects located in front and behind the object of fixation are formed. As a result, double vision inevitably occurs, called physiological. It is neutralized in the central section of the visual analyzer, but serves as a conditioned signal for the perception of the third spatial dimension, i.e. depth.
Such a displacement of images of objects (closer and farther from the point of fixation) to the right and left of the macula on the retinas of both eyes creates the so-called transverse disparation (displacement) of the images and their entry (projection) onto disparate areas (non-identical points), which causes double vision , including physiological.
Transverse disparity is the primary factor in depth perception. There are secondary, auxiliary factors that help in assessing the third spatial dimension. This is linear perspective, the size of objects, the location of light and shadow, which helps the perception of depth, especially in the presence of one eye, when transverse disparity is excluded.
The concept of binocular vision is associated with terms such as fusion(psychophysiological act of merging monocular images), fusion reserves, providing binocular fusion with a certain degree of convergence (convergence) and separation (divergence) of the visual axes (see Chapter 3).
18.2. Pathology of the oculomotor system
Disturbances in the function of the oculomotor system can manifest themselves in incorrect position of the eyes (strabismus), limitation or absence of their movements (paresis, paralysis of the extraocular muscles, etc.), and impaired fixation ability of the eyes (nystagmus).
Strabismus is not only a cosmetic defect, but is also accompanied by a pronounced disorder of monocular and binocular visual functions, depth vision, and diplopia; it complicates visual activity and limits a person’s professional capabilities.
Nystagmus often leads to low vision and visual impairment.
18.2.1. Strabismus
Strabismus (strabismus, heterotopia) is a deviation of one eye from the common point of fixation, accompanied by impaired binocular vision. This disease manifests itself not only in the formation of a cosmetic defect, but also in the disturbance of both monocular and binocular visual functions.
Strabismus is polyetiological. The cause of its development may be ametropia (hypermetropia, myopia, astigmatism), anisometropia (different refraction of the two eyes), uneven tone of the extraocular muscles, impaired function, diseases leading to blindness or a significant decrease in vision in one eye, congenital malformations of the binocular vision mechanism. All these factors influence the still unformed and insufficiently stable mechanism of binocular fixation in children and in the case of exposure to non-
favorable factors (infectious diseases, stress, visual fatigue) can lead to strabismus.
There are two types of strabismus - friendly and unfriendly (for example, paralytic), which differ both in pathogenesis and clinical picture.
Hidden and imaginary strabismus should be distinguished from true strabismus.
18.2.1.1. Hidden strabismus, or heterophoria
The ideal muscular balance of both eyes is called orthophoria (from Greek ortos - straight, correct). In this case, even when the eyes are separated (for example, by covering them), their symmetrical position and binocular vision are maintained.
The majority (70-80%) of healthy people experience heterophoria (from the Greek heteros - other), or hidden squint. With heterophoria, there is no ideal balance of the functions of the oculomotor muscles, however, the symmetrical position of the eyes is maintained due to the binocular fusion of visual images of both eyes.
Heterophoria can be caused by anatomical or neural factors (structural features of the orbit, tone of the extraocular muscles, etc.). Diagnosis of heterophoria is based on excluding conditions for binocular vision.
A simple way to determine heterophoria is the cover test. The subject fixes an object (the end of a pencil, the researcher’s finger) with both eyes, then the doctor covers one of his eyes with a shutter. In the presence of heterophoria, the closed eye will deviate in the direction of action of the predominant muscle: medially (with
esophoria) or outward (with exophoria). If the shutter is removed, this eye, due to the desire for binocular fusion (precluded when it is covered), will make an adjustment movement to the starting position. In case of orthophoria, the symmetrical position of the eyes will be preserved.
With heterophoria, no treatment is required; only if it is significant, binocular decompensation and asthenopia (pain in the eye area, eyebrows) may occur. In these cases, glasses that facilitate vision (spherical or prismatic) are prescribed.
18.2.1.2. Imaginary strabismus
Most people have a small angle (3-4°) between the optical axis passing through the center of the cornea and the nodal point of the eye, and the visual axis running from the central fovea of the macula to the object of fixation - the so-called gamma angle (γ). In some cases, this angle reaches 7-8 o or more. When examining such patients, the light reflex from the ophthalmoscope on the cornea is shifted from its center to the nose or temple, resulting in the impression of strabismus. The correct diagnosis can be established after determining binocular vision: with imaginary strabismus, binocular vision is present and no treatment is required.
18.2.1.3. Concomitant strabismus
Concomitant strabismus is a pathology observed mainly in childhood, the most frequently developing form of oculomotor disorders, which, in addition to deviation of the eye from the general point of fixation, is characterized by impaired binocular vision. It is detected in 1.5-3.5% of children. With a friendly oblique
ocular functions of the extraocular muscles are preserved, in this case, one eye will be fixing, the other - squinting.
Depending on the direction of deviation of the squinting eye, they distinguish between convergent strabismus (esotropia), divergent strabismus (exotropia), and vertical strabismus when one eye deviates up or down (hyper- and hypotropia). With torsional displacements of the eye (inclination of its vertical meridian towards the nose or temple) they speak of cyclotropia (ex- and incyclotropia). Combined strabismus is also possible.
Of all the types of concomitant strabismus, the most commonly observed are convergent(70-80% of cases) and divergent(15-20%). Vertical and torsional deviations are observed, as a rule, with paretic and paralytic strabismus.
Based on the nature of the deviation of the eye, they are classified as one-sided, i.e. monolateral, strabismus, when one eye constantly squints, and alternating, in which one or the other eye squints alternately.
Depending on the degree of participation of accommodation in the occurrence of strabismus, there are accommodative, partially accommodative And non-accommodative strabismus. The impulse to accommodation is increased with hypermetropia and decreased with myopia. Normally, there is a certain connection between accommodation and convergence, and these functions are carried out simultaneously. With strabismus, their relationships are disrupted. The increased impulse to accommodation in hypermetropia, most often observed in childhood, increases the incentive to convergence and causes a high incidence of convergent strabismus.
Accommodative strabismus (more than 15% of patients) is characterized by the fact that deviation (deviation of the eye) is eliminated with optical correction of ametropia, i.e.
proper wearing of glasses. In this case, binocular vision is quite often restored and patients do not need surgical treatment. In the case of non-accommodative strabismus, wearing glasses does not eliminate the deviation and treatment must necessarily include surgery. With partial accommodative strabismus, wearing glasses reduces but does not completely eliminate the deviation.
Strabismus can also be constant or periodic, when the presence of deviation alternates with a symmetrical position of the eyes.
Concomitant strabismus is accompanied by the following sensory disturbances: decreased visual acuity, eccentric fixation, functional scotoma, diplopia, asymmetric binocular vision (abnormal retinal correspondence), impaired depth vision.
One of the most frequently occurring sensory disorders in monolateral strabismus is amblyopia, i.e., a functional decrease in vision of the eye due to its inactivity and disuse.
According to the degree of decrease in visual acuity, according to the classification of E. S. Avetisov, low degree amblyopia is distinguished - with visual acuity of the squinting eye 0.8-0.4, average - 0.3-0.2, high - 0.1-0, 05, very high -0.04 and below. High degree amblyopia is usually accompanied by impaired visual fixation of the squinting eye.
Normal fixation is foveal (Fig. 18.2). Non-central fixation can be parafoveal, macular, paramacular, peridiscal (peripheral), and the image falls on an eccentric area of the retina.
According to the mechanism of occurrence, amblyopia can be disbinocular, i.e. arising as a result binocular vision disorders,
Rice. 18.2.Topography of visual fixation based on the fundus image on a monobinoscope.
what is observed with strabismus, when the participation of the deviated eye in the visual act is significantly reduced, or refractive, which is a consequence of untimely prescription and inconsistent wearing of glasses during ametropia, creating a blurry image in the fundus.
In the presence of uncorrected anisometropia, anisometropic amblyopia. Refractive amblyopia can be quite successfully overcome through rational and permanent optical correction (glasses, contact lenses).
Cloudiness of the eye media (congenital cataract, cataract) can cause obscuration amblyopia, which is difficult to treat, the elimination of which requires timely surgical intervention (for example, extraction of congenital cataracts, corneal transplantation).
Amblyopia can be unilateral or bilateral.
Amblyopia also reduces color and contrast sensitivity.
When strabismus appears, double vision inevitably occurs, since the image in the squinting eye falls on a disparate area of the retina, however, thanks to the adaptation
Through these mechanisms, the visual-nervous system adapts to the asymmetrical position of the eyes and functional suppression, inhibition, or “neutralization” [in the terminology of L. I. Sergievsky (1951)] occurs of the image in the squinting eye. Clinically, this is expressed in the appearance of a functional scotoma. Unlike true scotomas observed with organic lesions of the organ of vision, a functional scotoma with strabismus exists only if both eyes are open and disappears with monocular fixation (when the other eye is closed). Functional scotoma is a form of sensory adaptation that relieves double vision, which is observed in most patients with concomitant strabismus.
With monolateral strabismus, the presence of a permanent scotoma in the squinting eye leads to a persistent decrease in vision. In the case of alternating strabismus, the scotoma appears alternately in the right and then in the left eye, depending on which eye is currently squinting, so amblyopia does not develop.
One of the forms of sensory adaptation in concomitant strabismus is the so-called abnormal retinal correspondence,
or asymmetric binocular vision. Diplopia disappears due to the appearance of the so-called false macula. A new functional connection appears between the central fovea of the fixating eye and the area of the retina of the squinting eye, which receives the image due to deviation (deviation of the eye). This form of adaptation is observed extremely rarely (in 5-7% of patients) and only with small angles of strabismus (microdeviations), when the area of the retina of the deviated eye is organically and functionally little different from the central fovea. At large angles of strabismus, when the image falls on the insensitive peripheral part of the retina, the possibility of its interaction with the highly functional central fovea of the fixating eye is excluded.
Research methods. Assessment of the condition of the oculomotor system involves the study of both sensory (sensitive) and motor (motor) functions.
The study of sensory functions includes the determination of binocular vision and the degree of its stability, depth (or stereoscopic) vision, its acuity, the presence or absence of bifoveal fusion, fusion reserves, functional scotoma of suppression, and the nature of diplopia.
When studying motor functions, the mobility of the eyeballs, the amount of deviation, and the degree of dysfunction of various oculomotor muscles are determined.
When collecting an anamnesis, it is necessary to find out at what age strabismus arose, the presumed cause of its development, the presence of injuries and previous diseases, whether one eye was always squinted or alternating deviation of both eyes was manifested, the nature of the treatment, the duration of wearing glasses.
Study visual acuity should be carried out with or without glasses, as well as with two eyes open, which is especially important for nystagmus.
In addition to general ophthalmological examination, special methods are used.
For determining nature of strabismus(monolateral, alternating) a fixation test should be carried out: cover the fixating (for example, right) eye of the subject with a palm and ask him to look at the end of a pencil or the handle of an ophthalmoscope. When the deviated eye (left) begins to fixate the object, remove the palm and leave the right eye open. If the left eye continues to fixate the end of the pencil, then it means that the subject has alternating strabismus, but if with two eyes open the left eye squints again, then the strabismus is monolateral.
Type of strabismus and the amount of deviation (squint angle) is determined by the direction of eye deviation (convergent, divergent, vertical).
Strabismus angle can be determined using the Hirshberg method. The doctor, applying a manual ophthalmoscope to his eye, asks the patient to look into the opening of the ophthalmoscope and observes the position of the light reflexes on the corneas of both eyes of the patient from a distance of 35-40 cm. The magnitude of the angle is judged by the displacement of the reflex from the center of the cornea of the squinting eye in relation to the pupillary edge iris and limbus (Fig. 18.3) with an average pupil width of 3-3.5 mm. With convergent strabismus, they are oriented along the outer edge of the pupil, and with divergent strabismus, along the inner edge.
Eye mobility determined by moving the object of fixation, which is followed by the patient’s eyes, in eight directions of gaze: right, left, up, down,
Rice. 18.3.The position of the light reflex on the cornea of a squinting eye when determining the angle of strabismus using the Hirshberg method.
up - right, up - left,
down - right, down - left. With concomitant strabismus, the eyes move in a fairly full range. For paralytic strabismus, it is advisable to use special methods - co-ordimetry And provoked diplopia(see section 18.2.1.4) to identify the affected muscle.
In case of vertical deviation, the angle of strabismus is determined in the lateral positions - during adduction and abduction. An increase in the angle of vertical strabismus during adduction indicates damage to the oblique muscles, and during abduction - to the vertical rectus muscles.
In the presence of amblyopia, the state of visual fixation is assessed using a monobinoscope (Fig. 18.4) - one of the main instruments used for the study and treatment of strabismus. The device is designed like a stationary Gulstrand ophthalmoscope, which allows, when fixing the child’s head, to examine the fundus of the eye, determine the state of visual fixation, and carry out therapeutic procedures. The child looks at the end of the fixation rod (“needle”) of the monobinoscope, the shadow from which is projected (on the fundus) onto the fixation site (see Fig. 18.2).
Research methods binocular functions for strabismus are based on the principle separation of fields of view right and left eyes (haploscopy), which makes it possible to identify the participation (or non-participation) of the squinting eye in binocular vision. Haploscopy can be mechanical, color, raster, etc.
One of the main haploscopic devices is the synoptophore (Fig. 18.5). The visual fields of the right and left eyes are separated in this device mechanically, using two (separate for each eye) movable optical tubes, with the help of which
Rice. 18.4.Determination of visual fixation and exercises on a monobinoscope.
Rice. 18.5.Synoptophore lessons.
The subject is presented with paired test objects.
Test objects of the synoptophore (Fig. 18.6) can be moved (horizontally, vertically, torsionally, i.e. clockwise and counterclockwise) and installed in accordance with the angle of strabismus. They differ in the control elements for each eye, which allows, when combining paired (right and left) patterns, to judge the presence or absence of binocular fusion, i.e. fusion, and in its absence, the presence of a functional scotoma (when a detail or the entire pattern disappears before the squinting eye). If there is a fusion, fusion reserves are determined by bringing together or spreading test objects (optical tubes of the synoptophore) until the test doubles.
object. When the synoptophore tubes are brought together, positive fusion reserves (convergence reserves) are determined, when separated, negative fusion reserves (divergence reserves) are determined.
The most significant are positive fusion reserves. When studied on a synoptophore with test No. 2 (“cats”) in healthy individuals, they are 16 ± 8 o, negative - 5 ± 2 o, vertical - 2-4 prism diopters (1-2 o). Torsion reserves are: incycloreserves (when the vertical meridian of the pattern is tilted towards the nose) - 14 ± 2 o, excycloreserves (when tilted towards the temple) - 12 ± 2 o.
Fusion reserves depend on the research conditions (using different methods - synoptophore or prism), the size of the test
Rice. 18.6.An example of combining two images on a synoptophore.
Rice. 18.7. Four-point color test for studying binocular vision and red-green glasses filters.
objects, their orientation (vertical or horizontal) and other factors that are taken into account when determining treatment tactics.
To study binocular vision in natural and similar conditions, methods based on color, polaroid or raster division of visual fields are used. For this purpose, for example, red and green light filters are used (red - in front of one eye, green - in front of the other eye), polaroid filters with vertically and horizontally oriented axes, raster filters of mutually perpendicular orientation for both eyes. The use of these methods allows us to answer the question about the nature of the
the patient’s vision: binocular, simultaneous (diplopia) or monocular.
The Belostotsky-Friedman four-point color test has two green (or blue) circles, one red and one white circle (Fig. 18.7). The subject looks through red-green glasses: there is a red filter in front of the right eye, a green (or blue) filter in front of the left eye. The middle white circle, seen through the red and green filters of the glasses, will be perceived as green or red depending on the dominance of the right or left eye (Fig. 18.8). With monocular vision of the right eye (Fig. 18.8, a) through the red glass, the subject sees only red circles (there are two of them), with monocular vision of the left eye (Fig. 18.8, b) - only green circles (there are three of them). With simultaneous vision (Fig. 18.8, c) he sees five circles: two red and three green, with binocular vision (Fig. 18.8, d, e) he sees four circles: two red and two green.
When using polaroid or raster filters (the so-called Bagolini glasses), as in a color device, there is a common object to merge and objects visible only to the right or only to the left eye.
Methods for studying binocular vision differ in the degree of uncoupling (“dissociating”) action: it is more pronounced in a color device, less in the Polaroid test and in raster glasses.
Rice. 18.8. Patient-visible arrangement of four-point color test circles. Explanation in the text.
kakh, since the conditions for vision in them are closer to natural.
When using raster glasses, the entire surrounding space is visible, as in natural conditions (unlike vision in red-green color glasses), and the dissociating effect of rasters is manifested only by thin, mutually perpendicular light strips passing through a common round light source - the object of fixation. Therefore, when examining with different methods in the same patient, it is possible to identify simultaneous vision using a four-point test and binocular vision using Bagolini raster glasses. This must be remembered when assessing binocular status and to determine treatment tactics.
There are various depth-measuring instruments and stereoscopes that allow you to determine the acuity and thresholds (in degrees or linear quantities) of depth and stereoscopic vision. In this case, the examinee must correctly evaluate or position the presented test objects, shifted in depth. The degree of error will determine the acuity of stereo vision in angular or linear quantities.
Divergent concomitant strabismus is a more favorable form of oculomotor disorders than convergent strabismus; it is less often accompanied by amblyopia. Impaired binocular vision manifests itself in divergent strabismus in a milder form; convergence insufficiency is mainly detected.
Treatment. The ultimate goal of treatment for concomitant strabismus is the restoration of binocular vision, since only under this condition visual functions are restored and asymmetry in eye position is eliminated. For this purpose, a system of complex treatment of concomitant strabismus is used, which includes:
Optical correction of ametropia (glasses, contact lenses);
Pleoptic treatment (pleoptics - treatment of amblyopia);
Surgery;
Orthoptodiploptic treatment aimed at restoring binocular functions (pre- and postoperative) and depth vision.
Optical correction. Optical correction of ametropia helps restore visual acuity and normalize the ratio of accommodation and convergence. This leads to a reduction or elimination of the angle of strabismus and ultimately helps to restore binocular vision (with accommodative strabismus) or create conditions for this. Correction of ametropia is indicated for any form of strabismus. Glasses should be prescribed for constant wear under systematic monitoring of visual acuity (once every 2-3 months).
Pleoptics. Pleoptics is a system of methods for treating amblyopia.
One of the traditional and main methods of pleoptic treatment is direct occlusion - turning off the healthy (fixing) eye 1. It creates conditions for fixing objects with the squinting eye, including it in active visual activity and in a significant number of cases, especially if prescribed in a timely manner, leads to the restoration of visual acuity of the squinting eye. For this purpose, special plastic occluders are used, attached to spectacle frames, or homemade soft curtains (curtains), as well as translucent (with varying degrees of density) occluders. As the visual acuity of the amblyopic eye increases, the degree of transparency of the occluder in front of the dominant eye
1 Occlusion as a method of treating amblyopia was proposed in 1751 by the French researcher Buffon.
can be increased. Translucent occlusion also promotes the development of binocular coordination in both eyes. The occlusion mode is determined by the doctor. Occlusion is prescribed for the whole day (the occluder is removed at night), for several hours a day or every other day, depending on the degree of decrease in visual acuity.
It should be remembered that direct occlusion can lead to dysfunction and reduction of binocular cortical neurons, resulting in deterioration of binocular vision, so they use the tactic of a gradual transition to other treatment methods or the use of penalization. The principle of penalization (from the French penalite - fine, penalty) is to create artificial anisometropia in the patient using special temporary glasses. The reason for developing the method was the observation of French researchers (Pfandi, Pouliquen and Quera), who noted that amblyopia is absent in anisometropia against the background of mild myopia in one eye and emmetropia or mild hypermetropia in the other eye.
Penal glasses penalize the better seeing eye. They are selected individually, while artificially created anisometropia, for example, by overcorrection (by 3.0 diopters) of the better eye with plus lenses, sometimes in combination with its atropinization. As a result of this, the dominant eye becomes myopic and its distance vision deteriorates, while the amblyopic eye is connected to active work through full optical correction. At the same time, unlike direct occlusion, the possibility of vision with two eyes is preserved, so penalization is more physiological, but it is more effective at an earlier age - 3-5 years.
In combination with occlusion or separately, methods of light stimulation of the amblyopic eye are used:
the method of local “blinding” irritation of the central fovea of the retina with light, developed by E. S. Avetisov, the method of sequential visual images according to Küppers, illumination of the paracentral area of the retina (the area of eccentric fixation) according to the Bangerter method. These methods provide a disinhibitory effect and remove the phenomenon of suppression from the central zone of the retina.
The method is chosen depending on the child’s age, characteristics of his behavior and intelligence, and the state of visual fixation.
For treatment using the Avetisov method, which can be combined with direct occlusion, various brightness sources are used: light guide, laser light. The procedure lasts several minutes, so it can be used in young children.
Küppers' method of sequential images is based on their excitation by illuminating the fundus while simultaneously darkening the fovea with a round test object. Consecutive visual images after illumination are observed on a white screen, and their formation is stimulated by intermittent illumination of the screen. When using this method, higher demands are placed on the patient’s intelligence than when treated using the Avetisov method.
Treatment with the indicated methods, as well as with the use of general illumination, illumination through a red filter and their other varieties, is carried out on monobinoscope. The device allows, when fixing the child's head, to conduct an examination of the fundus of the eye, visual fixation, pleoptic and diploptic treatment under the control of ophthalmoscopy.
All of the above methods must be used in combination with active household visual training (drawing
learning, playing with small parts such as “Mosaic”, “Lego”, etc.).
Laser radiation is used in pleoptic treatment in the form of reflected laser light, so-called speckles, by observing the laser “grain”, which has a stimulating effect on the retina. They use domestic devices “LAR” and “MAKDEL”: the first is remote, the second is put to the eyes. Laser speckle can also be used on a monobinoscope.
The listed methods make it possible to influence mainly the light and brightness sensitivity of the eye. A complex effect on various types of sensitivity in amblyopia is successfully carried out using dynamic color and frequency-contrast stimuli of varying brightness, shape and semantic content. This is implemented in special domestic computer programs “EUE” (exercises “Shooting Range”, “Chase”, “Crosses”, “Spider”, etc.). The exercises are interesting for children and require their active participation. Stimulus tests are dynamic and easy to change. The principle of dynamic change of color and contrast-frequency stimuli is also used in the method based on the phenomenon of interference of polarized light by A. E. Vakurina. The complex effect on various types of visual sensitivity significantly increases the effectiveness of pleoptic treatment.
Surgery. For strabismus, the goal of surgery is to restore the symmetrical or nearly symmetrical position of the eyes by changing the muscle balance. Strengthen weak or weaken strong muscles.
Operations that weaken the action of muscles include recession (transfer of the muscle attachment site posteriorly from the anatomical one), partial myotomy (applying
pepper edge notches on both sides of the muscle), lengthening of the muscle through various plastic manipulations), tenotomy (intersection of the muscle tendon). Currently, tenotomy is practically not used, since it can lead to a sharp limitation of the mobility of the eyeball and exclude the possibility of restoring visual functions.
In order to enhance the action of the muscle, a section of the muscle is resected (4-8 mm long, depending on the degree of dosage of the intervention and the size of the strabismus angle) or the formation of a muscle fold or a muscle tendon fold - tenorrhaphy, as well as moving the attachment point of the muscle anteriorly (anteposition). With convergent strabismus, the internal rectus muscle is weakened and the external rectus muscle is strengthened; with divergent strabismus, the opposite actions are performed.
The basic principles of performing surgical intervention for strabismus are as follows.
It is necessary to abandon forced interventions and observe the principle of preliminary dosing of the operation in accordance with existing calculation schemes. The operation is performed in stages: first on one eye, then (after 3-6 months) on the other.
The dosed intervention is evenly distributed over several eye muscles (weakening strong muscles, strengthening weak muscles).
Be sure to maintain the connection between the muscle and the eyeball during surgery on it.
Restoring the correct position of the eyes creates conditions for the restoration of binocular vision, which can ensure self-correction of the residual strabismus angle in postoperative surgery.
Riode. For large strabismus angles (30 o or more), operations are performed in 2 (or 3) stages, depending on the initial value of the strabismus angle.
A high cosmetic and therapeutic effect is observed when using the dosing scheme for the effect of the operation, developed by E. S. Avetisov and Kh. M. Makhkamova (1966). This scheme provides for recession of the internal rectus muscle by 4 mm with a Hirschberg deviation of less than 10 o. A greater degree of recession often leads to limited mobility of the eyeball. At strabismus angles of 10 o, 15 o, 20 o, 25 o, this operation is performed in combination with resection (strengthening) of the antagonist - the external rectus muscle of the same eye - in a dosage of 4-5; 6; 7-8 and 9 mm respectively. If residual deviation persists, the second stage of the operation is performed on the other eye according to a similar dosing scheme no earlier than 4-6 months later. Symmetrical eye position is achieved in 85% of patients or more.
A similar dosing scheme is used in operations for divergent strabismus, but at the same time the external muscle is weakened (causing its recession) and the internal rectus is strengthened.
The indication for the operation is the absence of a therapeutic effect with constant (for 1.5-2 years) wearing glasses (if indicated).
Usually the operation is performed at the age of 4-6 years, which depends on the time of onset of the disease. In congenital forms of the disease and large eye deviation angles, surgery is performed earlier - at 2-3 years. It is advisable to eliminate strabismus in preschool age, which helps to increase the effectiveness of further functional treatment and has a beneficial effect on the restoration of visual functions.
Orthoptic and diploptic treatment. Orthoptics and diploptics are a system of methods for restoring binocular vision, or rather binocular functions, the elements of which are bifoveal fusion, fusion reserves, relative accommodation, stereo effect, depth perception of space and other functions. Wherein orthoptics is treatment using devices with complete artificial separation of the visual fields of both eyes: a separate object is presented to each eye and set at a strabismus angle; Diploptics is treatment in natural and similar conditions.
Binocular exercises are carried out after achieving the maximum possible visual acuity of the squinting eye, however, visual acuity of 0.3-0.4 is acceptable.
Orthoptic exercises
usually performed on devices with mechanical division of fields of view(mechanical haploscopy), the most important of which is the synoptophore (see Fig. 18.5; analogues - amblyophore, orthoamblyophore, synoptophore, etc.). Paired test objects for both eyes are movable and can be positioned at any angle of strabismus. This is a great advantage of the synoptophore over instruments with fixed patterns. Synoptophore has diagnostic and therapeutic purposes. For diagnostic purposes (determination of functional scotoma, bifoveal fusion), test objects for combination (“chicken and egg”) or small (2.5° or 5°) test objects for fusion (“cat with a tail” and “cat with ears"). To determine fusion reserves and for therapeutic purposes, test objects for fusion of large sizes (7.5°, 10°, etc.) are used.
The purpose of the exercises is to eliminate functional scotoma and develop bifoveal fusion (senior
weed fusia). To do this, two types of exercises are used: alternating (alternating) or simultaneous light stimulation (“blinking”). Test objects must be installed at the objective angle of strabismus, then they are projected onto the central fovea of the retina. The device allows you to change the frequency of blinks from 2 to 8 per 1 s, which is consistently increased during the exercises.
The third type of exercise is the development of fusion reserves: horizontal (positive and negative, i.e. convergence and divergence), vertical, cycloreserves (circular). Large tests are used first and then smaller tests are used for merging. Exercises are prescribed both in the pre- and postoperative period and are carried out in courses of 15-20 sessions with an interval of 2-3 months.
Orthoptic devices, for all their attractiveness and necessity (in the initial stages of treatment), limit the possibility of restoring binocular
functions in natural conditions and provide cure in only 25-30% of patients, which is due to artificial vision conditions on these devices. In this regard, after achieving a symmetrical position of the eyes, treatment should be carried out to restore binocular functions in “free space”, without mechanical separation of the visual fields.
One of these methods is the method of binocular sequential visual images [Kashchenko T. P., 1966]. It allows you to restore bifoveal fusion, eliminate functional scotoma and restore binocular vision. The method can be used in combination with exercises on the synoptophore with symmetrical or close to it eye position in the postoperative period. Follower-
These images (in the form of a circle with a right horizontal mark for the right eye and with a left mark for the left) are evoked, as when using the Küppers method (in the treatment of amblyopia), on a monobinoscope, but both eyes are illuminated, and sequentially: first one, and then another. Then the patient observes the images evoked in each eye on a white screen under intermittent lighting and combines them into a single image. After 1-2 minutes, the illumination procedure is repeated 2 more times. The use of the method of binocular sequential images increases the effectiveness of treatment and helps restore binocular vision.
The shortcomings of orthoptics methods gave rise to the development of another treatment system - diploptics [Avetisov E. S., 1977]. The basic principle of diploptics is to eliminate the phenomenon of suppression of the visual image of a squinting eye in natural conditions by inducing diplopia and developing a fusional bifixation reflex.
All diploptic methods are used with two open eyes, the presence of bifoveal fusion, symmetrical or close to it position of the eyes, achieved through surgery or optical correction. There are a number of diploptic methods, in which various dissociating (“provocative”) techniques are used to induce diplopia.
Restoration of the bifixation mechanism according to the method developed by E. S. Avetisov and T. P. Kashchenko (1976) is carried out using a prism, rhythmically presented in front of one eye for 2-3 s with an interval of 1-2 s. The prism deflects the image of the object of fixation to the paracentral areas of the retina, which causes double vision, which is a stimulus for binocular fusion - the so-called fusion.
Rice. 18.9. A set of prisms for diploptic treatment Diploptic-P and test objects for it.
onny reflex (bifixation). The prism power is successively increased from 2.0-4.0 to 10.0-12.0 diopters. A series of “Diploptic” devices has been developed, which includes a set of prisms (Fig. 18.9). There are devices that allow you to change the strength of the prism and the direction of its base, either towards the nose or towards the temple, in automatic mode.
The method of dissociating accommodation and convergence (the “dissociation” method) “teaches” binocular fusion under conditions of increasing load with negative lenses from 0 to -7.0 diopters with an interval of 0.5 diopters, and then under conditions of sequential relaxation with positive spherical lenses from 0 to +5.0 diopters. The patient overcomes the double vision caused by this. The method promotes the development of not only bifixation and fusion, but also binocular(relative) accommodation, without which binocular vision is impossible. Using the domestic Forbis device, you can train binocular vision and relative accommodation in conditions of color, raster and polaroid separation of visual fields.
Any diploptic exercise is performed for 15-25 minutes, 15-20 lessons are prescribed per course. When performing exercises, carry out
They control binocular vision from different working distances - 33 cm, 1 m, 5 m, with glasses and without glasses. The size of the transferred negative and positive spherical lenses is also controlled. When using the “dissociation” method on a color test for near 33 cm (on the Forbis device), negative reserves normally average +5.0 diopters, positive reserves - up to 7.0 diopters; in patients at the initial stages of treatment they are significantly less and can be approximately +1.0 and -1.0 diopters.
The diploptic method of using color (red, green, etc.) light filters of increasing density is implemented using special rulers - light filters [Kashchenko T. P., Tarastsova M. M., 1980]. The density (or throughput) of light filters differs by an average of 5%. The weakest filter is No. 1 (5% density, or high throughput - up to 95%), the densest is No. 15 (75% density) (Fig. 18.10).
A ruler with light filters is placed in front of one eye of the patient (with both eyes open, as when performing any diploptic exercise) and asked
Rice. 18.10. A set of color filters of increasing density and different wavelengths for diploptic treatment Diploptik-SF.
fix a round luminous test object with a diameter of 1-2 cm, located at a distance of 1-2 m. After double vision occurs, provoked by a color filter, the patient must connect (merge) images of the fixation object that are slightly different in color (for example, white and pink). The density of the color filter is successively increased and binocular fusion is trained on each of them.
For the first time, a ruler with red light filters was used by the Italian scientist V. Bagolini (1966) for diagnostic purposes. In domestic strabology, red light filters are used not only for therapeutic purposes, but also to determine the stability of the achieved binocular vision. The criterion for assessing stability is the density (measured as a percentage) of the light filter at which binocular vision is impaired and double vision occurs.
For therapeutic purposes, a set of neutral (light gray), green (blue), red and yellow light filters is used. If, when presented with red filters (which are also used as diagnostic ones), fusion is difficult to achieve, treatment begins with less dissociating (uncoupling) neutral filters. After achieving binocular fusion on neutral filters (of all degrees of density), green or blue filters are sequentially presented, and then red and yellow filters. This method entered clinical practice as chromatic diploptics.
For binocular training in the diploptic treatment system, computer programs (“EYE, Contour”) are used, based on the color division of visual fields. The exercises are fun, playful, and ensure the active participation of the patient.
Rice. 18.11. Exercises on the binarimeter.
In diploptics, the binarimetry method is also used (L. I. Mogilev, I. E. Rabichev, T. P. Kashchenko, V. V. Solovyova, etc.), which consists of presenting two paired test objects (Fig. 18.11) on a binarimeter in free space. In the process of performing the exercises, the merger of test objects is achieved by reducing the distance between them, bringing them closer and moving away along the axis of the device (search for a comfort zone).
In this case, a third, average binocular image appears - an imaginary one, and in depth it is located closer or further than the ring of the device and can coincide with its plane when the frame with test objects is moved. These exercises develop binocular, depth perception and train relative accommodation.
There are other methods for performing diploptic exercises. Diplopia is induced by creating artificial aniseikonia by enlarging the size of one of the monocular images using a variable magnification lens. Under natural conditions, a difference in image size between the right and left eyes of up to 5% is tolerated; artificially induced aniseikonia in healthy people can be tolerated with a difference in image size of up to
60-70%, and in patients with strabismus only up to 15-20%.
The diploptic method is original, based on the phase (in time) presentation of stimulating tests either for the right or for the left eye.
There is an opinion that visual information is transmitted alternately - either through the right or left visual channel. There is also a certain frequency (“phase”) of such transmission, which is disrupted in various pathological conditions, for example, with strabismus. This is the basis of the method of phase haploscopy using liquid crystal glasses
(ZhKO). When an electric pulse passes through the plates of such glasses in a certain frequency-phase mode, their transparency changes: one glass will be transparent, the other at this moment will be opaque. The subject does not feel the high frequency of changes in such time phases in the gastrointestinal tract (more than 80 Hz). This is the advantage of LKO compared to other methods of phase presentation of test objects.
These glasses are used in two versions. In the first, the patient must perform fascinating depth exercises “hitting the target” on a computer screen, on which pictures are presented with the same frequency, disparately located for both eyes, which creates the effect of depth. As the exercises are performed, the level of their complexity increases (bringing paired patterns closer together, decreasing depth thresholds), which helps to increase the acuity of depth vision.
In the second option, a liquid-bearing device is used for wearing with an autonomous power supply system. In these glasses, along with the phases alternately presented for each eye, the binocular phase is turned on, when both eyes look through the lens.
pupillary plates of glasses (I. E. Rabichev, T. P. Kashchenko, S. I. Rychkova, P. Shamon), as a result of which the trainee gradually approaches the natural conditions of visual perception.
Diploptic exercises, compared to orthoptic exercises, increase the effectiveness of treatment and contribute to a more significant restoration of binocular vision - from 25-30% (after orthoptics) to 60-65%, and with early use, even more.
Depth vision and stereo vision are trained using various depth-measuring devices and stereoscopes. Exercises using depth devices (a device for throwing balls, a three-stick Howard-Dolman device, a Litinsky device, etc.) are based on the presentation of a real depth difference. During the examination, the patient should not see the ends of the rods of the three-rod device (a movable middle one and two side ones, standing on the same transverse line). After displacement (by the researcher) of the middle rod, the patient must position it using a movable pin in the same row as the side ones. The degree of divergence of the rods determines the acuity of deep vision (in degrees or linear quantities). Normally, the acuity of depth vision when examined from 1-2 m is up to 1-2 cm. Depth vision is well trained in a real environment, for example, in ball games (volleyball, tennis, basketball, etc.).
Research using stereoscopes is based on the presentation of stereopair test objects with disparity (displacement) of varying degrees. They serve to measure the acuity of stereo vision, which depends on the size of the test objects, age and degree of training of the subject. In healthy individuals it is 10-30" (arcseconds).
In diploptic treatment, a certain role is assigned to prismatic glasses. Prismatic lenses are known to refract the light beam, shifting the image of the object of fixation on the retina towards the base of the prism. If there are small or residual strabismus angles in the postoperative period, prismatic glasses are prescribed to be worn along with diploptic treatment. As the angle of strabismus decreases, the power of the prismatic lenses is reduced, and then the glasses are discontinued.
Prisms are also used to develop fusion reserves in “free space”. In this case, it is convenient to use a Landolt-Herschel type biprism, the design of which allows you to smoothly increase (or decrease) its prismatic action by rotating the disk.
A domestically produced biprism (OKP - prism ophthalmic compensator) can be fixed in a special device or spectacle frame. Changing the direction of the base of the prism towards the temple promotes the development of positive fusion reserves, and towards the nose - negative ones.
18.2.1.4. Unfriendly strabismus
Unfriendly strabismus, unlike friendly strabismus, is caused by dysfunction of the extraocular muscles (paresis or paralysis). The causes may be different: traumatic brain or orbital injuries, tumors, congenital, inflammatory or endocrine pathologies.
Paralytic strabismus can be caused by paralysis of one or more extraocular muscles. It is characterized primarily limitation or lack of mobility mowing
eyes in the direction of action of the paralyzed muscle. When looking in this direction, it appears double vision, or diplopia. If with concomitant strabismus a functional scotoma relieves double vision, then with paralytic strabismus another adaptation mechanism arises: the patient turns his head in the direction of the action of the affected muscle, which compensates for its functional insufficiency. Thus, the third symptom characteristic of paralytic strabismus arises - forced turn of the head. So, with abducens nerve palsy (impaired function of the external rectus muscle), for example the right eye, the head will be turned to the right. Forced rotation of the head and tilt towards the right or left shoulder with cyclotropia (displacement of the eye to the right or left of the vertical meridian) is called torticollis. Ocular torticollis should be differentiated from neurogenic, orthopedic (torticollis), and labyrinthine (with otogenic pathology). Forced rotation of the head allows you to passively transfer the image of the object of fixation to the central fovea of the retina, which eliminates double vision and provides binocular vision, although not quite perfect.
A sign of paralytic strabismus is also inequality of primary strabismus angle(squinting eye) secondary deflection angle(healthy eye). If you ask the patient to fix a point (for example, look at the center of the ophthalmoscope) with a squinting eye, the healthy eye will deviate to a much larger angle.
In paralytic strabismus, it is necessary to determine the affected extraocular muscles. In preschool children, this is judged by the degree of eye mobility in different directions (determination of the visual field). At an older age
They use special methods - coordimetry and provoked diplopia.
Simplified method The definition of the field of view is as follows. The patient sits opposite the doctor at a distance of 50-60 cm, the doctor fixes the patient’s head with his left hand and asks him to alternately watch with each eye (the second eye is covered at this time) the movement of an object (pencil, hand ophthalmoscope, etc.) in 8 directions. Muscle deficiency is judged by the limitation of eye mobility in one direction or another. In this case, special tables are used. Using this method, only severe limitations in eye mobility can be identified.
If there is a visible deviation of one eye vertically, a simple method of adduction - abduction. The patient is asked to look at an object, move it to the right and left and observe whether the vertical deviation increases or decreases with extreme gaze aversions. Determination of the affected muscle in this way is also carried out using special tables.
Coordimetry according to Tess is based on dividing the visual fields of the right and left eyes using red and green filters.
To conduct the study, a coordimetric set is used, which includes a graphed screen, red and green flashlights, and red-green glasses. The study is performed in a darkened room, on one of the walls of which there is a screen divided into small squares. The side of each square is equal to three angular degrees. In the central part of the screen there are nine marks placed in the form of a square, the position of which corresponds to the isolated physiological action of the oculomotor muscles.
A patient wearing red-green glasses sits at a distance of 1 m from the screen. To examine the right eye, a red flashlight is placed in his hand (red glass in front of the right eye). The researcher holds a green flashlight in his hands, the beam of light from which he directs one by one to all nine points and asks the patient to combine the light spot from the red flashlight with the green light spot. When trying to combine both light spots, the examinee usually makes a mistake by some amount. The doctor records the position of the green spot to be fixed and the red spot to be trimmed on a diagram (sheet of graph paper), which is a small copy of the screen. During the examination, the patient's head should be motionless.
Based on the results of a coordimetric study of one eye, it is impossible to judge the state of the oculomotor system; it is necessary to compare the results of coordimetry of both eyes.
The field of view in the diagram drawn up based on the results of the study is shortened in the direction of action of the weakened muscle, while at the same time there is a compensatory increase in the field of view in the healthy eye in the direction of the action of the synergist of the affected muscle of the squinting eye.
Method for studying the oculomotor system in conditions of provoked diplopia according to Haab-Lancaster is based on assessing the position in space of images belonging to the fixating and rejected eye. Diplopia is caused by placing a red glass on the squinting eye, which makes it possible to simultaneously determine which of the double images belongs to the right and which to the left eye.
The nine-point study design is similar to that used for coordimetry, but there is one (rather than two).
The study is carried out in a dimly lit room. There is a light source at a distance of 1-2 m from the patient. The patient's head should be motionless.
As with coordimetry, the distance between the red and white images in nine gaze positions is recorded. When interpreting the results, it is necessary to use the rule according to which the distance between double images increases when looking in the direction of the action of the affected muscle. If during coordimetry the field of view is recorded (decreases with paresis), then with “provoked diplopia” the distance between double images is assessed, which increases with paresis.
Surgery - the main type of treatment for non-friendly forms of strabismus.
Plastic surgery is often indicated. So, with paralysis of the abducens nerve and the absence of outward movements of the eyeball, the fibers of the upper and lower rectus muscles (1/3 - 1/2 the width of the muscle) can be sutured to the external rectus muscle.
Surgical approaches to the oblique muscles, especially the superior oblique, are more difficult, due to the complexity of its anatomical course. Various types of interventions have been proposed on these, as well as vertically acting rectus muscles (superior and inferior rectus). The latter can also be recessed (weakened) or resected (strengthened).
When performing surgery on the extraocular muscles, it is necessary to handle them carefully, without disturbing the natural direction of the muscle plane, especially if this is not clinically justified. Special operations performed for complex types of strabismus can change not only the strength, but also the direction of action
muscles, however, before performing them, it is necessary to conduct a thorough diagnostic study.
One of the methods of treating paralytic strabismus is prismatic correction. More often it helps in the treatment of recent paresis and paralysis of the extraocular muscles in adults, for example after traumatic brain injury. Prismatic glasses combine double images, preventing the patient from developing diplopia and forced head rotation. Medication and physiotherapeutic treatment are also possible.
18.2.2. Nystagmus
Nystagmus is a severe form of oculomotor disorders, manifested in spontaneous oscillatory eye movements and accompanied by a significant decrease in visual acuity - low vision. The development of nystagmus can be caused by the influence of central or local factors.
Nystagmus usually occurs with congenital or early-acquired vision loss due to various eye diseases (optic clouding, optic nerve atrophy, albinism, retinal dystrophy, etc.), resulting in disruption of the mechanism of visual fixation.
With some types of nystagmus, sufficiently high visual acuity is maintained; in such cases, the reason for its development is disturbances in the regulation of the oculomotor system.
Depending on the direction of the oscillatory movements, horizontal (most often observed), vertical, diagonal and rotational nystagmus is distinguished; according to the nature of the movements, pendulum-like (with equal amplitude)
amplitude of oscillatory movements), jerk-like (with different amplitudes of oscillations: the slow phase - in one direction and the fast phase - in the other), mixed (either pendulum-like or jerk-like movements appear). Jerky nystagmus is called left- or right-sided depending on the direction of its fast phase. With jerky nystagmus, there is a forced rotation of the head towards the fast phase. With this rotation, the patient compensates for the weakness of the oculomotor muscles, and the amplitude of the nystagmus decreases, therefore, if the head is turned to the right, the “right” muscles are considered weak: the external rectus of the right eye and the internal rectus of the left eye. This type of nystagmus is called right-sided.
Nystagmus can be large-caliber (with an amplitude of oscillatory eye movements of more than 15 o), medium-caliber (with an amplitude of 15-5 o), small-caliber (with an amplitude of less than 5 o).
To determine the amplitude, frequency and nature of oscillatory nystagmoid movements, an objective research method is used - nystagmography. In the absence of a nystagmograph, the nature of the nystagmus amplitude can be determined by the degree of displacement of the light reflex from the ophthalmoscope on the cornea. If the light reflex during oscillatory movements of the eyes moves from the center of the cornea to the middle of the distance between the center and the edge of the pupil, they speak of small-caliber, small-scale nystagmus, if it goes beyond these limits - large-caliber. If the movements of both eyes are not the same, such nystagmus is called dissociated. It is observed extremely rarely.
When examining patients with nystagmus, the results of electrophysiological studies (electroretinogram, visual
evoked potentials, etc.), allowing you to clarify the diagnosis, determine the degree of organic lesions, the presence of amblyopia and determine treatment tactics.
With nystagmus, the visual acuity of each eye is examined with and without glasses, with the head in a straight and forced position. In this position, the amplitude of the nystagmus usually decreases and visual acuity becomes higher. This criterion is used to decide whether it is advisable to perform surgery on the extraocular muscles. It is important to determine visual acuity with two eyes open (with and without glasses), since with binocular fixation the amplitude of nystagmus also decreases and visual acuity becomes higher.
The system of measures to improve visual functions with nystagmus includes carefully selected optical correction for distance and near. It is also necessary to select special correction tools (magnifying glasses, hyperocular glasses), and use projection magnifiers. In case of albinism, retinal dystrophy, partial atrophy of the optic nerves, it is advisable to select protective and visual acuity-enhancing color filters (neutral, yellow, orange, brown) of the density that provides the greatest visual acuity.
With nystagmus, accommodative ability is also impaired and relative amblyopia is noted, so pleoptic treatment and accommodation training exercises are prescribed. Lights through a red filter (on a monobinoscope), selectively stimulating the central zone of the retina, stimulation with contrast-frequency and color test objects (the “Illusion” device, computer exercises according to the “Zebra”, “Spider”, “Cross” programs) are useful.
"EYE") These exercises can be performed sequentially for each eye and with both eyes open. Binocular exercises and diploptic treatment (dissociation method, binarimetry) are very useful, also helping to reduce the amplitude of nystagmus and increase visual acuity.
Drug therapy for nystagmus is used to improve nutrition of the tissues of the eye and retina (vasodilators, vitamin complex).
Surgical treatment of nystagmus is performed to reduce oscillatory eye movements. With jerky nystagmus, when a forced rotation of the head is diagnosed with an increase in visual acuity and a decrease in the amplitude of the nystagmus in this position (“rest zone”), the goal of the operation is to move the “rest zone” to the middle position. For
This is done by weakening stronger muscles (on the side of the slow phase) and strengthening by weaker muscles (on the side of the fast phase). As a result, the head position straightens, nystagmus decreases, and visual acuity increases.
Questions for self-control
1.What extraocular muscles and cranial nerves provide eye movements?
2. Why does functional scotoma occur?
3.Name the stages of complex treatment of concomitant strabismus.
4.What methods of pleoptic treatment are used for amblyopia?
5.What is diploptics? List its methods.
6. Is it possible to help a patient with nystagmus?
Oculomotor apparatus- a complex sensorimotor mechanism, the physiological significance of which is determined by its two main functions: motor (motor) and sensory (sensitive).
The motor function of the oculomotor system ensures the guidance of both eyes, their visual axes and the central fossae of the retinas to the object of fixation; the sensory function ensures the merging of two monocular (right and left) images into a single visual image.
The innervation of the extraocular muscles by the cranial nerves determines the close connection between neurological and ocular pathologies, as a result of which an integrated approach to diagnosis is necessary.
The constant stimulus for adduction (to ensure orthophoria) caused by the divergence of the orbits explains the fact that the medial rectus muscle is the most powerful of the rectus extraocular muscles. The disappearance of the stimulus for convergence with the onset of amaurosis leads to a noticeable deviation of the blind eye towards the temple.
All rectus muscles and the superior oblique begin in the depths of the orbit on the common tendon ring (anulus tendineus communis), fixed to the sphenoid bone and periosteum around the optic canal and partially at the edges of the superior orbital fissure. This ring surrounds the optic nerve and ophthalmic artery. The muscle that lifts the upper eyelid (m. levator palpebrae superioris) also begins from the common tendon ring. It is located in the orbit above the superior rectus muscle of the eyeball, and ends in the thickness of the upper eyelid. The rectus muscles are directed along the corresponding walls of the orbit, on the sides of the optic nerve, forming a muscular funnel, pierce the vagina of the eyeball (vagina bulbi) and with short tendons are woven into the sclera in front of the equator, 5-8 mm away from the edge of the cornea. The rectus muscles rotate the eyeball around two mutually perpendicular axes: vertical and horizontal (transverse).
Movements of the eyeball are carried out with the help of six extraocular muscles: four straight - external and internal (m. rectus externum, m.rectus internum), upper and lower (m.rectus superior, m.rectus inferior) and two obliques - upper and lower ( m.obliguus superior, m.obliguus inferior).
Superior oblique muscle of the eye originates from the tendon ring between the superior and internal rectus muscles and goes anteriorly to the cartilaginous block located in the superior internal corner of the orbit at its edge. At the pulley, the muscle turns into a tendon and, passing through the pulley, turns posteriorly and outward. Located under the superior rectus muscle, it is attached to the sclera outward from the vertical meridian of the eye. Two-thirds of the entire length of the superior oblique muscle is between the apex of the orbit and the trochlea, and one-third is between the trochlea and its attachment to the eyeball. This part of the superior oblique muscle determines the direction of movement of the eyeball during its contraction.
Unlike the five muscles mentioned inferior oblique muscle of the eye begins at the lower inner edge of the orbit (in the area of the entrance of the nasolacrimal canal), goes posteriorly outward between the orbital wall and the inferior rectus muscle towards the external rectus muscle and is fan-shaped attached under it to the sclera in the posteroexternal part of the eyeball, at the level of the horizontal meridian of the eye.
Numerous cords extend from the fascial membrane of the extraocular muscles and Tenon’s capsule to the orbital walls.
The fascial-muscular apparatus ensures a fixed position of the eyeball and gives smoothness to its movements.
Some elements of the anatomy of the extrinsic muscles of the eye
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Properties |
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Superior rectus muscle (m. rectus superior) |
Start : Lockwood's superior orbital tendon (a fragment of the common tendon ring of Zinn) in close proximity to the perineural sheath of the optic nerve. Attachment : to the sclera 6.7 mm from the limbus at an angle to it and slightly medial to the vertical axis of rotation of the eyeball, which explains the variety of its functions. Functions : primary - supraduction (75% of muscle effort), secondary - incycloduction (16% of muscle effort), tertiary - adduction (9% of muscle effort). Blood supply: the superior (lateral) muscular branch of the ophthalmic artery, as well as the lacrimal, supraorbital and posterior ethmoidal arteries. Innervation: superior branch of the ipsilateral oculomotor nerve (n. III). Motor fibers penetrate this and almost all other muscles, usually at the border of its posterior and middle thirds. Anatomy details: Attached behind ora serrata. As a consequence, perforation of the sclera when applying a frenulum suture will lead to a retinal defect. Together with the levator palpebrae superioris muscle, it forms the superior muscle complex |
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Inferior rectus muscle (m. rectus inferior) |
Start: inferior orbital tendon of Zinn (fragment of the common tendon ring of Zinn). Attachment: to the sclera 5.9 mm from the limbus at an angle to it and slightly medial to the vertical axis of rotation of the eyeball, which explains the variety of its functions. Function: primary - infraduction (73%), secondary - excycloduction (17%), tertiary - adduction (10%). Blood supply : inferior (medial) muscular branch of the ophthalmic artery, infraorbital artery. Innervation : inferior branch of the ipsilateral oculomotor nerve (n. III). Anatomy details : forms the lower muscle complex with the inferior oblique muscle |
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Lateral rectus muscle (m. rectus lateralis) |
Start : main (medial) leg - the superior orbital tendon of Lockwood (a fragment of the common tendon ring of Zinn); non-permanent (lateral) leg - a bony protrusion (spina recti lateralis) in the middle of the lower edge of the superior orbital fissure. Attachment : to the sclera 6.3 mm from the limbus. Function : primary - abduction (99.9% of muscle effort). Blood supply : superior (lateral) muscular artery from the ophthalmic artery, lacrimal artery, sometimes infraorbital artery and inferior (medial) muscular branch of the ophthalmic artery. Innervation : ipsilateral abducens nerve (n.VI). Anatomy details : has the most powerful fixing ligament |
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Medial rectus muscle (m. rectus medialis) |
Start : Lockwood's superior orbital tendon (a fragment of Zinn's tendon ring) in close proximity to the perineural sheath of the optic nerve. Attachment : to the sclera 5 mm from the limbus. Function: primary - adduction (99.9% of muscle effort). Blood supply : inferior (medial) muscular branch of the ophthalmic artery; posterior ethmoidal artery. Innervation: inferior branch of the ipsilateral oculomotor nerve (n. III). Anatomy details: most powerful oculomotor muscle |
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Inferior oblique muscle (m. obliquus inferior) |
Start: the periosteum of the flattened area of the orbital surface of the upper jaw under the anterior lacrimal ridge at the opening of the nasolacrimal canal. Attachment : the posterior outer surface of the eyeball slightly behind the vertical axis of rotation of the eyeball. Function : primary - excycloduction (59%), secondary - supraduction (40%); tertiary - abduction (1%). Blood supply : inferior (medial) muscular branch of the ophthalmic artery, infraorbital artery, rarely - lacrimal artery. Innervation: the lower branch of the contralateral oculomotor nerve (n. III), running along the outer edge of the inferior rectus muscle and penetrating the inferior oblique muscle at the level of the equator of the eyeball, and not at the border of the posterior and middle third of the muscle, as happens with all other extraocular muscles. This 1–1.5 mm thick trunk (containing parasympathetic fibers innervating the pupillary sphincter) is often damaged during reconstruction of a fracture of the inferior wall of the orbit, leading to postoperative Adie syndrome. Anatomy details: the absence of a tendon explains the bleeding that occurs when the muscle is cut from the sclera |
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Superior oblique muscle (m. obliquus superior) |
Start : periosteum of the body of the sphenoid bone above the superior rectus muscle. Attachment: sclera of the posterior superior quadrant of the eyeball. Function: primary - incycloduction (65%), secondary - infraduction (32%), tertiary - abduction (3%). Blood supply : superior (lateral) muscular artery from the ophthalmic artery, lacrimal artery, anterior and posterior ethmoidal arteries. Innervation: contralateral trochlear nerve (n. IV). Anatomy details: longest tendon (26 mm), pulley - functional origin of the muscle |
All these nerves pass into the orbit through the superior orbital fissure.
The oculomotor nerve, after entering the orbit, divides into two branches. The superior branch innervates the superior rectus muscle and the levator palpebrae superioris, the inferior branch innervates the internal and inferior rectus muscles, as well as the inferior oblique.
The nucleus of the oculomotor nerve and the nucleus of the trochlear nerve located behind and next to it (provides the work of the oblique muscles) are located at the bottom of the aqueduct of Sylvius (aqueduct of the brain). The nucleus of the abducens nerve (provides the work of the external rectus muscle) is located in the pons under the bottom of the rhomboid fossa.
The rectus oculomotor muscles of the eye are attached to the sclera at a distance of 5-7 mm from the limbus, the oblique muscles - at a distance of 16-19 mm.
The width of the tendons at the muscle attachment site ranges from 6-7 to 8-10 mm. Of the rectus muscles, the widest tendon is the internal rectus muscle, which plays a major role in the function of bringing together the visual axes (convergence).
The line of attachment of the tendons of the internal and external muscles of the eye, i.e., their muscular plane, coincides with the plane of the horizontal meridian of the eye and is concentric with the limbus. This causes horizontal movements of the eyes, their adduction, rotation to the nose - adduction during contraction of the internal rectus muscle and abduction, rotation towards the temple - abduction during contraction of the external rectus muscle. Thus, these muscles are antagonistic in nature.
The superior and inferior rectus and oblique muscles of the eye perform mainly vertical movements of the eye. The line of attachment of the superior and inferior rectus muscles is located somewhat obliquely, their temporal end is further from the limbus than the nasal end. As a result, the muscular plane of these muscles does not coincide with the plane of the vertical meridian of the eye and forms an angle with it that is on average 20° and open to the temple.
This attachment ensures rotation of the eyeball under the action of these muscles, not only upward (during contraction of the superior rectus muscle) or downward (during contraction of the inferior rectus muscle), but simultaneously inwardly, i.e. adduction.
The oblique muscles form an angle of about 60° with the plane of the vertical meridian, open to the nose. This determines the complex mechanism of their action: the superior oblique muscle lowers the eye and produces its abduction (abduction), the inferior oblique muscle is an elevator and also an abductor.
In addition to horizontal and vertical movements, these four vertically acting oculomotor muscles of the eye perform torsional eye movements clockwise or counterclockwise. In this case, the upper end of the vertical meridian of the eye deviates towards the nose (intrusion) or towards the temple (extortion).
Thus, the extraocular muscles of the eye provide the following eye movements:
- adduction (adduction), i.e. its movement towards the nose; this function is performed by the internal rectus muscle, additionally by the superior and inferior rectus muscles; they are called adductors;
- abduction (abduction), i.e. movement of the eye towards the temple; this function is performed by the external rectus muscle, additionally by the superior and inferior oblique muscles; they are called abductors;
- upward movement - under the action of the superior rectus and inferior oblique muscles; they are called lifters;
- downward movement - under the action of the inferior rectus and superior oblique muscles; they are called lowerers.
The complex interactions of the extraocular muscles of the eye are manifested in the fact that when moving in some directions they act as synergists (for example, partial adductors - the superior and inferior rectus muscles, in others - as antagonists (superior rectus - levator, inferior rectus - depressor).
The extraocular muscles provide two types of conjugal movements of both eyes:
- unilateral movements (in the same direction - right, left, up, down) - so-called version movements;
- opposite movements (in different directions) - vergence, for example, to the nose - convergence (bringing together the visual axes) or to the temple - divergence (spreading the visual axes), when one eye turns to the right, the other to the left.
Vergence and version movements can also be performed in the vertical and oblique directions.
|
Muscle |
Start |
Attachment |
Function |
Innervation |
|
External straight |
Fibrous ring of Zinn |
Lateral wall of the eyeball |
Abduction of the eyeball laterally (outward) |
Abducens nerve (VI pair of cranial nerves) |
|
Inner straight |
Fibrous ring of Zinn |
Medial wall of the eyeball |
Adduction of the eyeball medially (inward) |
|
|
Bottom straight |
Fibrous ring of Zinn |
Inferior wall of the eyeball |
Lowers the eyeball, slightly moves it outward |
Oculomotor nerve (III pair of cranial nerves) |
|
Top straight |
Fibrous ring of Zinn |
Raises the eyeball, slightly brings it inwards |
Oculomotor nerve (III pair of cranial nerves) |
|
|
Inferior oblique |
Orbital surface of the maxilla |
Inferior wall of the eyeball |
Lifts, abducts and slightly rotates outward |
Oculomotor nerve (III pair of cranial nerves) |
|
Superior oblique |
Ring of Zinn - block on the orbital surface of the frontal bone |
Superior wall of the eyeball |
Lowers, adducts and slightly rotates medially |
Trochlear nerve (IV pair of cranial nerves) |
The functions of the oculomotor muscles described above characterize the motor activity of the oculomotor apparatus, while the sensory one is manifested in the function of binocular vision.
Schematic representation of the movement of the eyeballs during contraction of the corresponding muscles:
The extraocular muscles are innervated by the III, IV and VI pairs of cranial nerves.
Oculomotor, or III cranial nerve. The third nerve (n. osiioshoi-gish) is mixed and includes motor and parasympathetic portions (Fig. 1.6).
Looking up and outwards M. rectus superior
Looking up and inward M. obliquus inferior
Outward movement of the eye (abduction) m. rectus
Inward eye movement
(cast)
Looking down and outwards M. rectus inferior
Looking down and inward M. obliquus superior
- - Somatic motor fibers
- - Preganglionic fibers Postganglionic fibers
All rectus muscles except the lateralis;
inferior oblique muscle;
muscle that lifts the upper eyelid
Rice. 1.6.
Motor portion innervates four of the six extraocular muscles of the eye and the muscle that lifts the upper eyelid. Vegetative parasympathetic portion innervates the smooth (intrinsic) muscles of the eye.
The nuclear complex of the III cranial nerve is located in the tegmentum of the mesencephalon at the level of the superior colliculi of the quadrigemina near the midline, ventral to the aqueduct of Sylvius.
This complex includes paired somatic motor and parasympathetic nuclei. The parasympathetic nuclei include: the paired accessory nucleus (n. oculomotorius accessorius), also called the Yakubovich-Edinger-Westphal nucleus, and the unpaired central nucleus of Perlia, located in the middle between the accessory nuclei.
The nuclei of the oculomotor nerve, through the fibers of the posterior longitudinal fascicle (fasc. longitudinalis posterior), are connected with the nuclei of the trochlear and abducens nerves, the system of vestibular and auditory nuclei, the nucleus of the facial nerve and the anterior nuclei of the spinal cord. The axons of the neurons of the nuclear complex go in the ventral direction, pass through the ipsilateral red nucleus and emerge on the surface of the brain in the interpeduncular fossa fossa interpeduncularis at the border of the midbrain and the Varoliev bridge in the form of a trunk of the oculomotor nerve.
The trunk of the III nerve pierces the dura mater in front and lateral to the posterior sphenoid process (processus clinoideus posterior), runs along the lateral wall of the cavernous sinus and then enters the orbit through the fissura orbitalis superior (Fig. 1.7, 1.8).
Processus clinoideus posterior
Rice. 1.7. Places of passage of cranial nerves on the internal base of the skull
Fissura orbitalis superior
Foramen rotundum
Foramen spinosum
Porusacusticus internus
Foramen jugulare
Canalis hypoglossalis
In the orbit, the III nerve is located below the IV nerve and such branches of the I branch of the V nerve, such as the lacrimal nerve (n. lacrimalis) and the frontal nerve (n. frontalis). The nasociliary nerve (p. nasociliaris) is located between the two branches of the III nerve (Fig. 1.9, 1.10).
N. oculomotorius N. trochlearis
N. ophthalmicus N. abducens N. maxillaris
Sinus cavernosus
Sinus sphenoidalis
Rice. 1.8. Diagram of the relationship between the cavernous sinus and other anatomical structures, section in the frontal plane (according to Drake R. et al., Gray’s Anatomy, 2007)
M. rectus superior
M. rectus lateralis
M. rectus inferior
M. obliquus inferior
M. obliquus superior
M. rectus medialis
Rice. 1.9. Extrinsic muscles of the eye, anterior view of the right orbit
Entering the orbit, the oculomotor nerve divides into two branches. The superior branch (the smallest) passes medially and above the optic nerve (n. opticus) and supplies the superior rectus muscle (m. rectus superior) and the muscle that lifts the upper eyelid (i.e. levator palpebrae superioris). The lower branch, which is larger, is divided into three branches. The first of them goes under the optic nerve to the medial rectus muscle (m. rectus medialis); the other - to the inferior rectus muscle (m. rectus inferior), and the third, the longest, follows forward between the inferior and lateral rectus muscles to the inferior oblique muscle (m. obliquus inferior). From here comes a short thick connecting branch - the short root of the ciliary ganglion (radix oculomotoria parasympathetica), carrying preganglionic fibers to the lower part of the ciliary ganglion.
glia (ganglion ciliare), from which postganglionic parasympathetic fibers for m. sphincter pupillae and m. ciliaris (Fig. 1.11).
N. oculomotorius, upper branch -
N. oculomotorius, lower branch
Rice. 1.10.
NN. ciliares longi
M. obliquus superior
M. levator palpebrae superioris
M. rectus superior
Ramus superior nervi oculomotorii
A. carotis interna
Plexus caroticus catoricus
N. oculomotorius
NN. ciliares breves
Ganglion trigeminale
M. rectus inferior
Ganglion ciliare
M. obliquus inferior
Ramus inferior nervi oculomotorii
Rice. 1.11. Branches of the oculomotor nerve in the orbit, lateral view (http://www.med.yale.edu/
caim/cnerves/cn3/cn3_1.html)
The ciliary ganglion (ganglion ciliare) is located near the superior orbital fissure in the thickness of the fatty tissue at the lateral semicircle of the optic nerve.
In addition, in transit through the ciliary ganglion, without interruption, pass fibers that conduct general sensitivity (branches of the nasociliary nerve from the V nerve) and sympathetic postganglionic fibers from the internal carotid plexus.
Thus, the motor somatic part of the oculomotor nerve includes a complex of motor nuclei and axons of the neurons that make up these nuclei, which innervate the muscles of the oculomotor. levator palpebrae superioris, m. rectus superior, m. rectus medialis, m. rectus inferior, m. obliquus inferior.
The parasympathetic part of the oculomotor nerve is represented by its parasympathetic nuclei, the axons of their cells (preganglionic fibers), the ciliary ganglion and the processes of the cells of this node (postganglionic fibers), which innervate the sphincter pupillae and the ciliary muscle (m. ciliaris). In other words, each Yakubovich-Edinger-Westphal nucleus contains the bodies of preganglionic parasympathetic neurons, the axons of which go as part of the trunk of the third cranial nerve, in the orbit they pass along with its lower branch and reach the ciliary (ciliary) ganglion (see Fig. 1.11). Axons of ciliary ganglion neurons (postganglionic fibers) form short ciliary nerves (nn. ciliares breves), and the latter pass through the sclera, enter the perichoroidal space, penetrate the iris and enter the sphincter muscle in separate radial bundles, innervating it sectorally. The unpaired parasympathetic nucleus of Perlia also contains the bodies of preganglionic parasympathetic neurons; their axons switch in the ciliary ganglion, and the processes of its cells innervate the ciliary muscle. It is believed that the Perlia nucleus is directly related to ensuring the convergence of the eyes.
Parasympathetic fibers coming from the Yakubovich-Edinger-Westphal nuclei constitute the efferent part of the reflex reactions of pupil constriction (Fig. 1.12).
Normally, pupil constriction occurs: 1) in response to direct lighting (direct reaction of the pupil to light); 2) in response to illumination of the other eye (reaction to light friendly with the other pupil); 3) when focusing the gaze on a nearby object (pupil reaction to convergence and accommodation).
The afferent part of the reflex arc of the pupil's reaction to light starts from the cones and rods of the retina and is represented by fibers that go as part of the optic nerve, then cross in the chiasm and pass into the optic tracts. Without entering the external geniculate bodies, these fibers, after partial decussation, pass into the handle of the superior colliculus of the midbrain roof plate (brachium quadrigeminum) and end at the cells of the pretectal region (area pretectalis), which send their axons to the nuclei
Yakubovich-Edinger-Westphal. Afferent fibers from the macula of the retina of each eye are represented in both Yakubovich-Edinger-Westphal nuclei.
Rice. 1.12.
E.J., Stewart P.A., 1998)
The efferent pathway of innervation of the sphincter of the pupil, described above, begins from the Ya Kubovich-Edinger-Westphal nuclei (see Fig. 1.12).
The mechanisms of the pupil's response to accommodation and convergence are not well understood. It is possible that during convergence, contraction of the medial rectus muscles of the eye causes an increase in the proprioceptive impulses coming from them, which are transmitted through the trigeminal nerve system to the parasympathetic nuclei of the 111th nerve. As for accommodation, it is believed that it is stimulated by defocusing images of external objects on the retina, from where information is transmitted to the center of the eye's close position in the occipital lobe (Brodmann's 18th field). The efferent pathway of the pupillary response also ultimately includes parasympathetic fibers of the 111 pair on both sides.
The proximal part of the intracranial segment of the third nerve is supplied with blood from arterioles arising from the superior cerebellar artery.
terpi, the central branches of the posterior cerebral artery (thalamoperforating, mesencephalic paramedian and posterior villous arteries) and the posterior communicating artery. The distal part of the intracranial segment of the III nerve receives arterioles from the branches of the cavernous part of the ICA, in particular from the tentorial and inferior pituitary arteries (Fig. 1.13). The arteries give off small branches and form numerous anastomoses in the epineurium. Small vessels penetrate the perineurium and also anastomose with each other. Their terminal arterioles pass into the nerve fiber layer and form capillary plexuses along the entire length of the nerve.
A. chorioidea anterior
A. hypophysialis inferior
Rice. 1.13. Branches of the internal carotid artery (according to Gilroy A.M. et al., 2008)
The trochlear, or IV cranial, nerve (n. trochlearis) is purely motor. The nucleus of the trochlear nerve (nucl. n. trochlearis) lies in the tegmentum of the midbrain at the level of the lower colliculi of the quadrigeminal, i.e. below the level of the nuclei of the third nerve (Fig. 1.14).
The fibers of the trochlear nerve emerge on the dorsal surface of the midbrain under the lower tubercles of the quadrigeminal, cross, bend around the cerebral peduncle from the lateral side, follow under the tentorium of the cerebellum, enter the cavernous sinus, where they are located under the trunk of the III nerve (see Fig. 1.8), after exiting from which they pass into the orbit through the superior orbital fissure outward from the tendon ring of Zinn surrounding the optic nerve. The IV nerve innervates the superior oblique muscle of the opposite eye (see Fig. 1.9).
To the superior oblique muscle
Rice. 1.14. Course of trochlear nerve fibers at the level of the midbrain
The nucleus of the trochlear nerve through the fibers of the posterior longitudinal fascicle (fasc. longitudinalis posterior) is connected with the nuclei of the oculomotor and abducens nerves, the system of vestibular and auditory nuclei, and the nucleus of the facial nerve.
Blood supply. The nucleus of the IV nerve is supplied by branches of the superior cerebellar artery. The trunk of the IV nerve is supplied with blood from the subpial arteries and the posterior lateral villous branch of the posterior cerebral artery, and at the level of the superior orbital fissure - by the branches of the external carotid artery (Schwartzman R.J., 2006)
The abducens, or VI, cranial nerve (p. abducens) is purely motor. Its only motor nucleus is located in the tegmentum of the Varoliev bridge under the bottom of the IV ventricle, in the rhomboid fossa (Fig. 1.15). The abducens nucleus also contains neurons that are connected through the medial longitudinal fasciculus to the nucleus of the oculomotor nerve, which innervates the medial rectus muscle of the contralateral eye.
The axons of the cells of the nucleus of the abducens nerve emerge from the substance of the brain between the edge of the pons and the pyramid of the medulla oblongata from the bulbar-pontine groove (Fig. 1.16).
In the subarachnoid space, the VI nerve is located between the pons and the occipital bone, ascending towards the pontine cistern lateral to the basilar artery. Next, it pierces the dura mater slightly below and outward from the posterior sphenoid process (Fig. 1.17), follows in the Dorello canal, which is located under the ossified petro-sphenoid ligament of Gruber (this ligament connects the apex of the pyramid with the posterior sphenoid process -
lump of the main bone), and penetrates the cavernous sinus. In the cavernous sinus, the abducens nerve is adjacent to the III and IV cranial nerves, the first and second branches of the trigeminal nerve, as well as the ICA (see Fig. 1.8). After leaving the cavernous sinus, the abducens nerve enters the orbit through the superior orbital fissure and innervates the lateral rectus muscle of the eye, which rotates the eyeball outward.
Rice. 1.15.
Abductor
Rice. 1.1V. Position of the abducens nerve on the ventral surface of the brainstem
brain (according to Drake R. et al., Gray’s Anatomy, 2007)
Direction of the course of the VI nerve in the cranial cavity
The human visual system is one of the most complex biological mechanisms in the world. Structurally, it is a combination of elements of the most diverse structures of the body, which, when working simultaneously, implement the visual function.
An important role in the process of implementing the latter is played by the oculomotor apparatus, represented by muscle fibers and those that control them. In today’s material, we’ll talk in more detail about the muscles of the eye, looking at their anatomy and possible pathologies. Interesting? Then be sure to read the material below to the end.
The muscles of the eye have a complex structure
As noted above, the human visual system is a rather complex system.
Its components are no exception and are also extremely complex. Perhaps, the oculomotor apparatus of the eyes considered today is still relatively uncomplicated. But first things first.
Consideration of the anatomy of the muscles of the ocular system should begin with the fact that they are combined into a complex sensorimotor mechanism. The latter, by its nature, immediately implements two most important visual functions:
- Firstly, it ensures the movement of the eyeballs behind the object of gaze.
- Secondly, the resulting image for each eye is combined into a single picture.
This functional purpose also determines the main feature of the oculomotor system, expressed in the close connection of muscles (motor components) and nerve fibers (sensory elements).
Working together, these nodes of the muscular mechanism allow a person to see stably and efficiently. Structurally, the eye muscles can be of two types:
- Straight ones, which move the eyeballs along a straight axis and are attached to them only on one side.
- Oblique, moving them more flexibly and having a double fastening with those.
Both the first and second muscles of the oculomotor system act under the control of nerves, the main ones of which are considered to be oculomotor, abducens and trochlear.
All nerve endings are responsible for the implementation of specific tasks and functions, but invariably go to the cerebral cortex, from which they are controlled.
The eye muscles, due to their diversity, can jointly organize eye movements in synchronous and asynchronous versions. In any case, the eye muscles are divided into main and auxiliary.
The main difference between the types of fibers is that the first organize the movement of the eyeballs along the main axes, while others complement the variability of their functions (for example, they are responsible for lacrimation).
Examination of the oculomotor system
The anatomy of the eye muscles is much more complex than what was discussed above. In the first paragraph of today’s article, our resource drew attention only to the basis of the summarized question, since its in-depth study within the framework of the article material is almost impossible.
In any case, the noted information will be sufficient to understand the entire essence of the human oculomotor system, so let’s begin to consider methods for examining it for pathologies.
Firstly, one important aspect should be noted - many techniques from the field of ophthalmology are used to diagnose the correct functioning of the extraocular muscles. The main tests and instrumental measures are:
- Examination of the eyeball.
- Evaluation of the process of eye tracking the movement of an object, both together with two apples and separately.
- (ultrasound).
- Computed tomography (CT).
- Magnetic resonance imaging (MRI).
To obtain the most accurate and high-quality information about the correct operation of the oculomotor mechanism, the noted diagnostic procedures are carried out in a single complex.
Some of them (examination, tracking testing) are necessary to obtain basic data on the condition of the eye muscles and identify the first signs of their pathologies. If there are unfavorable suspicions, a more global examination is required, so they resort to ultrasound, CT and MRI.
By the way, these diagnostic methods make it possible to identify the pathological condition of not only the muscle fibers themselves, but also the nerves that control them.
An examination of the oculomotor system is carried out exclusively by a professional doctor, namely.
For really high-quality, quick and effective diagnostics, it is advisable to be examined in specialized centers specializing in ophthalmology. Do not forget that only such medical institutions have the necessary equipment and specialists with the required qualifications.
Possible pathologies of the muscles of the organs of vision
Muscles of the eye: schematically There is probably no need to talk about the importance of a completely healthy state of the eye muscles.
Everyone understands that only with the correct operation of the oculomotor mechanism, the human visual system is able to realize its functions.
Any deviation in the functioning of muscle fibers or nerves manifests itself in visual impairment and the development of corresponding pathologies. Most often, the muscular system of the eyes suffers from:
- Myasthenia gravis is a weakness of muscle fibers that does not allow them to properly move the eyeballs.
- Muscle paralysis or paresis, expressed in structural damage to the muscular-nervous structure and the inability of muscle fibers to perform their functions.
- Muscle spasm, accompanied by excessive tension in the eye muscles and associated problems (for example, inflammation).
- Congenital anomalies of the oculomotor system (aplasia, hypoplasia, etc.) are pathologies that are expressed in disturbances in the functioning of the eye muscles or their nerves from the very birth of a person and are anatomical defects.
Symptoms of damage to the muscular-nervous structure of the human ocular system have a typical formation for different lesions. As a rule, signs of pathology include:
- Diplopia is a violation of binocular vision (doubling the image of the surrounding reality received through the eyes).
- Nystagmus is an involuntary movement of the eyes that naturally interferes with the ability to focus on a specific area.
- Pain in the eye sockets or head, which is a consequence of constant muscle spasm or improper functioning of their nerves.
If the noted symptoms are present, the patient must be prescribed a set of examination measures described in the previous paragraph of the article. Based on the results of all types of diagnostics, treatment is organized, which can be either conservative or surgical.
Note that in the case of damage to the muscles of the ocular apparatus, direct surgery is most often used, since other methods of therapy, as a rule, are not particularly effective or are completely pointless.
The severity of the disease and methods of its treatment are determined exclusively by a professional ophthalmologist, which should not be forgotten.
The prognosis for treatment of 2/3 of the pathologies of the muscular mechanism of the eyes is favorable. However, it is important to understand that even with such a prognosis, there are risks of not fully returning vision. If we are talking about congenital anomalies of the apparatus, then the situation is even more complicated.
With these pathologies, often nothing can be done at all. Unfortunately, ophthalmology has not yet fully studied all aspects of the treatment of eye diseases of this kind.
On this note, we will conclude the story on the topic of today’s article. We hope that the material presented was useful to you and provided answers to your questions. As you can see, the anatomical structure of the eye muscles and their pathologies are not so difficult to consider. Good health to you!
Anatomy of the eye muscles - topic of the video:
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