Muscles of the eye

The eyeball is attached six striated muscles: four straight - upper, lower, lateral and medial and two oblique - upper and lower. All straight muscles and the upper oblique begin at the depth of the orbit on the common tendon ring (anulus tendineus communis), fixed to the sphenoid bone and periosteum around the optic canal and partly on the edges of the upper globular fissure. This ring surrounds the optic nerve and the eye 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 upper rectus muscle of the eyeball, and ends in the thickness of the upper eyelid. The straight muscles are guided along the corresponding walls of the orbit, to the sides of the optic nerve, perforate the vagina of the eyeball (vagina bulbi) and short tendons are weaved into the sclera in front of the equator, 5-8 mm away from the corneal margin. Straight muscles rotate the eyeball around two mutually perpendicular axes: vertical and horizontal (transverse).

The lateral and medial rectus muscles (mm. Recti lateralis et medialis) rotate the eyeball outside and inside around the vertical axis, each in its direction, respectively, and the pupil turns. The upper and lower rectus muscles (mm. Recti superior et inferior) rotate the eyeball up and down around the transverse axis. The pupil, with the contraction of the upper rectus muscle, is directed upward and somewhat outward, and when the lower rectus muscle is working downward and inside. The upper oblique muscle (m. Obliquus superior) lies in the upper medial part of the orbit between the superior and medial rectus muscles. Near the block fossa, it passes into a round round tendon wrapped in the synovial vagina, which is thrown over the block (trochlea), constructed in the form of a ring of fibrous cartilage. Passing through the block, the tendon lies under the upper rectus muscle and is attached to the eyeball in the upperlateral part of it, behind the equator. The lower oblique muscle (m. Obliquus inferior) unlike the other muscles of the eyeball begins on the orbital surface of the maxilla, near the opening of the nasolacrimal canal, on the lower wall of the orbit. The muscle is directed between the lower wall of the orbit and the lower rectus muscle obliquely up and back. Its short tendon is attached to the eyeball from its lateral side, behind the equator. Both oblique muscles rotate the eyeball around the anteroposterior axis: the upper oblique muscle turns the eyeball and the pupil down and laterally, the lower one - up and laterally. The movements of the right and left eyeballs are coordinated thanks to the friendly action of the oculomotor muscles.

The oculomotor apparatus is a complex sensorimotor mechanism, the physiological significance of which is determined by its two main functions: motor (motor) and sensory (sensory).

The motor function of the oculomotor apparatus ensures the guidance of both eyes, their visual axes and central retinal cavities on the fixation object, the sensory one - the fusion of two monocular (right and left) images into a single visual image.

The innervation of the oculomotor muscles with cranial nerves determines the close connection of the neurological and ocular pathology, which necessitates a complex approach to diagnosis.

[1], [2], [3], [4], [5],

Anatomical and physiological features of the muscles of the eye

The movements of the eyeball are carried out with the help of six oculomotor muscles: the four straight lines - the outer and the inner (m. Rectus externum, m.rectus internum), the upper and lower (m.rectus superior, m.rectus inferior) and the two oblique ones - the upper and lower m.obliguus superior, m.obliguus inferior).

All the straight and upper oblique muscles of the eye begin at the tendon ring located around the optic nerve channel at the apex of the orbit and fused with its periosteum. Straight muscles in the form of ribbons are directed anteriorly parallel to the corresponding walls of the orbit, forming a so-called muscle funnel. At the equator of the eye, they perforate the Tenon capsule (the vagina of the eyeball) and, not reaching the limb, are weaved into the surface layers of the sclera. The Tenon capsule supplies the muscles with a fascial coating that is absent in the proximal part of the place where the muscles begin.

The upper oblique muscle of the eye originates in the tendon ring between the upper and inner rectus muscles and goes anteriorly toward the cartilaginous block located in the upper-right corner of the orbit at its edge. At the block the muscle turns into a tendon and, passing through the block, turns backwards and outwards. Located under the upper rectus muscle, it is attached to the sclera outside of the vertical meridian of the eye. Two-thirds of the entire length of the upper oblique muscle is between the vertex of the orbit and the block, and one third is between the block and the attachment site to the eyeball. This part of the upper oblique muscle determines the direction of movement of the eyeball when it is contracted.

In contrast to the five muscles mentioned, the lower oblique muscle of the eye begins at the lower inner edge of the orbit (in the zone of the lacrimal-nasal canal entrance), extends posteriorly to the outside between the orbital wall and the lower rectus muscle towards the external rectus muscle and is fan-attached underneath it to the sclera in the posterior section eyeball, at the level of the horizontal meridian of the eye.

From the fascial membrane of the oculomotor muscles and the tenon capsule there are numerous strands to the walls of the orbit.

The fascial-muscular apparatus provides a fixed position of the eyeball, gives smoothness to its movements.

Innervation of the muscles of the eye is carried out by three cranial nerves:

• oculomotor nerve - n. Osulomotorius (III pair) - innervates the inner, upper and lower rectus muscles, as well as the lower oblique;
• nerve block - n. Trochlearis (IV pair) - the upper oblique muscle;
• Abduction nerve - n. Abducens (VI pair) - the external rectus muscle.

All these nerves pass into the orbit through the upper orbital fissure.

The oculomotor nerve, after entering the orbit, is divided into two branches. The upper branch innervates the upper rectus muscle and the muscle lifting the upper eyelid, the lower branch - the inner and lower rectus muscles, as well as the lower oblique muscle.

The nucleus of the oculomotor nerve and the nucleus of the block nerve located behind and adjacent to it (ensures the work of the oblique muscles) are located on the bottom of the Sylvian aqueduct (brain drainage). The nucleus of the abduction nerve (ensures the work of the external rectus muscle) is located in the variolic bridge under the bottom of the rhomboid fossa.

The straight eye muscles of the eye attach to the sclera at a distance of 5-7 mm from the limbus, oblique muscles at a distance of 16-19 mm.

The width of the tendons at the place of attachment of the muscles varies from 6-7 to 8-10 mm. Of the straight muscles, the widest tendon in the inner rectus muscle, which plays a major role in the function of reducing the visual axes (convergence).

The line of attachment of the tendons of the inner and outer muscles of the eye, that is, their muscular plane, coincides with the plane of the horizontal meridian of the eye and concentric with the limb. This causes the horizontal movements of the eyes, their reduction, turning to the nose - adduction with a contraction of the internal rectus muscle and retraction, turning to the temple - abduction with a contraction of the external rectus muscle. Thus, these muscles are antagonists by the nature of the action.

The upper and lower lines and oblique muscles of the eye carry out mainly vertical movements of the eye. The line of attachment of the upper and lower rectus muscles is somewhat oblique, their temporal end is farther from the limbus than the nasal. As a consequence, the muscular plane of these muscles does not coincide with the plane of the vertical meridian of the eye and forms with it an angle equal to an average of 20 ° and open to the temple.

Such an attachment ensures that the eyeball rotates when these muscles act not only upward (with the contraction of the upper rectus muscle) or downward (when the lower line is shortened), but simultaneously and internally, i.e., adduction.

The oblique muscles form an angle of about 60 ° with the plane of the vertical meridian open to the nose. This causes a complex mechanism of their action: the upper oblique muscle lowers the eye and produces its abduction (abduction), the lower oblique muscle is a lifter and also an abductor.

In addition to horizontal and vertical movements, these four eye-moving muscles of the eye of vertical action carry out torsion movements of the eyes clockwise or counterclockwise. At the same time, the upper end of the vertical meridian of the eye deviates to the nose (intorsia) or to the temple (extrusion).

Thus, the oculomotor muscles of the eye provide the following eye movements:

• reduction (adduction), i.e., movement of it towards the nose; This function is performed by the internal rectus muscle, in addition - the upper and lower rectus muscles; they are called adductors;
• the abduction (abduction), i.e. The movement of the eye towards the temple; This function is performed by the external rectus muscle, in addition - the upper and lower oblique; they are called abductors;
• movement upwards - under the action of the upper straight and lower oblique muscles; they are called lifters;
• movement downward - with the action of the lower line and the upper oblique muscles; they are called descenders.

Complex interactions of the oculomotor muscles of the eye are manifested in the fact that when moving in one direction they act as synergists (for example, partial adductors - upper and lower rectus muscles, in others - as antagonists (upper straight - lift, lower line - sinker).

Oculomotor muscles provide two types of friendly movements of both eyes:

• one-sided movements (in the same direction - to the right, to the left, up, down) - the so-called verious movements;
• opposing movements (in different directions) - vergent, for example to the nose - convergence (reduction of visual axes) or to the temple - divergence (dilution of visual axes), when one eye turns to the right, the other - to the left.

Vertical and vertex movements can also occur in vertical and oblique directions.

The functions of oculomotor muscles described above characterize the motor activity of the oculomotor apparatus, the sensory one is manifested in the function of binocular vision.

[6], [7], [8], [9], [10]

Pathology of the oculomotor apparatus

Violations of the function of the oculomotor apparatus may manifest in the wrong position of the eyes (strabismus), the limitation or absence of their movements (paresis, paralysis of the oculomotor muscles), violation of the fixative capacity of the eyes (nystagmus).

Strabism is not only a cosmetic defect, but also accompanied by a pronounced disorder of monocular and binocular visual functions, deep vision, diplopia; it hinders visual activity and limits the professional capabilities of a person.

Nystagmus often leads to vision impairment and vision impairment.