Eye movements

The normal position of the eyeballs is the parallelism of the visual axes when fixing a distant object or crossing them while fixing a nearby object.

1. Strabismus is an abnormal position of the eyeballs.
2. Orthophoria - the ideal position of eyeballs (without effort), including in the absence of stimulus to fusion reflex, is rare (most people have a small heterophory).
3. Heterophoria (foria) - the tendency of the eyeballs to deviate (latent strabismus). An additional force is required to maintain the correct position.
4. Heterotrophy (trophia) - wrong position of the eyeballs (manifest form); Foria can become a tropic if:
   • Insufficient strength of muscles to maintain the correct position of the eyes.
   • The stimulus to the fusion reflex is weakened (monocular blurring of the visual image).
   • Violated neurogenic mechanisms that coordinate binocularity.
5. The prefixes "ezo" and "exo" mean the deviation of the eyeball inside and out, respectively. Exophoria is the tendency of the eyeballs to deviate to the outside, esotropia is a manifesting convergent strabismus. The deviation can be vertical (then use the prefixes "gith" - down and "hyper" - up) or torsion.
6. The visual axis (line of sight) connects the fovea with the fixation point, passing through the center of the eyeball. Normally, the visual axes of the two eyes intersect at the fixation point. Fovea is somewhat more temporal than the posterior pole (geometric center); the optic axis passes somewhat nasal to the center of the cornea.
7. The anatomical axis is the line passing through the posterior pole and the center of the cornea.
8. The angle of the kappa is the angle between the visual axis and the anatomical axis, usually about 5. The positive angle of the kappa occurs when the fovea is located more vaguely than the posterior pole, and the negative angle when it is more nasally located. An abnormal angle of the kappa can cause false strabismus (see below).

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

Ducions

Monocular eye movements around the Fick axes include adduction, abduction, elevation, depression, intorsia and extrersion. They are evaluated with monocular occlusion, when the patient follows the object in each position of the gaze.

[6]

Versions

Versions are binocular, simultaneous, conjugate (unidirectional) eye movements.

• Dextrower and left-eyed (gaze to the right, gaze to the left), lifting (gaze up) and lowering (gaze downwards). These four actions translate the eyeball into the secondary position of the eye by rotating around the horizontal (X) or vertical (Z) Fick axes.
• Dextrolevation and dextrodepression (gaze up to the right, gaze down to the right), left-levation and levodepressia (gaze upward to the left and down to the left). These four oblique positions are tertiary positions of the eye, into which the eyeball is translated by rotation around the horizontal and vertical axes.
• Dextrocyclosis and levocyclosis (torsional movements of the upper limb of both eyes to the right, torsion to the left).

Vergencii

These are binocular, simultaneous, disjugate eye movements (oppositely directed). Convergence is a simultaneous adduction (turning inside). Divergence - turning outward from the position of convergence. Convergence can be an arbitrary reflex consisting of 4 components.

1. Tonic convergence with the mandatory innervation tone of the internal rectus muscle, when the patient is in a wakeful state.
2. Proximal convergence is caused by awareness of the proximity of the object.
3. Fusion convergence is an optomotor reflex that supports a binocular single vision and ensures the projection of the same images onto the corresponding areas of the retina of each eye. The reflex is initiated by the bitemporal disparity of the image, no refraction changes occur in this case.
4. The accommodative convergence is induced by accommodation and is part of the synkinetic reflex. Each dioptric accommodation is accompanied by a strengthening of accommodative convergence with a certain ratio of accommodative convergence and accommodation (LC / L). The index is the ratio of the number of prism dioptres (D) to the accommodation diopters (liter). In norm it is 3-5 D (for 1 dpt of accommodation 3-5 D of accommodative convergence are necessary). The pathological index AK / L is important in the event of strabismus.

View Positions

1. The six basic positions of the eye are the positions of the eye yolk, depending on the action of one of the muscles.
   • Dextrowerzia (right outer and left internal muscles).
   • Leftover (left and right inner muscles).
   • Dextroelivation (right upper straight and left lower oblique muscle).
   • Left left (right upper and right lower oblique muscles).
   • Dextrodepression (right lower right and left upper oblique muscles).
   • Levedopressia (left lower right and upper right oblique muscles).
2. Nine diagnostic positions of the eye, in which the eyeball deviation is assessed: six cardinal positions, the primary position, lifting and lowering (Fig.).

Laws of eye movements

1. Agonist and antagonist - a pair of muscles of one eye, driving it in opposite directions. The agonist is the primary muscle that causes the eye to move in a certain direction, the antagonist acts in the opposite direction. For example, the right outer rectus muscle is the antagonist of the right internal rectus muscle.
2. Synergists are the muscles of the same eye acting in the same direction. For example, the upper rectus muscle and the lower oblique muscle of one eye are elevators synergists.
3. Paired muscles are a pair of muscles of different eyes that produce conjugate movements. For example, the paired muscle of the left upper oblique - the lower line of the right eye.
4. Sherrington's law of reciprocal innervation (inhibition) states: increased innervation of the extraocular muscle (for example, the inner rectus muscle of the right eye) is accompanied by a reciprocal decrease in the innervation of the antagonist (the external rectus muscle of the left eye). This means that the contraction of the internal rectus muscle is accompanied by relaxation of the external muscle and vice versa. The law of Sherrington applies to verities and vergences.
5. Hering's law on equal innervation states that when conjugate eye movements, paired muscles receive an equally strong impulse. In the case of paralytic strabism, symmetrical innervation to both muscles is determined by the fixing eye, so the angle of strabismus will vary depending on the fixing eye. For example, when the outer muscle of the left eye is paresis, the fixing eye is the right eye; the deviation of the left eye to the inside arises from the tone of the inner rectus muscle in the absence of the antagonist function - the paretic outer rectus muscle of the left eye. This angle of deflection of the eyeball is called the primary angle. To maintain fixation with a paretic eye, additional innervation is required. However, according to the Hering law, a pulse of the same force is directed to the inner rectus muscle of the right eye (paired muscle), which leads to its hyperfunction and excessive adduction of the right eye. The angle of deviation between the two eyes is called the secondary angle. With paralytic strabism, the secondary angle exceeds the primary angle.

Anatomy of the muscles of the eye

The outer and inner walls of the orbit are located at an angle to 45 relative to each other. Thus, the angle between the orbital axis and the lateral and medial walls of the orbit is 11.4, but for simplicity is equal to 23. When you look directly at the fixation point at the level of the horizon and the raised head (the primary position of the eye), the visual axis forms with an orbital axis an angle of 23 The action of extraocular muscles depends on the position of the eyeball at the time of muscle contraction.

1. Primary action of the muscle is its main action in the primary position of the eyes.
2. Secondary action is an additional effect on the position of the eyeball.
3. The Listing plane is an imaginary coronal plane passing through the center of the eyeball rotation, which rotates relative to the Fick axis, intersecting with the Listing plane.
   • Rotate left and right with respect to the vertical Z axis.
   • Move up and down with respect to the horizontal axis X.
   • Torsional movements about the Y axis, which runs from the front pole to the rear pole as the visual axis.

Direct muscles of the eye of horizontal action

In the primary position of the eye, horizontal straight muscles move only in the horizontal plane relative to the vertical axis Z, i.e. Are limited by their primary action.

1. The internal rectus muscle starts from the Zinn ring at the apex of the orbit and attaches to the sclera nasally at 5.5 mm posterior to the limbus. Its only function is adduction.
2. The external rectus muscle starts from the Zinn ring and is attached to the sclera temporally at 6.9 mm from the limb. Its only function is abduction.

Direct muscles of the eye of vertical action

Vertical straight muscles pass along the axis of the orbit and are attached to the eyeball anterior to the equator, forming an angle of 23 with the visual axis.

The upper rectus muscle starts from the top of the Zinn ring and is attached 7.7 mm posterior to the upper limb.

• The primary function is lifting the eyeball. Secondary actions - adduction and intorsia.
• When the eyeball is diverted by 23 the visual axis and the axis of the orbit coincide. In this position, the muscle does not possess a secondary action and works as a lifting action, which makes the position of the lead optimal for the investigation of the function of the upper rectus muscle.
• If the eyeball could be brought to 67, then the angle between the visual axis and the axis of the orbit would be 90, and the upper rectus muscle would act only as an intortor.

The lower rectus muscle starts from the lower part of the Zinn ring and is attached 6.5 mm posterior to the lower limb.

• Primary function - lowering the eyeball. Secondary - adduction and extrusion.
• With the eyeball on 23, the lower rectus muscle acts only as a lowering muscle. As with the upper rectus muscle, this is the best position for examining the function of the lower rectus muscle.
• If the eyeball could be brought to 67, the lower rectus muscle would act only as an extenter.

Spiral Tillauch

An imaginary line running along the attachment points of the straight muscles is an important anatomical reference point for strabismus surgery. The attachment points are removed from the limb, the line forms a spiral. The closest to the limb is the place of attachment of the internal rectus muscle (5.5 mm), followed by the lower line (6.5 mm), the outer straight line (6.9 mm) and the superior rectus muscle (7.7 mm).

Oblique muscles of the eye

The oblique muscles are attached behind the equator; the angle between the muscles and the visual axis is 51.

The upper oblique muscle starts from the uppermost edge of the visual aperture. It is thrown over the block in the corner between the upper and inner walls of the orbit, then passes posteriorly and laterally, being attached to the posterior upper temporal quadrant of the eyeball.

• The primary function is inversion. Secondary - subsidence and abduction.
• When the eyeball is in the state of 51 reduction, the visual axis coincides with the line of action of the muscles; the muscle acts only as a lowering, which makes this position optimal for examining the function of the upper oblique muscle.
• When the eyeball is diverted to 39, the visual axis and the upper oblique form an angle of 90. In this position, the upper oblique muscle has only the function of the intortor.

The lower oblique muscle begins from a small fossa behind the orbital fissure lateral to the lacrimal sac, passes posteriorly and laterally and is attached to the posterior lower temporal quadrant of the eyeball, close to the macula.

• Primary function - extrusion, secondary - lifting and abduction.
• When the eyeball is in the adduction state 51, the lower oblique muscle acts only as a lift.
• When the eye is shown at 39 ', the main action is extrusion.

Innervation of the muscles of the eye

1. The external rectus muscles are innervated by a 6th pair of cranial nerves (a distracting nerve - an abduction muscle).
2. The upper oblique muscles are inferior to the IV pair of cranial nerves (the nerve block - the muscle is thrown across the block).
3. Other muscles and a levator of the upper eyelid are innervated by a third pair of cranial nerves (oculomotor).

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