Eye movement study

Eye movement testing includes assessment of eye movement control and assessment of saccades.

1. The versions are assessed in 8 eccentric gaze positions. Typically, the patient follows an object (pen or flashlight) that allows corneal reflexes to be assessed. Movements in these directions can be induced voluntarily, acoustically, or by the "doll's head" maneuver.
2. Ductions are assessed when muscle mobility is limited in one or both eyes. A flashlight is needed to accurately assess corneal reflexes. The fellow eye is covered and the patient follows the light source in various gaze positions. A simple motility rating system from 0 (full movement) and -1 to -4 indicates the degree of increasing impairment.

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ]

Nearest point of convergence

This is the point at which fixation is maintained binocularly. It can be assessed using the RAF ruler, which is placed against the patient's cheeks. The object is slowly moved in the direction of the eyes until one of them stops fixating on it and deviates to the side (objective nearest point of convergence). Subjective nearest point of convergence is the point at which the patient begins to complain of diplopia. Normally, the nearest point of convergence should be less than 10 cm.

Nearest point of accommodation

This is the point at which binocular image clarity is maintained. It can also be assessed using the RAF ruler. The patient fixes the line, which is then slowly moved proximally until it becomes defocused. The distance at which the image becomes blurred determines the nearest point of accommodation. The nearest point of convergence moves away with age, and its significant movement is accompanied by difficulties in reading without adequate optical correction, which indicates presbyopia. At the age of 20, the nearest point of convergence is 8 cm, and at the age of 50 it can be more than 46 cm.

Fusion amplitude

It is a measure of the efficiency of disjugate movements and can be studied using prisms or a synoptophore. Prisms of increasing power are placed in front of the eye, which goes into a state of abduction or adduction (depending on the base of the prism: inwards or outwards, respectively) to maintain bifoveal fixation. If the prism power exceeds the fusion reserves, diplopia occurs or one eye deviates to the opposite side. This is the limit of vergence ability.

Fusion reserves should be assessed in each patient at risk of developing diplopia in the postoperative period.

Refraction and ophthalmoscopy

Ophthalmoscopy with a wide pupil is mandatory when examining a patient with strabismus to exclude pathology of the fundus, such as macular scars, optic disc hypoplasia, or retinoblastoma. Strabismus may be of refractive origin. A combination of hyperopia, astigmatism, anisometropia, and myopia with strabismus is possible.

[ 7 ], [ 8 ], [ 9 ], [ 10 ], [ 11 ]

Cycloplegia

The most common cause of strabismus is hyperopia. To accurately assess the degree of hyperopia, maximum paresis of the ciliary muscle (cycloplegia) is necessary to neutralize accommodation, which masks the true refraction of the eye.

Cyclopentolate allows achieving adequate cycloplegia in most children. Up to 6 months of age, 0.5% cyclopentolate should be used, later - 1%. Two drops instilled at an interval of 5 minutes lead to maximum ophthalmoplegia in 30 minutes with subsequent restoration of accommodation in 24 hours. The adequacy of cycloplegia is checked skiascopically when the patient fixates distant and close objects. With adequate cycloplegia, the differences will be minimal. If a difference still exists and cycloplegia has not reached its maximum, then it is necessary to wait another 15 minutes or instill an additional drop of cyclopentolate.

Local anesthesia, such as proxymetacaine, is advisable before instillation of cyclopentolate to prevent irritation and reflex lacrimation, allowing cyclopentolate to remain in the conjunctival cavity longer and achieving more effective cycloplegia.

Atropine may be necessary in children under 4 years of age with high hyperopia or heavily pigmented irises, for whom cyclopentolate may be insufficient. It is easier to instill atropine drops than to apply ointment. Atropine 0.5% is used in children under 1 year and 1% - over 1 year. Maximum cycloplegia occurs after 3 hours, accommodation begins to recover after 3 days and is completely restored after 10 days. Parents instill atropine to the child 3 times a day for 3 days before skiascopy. It is necessary to stop instillations and seek medical help at the first signs of systemic intoxication, hot flashes, fever or restlessness.

[ 12 ], [ 13 ], [ 14 ], [ 15 ], [ 16 ], [ 17 ], [ 18 ]

When to prescribe glasses?

Any significant refractive error should be corrected, especially in patients with anisohyperopia or anisoastigmatism accompanied by amblyopia.

1. Hyperopia. The minimum hyperopic correction depends on the age and position of the eyes. In the absence of esotropia in a child under 2 years of age, the minimum correction is +4 D, although in older children it makes sense to correct hyperopia and +2 D. However, in the presence of esotropia, hyperopia should be corrected by +2 D even at the age of up to 2 years.
2. Astigmatism. Cylindrical lenses of 1 D or more should be prescribed, especially in cases of anisometropia.
3. Myopia. The need for correction depends on the child's age. Up to 2 years, it is recommended to correct myopia of -5 D or more. From 2 to 4 years, it is recommended to correct -3 D, and for older children - even a lower degree of myopia to ensure clear fixation of a distant object.

Change in refraction

Since refraction changes with age, examination is recommended every six months. Most children are born with hyperopia. After 2 years, the degree of hyperopia may increase, and astigmatism may decrease. Hyperopia may increase until 6 years, and then (between 6 and 8 years) gradually decrease until adolescence. Children under 6 years of age with hyperopia of less than +2.5 D become emmetropic at the age of 14. However, with esotropia under 6 years of age with a refraction of more than +4.0 D, the probability of decreasing the degree of hyperopia is so small that the correct position of the eyes is not achieved without glasses.

[ 19 ], [ 20 ], [ 21 ], [ 22 ], [ 23 ]

Diplopia study

The Hess test and the Lees screen allow one to depict the position of the eyeballs depending on the function of the extraocular muscles and allow one to differentiate paretic strabismus of neuro-ophthalmological origin from restrictive myopathy in endocrine ophthalmopathy or rupture fractures of the orbit.

Hess test

The screen is a tangential grid applied to a dark gray background. A red flashlight, which can be used to illuminate each object separately, allows each extraocular muscle to be identified in different gaze positions.

1. The patient is seated in front of the screen at a distance of 50 cm, put on red-green glasses (the red glass is in front of the right eye) and given a green “laser” pointer.
2. The examiner projects a vertical red slit from a red "laser" pointer onto the screen, which serves as a fixation point. This is visible only to the right eye, which thus becomes the fixation eye.
3. The patient is asked to place the horizontal slit of the green lamp on the vertical red slit.
4. In orthophoria, the two slits approximately overlap each other in all positions of gaze.
5. Then the glasses are turned over (red filter in front of the left eye) and the procedure is repeated.
6. The dots are connected with straight lines.

Lees Screen

The apparatus consists of two frosted glass screens, positioned at right angles to each other and divided in half by a two-sided flat mirror, which separates the two visual fields. The back surface of each screen has a grid that becomes visible only when the screen is illuminated. The test is conducted with each eye fixated separately.

1. The patient sits in front of an unlit screen and fixes points in the mirror.
2. The examiner indicates the point that the patient should mark.
3. The patient marks with a pointer a point on an unlit screen, which he perceives next to the point shown by the examiner.
4. Once all the points have been plotted, the patient is seated in front of another screen and the procedure is repeated.

Interpretation

1. Compare two schemes.
2. The reduction in the diagram indicates muscle paresis (right eye).
3. Expansion of the scheme - to hyperfunction of the muscle of this eye (left eye).
4. The greatest contraction in the diagram indicates the main direction of action of the paralyzed muscle (the external muscle of the right eye).
5. The greatest expansion of the muscle is in the main direction of action of the paired muscle (the internal rectus muscle of the left eye).

Changes over time

Changes over time serve as a prognostic criterion. For example, in the case of paresis of the superior rectus muscle of the right eye, the Hess test pattern indicates hypofunction of the affected muscle and hyperfunction of the paired muscle (left inferior oblique). Due to the difference in the patterns, the diagnosis is not in doubt. If the function of the paralyzed muscle is restored, both patterns return to normal. However, if the paresis persists, the pattern may change as follows:

• The secondary contracture of the ipsilateral antagonist (the inferior rectus muscle of the right eye) appears on the diagram as hyperfunction, which leads to secondary (inhibitory) paresis of the antagonist of the paired muscle (the left superior oblique), which appears on the diagram as hypofunction. This may lead to the incorrect conclusion that the lesion of the superior oblique muscle of the left eye is primary.
• Over time, the two patterns become increasingly similar until identification of the initially paralyzed muscle becomes impossible.

[ 24 ], [ 25 ], [ 26 ]