Strabismus diagnosis

Evaluation of the state of the oculomotor apparatus involves the study of both sensory and motor functions.

When diagnosing strabismus, the patient's medical history must also be taken into account.

1. The timing of onset may indicate the etiology of strabismus. The earlier the onset of strabismus, the more likely it is to require surgical correction. The later the onset of strabismus, the more likely it is to have an accommodative component. Evaluation of previous photographs may be helpful in documenting strabismus or forced head posture.
2. Variability of the angle is an important criterion, since periodic strabismus indicates some preservation of binocular vision. Alternating strabismus suggests symmetrical visual acuity in both eyes.
3. The general condition or developmental anomalies have a sign (for example, the frequency of strabismus in children with cerebral palsy).
4. History of childbirth, including period of pregnancy, birth weight, pathology of intrauterine development or at birth.
5. Family history is important because strabismus is often a hereditary condition, although no specific pattern of inheritance has been found. It is important to know what treatment has been given to other family members.

The study of sensory functions includes 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 suppression scotoma, and the nature of diplopia.

When examining motor functions, the mobility of the eyeballs, the magnitude of deviation, and the degree of dysfunction of various oculomotor muscles are determined.

When collecting anamnesis, it is necessary to find out at what age the strabismus developed, the supposed cause of its development, the presence of injuries and past illnesses, whether one eye always squinted or whether there was an alternating deviation of both eyes, the nature of the treatment, and the duration of wearing glasses.

Visual acuity testing should be performed with and without glasses, as well as with both eyes open, which is especially important in the case of nystagmus.

In addition to the general ophthalmological examination, special methods are used.

To determine the nature of strabismus (unilateral, alternating), a fixation test should be performed: cover the fixating (for example, right) eye of the subject with the 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 the subject has alternating strabismus, but if with both eyes open the left eye squints again, then the strabismus is unilateral.

The type of strabismus and the magnitude of deviation (angle of strabismus) are determined by the direction of deviation of the eye (convergent, divergent, vertical).

The angle of strabismus can be determined using the Hirschberg method. The doctor, having applied a hand ophthalmoscope to his eye, asks the patient to look into the ophthalmoscope opening 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 size 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 of the iris and the limbus with an average pupil width of 3-3.5 mm. In case of convergent strabismus, the outer edge of the pupil is used as a guide, and in case of divergent strabismus, the inner edge is used.

Eye mobility is determined by moving the object of fixation, which the patient follows with his eyes, in eight directions of gaze: right, left, up, down, up - right, up - left, down - right, down - left. With concomitant strabismus, the eyes perform movements in a fairly full volume. With paralytic strabismus, it is advisable to use special methods - coordinatemetry and induced diplopia, which allow identifying the affected muscle.

In case of vertical deviation, the angle of strabismus is determined in 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 rectus muscles of vertical action.

In the presence of amblyopia, the state of visual fixation is assessed using a monobinoscope, one of the main devices used to examine and treat strabismus. The device is designed like a stationary Gulstrand ophthalmoscope, which allows, when the child's head is fixed, to examine the fundus, determine the state of visual fixation, and perform treatment procedures. The child looks at the end of the fixation rod ("needle") of the monobinoscope, the shadow of which is projected (on the fundus) onto the fixation area.

Methods for studying binocular functions in strabismus are based on the principle of separating the fields of vision of the right and left eyes (haploscopy), which allows us 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. The separation of the visual fields of the right and left eyes in this device is carried out mechanically, using two (separate for each eye) movable optical tubes, with the help of which paired test objects are presented to the subject.

The synoptophore test objects can move (horizontally, vertically, torsionally, i.e. clockwise and counterclockwise) and be installed in accordance with the angle of strabismus. They differ in control elements for each eye, which allows, when combining paired (right and left) drawings, to judge the presence or absence of binocular fusion, i.e. fusion, and in its absence - the presence of functional scotoma (when a detail or the entire drawing in front of the squinting eye disappears). In the presence of fusion, fusion reserves are determined by bringing together or moving apart the test objects (optical tubes of the synoptophore) until the test object doubles. When bringing the synoptophore tubes together, positive fusion reserves (convergence reserves) are determined, when moving apart - negative fusion reserves (divergence reserves).

The most significant are positive fusion reserves. When examined on a synoptophore with test No. 2 ("cat") in healthy individuals, they are 16 ± 8°, negative - 5 + 2°, vertical - 2-4 prism diopters (1-2°). Torsion reserves are: incycloreserves (with the vertical meridian of the pattern tilted toward the nose) - 14 ± 2°, excycloreserves (with tilted toward the temple) - 12 + 2°.

Fusion reserves depend on the research conditions (when using different methods - synoptophore or prism), the size of the test 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 the 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), 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 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. The subject looks through red-green glasses: there is a red filter in front of the right eye, and a green (or blue) filter in front of the left. The middle white circle, visible 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. With monocular vision of the right eye through the red glass, the subject sees only red circles (there are two), with monocular vision of the left eye - only green (there are three). With simultaneous vision, he sees five circles: two red and three green, with binocular vision - four circles: two red and two green.

When using polaroid or raster filters (the so-called Bagolini glasses), just as in a color instrument, there is a common object for merging and objects visible only to the right or only to the left eye.

Methods for studying binocular vision differ in the degree of the separating ("dissociating") effect: it is more pronounced in a color device, less so in a Polaroid test and in raster glasses, 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 (in contrast to vision in color red-green glasses), and the separating effect of the rasters is manifested only by thin, mutually perpendicular light stripes passing through a common round light source - the object of fixation. Therefore, when examining with different methods in one and the same patient, it is possible to detect simultaneous vision on a four-point test and binocular vision - in Bagolini raster glasses. This must be remembered when assessing the binocular status and determining treatment tactics.

There are various depth-measuring devices and stereoscopes that allow one to determine the acuity and thresholds (in degrees or linear values) of depth and stereoscopic vision. In this case, the subject 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 values.

Conjugate divergent strabismus is a more favorable form of oculomotor disorders than convergent strabismus, it is less often accompanied by amblyopia. Binocular vision disorders are manifested in divergent strabismus in a milder form, mainly convergence insufficiency is revealed.

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