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Strabismus
Last reviewed: 04.07.2025
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Strabismus (heterotropia) is a deviation of one eye from a common fixation point, accompanied by a violation of binocular vision. This disease manifests itself not only by the formation of a cosmetic defect, but also by a violation of both monocular and binocular visual functions.
Strabismus is one of the most common forms of visual organ pathology. Strabismus is detected in 1.5-2.5% of children. In addition to a cosmetic defect, which is very distressing psychologically, strabismus is accompanied by a serious disorder of binocular functions. This complicates visual activity and limits the possibility of choosing a profession.
[ Causes of strabismus
Strabismus is polyetiological. Its development can be caused by ametropia (hypermetropia, myopia, astigmatism), anisometropia (different refraction of the two eyes), uneven tone of the oculomotor muscles, dysfunction of their function, diseases leading to blindness or significant reduction in vision of one eye, congenital defects of the binocular vision mechanism. All these factors affect the not yet formed and insufficiently stable mechanism of binocular fixation in children and in case of exposure to unfavorable factors (infectious diseases, stress, visual fatigue) can lead to the development of strabismus.
Types and symptoms of strabismus
There are two types of strabismus - concomitant and paralytic, which differ in both pathogenesis and clinical picture.
In imaginary strabismus, the angle formed by the visual line and the optical axis of the eye is 2-3° larger than its normal value (normally, the angle is within 3-4"). The impression of strabismus can be created by epicanthus, features of the width of the palpebral fissure, an unusually small or large distance between the pupils of both eyes. The absence of adjustment movements and the presence of binocular vision confirm the diagnosis of imaginary strabismus, in which case treatment is not required.
Latent strabismus (heterophoria) is characterized by the correct position of both open eyes, the absence of binocular vision. With latent strabismus, the eye can deviate inward, outward, upward or downward.
Ideal muscular balance of both eyes is called orthophoria. Heterophoria is much more common than orthophoria. Heterophoria can be detected by observing the adjustment movement and excluding conditions for binocular vision. If one eye deviates to one side or another according to the type of heterophoria, and after removing the hand makes an adjustment movement to the side opposite to that to which it was deviated, this indicates the presence of strabismus, corrected by an impulse to binocular vision. With orthophoria, the eye remains at rest. Imaginary strabismus, most types of heterophoria are not considered a pathology of the oculomotor apparatus. Only true strabismus is a pathology, which is divided into concomitant and paralytic.
Latent strabismus, or heterophoria
Ideal muscular balance of both eyes is called orthophoria (from the 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 preserved.
The majority (70-80%) of healthy people have heterophoria (from the Greek heteros - other), or hidden strabismus. With heterophoria, there is no ideal balance of the functions of the oculomotor muscles, but the symmetrical position of the eyes is maintained due to the binocular fusion of the visual images of both eyes.
Heterophoria may be caused by anatomical or neural factors (features of the structure of the orbit, tone of the oculomotor muscles, etc.). The diagnosis of heterophoria is based on the exclusion of conditions for binocular vision.
A simple way to determine heterophoria is the covering test. The patient fixes an object (the end of a pencil, the examiner's finger) with both eyes, then the doctor covers one eye with his hand. If heterophoria is present, the covered eye will deviate in the direction of the predominant muscle: inward (with esophoria) or outward (with exophoria). If the hand is removed, this eye, due to the desire for binocular fusion (which is excluded when covered with the hand), will perform an adjustment movement to the initial position. In the case of orthophoria, the symmetrical position of the eyes will be preserved.
In case of heterophoria, no treatment is required, only if it is significantly expressed, binocular decompensation and asthenopia (pain in the eye area, above the eyebrows) may occur. In these cases, glasses (spherical or prismatic) are prescribed to facilitate vision.
False squint
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 going from the central pit of the macula to the object of fixation - the so-called gamma angle (y). In some cases, this angle reaches 7-8° 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 does not require treatment.
Concomitant strabismus
Concomitant strabismus is a pathology observed mainly in childhood, the most frequently developing form of oculomotor disorders, which, in addition to the deviation of the eye from the common fixation point, is characterized by a violation of binocular vision. It is detected in 1.5-2.5% of children. With concomitant strabismus, the functions of the oculomotor muscles are preserved, while one eye will be fixing, the other - squinting.
Depending on the direction of deviation of the squinting eye, a distinction is made between convergent strabismus (esotropia), divergent strabismus (exotropia), vertical strabismus with one eye deviating upward or downward (hyper- and hypotropia). With torsional displacements of the eye (tilt of its vertical meridian toward the nose or temple), we speak of cyclotropia (ex- and incyclotropia). Combined strabismus is also possible.
Of all the types of concomitant strabismus, the most frequently observed are convergent (70-80% of cases) and divergent (15-20%). Vertical and torsional deviations are usually observed in paretic and paralytic strabismus.
Depending on the nature of the deviation of the eye, a distinction is made between unilateral, i.e. monolateral, strabismus, when one eye constantly squints, and alternating, in which one eye then the other squints alternately.
Depending on the degree of participation of accommodation in the occurrence of strabismus, a distinction is made between accommodative, partially accommodative and non-accommodative strabismus. The impulse to accommodation is increased in hyperopia and decreased in myopia. Normally, there is a certain connection between accommodation and convergence, and these functions are carried out simultaneously. In strabismus, their relationships are disrupted. An increased impulse to accommodation in hyperopia, most often observed in childhood, enhances the stimulus to convergence and causes a high frequency of convergent strabismus.
Accommodative strabismus
Accommodative strabismus (more than 15% of patients) is characterized by the fact that deviation (deviation of the eye) is eliminated by optical correction of ametropia, i.e. constant wearing of glasses. In this case, binocular vision is 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 surgical intervention. In case of partial-accommodative strabismus, wearing glasses reduces, but does not completely eliminate the deviation.
Strabismus can also be permanent or periodic, when the presence of deviation alternates with 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), and impaired depth vision.
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Treatment of strabismus
Treatment for strabismus includes the prescription of glasses, pleoptics, orthoptics, and surgical intervention on the oculomotor muscles.
Glasses for strabismus are prescribed to correct the refractive error. This improves vision, has a significant effect on the position of the eyes, normalizes the relationship between accommodation and convergence, and creates conditions for the development of binocular vision. Glasses are prescribed based on objective refraction determination data under conditions of medicinal relaxation of accommodation (atropine instillation). Subsequently, as the eye grows and refraction changes towards emmetropia, the power of the corrective lenses should decrease, and eventually glasses may be completely discontinued.
With convergent strabismus, almost 70% of children have hyperopia. It is fully corrected with a discount of 0.5-1 D for the tone of the ciliary muscle. In 60% of children with divergent strabismus, myopia develops. In these cases, full correction of myopia is prescribed.
Treatment of strabismus with surgery
To eliminate strabismus, two types of operations are used: strengthening and weakening the action of muscles. Operations that strengthen the action of muscles include resection - shortening the muscle by excising its section at the point of attachment to the sclera and suturing it back to this place. Of the operations that weaken the action of muscles, the most common is recession - moving the muscle, cut at the point of attachment, backwards (in interventions on the straight muscles) or forwards (in interventions on the oblique muscles) with suturing it to the sclera.
The optimal age for performing surgery for concomitant strabismus should be considered to be 3-5 years, when the ineffectiveness of optical correction of ametropia has already become quite clear and active orthoptic exercises can be performed in the pre- and postoperative periods.
The type of surgical intervention, the size of resection or recession are selected depending on the type and angle of strabismus. In many cases, it is necessary to resort to combined operations (for example, recession and resection simultaneously), interventions on both eyes (in case of alternating strabismus), and perform surgical correction of strabismus in several stages. If after the first stage of the operation a residual angle of strabismus remains, then the second stage of the operation is performed after 6-8 months.
In the postoperative period, pleopto-orthoptic treatment is continued, aimed at restoring and strengthening binocular vision using the methods listed above.