Strabismus
Last reviewed: 23.04.2024
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Strabismus (heterotrophy) - the deviation of one eye from the common fixation point, accompanied by a violation of binocular vision. This disease is manifested not only the formation of a cosmetic defect, but also a violation of both monocular and binocular visual functions.
Strabismus is one of the most common forms of pathology in the organ of vision. Strabismus is detected in 1.5-2.5% of children. In addition to the cosmetic drawback, which is very painful psychologically, strabismus is accompanied by a serious disorder of binocular functions. This makes it difficult for visual activity and limits the choice of a profession.
[The causes of strabismus
Strabismus is polyethiologic. The cause of its development may be ametropia (hypermetropia, myopia, astigmatism), anisometropia (different refraction of the two eyes), irregularity of the tonus of the oculomotor muscles, impairment of their function, diseases leading to blindness or a significant decrease in the visualization of one eye, congenital malformations of the binocular vision mechanism. All these factors influence the yet unformed and insufficiently stable mechanism of binocular fixation in children and in the case of adverse factors (infectious diseases, stress, visual fatigue) can lead to strabismus.
Types and symptoms of strabismus
There are two types of strabismus - friendly and paralytic, which differ both in pathogenesis and in the clinical picture.
With imaginary strabismus, the angle formed by the visual line and the optic axis of the eye is greater than its usual value by 2-3 ° (the normal angle is within 3-4 ") .The impression of strabismus can create epicanthus, the width of the eye gap, unusually small or large the distance between the pupils of both eyes.The lack of adjusting movements, the presence of binocular vision confirms the diagnosis of imaginary strabismus, in which treatment is not required.
The latent squint (heterophory) is characterized by the correct position of two open eyes, the absence of binocular vision. With concealed strabismus, the eye can swing to the inside, outward, upward or downward.
The ideal muscular balance of both eyes is called orthophoria. Heterophoria occurs much more often than orthophory. You can detect heterophore by observing the installation movement and excluding the conditions for binocular vision. If one eye deviates in this or that direction according to the type of heterophory, and after taking a hand makes the installation movement in the direction opposite to the one to which it was rejected, this indicates the presence of strabismus, corrected by the impulse to binocular vision. At orthophory the eye remains at rest. Imaginary strabismus, most types of heterophoryia do not belong to the pathology of the oculomotor apparatus. Pathology is only true strabismus, which is divided into friendly and paralytic.
Hidden squint, or heterophory
The ideal muscular balance of both eyes is called orthophoresis (from Greek ortos - straight, regular). In this case, even when the eyes are separated (for example, by covering), their symmetrical position and binocular vision are preserved.
The majority (70-80%) of healthy people have heterophory (from Greek heteros - another), or hidden strabismus. At heterophory there is no perfect balance of the functions of the oculomotor muscles, however the symmetrical position of the eyes is preserved due to the binocular fusion of the visual images of both eyes.
Heterophoria can be caused by anatomical or nervous factors (peculiarities of the structure of the orbit, the tone of the oculomotor muscles, etc.). The diagnosis of heterophory is based on the exclusion of conditions for binocular vision.
A simple way to determine heterophoria is a sample with a cover. The subject fixes an object (the end of the pencil, the finger of the researcher) with two eyes, then the doctor covers one eye with his hand. In the presence of heterophoria, the closed eye will deviate towards the action of the prevailing muscle: inside (with esophoria) or outside (exophory). If the hand is removed, this eye, due to the desire for binocular merging (excluded when covering with the hand) will make the adjusting movement to the starting position. In the case of orthophores, the symmetrical position of the eyes will persist.
When heterophore treatment is not required, only with its significant severity can occur binocular decompensation and asthenopia (pain in the eye, superciliary). In these cases, appoint glasses that facilitate vision (spherical or prismatic).
Imaginary strabismus
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 from the central fovea of the yellow spot to the fixation object, 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 to the temple, resulting in the impression of strabismus. The correct diagnosis can be established after determining binocular vision: with imaginary strabismus, binocular vision is available and no treatment is required.
Friendly strabismus
Friendly strabismus is a pathology that occurs mainly in childhood, the most frequently developing form of oculomotor disorders, which, in addition to deviating from the general fixation point, is characterized by a violation of binocular vision. It is detected in 1.5-2.5% of children. With a friendly strabismus, the functions of the oculomotor muscles remain, with one eye fixing, the other with a mowing one.
Depending on the direction of the deflection of the mowing eye, the converging strabismus (esotropia), divergent (exotrophy), vertical strabismus are distinguished with one eye upward or downward (hyper- and hypotrophy). With torsional displacement of the eye (tilt of its vertical meridian toward the nose or temple), one speaks of cyclotropy (ex-and incisotropy). It is also possible to combine strabismus.
Of all kinds of friendly strabismus, convergence (70-80% of cases) and divergent (15-20%) are most often observed. Vertical and torsional abnormalities are noted, as a rule, with paretic and paralytic strabismus.
By the nature of the deviation, the eyes distinguish one-sided, that is, monolateral, strabismus, when one eye constantly mows, and alternating, in which one or the other eye alternately mows.
Depending on the degree of participation of accommodation in the appearance of strabismus, the accommodative, partially-accommodative and non -accomodational strabismus are distinguished. The impulse to accommodation was increased with hypermetropia and decreased in myopia. Normally, there is a definite link between accommodation and convergence, and these functions are carried out simultaneously. When strabismus, their ratio is violated. The increased impulse to accommodation with hypermetropia, most often observed in childhood, increases the incentive for convergence and causes a high frequency of convergent strabismus.
Accommodation strabismus
The accommodative strabismus (more than 15% of patients) is characterized by the fact that deviation (eye deviation) 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 unaccustomed strabismus, wearing glasses does not eliminate deviation and treatment should necessarily include surgical intervention. With partial-accommodative strabismus, wearing glasses reduces, but does not completely eliminate deviation.
Strabismus can also be permanent or periodic, when the presence of deviation alternates with the symmetrical position of the eyes.
Friendly strabismus is accompanied by the following sensory impairments: decreased visual acuity, eccentric fixation, functional scotoma, diplopia, asymmetric binocular vision (abnormal correspondence of the retina), violation of deep vision.
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Treatment of strabismus
Treatment with strabismus includes the appointment of glasses, pleoptics, orthotics, and surgical intervention on the oculomotor muscles.
Points with strabismus are prescribed in order to correct the refraction anomaly. This improves vision, has a significant effect on the position of the eyes, normalizes the relationship of accommodation and convergence, creates the conditions for the development of binocular vision. The glasses are prescribed on the basis of data by objective determination of refraction in conditions of drug relaxation of accommodation (instillation of atropine). Further, with the growth of the eye and the change in refraction towards the emmetropy, the strength of the corrective glasses should decrease, as a result, glasses can generally be canceled.
With convergent strabismus, almost 70% of children have hypermetropia. It is corrected completely at a discount of 0.5-1 diopters per ton of ciliary muscle. In 60% of children with divergent strabism develop myopia. In these cases, a full correction of myopia is prescribed.
Treatment of strabismus by operation
To eliminate strabismus, two types of operations are used: amplifying and relaxing muscles. To operations that enhance the action of muscles, include resection - shortening of the muscle by excising its site at the place of attachment to the sclera and sewing again to this place. Of the operations weakening the action of muscles, the most common recession - the movement of the muscle, crossed at the attachment, back (with the intervention of the straight muscles) or anterior (with interventions on the oblique muscles) with filing it to the sclera.
The optimal operation for a friendly strabismus should be considered the age of 3-5 years, when the ineffectiveness of optical correction of ametropia has already been clearly demonstrated and active orthoptic exercises can be performed in pre- and postoperative periods.
Type of surgery, the amount of resection or recession is chosen depending on the type and angle of strabismus. In many cases it is necessary to resort to combined operations (for example, recession and resection at the same time), interventions in both eyes (with alternating strabismus), to perform surgical correction of strabismus in several stages. If the residual angle of strabism remains after the first stage of the operation, the second stage of the operation is carried out after 6-8 months.
In the postoperative period, pleopto-orthoptic treatment is continued, aimed at restoring and strengthening binocular vision in the ways listed above.