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Conjointed strabismus
Last reviewed: 05.07.2025
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[ What causes concomitant strabismus?
The causes of concomitant strabismus may be congenital and acquired diseases of the central nervous system, ametropia, a sharp decrease in visual acuity or blindness in one eye. The immediate causes of concomitant strabismus are the lack of precise alignment of the visual axes of the eyeballs with the object of fixation and the inability to hold them on this object, since the main regulator (binocular vision) is out of order.
The accommodation-refractive factor is of the utmost importance in the development of concomitant strabismus. Optimal relationships between accommodation and convergence are formed under conditions of emmetropia: each diopter of accommodation corresponds to one metroangle of convergence. In farsightedness, accommodation is excessively enhanced. As a result, in hyperopia, an increased impulse for convergence occurs. On the contrary, in myopia, the need for accommodation is either significantly reduced or absent. This weakens the stimulus for convergence. Thus, in uncorrected hyperopia, there is a tendency toward convergent strabismus, and in uncorrected myopia, toward divergent strabismus.
The nature of concomitant strabismus is associated with a congenital lack of ability to develop fusion (fusion theory) and a congenital deficiency of binocular vision (functional theory). A number of researchers attribute an important role to heredity, and it is not strabismus that is inherited, but a complex of factors that contribute to its appearance.
Symptoms of concomitant strabismus
The primary angle of deviation is the angle of deviation of the squinting eye, and the secondary angle is the angle of deviation of the healthy eye. The Hirschberg method is convenient for determining the angle of strabismus. The patient fixes the eye opening of the hand ophthalmoscope, and the doctor observes the position of the light reflexes on the cornea of one and the other eye from a distance of 35-40 cm. The coincidence of the light reflex with the edge of the pupil (with an average width of 3.5 mm) corresponds to a squint angle of 50°, the reflex on the iris near the edge of the pupil - 20°, at the middle of the distance between the edge of the pupil and the limbus - 30°, on the limbus - 45°, on the sclera 3 mm from the limbus - 60°.
According to the clinical classification of concomitant strabismus, the following types of strabismus are distinguished: periodic, constant, unilateral (one eye squints), alternating (both eyes squint alternately), convergent (the eye deviates from the fixation point toward the nose), divergent (the eye deviates toward the temple), supravergent (strabismus upward), infravergent (strabismus downward). Concomitant strabismus is called accommodative if the deviation is eliminated under the influence of wearing glasses, and non-accommodative when optical correction does not affect the position of the squinting eye. If the angle of deviation is not completely eliminated when wearing glasses, it is called partially accommodative strabismus.
Accommodative strabismus
Accommodative strabismus develops at 2-4 years of age with uncorrected hyperopia above the age norm (+3 diopters).
During these years, the child begins to examine closely located and small objects, which places greater demands on accommodation. Excessive accommodation strain, especially with uncorrected hyperopia, causes an excessive convergence reflex. The eyes deviate inward, at first inconstantly, and then the strabismus becomes permanent quite quickly.
Partial accommodative strabismus has all the features of accommodative strabismus, as well as motor disorders: incomplete abduction, nystagmus at extreme eye positions, vertical deviations.
Non-accommodative strabismus is based on paresis of the oculomotor muscles caused by intrauterine and birth trauma or disease in the postnatal period.
Regardless of the type of strabismus, complications arise that make it difficult to correct: inhibition scotoma, disbinocular amblyopia, abnormal retinal correspondence.
Inhibition scotoma is the suppression by consciousness of the image coming from the squinting eye, which frees the patient from double vision. As soon as the fixing eye is switched off from the act of binocular vision (covered), the scotoma disappears, and central vision in the squinting eye is restored. Therefore, inhibition scotoma is also called functional scotoma.
In monocular strabismus, a persistent scotoma of inhibition can lead to a significant decrease in the vision of the squinting eye, despite the absence of changes in the fundus. Such a decrease in the vision of the squinting eye without visible organic causes is called amblyopia from disuse or disbinocular amblyopia.
The adaptive reaction of the eye, which relieves the patient from diplopia (double vision), is the abnormal correspondence of the retina. Its essence lies in the fact that between the yellow spot of the squinting eye and the area of the retina on which the image of the object falls in the squinting eye, a new functional connection arises, adapting the deviated eye to binocular vision at the angle of strabismus. In this case, binocular vision is incomplete, real fusion of images does not occur (simultaneous vision is noted).