With the loss of binocular vision, so-called friendly strabismus may occur. In this case, the object fixes only one eye, the second eye, even with high visual acuity, the object does not fix and deviates in one direction or another, which is a visible sign of strabismus.
A feature of friendly squint is that the mobility of each eye is not limited and the squinting eye makes the same amount of movement (up, down, right, left) as non-squinting. Friendly strabismus usually occurs at an early age and adversely affects the psyche of the child, causing him fear of ridicule, isolation and alienation. Strabismus is not only a cosmetic defect, but also a reason for limiting the choice of professions, since strabismus does not have binocular vision.
A serious complication of strabismus is a sharp decrease in the visual acuity of the squinting eye “from inaction,” that is, from non-participation in the act of vision. This decrease in healthy eye vision is called ambiopia.
Types of friendly strabismus.
Depending on which side the eye deviates, distinguish:
• strabismus converging (to the nose),
• divergent (to the temple) and
• vertical (up or down).
If one eye squint, then squint is called monolateral,
If one alternately mows, then the other eye is alternating.
If the strabismus disappears in correctly selected glasses, then it is called accommodative,
If it decreases – partially accommodative,
Does not change in glasses – non – accommodative.
The amount of deviation of the eye (strabismus angle), or deviation, is expressed in degrees and is determined in various ways. The simplest of them, although not very accurate, is the Hirschberg method (Fig .).
It lies in the fact that the researcher is asked to fix the eye with an ophthalmoscope. Naturally, a beam of light reflected from it on the cornea of a non-squinting eye coincides with the center of the pupil. In the second eye, the corneal reflection of light will be displaced (not in the center of the cornea).
If with an average pupil width (3–3.5 mm) the corneal reflection of light will correspond to the edge of the pupil, then the strabismus angle will be 15 °, if the reflection of light is projected between the edge of the pupil and the edge of the cornea – 25-30 °, on the edge of the cornea – 45 ° , beyond the edge of the cornea – 60 ° or more. More precisely, the strabismus angle can be determined on the perimeter or on a special device for the diagnosis and treatment of strabismus – synoptophore.
Strabismus angle measurement by the Hirschberg method.
Above is a diagram,
Below – the position of the light reflex in the study of dependence on the angle of squint.
The main goal of treating friendly strabismus is to restore binocular vision. To do this, it is necessary to solve several problems: correct the incorrect position of the eyes, eliminate amblyopia, restore normal binocular vision.
Treatment of children with strabismus, therefore, includes the following steps:
• treatment of amblyopia, that is, the restoration of high visual acuity of each eye (this treatment is called pleoptic);
• restoration of binocular vision ( orthoptic treatment );
• if necessary, surgical elimination of strabismus through operations on the oculomotor muscles.
Approximately 2-3% of children suffer from amblyopia and strabismus .