What is a strabismus?

Causes and Symptoms

Strabismus affects approximately 5 percent of the population. It may be caused by a problem with the nerve supply to the muscles that move the eye or by poor vision or obstruction of vision in one or both eyes.

The most common type of strabismus is an esotropia (inward deviation) of the eye, which accounts for 75 percent of the cases of crossed eyes. There is also exotropia (outward deviation), hypertropia (upward deviation), and hypotropia (downward deviation) of the eye. When a child with strabismus has a penlight shone in the eye, the light reflected back does not fall on the pupil in the same place. This is referred to as the "corneal light reflex test." When the eyes are aligned, the corneal light reflex will be placed symmetrically on the pupil. It is important to identify strabismus and to have it evaluated to prevent amblyopia (dimness of vision) or blindness in the eye that is deviated. It is also important because, without input from both eyes, it is difficult to perceive depth.

A condition called "pseudostrabismus" gives the appearance of having crossed eyes. It occurs because there is a flat bridge of the nose or extra skin near the nose. In this situation, the corneal light reflex will be symmetrical in the pupil.

Treatment and Therapy

Treatment of strabismus is aimed at avoiding amblyopia and realigning the eyes to restore depth perception. This realignment frequently requires eye muscle surgery. Some cases can be treated with glasses and bifocals. Patients with strabismus and amblyopia are typically prescribed glasses and may be given an eye patch to be worn over the stronger eye in order to strengthen the affected eye. Eye drops are may be substituted for patching. An ophthalmologist should be consulted for the treatment of strabismus.

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