Muscular eye disorders can be caused by damage to the nerves that control the muscles in the eye or by damage to the muscles themselves. There are several ocular muscle disorders; some are common, and others are very rare. Muscular eye disorders affect vision, but the extent and the type of vision loss depends on the disease.
Strabismus
Strabismus is a term used to describe any condition in which the two eyes are not lined up properly, often as a result of a muscle disorder in one eye. Strabismus often starts in childhood; it affects around 4 percent of children, VisionRx explains, with males and females being equally affected. Two common types of strabismus are esotropia and exotropia. Esotropia means that one eye turns inward, toward the nose; this is the most common type of strabismus in infants. Exotropia means that one eye drifts or deviates outward; it commonly begins in children ages 2 to 4. Esotropia and exotropia can be constant or intermittent; constant strabismus usually is caused by a muscle weakness and requires surgical correction.
Ocular Myasthenia Gravis
Myasthenia gravis (MG) affects the release of acetycholine, a substance released from nerve endings that causes muscle contraction. MG usually develops in people over age 40. Ocular myasthenia gravis may occur as part of systemic disease or may be found as the only symptom. According to the Myasthenia Gravis Foundation of America, one in every six or seven people with MG have eye involvement only. Because the eyes can be affected differently, eye movements aren't coordinated with one another; this causes double vision and sometimes blurred vision. Eyelids droop and may cover the pupil, reducing vision. Resting the eyes frequently may help decrease the symptoms, which change from day to day in ocular MG.
Kearns-Sayre Syndrome
Kearns-Sayre syndrome is a rare abnormality of mitochondria, energy-producing structures found within cells. Kearns-Sayre syndrome affects the muscles of the eyes, among other muscles; as the diseases progresses, the ability of the eye muscles to move decreases until the eye is unable to move at all, according to the National Institute of Neurological Disorders and Stroke. The retina also is affected, as are heart and other muscle tissues. The disease is fatal.
