When you look at an object, you're using several muscles to move both eyes to focus on it. If you have a problem with the muscles, the eyes don't work properly.

There are many kinds of eye movement disorders. Two common ones are

• Strabismus - a disorder in which the two eyes don't line up in the same direction. This results in "crossed eyes" or "walleye."
• Nystagmus - fast, uncontrollable movements of the eyes, sometimes called "dancing eyes"

Some eye movement disorders are present at birth. Others develop over time and may be associated with other problems, such as injuries. Treatments include glasses, patches, eye muscle exercises, and surgery. There is no cure for some kinds of eye movement disorders, such as most kinds of nystagmus.

Strabismus is derived from a Greek word, which means “eyes looking obliquely.” Strabismus means misaligned eyes. Often strabismic eyes are referred to as “squinting eyes,” “crossed eyes,” and “wall eyes.” Usually, both eyes fixate equally while focusing on an object with the head held in the primary position. In strabismus or squint, one or both eyes deviate inwards or outwards and appear to be in non-alignment towards the direction of the focused object. It can be due to refractive error or binocular fusion abnormalities or neuromuscular anomalies of ocular movements. If diagnosed and treated early, strabismus has a very good prognosis. Treatment is usually by refractive error correction, orthoptic exercises, occlusive patching, topical medications, and extraocular muscle surgery.

Strabismus involves an imbalance in the positioning of the two eyes. Strabismus can cause the eyes to cross in (esotropia) or turn out (exotropia). Strabismus is caused by a lack of coordination between the eyes. As a result, the eyes look in different directions and do not focus simultaneously on a single point. In most cases of strabismus in children, the cause is unknown. In more than half of these cases, the problem is present at or shortly after birth (congenital strabismus). When the two eyes fail to focus on the same image, there is reduced or absent depth perception and the brain may learn to ignore the input from one eye, causing permanent vision loss in that eye (one type of amblyopia).

The prevalence of strabismus is 2 to 5 percent in the general population. Five to fifteen million population of the United States of America is affected by strabismus. In a National Health Survey, exotropia is seen in 2.1 percent and esotropia in 1.2 percent of the population between 4 to 74 years of age. This difference is due to the higher prevalence of exotropia in the population between 55 to 75 years of age. In a population-based study done in Los Angeles, California, involving children aged between 6 to 72 months, Hispanic/Latino kids showed 2.4 percent, and African Americans showed 2.5 percent of strabismus. Exodeviations were more common than esodeviations.

Fifty percent of all childhood esotropias are either fully or partially accommodative. Non-accommodative esotropia is seen in 10 percent of all strabismus and is the second most common form of childhood esotropia. Infantile esotropia affects one in every 100 to 500 persons, which accounts for 8.1 percent of cases of esotropia. Intermittent esotropia is seen in one percent of the population and is the most common form of exotropia. Exotropia is more prevalent in Asian and African American populations than in Whites. Women are affected in 60 to 70 percent of patients with exotropia.

Nystagmus, sometimes called dancing eyes, is an involuntary movement of the eyes. In a baby or young child, it is usually the parents who first notice that their child's eyes seem to “jiggle” with a motion that is rapid, rhythmic and continuous. The child cannot hold the eyes still and cannot fixate steadily.

Typically, both eyes are involved and move together from side to side; other directions are less common, and some children's eyes seem to move aimlessly. The degree of movement may vary during the day. Most of the time it is small and may be barely visible, especially when the child is concentrating on something up close. At other times it can be more obvious. During sleep, it stops completely.

The movement of the eyeball is under the control of the extrinsic eye muscles, which originate outside the eye and insert onto the outer surface of the white of the eye. These muscles are located inside the eye socket and cannot be seen on any part of the visible eyeball (image and image). If you have ever been to a doctor who held up a finger and asked you to follow it up, down, and to both sides, he or she is checking to make sure your eye muscles are acting in a coordinated pattern.