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Six eye muscles that are attached to the outside of each eye are responsible to control eye movement. These six muscles are known as the extraocular muscles. One muscle is responsible is move the eye to the right, one muscle is responsible to move the eye to the left and the remaining four muscles are responsible for vertical, horizontal and angular movement. With proper binocular vision, both eyes are able to work together to focus on an object. The brain is responsible to ensure that all of the muscles in a single eye are balanced to work together and that both eyes are coordinated to move together. Strabismus is lack of such balance and coordination. Strabismus may be caused by either a brain disorder where the brain has trouble coordinating the eyes or a muscle disorder where the direction or power of one or more eye muscles fails to properly function. Strabismus has been shown to occur equally in males and females.

Strabismus may also be an indication of a lesion on either the Oculomotor, Trochlear or Abducens nerves of the eye, which are known as Cranial Nerves III, IV and VI, respectively. Such lesions are cause for failure of innervations in the eye muscles, which causes changes in the positioning of the eye.

A family history of Strabismus1, the loss of circulation that results from diabetes, cataracts, farsightedness, eye tumors and any other disease that is cause for a loss of vision are contributing factors in the development of Strabismus. While a family history of Strabismus is common with many Strabismus patients, other patients have no family history of the condition. Neurological conditions, such as Cerebral Palsy, hydrocephalus premature birth, brain tumors and Down’s syndrome, may also contribute to Acquired (adult) Strabismus, but Congenital (child) Strabismus is rarely complemented with such neurological conditions. Acquired Strabismus may also develop as a result of untreated or unsuccessfully treated Congenital Strabismus.

A diagnosis of individuals with the following symptoms is necessary to confirm the existence and extent of Strabismus as well as the required treatment for the condition.

  1. The eyes appear to be crossed
  2. The eyes do not align in the same direction
  3. There is visible indication that the eyes do not move together in coordination.
  4. An individual experiences double vision
  5. An individual experiences vision in only one eye
  6. An individual experiences a loss of depth perception


1. FERREIRA, Rosane da Cruz, OELRICH, Faye and BATEMAN, Bronwyn. Genetic aspects of strabismus. Arq. Bras. Oftalmol. [online]. 2002, vol. 65, no. 2 [cited 2008-07-06], pp. 171-175. Available from: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0004-27492002000200004&lng=en&nrm=iso .
ISSN 0004-2749. doi: 10.1590/S0004-27492002000200004