Strabismus, commonly known as 'squint' or 'cross-eye' is a misalignment of the visual axes of the eye, usually caused by a lack of co-ordination between the extraocular muscles. As a result, the eyes look in different directions, and cannot focus simultaneously on a single point, preventing binocular vision, and affecting depth perception. Strabismus may be of different types. In incomitant strabismus, the degree of ocular misalignment differs with the direction of gaze; whereas in concomitant strabismus, the degree remains the same, irrespective of the direction or the eye which is fixing. Amblyopia is a complication of strabismus, in which the brain learns to ignore the messages from one of the eyes, leading to loss of vision in that eye. Strabismus may appear in an individual by itself, or as a part of one of several syndromes, such as Duane's syndrome, Brown's syndrome, Mobius syndrome, and sixth nerve palsy.
Various studies in different populations have shown a prevalence of 1-5% for strabismus in the general population. A comprehensive eye examination can easily detect strabismus. Some special tests, such as prism test and Krimsky test are also used to evaluate the degree of alignment of the eyes. Correction of the abnormality requires ocular exercises to strengthen the muscles. Glasses may also be prescribed. In case of a failure to correct the misalignment by exercise alone, surgery can be performed. Amblyopia is corrected by patching the preferred eye, so that the weak eye is forced to be used.
Several studies have conclusively shown the genetic etiology of strabismus, with an average of 37% of the cases showing a positive family history. Linkage of the condition to gene locus 7p22.1 was shown in a large family with strabismus. However, the disorder shows genetic heterogeneity, with chances of more than one gene being involved in its development.