Strabismus is a misalignment of the eyes. This can mean that one or both eyes deviate inward, outward, upward, or downward. The eye that is deviated typically is not being used by the brain for regular vision. The eyes work together, so if there is vision in both eyes, either eye will deviate depending on which eye is fixating (being used for vision). Usually the brain prefers to use one eye over the other eye, and so one eye will appear more chronically deviated.
Strabismus can be congenital (meaning that a child can be born with it), or acquired. Congenital cases of strabismus are typically do not cause double vision. This problem is usually treated surgically, with attention to any eye preference that develops because this can lead to amblyopia (see pediatric ophthalmology section). The causes of acquired strabismus vary widely, and can be harmless or may herald a dangerous process within the brain or orbit. Therefore, it is important to have acquired types of strabismus evaluated. Acquired types of strabismus typically cause double vision, especially in adults, unless the vision in the deviating eye is extremely poor. Treatment for the double vision usually involves prisms or surgery. Prisms are optical devices placed on spectacles which bend light rays toward their base, which, when given in the proper strength, can often allow patient’s eyes to remain in a deviated position but for the light to be placed into the correct location in their retina so that they see “single”, instead of double.