Strabismus is a medical term for any misalignment of the eyes. It is estimated that 4% of the United States population has strabismus, and there are a number of different types. The type of strabismus is usually described by the direction of the eye misalignment; esotropia, exotropia, hypotropia, and hypertropia.(described later). Strabismus can also be described by its cause. The 3 cranial nerves (III, IV, VI) responsible for eye movement can be weak or “palsied” and cause strabismus (third nerve palsy, superior oblique palsy). Some special patterns of strabismus have unique names including Brown syndrome and Duane syndrome.
Four common types are defined here:
- Esotropia is the inward turning of one or both eyes. A commonly used term for esotropia is “cross-eyed.” (infantile esotropia, accommodative esotropia).
- Exotropia is the outward turning of one or both eyes. A commonly used term for exotropia is “wall-eyed.”
- Hypertropia is one eye higher than the other.
- Hypotropia is one eye lower than the other.
What causes strabismus?
Most strabismus is caused by a malfunction in how the brain controls the eye movements. The reason this happens is not well understood. Less commonly, a problem with the eye muscles themselves causes strabismus.
How is strabismus related to amblyopia?
Also known as “lazy eye,” amblyopia is reduced vision in an otherwise healthy eye. Vision must develop throughout childhood, and development is impaired when eyes do not focus equally or maintain proper alignment. The brain ignores the information from the less favored eye. When the eyes are looking in different directions, the brain receives 2 different visual images. The brain ignores the image from the misaligned eye to avoid double vision, resulting in poor vision development.
Treatment
The goal of strabismus and amblyopia treatment is to straighten the eyes and allow the eyes to be used together (binocular vision). Treatment may involve eye glasses (glasses for children), patching, eye exercises and/ or eye muscle surgery (strabismus surgery). Other problems present along with the strabismus (including amblyopia, ptosis, and cataract) are usually treated prior to eye muscle surgery.