Strabismus and Amblyopia

Strabismus refers to misaligned eyes. Esotropia (crossed eyes) occurs when the eyes turn inward. Exotropia (wall-eye) occurs when the eyes turn outward. When one eye is higher than the other, it is called hypertropia (for the higher eye) or hypotropia (for the lower eye). Strabismus can be subtle or obvious, and can occur occasionally or constantly. It can affect one eye or shift between the eyes.

Strabismus usually begins in infancy or childhood. Some toddlers have accommodative esotropia. Their eyes cross because they need glasses for farsightedness. But most cases of strabismus do not have a well-understood cause. It seems to develop because the eye muscles are uncoordinated and do not move the eyes together. Acquired strabismus can occasionally occur because of a problem in the brain, an injury to the eye socket, or thyroid eye disease.

When young children develop strabismus, they typically have mild symptoms. They may hold their heads to one side if they can use their eyes together in that position. Or, they may close or cover one eye when it deviates, especially at first. Adults, on the other hand, have more symptoms when they develop strabismus. They have double vision (see a second image) and may lose depth perception. At all ages, strabismus is disturbing. Studies show school children with significant strabismus have self-image problems.


Amblyopia

Amblyopia is poor vision in an eye that did not develop normal sight during early childhood. This condition, sometimes referred to as lazy eye, can run in families. The main causes of amblyopia are strabismus, refractive errors, or cloudiness of the eye tissues.

Amblyopia affects about 3-4 out of every 100 people. The best time to correct it is during infancy or early childhood, because after the first nine years of life, the visual system is normally fully developed and usually cannot be changed. It is recommended that children have their eyes and vision monitored by their primary care physician at their well-child visits. If there is a family history of amblyopia, children should be screened by an ophthalmologist.

Strabismus
, or misaligned eyes, is the most common cause of amblyopia. The eye that is misaligned is ignored by the brain and turns off. A refractive error (meaning an eye is nearsighted, farsighted, or has astigmatism) is another cause of amblyopia. If one eye has a very different refractive error from the other eye, or if both eyes have a very strong refractive error, amblyopia can develop in the eye or eyes that are out of focus. The most severe form of amblyopia occurs when cloudiness of the eye tissues prevents any clear image from being processed. This can happen in conditions such as infantile or developmental cataracts.

Amblyopia is detected by finding a difference in vision between the two eyes or poor vision in both eyes. The ophthalmologist will also carefully examine the eyes to see if other eye conditions are causing decreased vision.

Amblyopia is treated by forcing the brain to use the affected eye or eyes. If refractive errors are present, they are corrected with eyeglasses or, less commonly, with contact lenses or refractive surgery. If a cataract or other cloudiness is present, surgery may be necessary to clear the line of sight. Strabismus may require surgery before, during, or after the amblyopia treatment. Patching or blurring the sound eye is then used to improve the vision by forcing the brain to recognize and process information from the affected eye or eyes. Once maximum vision has been obtained, treatment often needs to be continued at least part time for months to years to maintain the recovered vision. The earlier the treatment is begun, the more successful it will be.

Amblyopia
(lazy eye) is closely related to strabismus. Children learn to suppress double vision so effectively that the deviating eye gradually loses vision. It may be necessary to patch the good eye and wear glasses before treating the strabismus. Amblyopia does not occur when alternate eyes deviate, and adults do not develop amblyopia.

Strabismus is often treated by surgically adjusting the tension on the eye muscles. The goal of surgery is to get the eyes close enough to perfectly straight that it is hard to see any residual deviation. Surgery usually improves the conditions though the results are rarely perfect. Results are usually better in young children. Surgery can be done with local anesthesia in some adults, but requires general anesthesia in children, usually as an outpatient. Prisms and Botox injections of the eye muscles are alternatives to surgery in some cases. Eye exercises alone are rarely effective when large degrees of strabismus or amblyopia are present.