what is lazy eye?

Amblyopia also known as a "lazy eye" is a disorder of the visual system that is characterized by poor vision in an eye that is otherwise physically normal. The disorder has been estimated to affect up to 5% of the population and is commonly detected at an early age. The disorder is caused by either no communication or poor communication of visual images to the brain. The disorder normally only affects one eye but has been detected in both eyes of patients. While "lazy eye" is frequently used to refer to amblyopia, the term is misleading because there is no "laziness" of either the eye or the amblyope involved in the condition. The condition is a developmental problem in the brain, not a physical problem in the eye. However, physical problems have been known to induce amblyopia. The part of the brain directly connected to the visual system from the affected eye is not stimulated properly, develops abnormally and is the cause of the disorder. This has been confirmed via direct brain examination. The maximum critical period in humans is from birth to two years old.

 

Many people with amblyopia, especially those who are only mildly affected, are not even aware that they have the condition until testing is carried out later on life, since the vision in their stronger eye is normal. However, people who have severe amblyopia may experience associated visual disorders, most notably poor depth perception. Amblyopia causes low sensitivity to contrast, poor spatial acuity and some higher-level deficits to vision such as reduced sensitivity to motion. These defects are usually specific to the amblyopic eye. Amblyopia also causes problems in vision such as depth perception and difficulty seeing three-dimensional images in hidden stereoscopic displays.

 

Amblyopia can be caused by depriving vision early in life by disorders such as congenital cataracts, strabismus (misaligned eyes), or by anisometropia (different degrees of myopia or hyperopia in each eye). Ambylopia can also occur physiologically after tobacco or alcohol consumption. There are 3 types of amblyopia, strabismic amblyopia, refractive or anisometropic amblyopia and form-deprivation and occlusion amblyopia. Strabismic amblyopia is a condition in which the eyes are misaligned and the condition usually causes double vision since the two eyes are not focused on the same object. Strabismic amblyopia is treated by adjusting the visual image with eyeglasses or placing an eyepatch over the dominant eye. Anisometropic amblyopia is a condition whereby there is a difference in the refraction between the two eyes. The eye that provides the brain with a clearer image typically becomes the dominant eye. The image in the other eye is blurred, which results in abnormal development of one half of the visual system. Pure refractive amblyopia is treated by correcting the refractive error early with prescription lenses and patching the good eye. Form-deprivation amblyopia (amblyopia ex anopsia) results when the ocular media becomes opaque, such as is the case with cataracts or corneal scarring from injuries during birth. These opacities disrupt visual input from reaching the eye, and therefore can hinder development. If not treated quickly, amblyopia can persist even after the cause of the opacity is removed.

 

Treatment for amblyopia begins as soon after diagnosis as possible. Early treatment usually can reverse the condition. Treatment should begin before a child's vision has fully developed (around age 9 or 10). The younger the child is when treatment begins, the better his or her chances are for developing good vision. Early treatment is usually simple, employing glasses, drops, vision therapy, and/or eye patching.

 

Amblyopia can be hard to correct after age 9. But studies suggest that treatment beyond this age can still correct amblyopia. While detection and correction before the age of two is considered to offer the best outcomes, recent scientific research has disproven the long held belief that children over seven years old can not be successfully treated.

 

A child born with a cataract or any defect that keeps light out of the eye needs immediate treatment because amblyopia can become permanent within a few months. Amblyopia that results from misaligned eyes (strabismus) or unequal vision in the eyes (anisometropia) usually develops more slowly. There are several ways to force the weak eye to get stronger. Methods include wearing an eye patch (also called occlusion) and using eyedrops or glasses (also called penalization).

 

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