Amblyopia (lazy vision) is a decrease in vision different from being nearsighted or farsighted. Instead of a problem with how the eye focuses light rays, it stems from a problem with how the brain processes information, so the condition usually cannot be corrected with eyeglasses alone. Amblyopia can be mild or severe, and usually only affects one eye.

The part of the brain responsible for clear vision can only develop normally if it is constantly stimulated by clear visual information from both eyes. Amblyopia occurs when the brain chooses to rely more heavily on one eye while ignoring the other. This can happen if the eyes are misaligned (strabismus); if there is a physical blockage to vision in one eye, such as a cataract or a droopy eyelid (ptosis); or if there is a large difference between the prescription strength in one eye compared to the other (anisometropic amblyopia).

The part of the brain responsible for clear vision develops early and rapidly in a child’s life, and amblyopia must be treated as early as possible. Once the visual part of the brain stops developing, usually around age 7-9, the condition may not be reversible.