When there is any kind of imbalance between the eyes, the brain sometimes begins to "ignore" signals from the weaker eye. As a result, even though the eye may be structurally sound, it becomes functionally blind. This condition is known as amblyopia, or "lazy eye."
Amblyopia most often results when the eyes are not aligned (strabismus) or when one eye is significantly more nearsighted (myopia), farsighted (hyperopia) or astigmatic (astigmatism) than the other. It can also occur when the vision in one eye is weakened by cataracts. Amblyopia affects two or three children out of every hundred, and it is the most common cause of visual impairment in the young. Treatment for amblyopia is most successful when begun before the age of seven. Children with amblyopia who do not receive treatment will likely suffer from it their whole life.
At the Eye Institute, most patients with amblyopia receive treatment through our Adult Strabismus and Pediatric Ophthalmology unit. The key to preventing or reversing amblyopia is encouraging the brain to start using the weak eye. There are two ways to do this: In the first, the child wears an adhesive patch over the strong eye for several hours a day. This forces the brain to begin to use nerve signals from the weaker eye, and the section of the brain responsible for vision in that eye begins to develop. One drawback to this treatment is that the child must wear the patch for two or more hours each day for many weeks or months.
An alternative treatment is to use special eye drops that cause the vision to blur in the dominant eye. Again, deprived of using the good eye, the brain begins to use the weaker eye. The advantage of this method is that it eliminates the patch struggle. The Eye Institute recently took part in a national study that found eye drops work as well as patching in cases of moderate amblyopia. To find out which method might be better for your child, talk to your eye care specialist.