Good vision requires the coordination of signals from both eyes in the visual cortex of the brain. Amblyopia, also known as "lazy eye," results when one eye is significantly weaker than the other, so that the brain comes to ignore the input from that eye. If left untreated, amblyopia can cause permanent visual impairment and loss of depth perception.
Purpose
Patching involves the application of an opaque barrier--usually an adhesive bandage--over the stronger eye for several hours per day. With no input from the strong eye, the brain must rely solely on input from the weaker eye. Over time, the brain strengthens its existing connections to the weaker eye, and vision improves.
Prognosis
When detected early, treatment of amblyopia by patching can significantly and permanently improve vision. Children under the age of seven have the best results, because at that age the connections between the eyes and brain are still forming, says the National Eye Institute. However, the results of a study sponsored by the National Eye Institute show that older children, once believed not to benefit from treatment for amblyopia, also improve with patching. Children from seven to 12 years old received glasses alone or glasses and patching treatment for amblyopia. When tested with a standard eye chart, 53 percent of the children who had worn a patch were able to read two extra lines further than before, as compared to only 25 percent of those who were not patched.
Advantages
In a 2002 clinical trial sponsored by the National Eye Institute, 79 percent of children who wore an eye patch showed significant improvement in their vision after six months. In addition to being highly effective, patching is also a simple and very low cost option with no side effects.
Disadvantages
The major problem with patching is that many children intensely dislike wearing the patch. Adhesive patches can be uncomfortable or irritating to the skin around the eye. Children might dislike the distorted vision that results from seeing only with their weaker eye, or they might suffer from teasing when wearing the patch. Children often refuse to wear the patch or remove it, so the burden of compliance falls on parents. Doctors often recommend that children wear the patch for six hours per day for weeks to months, so this is a significant burden.
Expert Insight
In the "Two vs. Six" study funded by the National Eye Institute, researchers found that for children younger than seven years old with moderate amblyopia, two hours per day of patching was equally effective as the standard regimen of six hours per day. This result should help increase compliance rates for patching therapy.
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