Definition & Facts
Amblyopia involves the eye being unable to attain visual acuity. Amblyopia usually begins in infancy or early childhood. It is the leading cause of vision loss in children. Many people who have had amblyopia since childhood may not become aware of it until adulthood because their vision in one eye is normal. One cause of amblyopia involves the brain attempting to prevent double vision by effectively “shutting off” visual input from a misaligned eye.
Symptoms & Complaints
However, in many cases of amblyopia the eyes appear to move together normally and the major symptom is blurred vision in one or both eyes. Patients may also experience poor depth perception because of lack of visual input from one eye. They may be less sensitive in perceiving contrast and motion than average.
There are three main types of amblyopia: strabismic, deprivational, and refractive.
- Strabismic: Strabismus, or misalignment of the eyes, is a common cause of amblyopia.
- Deprivational: Amblyopia can be caused by a visual obstruction such as a cataract, or a clouding of the front of the eye.
- Refractive: Amblyopia can also occur when one eye is not able to focus as well as the other one. For example, one eye may have perfect vision while the other is farsighted or nearsighted. The brain ignores the weaker eye.
Diagnosis & Tests
It is important to diagnose and treat amblyopia as early as possible, but since the disorder often develops in infancy or early childhood it can be difficult to diagnose in very young children. Generally it is diagnosed by testing both eyes for visual acuity and finding low acuity that cannot be ruled out by structural problems with the eye or any identifiable disease process. Since young children cannot usually verbalize their ability to see clearly, a doctor may observe them during a test that measures their ability to follow a moving object with one eye while the other is covered.
A type of test called retinal birefringence scanning (RBS) may be able to identify amblyopia in young children by determining the central fixation point of the eye, thereby detecting misalignment and strabismic amblyopia. Another test, the Lang stereotest can rule out strabismic but not refractive or deprivational amblyopia.
Treatment & Therapy
Treatment for amblyopia is most likely to be successful in early childhood. Most treatments use some form of hindrance to the stronger eye to encourage the brain to use the weaker eye. Frequently this involves intermittent use of an eyepatch to cover the stronger eye.
The best kind of patch is an adhesive “band-aid”-type patch that can be placed over the eye. “Pirate patches”, usually a piece of cloth secured with an elastic band, are not as recommended because they can be easy to peek around. Eyepatching should be done for only part of the day for about 4-6 hours in order to prevent over-inhibiting the good eye, because this could actually lead to reverse-amblyopia affecting the opposite eye due to the the continuous disuse.
Sometimes treating the strong eye with topical atropine has been used instead of an eyepatch, because it can temporarily dilate the pupil and induce blurring of the eye, but this method has been criticized for its potential to cause nodules to develop in the good eye. In deprivational amblyopia, the visual obstruction should be removed, such as via cataract surgery if necessary.
It is very important to correct refractive vision errors with glasses or contact lenses. However, corrective lenses, though able to be worn as early as one week old, are usually not completely effective at treating amblyopia on their own because the brain is not used to processing a clear image from the affected eye and in many cases will continue to see a blurred image from that eye even with the use of corrected lenses. That is why most treatments focus on “forcing” the brain to use the weaker eye by obstructing the stronger one.
If amblyopia is not improved through treatment during early childhood it can become harder to treat at an older age, but there is some evidence from research at the National Institutes of Health that therapies such as combining an eyepatch with activities designed to challenge and strengthen the weaker eye can cause some improvement of amblyopia in younger teens (up to age 14). For example, there are several apps and computer games available that are designed to exercise the weaker eye.
Prevention & Prophylaxis