Amblyopia is a term used to describe an uncorrectable loss of vision in an eye that appears to be normal. It's commonly referred to as "lazy eye" and can occur for a variety of reasons.
A child's visual system is fully developed between approximately the ages of 9-11. Until then, children readily adapt to visual problems by suppressing or blocking out an image. If caught early, the problem can often be corrected and the vision preserved. However, after about age 11, it is difficult if not impossible to train the brain to use the eye normally.
Some causes of amblyopia include: strabismus (crossed or turned eye), congenital cataracts, cloudy cornea, droopy eyelid, unequal vision and uncorrected nearsightedness, farsightedness or astigmatism. Amblyopia may occur in various degrees depending on the severity of the underlying problem. Some patients just experience a partial loss; others are only able to recognize motion.
Patients with amblyopia lack binocular vision, or stereopsis - the ability to blend the images of both eyes together. Stereopsis is what allows us to appreciate depth. Without it, the ability to judge distance is impaired.
When amblyopia is suspected, the optometrist will evaluate the following: vision, eye alignment, eye movements, and fusion (the brain's ability to blend two images into a single image).
The treatment for amblyopia depends on the underlying problem. In some cases, the strong eye is temporarily patched so the child is forced to use the weaker eye. For children with problems relating to a refractive error, glasses may be necessary to correct vision. Problems that impair vision such as cataracts or droopy eyelids often require surgery. Regardless of the treatment required, it is of utmost importance that intervention is implemented as early as possible before the child's brain learns to permanently suppress or ignore the eye.
Illustrations by Mark Erickson
With acknowledgement to St. Lukes Eye Hospital.