Lazy Eye (Amblyopia) and Crossed Eyes (Strabismus) are not the same condition.
Many people make the mistake of saying that a person who has a crossed or turned eye has a "lazy eye," but amblyopia and strabismus are not the same condition. Some of the confusion may be due to the fact that an eye turn can cause lazy eye. In other words, amblyopia can result from a constant unilateral strabismus (i.e., an eye that turns or deviates all of the time). Alternating or intermittent strabismus (an eye turn which occurs only some of the time) rarely causes amblyopia.
While a deviating eye (strabismus) can be easily spotted by the layman, amblyopia without strabismus or associated with a small deviation usually can be not noticed by either you or your pediatrician. Only an eye doctor comfortable in examining young children and infants can detect this type of amblyopia. This is why early infant and pre-school eye examinations are so necessary.
Due to misunderstanding or misuse of the terms for different visual conditions (i.e., deviating eyes vs. lazy eye), many people are inaccurately labeled as having a "lazy eye."
Amblyopia, commonly known as lazy eye, is the eye condition noted by reduced vision not correctable by glasses or contact lenses and is not due to any eye disease. The brain, for some reason, does not fully acknowledge the images seen by the amblyopic eye. This almost always affects only one eye but may manifest with reduction of vision in both eyes. It is estimated that three percent of children under six have some form of amblyopia.
Anything that interferes with clear vision in either eye during the critical period (birth to 6 years of age) can cause amblyopia. The most common causes of amblyopia are constant strabismus (constant turn of one eye), anisometropia (different vision/prescriptions in each eye), and/or blockage of an eye due to cataract, trauma, lid droop, etc.
Amblyopia is a neurologically active process. In other words, the loss of vision takes place in the brain. If one eye sees clearly and the other sees a blur, the brain can inhibit (block, ignore, suppress) the eye with the blur. The brain can also suppress one eye to avoid double vision. The inhibition process (suppression) can result in a permanent decrease in the vision in the blurry eye that can not be corrected with glasses, lenses, or lasik surgery.
Treatment involves glasses, drops, vision therapy and/or patching. Recent medical research has proven that amblyopia is successfully treated up to the age of 17. See National Institutes of Health -- National Eye Institute; Older Children Can Benefit From Treatment; Lazy Eye.
Treatment of amblyopia after the age of 17 is not dependent upon age but requires more effort including vision therapy. Although improvements are possible at any age with proper treatment, early detection and treatment still offer the best outcome.
To quote Dr. Leonard J. Press, FAAO, FCOVD: "It's been proven that a motivated adult with strabismus and/or amblyopia who works diligently at vision therapy can obtain meaningful improvement in visual function. As my patients are fond of saying: "I'm not looking for perfection; I'm looking for you to help me make it better". It's important that eye doctors don't make sweeping value judgments for patients. Rather than saying "nothing can be done", the proper advice would be: "You won't have as much improvement as you would have had at a younger age; but I'll refer you to a vision specialist who can help you if you're motivated."
Every amblyopic patient deserves an attempt at treatment.