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.
According to researchers at New York University's Center for Neural Science, "Amblyopia results from developmental problems in the brain. When the parts of the brain concerned with visual processing do not function properly, problems ensue with such visual functions as the perception of movement, depth (depth perception), and fine detail (acuity, clear eyesight, sharp vision). Amblyopia is the most prevalent neurological defect of vision in children and adults, affecting 1-3 percent of the population."
Anything that interferes with clear unobstructed vision in either eye during the early or "critical" period of visual and brain development (birth to 6 years of age) can cause a lazy eye. In addition, interference to or lack of simultaneous use of both eyes together (binocular vision) can cause what is called a "suppression" or "inhibition" response in the brain. In some cases, this suppression pattern can result in a decrease in the vision in the blurry eye that can not be corrected with glasses, lenses, or lasik surgery. Again, it is important to understand that the loss of vision is taking place in the brain. That is, Lazy Eye (Amblyopia) is a neurological condition. Notably, current scientific research shows that the brain can change, develop, and recover at any age with occupational, physical, and visual therapies (Vision Therapy).
The Image from One Eye is Suppressed in the Brain (Suppression) The following visual conditions can cause suppression of one eye's image in the brain which can cause to the development of a lazy eye condition:
The most common causes of amblyopia are constant strabismus (constant turn of one eye in any direction, but an inward turn or crossed eyes is much more common), Anisometropia (differences in vision and/or prescription between the two eyes) which leads to anismetropic amblyopia or refractive amblyopia, and/or physical blockage of an eye due to cataract, trauma, lid droop (ptosis), blocked tear duct, etc. Other less common causes are reported to be congenital disorders and vitamin A deficiency.
Since amblyopia usually occurs in one eye only AND a lazy eye condition can exist without a noticable eye turn, many parents and children are not aware of any symptoms. In other words, unfortunately, symptoms of lazy eye are often NOT obvious to the outside observer (parent, teacher, school nurse or pediatrician, etc.).
An eye exam by a pediatrician or the 20/20 eye chart screening simply is not adequate for the detection of amblyopia (and other early childhood visual conditions). The most important diagnostic tools are the special visual acuity tests other than the 20/20 eye test charts currently used by schools and pediatricians. and general eye doctors. Examination with cycloplegic drops can be necessary to detect this condition in young children.
Comprehensive vision evaluations are highly recommended for infants and pre-school children. Otherwise, many children go undiagnosed until they have their eyes examined at the eye doctor's office at a much later age.
Neuroscience has proven that the human brain can change at any age (neuroplasticity), so lazy eye is treatable at any age, too. Treatment involves glasses, atropine drops, eye patching, and/or vision therapy, which includes eye exercises, visual-motor processing activities and neurological therapies. Medical research has proven that lazy eye is successfully treated up to the age of 17 with therapies. See National Institutes of Health -- National Eye Institute; Older Children Can Benefit From Treatment; Lazy Eye.
To quote Dr. Leonard J. Press, FAAO, FCOVD:
Treatment of amblyopia after the age of 17 is not dependent upon age, but requires more effort including vision therapy. 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 adult 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!
Although improvements are possible at any age with proper treatment, early detection and treatment still offer the best outcome. Nevertheless, a desire for treatment at an early age should not motivate a rush to lazy eye surgery. When considering treatment options, it is important to understand that lazy eye results from problems in the brain (neurological deficit) and surgery commonly done for lazy eye is performed on the muscles on the outside of the eye(s) only. In many cases, lazy eye surgery will provide cosmetic benefits only and does not improve the patient's vision. Treatment options that are directed specifically toward vision improvement should be exhausted before eye muscle surgery is considered.
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.
Convergence Insufficiency is a fairly common visual condition which is also (1) confused with lazy eye; (2) not easily discernable to the observer and (3) not detected by the standard 20/20 eye test. Convergence Insufficiency is estimated to affect 5 out of 100 children and adults.