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.
Many people make the mistake of saying that a person who has a crossed or turned eye (strabismus) has a "lazy eye", but lazy eye (amblyopia) and strabismus are not the same condition. Some of the confusion may be due to the fact that strabismus can cause amblyopia. Amblyopia can result from a constant unilateral strabismus (i.e., either the right or left eye turns all of the time). Alternating or intermittent strabismus (an eye turn which occurs only some of the time) rarely causes amblyopia.
While a large eye turn or deviation (strabismus) is easily spotted by the layman, amblyopia without strabismus or associated with a small deviation is usually not noticed by parents or pediatricians. 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., crossed eyes vs. lazy eye), many people are inaccurately labelled as having a "lazy eye." If you think you or someone you know has lazy eye, it is recommended that you learn more at What is Lazy Eye? and What is Strabismus?, Learn, also, about a common related visual condition which is not detected by the standard 20/20 eye test. See What is Convergence Insufficiency?
To complete the picture, find out about the treatment options for amblyopia and strabismus.
Both eyes must receive clear images during the critical period. Anything that interferes with clear vision in either eye during the critical period (birth to 6 years of age) can result in amblyopia (a reduction in vision not corrected by glasses or elimination of an eye turn). 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 trauma, lid droop, etc. If one eye sees clearly and the other sees a blur, the good eye and brain will inhibit (block, suppress, ignore) the eye with the blur. Thus, amblyopia is a neurologically active process. The inhibition process (suppression) can result in a permanent decrease in the vision in that eye that can not be corrected with glasses, lenses, or lasik surgery.
Since amblyopia usually occurs in one eye only, many parents and children may be unaware of the condition. Far too many parents fail to take their infants and toddlers in for an early comprehensive vision examination and many children go undiagnosed until they have their eyes examined at the eye doctor's office at a later age.
The most important diagnostic tools are the special visual acuity tests other than the standard 20/20 letter charts currently used by schools, pediatricians and eye doctors. Examination with cycloplegic drops can be necessary to detect this condition in the young.