Many people have heard of a “lazy eye”, but aren’t exactly sure what it is, how to avoid it or how to get rid of it. The medical term for a “lazy eye” is amblyopia, which refers to a person who has reduced vision in one eye that is not associated with eye damage or disease. Amblyopia occurs during childhood and is usually due to either an eye that turns in or out (also known as strabismus), or a person who has a very strong glasses prescription in one eye only. While amblyopia is preventable, it is also the most common visual impairment among children and occurs in ~2% of the population. The most significant word of that previous sentence is preventable. So what can you do?
The most important thing is for your children to have annual eye exams by an optometrist. How young is too young? Children should definitely have a complete eye exam before entering kindergarten or pre-school to ensure proper vision and eye health for learning. However, kids can be examined at any age, even less than one year, to check for proper focusing, eye movement, and ocular health. Most importantly, see your eye care professional right away if you notice your child’s eye turning either in or out, if they close one eye a lot of the time or if they complain about seeing double images or blurred images. The visual pathways that lead to good vision and eye health over a lifetime are formed primarily by approximately age ten. Therefore, it is important to address any potential problems during that time in order to prevent irreversible vision loss.
Common Causes of Lazy Eye: Developmental Problems in the Brain
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).
Common Causes of Lazy Eye: Strabismus, Anismetropia, Blockage of Eye
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.
Less common causes of lazy eye are reported to be congenital disorders and vitamin A deficiency.
Common Causes of Lazy Eye: "Suppression"
Frequent suppression (blocking out or ignoring) of one eye's image by the brain can lead to the development of a lazy eye condition. The following visual conditions can cause suppression:
- Strabismus: the two eyes do not aim at the same place, so the brain will suppress -- block, ignore, inhibit -- one eye in order to avoid confusion and/or double vision (diplopia). This type of lazy eye condition is easier to detect because there is an eye turn that is visible to the outside observer.
- Anismetropic Amblyopia: the two eyes have significant differences in eyesight, visual perception, or prescription (e.g., differences in astigmatism, nearsightedness, farsightedness, etc.). In this case, the brain perceives two mismatching images and opts to throw one out (suppress) to avoid rivalry between the two eyes or double vision (diplopia). This type of lazy eye often goes undetected and untreated because there can be no visible eye misalignment or the eye turn is occasional.
- Refractive Amblyopia (a type of anismetropic amblyopia): one eye sees clearly and the other eye sees blurry, so the brain suppresses the eye with the blur.
- Convergence Insufficiency: this common near vision disorder can cause suppression in one eye, but because the suppression is occasional (intermittent) and/or might alternate between one eye and then, the other, it rarely leads to a true lazy eye condition (Amblyopia).
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.
In conclusion, improvements are possible at any age, but early detection and treatment offer the best outcome. If not detected and treated early in life, amblyopia can cause a permanent loss of vision with associated loss of stereopsis (two eyed depth perception). Better vision screenings are needed for young children. The 20/20 eye chart screening is not adequate.
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.