Amblyopia also known as “lazy eye” or “lazy vision” may occur in one eye or both eyes. Unilateral amblyopia (reduced vision in one eye) is known to occur in approximately 2-4 % of the general population. Early detection and treatment are necessary to achieve the best possible vision in adulthood.
Amblyopia simply put, means reduced vision without obvious defect or problem in an eye. While people think of vision as something that occurs in the eye, it actually is a complex process which occurs in the brain where the signals from the eye are processed. Amblyopia is actually a problem in the brain where the visual input is either not fully processed, or is suppressed. This usually occurs in one eye, but sometimes can affect both.
Babies are not born being able to see. An infant’s brain needs to learn how to see by being exposed to input from the eyes. Visual development begins at birth, has a very significant progression until the age of about two years, and continues until the age about nine years on average. Any disruption in how vision forms in one or both eyes during this time frame will disrupt a child’s future visual ability. There are many causes for amblyopia, but it is usually categorized into three groups, based on the underlying problem:
- Refractive: In these cases, there is a very unequal need for glasses between the eyes with one eye always out of focus (anisometropia) causing vision loss in the blurred eye. There may also be a very strong need for glasses in both eyes, causing subnormal visual development on both sides. This can be caused by hyperopia (far-sightedness), myopia (near-sightedness), astigmatism (irregularly shaped corneas), or a combination of one or more.
- Deprivational: In these cases, there is a physical blockage of vision that deprives the eye of visual input. Common causes of this type of amblyopia are congenital cataract (clouded lens of the eye) and ptosis (droopy upper eyelid covering the pupil).
- Strabismic: In these cases, strabismus (eye misalignment – discussed on another page on this website) prevents the patient from using both eyes simultaneously since each is pointed in a different direction. As an adaptation, rather than seeing double, the brain suppresses the vision in one eye. Over time, during the period of visual development, this suppression becomes permanent.
Amblyopia treatment is a two-pronged approach. One is treating the underlying cause. Refractive amblyopia will initially be treated with glasses. In most cases, glasses are to be worn full time during waking hours. Cases of deprivational amblyopia usually require surgery, with removal of a cataract (clouded lens) or repair of ptosis (droopy lid). Strabismic amblyopia requires straightening of the eyes to enable simultaneous use. This may require surgery, glasses, or other modalities.
The second prong of attack is forcing the patient’s brain to begin using the amblyopic eye more. In cases where simply correcting the underlying cause is not enough to restore vision, this becomes necessary. The mainstay of this treatment is penalizing the good eye to force the brain to use the amblyopic eye by temporary occlusion of the better eye with a patch or blurring of the better eye by the use of drops called atropine.
The goal of amblyopia treatment is to correct vision to the best possible level while the visual system is maturing and then to maintain it there until the visual system reaches maturity, which occurs approximately at the age nine years. Visual outcome will depend greatly both on the age when a problem begins and how long it is present before treatment is started. Given this, early detection and treatment are essential.