Amblyopia (the lazy eye)

Amblyopia

Amblyopia also known as the lazy eye, is a term given to any condition when vision in one eye is reduced (less than 6/6), with corrective lenses with no obvious cause. The eye looks normal but is not in proper use. The brain does not work properly with the eye.

Amblyopia begins in infancy and early childhood. In most of the cases, only one eye is affected. But there are cases where visual acuity is reduced in both eyes. Amblyopia can be organic or functional. Functional amblyopia includes refractive, strabismic and psychogenic (hysterical) amblyopia. Amblyopia due to strabismus and uncorrected refractive error often expresses suppression phenomenon.

Strabismic Amblyopia being most common form of amblyopia occurs in strabismic patients as a result of long-continued suppression of the visual inputs of the deviating eye. To prevent double vision from the misaligned eye, the brain ignores the inputs from the deviating eye leading to amblyopia of that eye.

Strabismic amblyopia normally occurs in children, the integrating area for the visual sensation in the brain is poorly developed for the amblyopic eye. The visual acuity in the strabismic eye may be as poor as 6/60. Visual acuity assessment is quite difficult with amblyopic patients; they read few letters on each line. Visual acuity improves with decrease in the number of stimulus presented.

Refractive Amblyopia results from uncorrected anisometropia or uncorrected astigmatism. The brain suppresses vision from the more defective eye and shifts its concentration to vision from the less defective eye. For example, if the right eye is more hyperopic than the left eye, the more hyperopic eye will be regularly suppressed and will never see a sharply focused image. This will lead to amblyopia of that eye.

Psychogenic Amblyopia is an amblyopia caused by emotional stressors. It is of psychological origin and not physiologic. It usually occurs in children and the prognosis is usually good.

Organic Amblyopia- occurs at any age in life. An example is deprivational amblyopia, it is usually due to cataract, opacity of the cornea, or haziness of the ocular media. Here, there is obstruction of vision leading to poor vision in that eye. Organic amblyopia may resolve if detected early, with treatment of the underlying cause. But in long standing cases the amblyopia may persist even after resolution of the underlying cause.

Treatment

Amblyopia can be treated in cases of uncorrected refractive errors by fully correcting the refractive errors in both eyes with glasses or contact lenses.

Amblyopia can be managed by patching the good eye for several hours in a day for weeks or months. This forces the brain to make use of the amblyopic eye. There by, improving vision in that eye. Contact lenses that prevent light from entering the eye and still maintain the child’s appearance can be used in place of patching.

Penalization is another treatment option for amblyopia. This involves use of atropine to cause mydriasis of the “good” eye. Atropine is instilled once a day, this blurs vision in that eye and prevents bullying of the other eye. The side effects of atropine should be considered while treating with atropine. Atropine relaxes the ciliary muscles therefore preventing accommodation. Atropine also disturbs change in focus, and increases the light sensitivity of the individual as there is an increase in the diameter of the pupil allowing excessive light to get into the eye.

Flicker Glass by Eyetronix treats amblyopia by using rapid alternating occlusion to improve coordination of both eyes.

Strabismic surgery is another alternative. It involves aligning both eyes to improve coordination and vision.

Revitalvision is the only FDA-approved computerized treatment for amblyopia. This program helps older amblyopes (from age 9 and above) improve their vision. It consists of 40 training sessions of 40 minutes each which are conducted over a period of several weeks.

Eccentric Fixation is another adaptation mechanism to strabismus, which occur along with amblyopia. Here, an off-foveal point in the retina of the strabismic eye is used for fixation, in both monocular and binocular vision.

The amount of eccentric fixation is related to the depth of amblyopia present. Greater amblyopia results in larger angle of fixation. It is considered (eccentric fixation) parafoveal if it is between 1 and 3 degrees, paramacular if 3 and 5 degrees, and peripheral if greater than 5 degrees. Detection and measurement of eccentric fixation can be achieved using most modern ophthalmoscope.