“Taking Cognizance of Amblyopia and Amblyopia Therapy”
Unilateral or Bilateral decrease in the vision for which no cause is found even after physical examination of the eye is referred to asamblyopia.Understanding of amblyopia and amblyopia therapy has now gained prominence. Two types of amblyopia are known:
1. Functional amblyopia
2. Organic amblyopia.
While functional amblyopia is a potentially reversible condition that can be managed by occlusion therapy, organic amblyopia is irreversible. With correct intervention is initiated, vision loss can be prevented. The recovery of vision depends on some factors such as length of the deprivation, age whenthe therapy began and level of maturity of visual connections. Ruling out of organic cause of decreased vision is advised as diseases may not be diagnosed during routine examination. Amblyopia is also caused from disuse from peripheral or foveal retinal stimulation or even by the abnormal binocular interaction, causing different visual input from fovea.
There are three critical periods of human visual acuity development:
1. From Birth to 3-5 years: Development of visual acuity from 20/200 to 20/20.
2. From few months to 7 or 8 years: Period of highest risk of amblyopia.
3. From time of deprivation - teenage years: Period of recovery from amblyopia can be done.
Causes of Amblyopia:
1. Elimination of the abnormal binocular interaction caused by a defocused and a focused image can cause inhibition of fovea.
2. In strabismus, the patient favors fixation strongly with one eye, causing inhibition of visual input to the visual pathways.
3. When there is an underutilization of the retina, it can lead to unilateral or bilateral amblyopia. For example in cataract, ptosis or surgical lid closure.
4. Sometimes there are structural abnormalities to the retina or the optic nerve causing amblyopia. In such patients, sometimes functional amblyopiamay be superimposed leading to vision loss.
Amblyopia and Amblyopia Therapy:
1. Rule out organic causes: Once the clinician has ruled out the organic cause and other obstacles of vision such as cataract, in amblyopia and amblyopia therapy is initiated, first step must be to treat refractive errors and/or cataract. Amblyopic eye must have the most accurate optical correction.
2. Subject amblyopic eye to occlusion therapy: This therapy has been the mainstay to treat amblyopia since the 18th century. In this type of amblyopia therapy, patching of the amblyopic eye; full-time or part-time is done. Children must be observed at intervals of 1 week per year of age. Patching can be done by using adhesive patches, use of opaque contact lenses or occluders or adhesive tapes on the glasses. Evidence has suggested that children who wear eye-patch daily for 6 hours can yield better visual acuity at 10 weeks.
3. Penalization Therapy: In children who do not comply with the patch have shown good response with penalization therapy. In one study, it was established that in the atropine penalized patient with moderate amblyopia, penalization therapy was as effective as patching. In the same study (The Amblyopia Treatment Study), it was seen that weekend use of Atropine provided a similar improvement in the amblyopic children aged 3-7 years as that of daily use of atropine. Atropine use is also beneficial for maintenance therapy. During the occlusion therapy, care must be taken to closely supervise the children so that they do not peek. Reward system for older children and use of mittens or splints for infants can be used for this purpose.
4. Surgery: After strabismus is reversed, surgical therapy must be initiated.