People with refractive errors, need glasses to be able to see clearly. They cannot see without their glasses, but as soon as they put their glasses on, the world becomes clear. When the vision cannot be improved even with glasses, even though there is no obvious reason for it, then it is known as Amblyopia or in layman’s terms, lazy eye.

For a newborn child’s vision to develop, normally, clear visual stimulus from the eye has to reach the brain, so that the areas in the brain responsible for processing of vision develops normally. If for any reason, the vision in one or both eyes are poor, the brain is not stimulated to develop normally. The first seven to eight years of life are critical for the treatment of amblyopia as the brain’s plasticity is still high at this time and it is easier to reverse the effects of a lazy eye. As the child gets older, the brain tends to lose its plasticity and it is very difficult to reverse the poor vision of an amblyopic eye with treatment at an older age. 

If the vision in one eye is poor, the child and the parents may not even notice it as the child may continue normally with the good eye. Low vision in both eyes may also be missed sometimes. This is why all children must have their first eye check up by 3 years of age even if they are apparently normal.

The reasons for developing a lazy eye are many. Anything that prevents formation of a clear image on the retina in newborns and very young children may cause a lazy eye.

The most common cause of a lazy eye is high refractive errors (Ametropic amblyopia and Anisometropic amblyopia). Children with high plus powers or high astigmatic errors are particularly at risk. Interestingly, children with low to moderate myopia do not usually develop amblyopia as their near vision remains clear - the brain continues to be well stimulated for near vision and therefore develops normally.

Another common cause of lazy eye is squint. Normally, both eyes move in unison in all directions and always fixate on the same object at all times. The brain receives similar image inputs from both eyes and fuses them into one three-dimensional image. If for some reason, the alignment of the eyes is lost, a squint develops. In this case, the two eyes fixate on two different objects. The images sent to the brain by the eyes are dissimilar and the brain can no longer fuse them into one single image. This leads to confusion and double vision. In an effort to overcome confusion and diplopia, the brain shuts off the image from the squinting eye and this will lead to lazy eye (strabismic amblyopia).

Any opacity in the visual axis may lead to amblyopia (Stimulus deprivation amblyopia). Children born with congenital cataracts, or with congenital drooping of the eyelids (ptosis) will develop dense amblyopia and may need early surgery. Children with corneal opacities resulting from trauma or corneal ulcers also often develop amblyopia. There are many other congenital diseases of the eye that may lead to amblyopia.

The treatment of amblyopia is primarily aimed at treatment of the cause followed by occlusion therapy. Congenital cataracts need to be operated early and glasses prescribed. Children with refractive errors need to be prescribed full refractive correction and need to wear their glasses constantly during all waking hours.

Occlusion (patching) is the mainstay of amblyopia therapy. After careful assessment of the visual acuity, the eye with normal vision is patched so that the eye with low vision may receive maximal stimulation. In children with squints, the good eye is patched so that the squinting eye may be stimulated. Patching may need to be continued even after the eyes have been straightened surgically. Earlier, it was thought that it is necessary to patch the bad eye continuously throughout waking hours, but recent studies by PEDIG (The Pediatric Eye Disease Investigation Group) have shown that patching for six hours a day is sufficient in cases of moderate to severe amblyopia and patching of only two hours a day suffices for mild amblyopia.

In some cases supplementary exercises are also given for amblyopia in addition to patching.