Amblyopia (lazy eye)

Up until about the age of eight, the visual system is immature and susceptible to amblyopia, in which a “healthy” eye does not see well because it is “turned off” by the brain. Under normal circumstances the brain receives input from both eyes and information from both is precisely integrated resulting in fine depth perception and correct alignment of the eyes. If poor information is sent to the brain from one eye because it is out of focus, usually because of a squint, refractive error or other problem (e.g. cataract), the brain chooses to use the other eye in preference. The other eye is ignored although it is anatomically normal and has the potential to see well. Early detection of amblyopia is essential to institute appropriate treatment and reverse the effects of amblyopia. As a principle the more severe the visual deprivation (e.g. cataract) the earlier it needs to be treated.

Mild to moderate amblyopia affects about 2% of the population. The risk of amblyopia is greatest in early childhood and reduces as the child gets older. With early recognition and treatment of the underlying cause visual loss can be minimised or even completely restored. The extent of the visual impairment from amblyopia ranges from mild to profound and depends upon the underlying cause, the age of onset and delay in identification and treatment.

Early treatment of amblyopia involves correcting the underlying cause, such as correcting a refractive error with spectacles, correcting a squint or surgically removing a cataract. The other key aspect of treatment is to force the brain to use the amblyopic eye by one of three techniques which are patching, pharmacological penalisation and optical penalisation. For a child with severe amblyopia the first line of treatment is patching, which involves covering the good eye every day with an occlusive bandage patch until the vision in the amblyopic eye is optimised. Infants can only be patched for some hours whereas older children may be patched during all of their waking hours. All children must be followed up by an ophthalmologist, optometrist and orthoptist to determine the treatment required, treatment duration and to avoid over treatment of the good eye. Children with moderate amblyopia or those who refuse to use a patch can be treated by pharmacological penalisation with atropine eye drops which blur the good eye. Optical penalisation involves blurring the vision in the good eye by using a spectacle lens.

Prognosis: If detected early and treatment instituted with good compliance, the outlook is good.