Amblyopia or lazy eye is the condition affecting 4% of the general population wherein one eye has less vision than the other . It is usually detected on school vision screening or following a routine visit to the optician. It is usually entirely asymptomatic but may be associated with a squint in some cases. Confusingly, a squint or misallgnment of the eyes or a droopy eyelid (ptosis) may be referred to as a lazy eye as well. It is important to differentiate between these and this page deals exclusively with amblyopia.
The causes of amblyopia can be
Difference in the power of the two eyes: If the refractive power of the two eyes a significantly different e.g if one eye has a high minus or plus power, the brain prefers to use the other eye to see and the development of the eye with the high error lags behind.
Squint or Strabismus: some children may be born with or develop a squint which leads to the eyes being misaligned. As a result, when one eye looks straight ahead the other may be turned in or outwards. If this is a constant phenomenon it leads to poor vision in the deviating eye.
Stimulus Deprivation : This occurs when the vision out of one (or both ) eyes is impaired temporarily by a cataract, droopy eyelid etc. In childhood. This leads to an unequal signal to the brain from the two eyes and as a result the eye with the worse vision lags behind even when the deprivation is removed.
Treatment of Amblyopia: The principle behind amlyopia treatment is penalising the good eye to allow the eye with the worse vision to develop better. Treatment should be instituted as soon as possible after diagnosis and works best before the age of seven. The treatment methods include:
Patching of the good eye: This can be carried out between half and hour to three hours a day depending on the severity of the amblyopia. Recent reports suggest that a maximum patching time of two hours is sufficient for most moderate cases.
Drops: In children unable ( or unwilling ) to patch, drops can be used to blur the vision on the good eye on a semi permanent basis. This has the advantage of avoiding a potentially socially stigmatising patch and has been shown to be as good as patching in most cases.
Squint surgery in patients with amblyopia should be carried out once the treatment is complete and no further improvement in vision is expected , for the best results.