Amblyopia is a fairly common disease affecting between 1% and 2% of the population of most developed countries.1Amblyopia is the unilateral or, less commonly, bilateral loss of vision caused by abnormal visual inputs during a critical period of visual development. The critical period is seen as the period of time during which abnormal visual inputs can result in amblyopia, but it is also the time during which amblyopia can be reversed by eliminating the abnormal visual inputs and, usually, occluding the normal eye for some periods of time.

However, there are now reasons to believe that these critical periods for development and treatment of amblyopia cannot be rigidly defined. Firstly, it is clear that visual acuity of the amblyopic eye is not always firmly established even after amblyopia therapy has been terminated, because the age of the patient is beyond what is generally considered to be the critical period.2-4 Scott and Dickey reported a short term follow up study of amblyopic patients after patching therapy was stopped. Seventeen per cent of patients lost a line of visual acuity and 8% lost two lines or more.3 In a study of patients 10 years after …