Update on squint and amblyopia.

At birth a baby’s vision is very immature, with an acuity of around 3/601,2. Visual experience in infancy and childhood has a major influence on the development of the visual pathways, particularly the visual cortex3,4. During the critical periods of visual development visual acuity develops as do other modalities such as contrast sensitivity, colour, pattern and motion perception, and binocular function with stereopsis1,2. Disturbance to normal visual development will affect the maturation of these different visual functions, with associated structural changes in the visual pathways and cortex, resulting in amblyopia—i.e. reduced acuity in one or sometimes both eyes without any ocular lesion. Either these children lose binocular function as a result of a squint or they acquire a squint because of poor development of binocular function. The commonest causes for amblyopia are a squint (strabismic amblyopia) or blurring of the image in one eye due to unequal refractive power in the two eyes (anisometropic amblyopia). Psychophysical tests show differences between strabismic and anisometropic amblyopia, but for the patient the effects are similar. Squint and amblyopia are common conditions: about one in fifty children have a squint5, and up to 5% of the population have an amblyopic or lazy eye6,7. In view of their lifelong impact on visual function and physical appearance, with consequences for education, jobs and psychological wellbeing8, good management offers substantial long-term benefits. Recent work favours early diagnosis and treatment, and there has been increasing effort to treat children as soon as possible. There is also renewed interest in the treatment of adults. This article reviews these areas.