Amblyopia, known colloquially as “lazy eye”, refers to a visual disorder characterised by undeveloped vision in an otherwise normal and healthy eye. Amblyopia is caused by poor or no transmission of visual images from the affected eye to the brain, and is most successfully treated if detected in early childhood.
The term “lazy eye” is somewhat deceiving, as neither the eye’s nor the individual’s laziness is the cause of the condition. Amblyopia is in fact caused by a developmental issue in the brain, when the area of the brain corresponding to the affected eye develops abnormally because of under-stimulation.
Amblyopia should not be confused with strabismus, which refers to eyes that are not aligned with each other, although strabismus in infancy can eventually lead to amblyopia as the brain ignores the image coming from one eye to avoid seeing double. Congenital cataracts in early years can also lead to amblyopia, as a result of the deprivation of visual input from the clouded eye. In addition, in children with different refractive errors in their two eyes, the brain may learn to ignore the signals from the worse eye, which can also cause amblyopia. A difference in refractive errors between eyes is referred to as anisometropia.
Amblyopia may go unnoticed for many years, as individuals rely on vision from their stronger eye. In more severe cases, however, amblyopes may suffer from poor depth perception, special acuity, and low sensitivity to contrast.
Amblyopia is typically treated by forcing use of the amblyopic eye, using either a patch or otherwise temporarily disabling the healthy eye. This treatment is most effective in children under the age of 5, but has also been shown to benefit older children and adults.
It is also important to address the underlying cause of amblyopia. If amblyopia is caused by refractive errors, it is also important to correct the errors using glasses or contact lenses, and cataracts should be removed as early as possible. Surgical or non-surgical means may be used to straighten misaligned eyes.