DESCRIPTION

Amblyopia is a reduction in best corrected visual acuity in one or both eyes that is not attributed directly to a structural abnormality of the eyes or visual pathway. There are three types:

• Refractive amblyopia is due to uncorrected refractive error. Anisometropic amblyopia, which is the most common, is caused by blur in one eye from asymmetric refractive error. Isoametropic amblyopia is caused by significant refractive error in both eyes.
• Strabismic amblyopia is due to misalignment of the eyes, which results in two images that cannot be integrated into a single image in the brain. The visual cortex is dominated by the image from the fixating eye. This condition is most likely with early onset, constant strabismus.
• Deprivation amblyopia is due to eye abnormalities (such as cataract, ptosis, or corneal opacities) that interfere with central vision. This type causes the most severe amblyopia.

EPIDEMIOLOGY

• Amblyopia is the most common cause of unilateral vision loss in children and young adults.
• The prevalence is 2–4% in North America.

PATHOPHYSIOLOGY

During the critical periods of cortical development, the visual system requires sensory input for proper development and is thus vulnerable to abnormal input. In amblyopia, the cells of the primary visual cortex lose their ability to respond to stimulation or show significant functional deficiencies.