Aniridia is a congenital eye defect characterized by the partial or complete absence of the iris, the part of the eye that controls the amount of light reaching the retina. It is often associated with poor development of the cornea, lens, retina and optic nerve, therefore it is associated with reduced optical properties.

Aniridia manifests itself in combination with nystagmus, amblyopia and sometimes mental retardation. Eyes affected by the absence of the iris are extremely photophobic and find it difficult to adapt to sudden changes in lighting conditions. This defect can be most effectively corrected by contact lenses.