A cataract is when the clear part of the eye, the lens, loses transparency. The acquired form is associated with aging (senile cataract), but some cataracts can be caused by an eye injury or ionizing radiation, or can be associated with pharmacological products.

A congenital cataract is a loss of transparency from birth. The patient complains of a slow and progressive loss of vision associated with changes in their perception of primary colors. Surgery is required and involves removing the cataract and replacing it with a customized artificial lens implant.