Aniridia is a congenital ocular disorder characterized by partial or complete absence of the iris. The most obvious manifestation of the condition is iris hypoplasia. However, this can also be accompanied by many other clinical features, including corneal degeneration, cataracts, nystagmus, and foveal and optic nerve hypoplasia. Aniridia typically causes severe visual impairment.
The incidence of congenital aniridia ranges from 1:64,000 to 1:96,000. Aniridia generally occurs in isolation. Rarely, it may be accompanied by other ocular malformations or as part of the rare WAGR (Wilms' Tumor Aniridia Genitourinary Abnormalities and Mental Retardation) Syndrome. Several treatment options are available for managing the glaucoma associated with the condition. These include the use of miotics to improve the aqueous outflow, adrenergic agonists, beta blockers, or carbonic anhydrase inhibitors. Patients may require spectacles to correct refractive errors, and tinted glasses to guard against photophobia. No surgical procedure has been convincingly found to be the treatment of choice for the glaucoma associated with Aniridia.
Aniridia is generally inherited in an autosomal dominant manner with almost complete penetrance and variable expressivity. However, in a third of the cases, it may occur sporadically. In most patients with aniridia, causal mutations have been found in the PAX6 (Paired Box 6) gene, located on chromosome 11. PAX6 codes for a transcription factor that is involved in several development pathways and is expressed early in the development of the eye, numerous regions of the brain, and the pancreas. Within the brain, PAX6 is also involved in the development of the olfactory bulb.