Isolated aniridia is a congenital bilateral ocular malformation characterized by the complete or partial absence of the iris.
The annual incidence is estimated at 1/ 64,000- 1/ 96,000.
Isolated aniridia can occur in association with a range of other ocular anomalies including cataract, glaucoma (usually occurring during adolescence), corneal pannus, optic nerve hypoplasia, absence of macular reflex, ectopia lentis, nystagmus, and photophobia, all of which generally result in poor vision.
Aniridia is due to mutations in the PAX6 gene (11p13) encoding a transcriptional regulator involved in oculogenesis. PAX6 mutations result in alterations in corneal cytokeratin expression, cell adhesion and glycoconjugate expression.
Diagnosis is based on ophthalmological examination and is confirmed by mutation detection of the PAX6 gene.
Antenatal diagnosis is only possible when the underlying genetic defect is known. It is performed by invasive procedures like chorionic villus sampling (CVS) or amniocentesis and molecular analysis of fetal DNA.
Aniridia is inherited in an autosomal dominant manner with high penetrance and variable expression. About two-thirds of affected children have an affected parent and one-third of cases occur in sporadic form.
A regular follow-up is necessary. Intraocular pressure should be measured yearly for detection of glaucoma. Keratolimbal allograft (a stem cell transplantation technique) has been evaluated as a treatment of the aniridic keratopathy, which is a major cause of vision loss in aniridia patients. Glaucoma drainage is used to treat secondary angle closure glaucoma.
Aniridia results in poor vision, the mean visual acuity being around 0,19 in young adulthood.