February 2015 Online Photo Diagnosis

By William Townsend, OD, FAAO

This is an image of a retroilluminated cornea of a 23-year-old female who has aniridia. Aniridia is a congenital disease so named because of the absence of irides in affected individuals.¹ It is a relatively rare condition; the frequency is estimated to be 1 in 64,000 to 1 in 96,000. The underlying cause of aniridia is a genetic abnormality in the PAX6 gene, located on the 11th chromosome pair. Gillespie syndrome (aniridia, cerebellar ataxia, and mental retardation) and Peters’ anomaly are ocular conditions also associated with PAX6 anomalies.¹

Corneal neovascularization (aniridia-associated keratopathy) refers to the progressive pannus and stromal clouding that eventually develops in aniridia. Other findings associated with aniridia include nystagmus, foveal hypoplasia, cataracts, glaucoma, dry eye, and limbal stem cell deficiency.²

The underlying cause of aniridia-associated keratopathy (AAK) is not well understood, but it is believed to result from primary stem cell deficiency associated with the PAX6 gene.¹ Progressively diminishing vision occurs in the majority of patients who have aniridia and results from progressive neovascularization and scarring of the cornea as well as from cataract development. The dark areas within the non-vascularized portion of the image are nuclear cataracts.

Penetrating keratoplasty is one surgical option for aniridia, but it has a less than stellar success rate. Although there is often an improvement in vision, most grafts ultimately fail due to a recurrence of AAK; one study reported failure in 22 of 22 eyes.³ Allogenic stem cell transplantation has reportedly stabilized the ocular surfaces of up to 70% of individuals who underwent the procedure.³ The use of allografts requires long-term immunosuppression, which can be problematic because of the increased risk for glaucoma in individuals who have aniridia. The Boston keratoprosthesis was implanted in 21 individuals who had severe AAK; 20 of the subjects had visual acuity worse than counting fingers. Postoperative vision at the last visit equal to or better than 20/200 in 15 eyes and equal to or better 20/50 in four eyes.⁴ As opposed to penetrating keratoplasty, the Boston keratoprosthesis procedure has the advantage of not requiring long-term immunosuppression.⁵

Our patient demonstrated significant corneal irregularity; we fit her in toric monthly replacement silicone hydrogel contact lenses in an attempt to reduce distortion of her vision. Her final visual acuity in each eye was 20/80, and she continues to wear her lenses successfully.