Aniridia is a panocular, bilateral congenital disorder characterized by iris hypoplasia (Fig 5-11). Most patients with aniridia have only a rudimentary stump of iris; however, the iris appearance may vary greatly, with some patients having nearly complete but thin irides. Aniridia is associated with other ocular anomalies, including microcornea, anterior polar cataracts that may present at birth or develop later in life, and optic nerve and foveal hypoplasia resulting in pendular nystagmus and reduced visual acuity.
It had been thought that patients with aniridia develop glaucoma after the rudimentary iris stump rotates anteriorly to progressively cover the trabecular meshwork, resulting in synechial angle closure. A recent study, however, showed that aniridia patients without previous intraocular surgery did not have angle closure even when they had glaucoma. This suggests intraocular surgery, especially angle surgery, may trigger the formation of angle closure. IOP elevation in aniridia may not occur until the second decade of life or later. Occasionally, however, aniridia is associated with congenital glaucoma; primary maldevelopment of the drainage angle may result in elevated IOP at a younger age.
Figure 11-5 Iris morphology in aniridia in 2 patients with documented PAX6 mutations. A, An eye with aniridia with no iris visible on slit-lamp biomicroscopy, exposing zonules and lens edge. B, An eye with aniridia in which remnants of rudimentary, hypoplastic iris tissue are present. Peripheral aniridic keratopathy, a classic finding in aniridia, is also present.
(Courtesy of Peter A. Netland, MD, PhD.)
Patients with aniridia may have limbal stem cell abnormalities that eventually result in a corneal pannus, which begins in the peripheral cornea and slowly extends centrally. If corneal opacification threatens visual acuity, keratolimbal allograft stem cell transplantation can be performed. Implantation of an artificial iris can be performed for cosmesis; however, this implant is not recommended for children younger than 16 years.
Most cases of aniridia are familial and are transmitted with an autosomal dominant inheritance pattern; however, about one-third of cases result from isolated sporadic mutations in PAX6. Approximately 20% of sporadic cases are associated with a large chromosomal deletion that includes the adjacent Wilms tumor 1 gene (WT1), a tumor suppressor gene, which results in an increased risk of Wilms tumor. Relatively few cases of Wilms tumor are seen in the familial form.
Two less-common forms of aniridia are associated with systemic abnormalities. WAGR (Wilms tumor, aniridia, genitourinary anomalies, and mental retardation) syndrome is an autosomal dominant form seen in 13% of patients with aniridia. Gillespie syndrome is an autosomal recessive form of aniridia associated with cerebellar ataxia and intellectual disability that occurs in 2% of those with aniridia.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.