What is Aniridia?
Aniridia is a complete or partial absence of the iris, the colored part of the eye. Aniridia is a rare genetic disorder which may be present at birth or may progress over time. The exact cause for aniridia is unknown but may be due to a failure in optic vesicle rim development during gestation. The prevalence is estimated to range from 1:40,000 births to 1:100,000.
- Aniridia is the underdevelopment or absence of the iris.
- Aniridia is a rare, inherited disorder with ocular and systemic complications
- Those diagnosed have an increased risk of glaucoma, cataracts, and cornea damage.
Aniridia is a rare, sight-threatening disorder that affects many ocular structures including the iris, retina, optic nerve, lens, and cornea. Individuals with aniridia may have an underdeveloped iris or fovea, corneal changes, glaucoma, cataract, lens subluxation, strabismus, optic nerve coloboma and hypoplasia.
Cataracts typically develop in 50–85% of individuals with aniridia during the teenage years or early adulthood. Lens changes in aniridia can be alterations of size and shape, position, and changes in transparency. Cataracts may be polar, cortical, subcapsular, lamellar, and more rarely, the nuclear type.
Elevated intraocular eye pressure (IOP) and glaucoma are common and develop in 30–50% of patients. Studies demonstrate there is an association between the degree of iris hypoplasia and the development of glaucoma. Researchers are unsure whether glaucoma development is due to closure of the angle, the absence of Schlemm canal in patients with aniridia, or abnormalities in the trabecular meshwork.
Keratopathy, a corneal abnormality, occurs later in the disease process. Corneal complications range from mild peripheral vascularization to pan corneal vascularization, opacification, and keratinization. Ocular surface problems like dry eye are common due to inadequate tear production.
56% of patients report a dry eye disease diagnosis. Patients with the condition have elevated tear film osmolarity resulting in inflammation. Individuals with aniridia also have increased atrophy of the meibomian glands resulting in the development of dry eye disease.
Underdevelopment of the fovea (hypoplasia) is usually present. A reduced foveal reflex, macular hypopigmentation and crossing of the usual foveal avascular zone by retinal vessels can be observed with a dilated eye exam.
Optic Nerve Hypoplasia
Optic nerve hypoplasia is present in 10.7% of patients with aniridia. Studies seem to indicate a correlation between foveal hypoplasia and optic nerve hypoplasia.
Aniridia may affect only the eyes or be associated with a systemic disorder like Wilms tumor-aniridia-genital anomalies-retardation (WAGR). Individuals with WAGR have a significant risk of developing Wilms tumor, a malignant tumor of the kidney. Genetic evaluation of aniridia patients exhibit PAX6 deletions that may cause the WT1 (Wilms tumor 1) gene.
Other systemic complications associated with aniridia include reduced olfaction (smell), hearing difficulties, and brain abnormalities.
Risk Factors for Aniridia
Most cases are dominantly inherited gene mutations or deletions of the PAX6 gene. No differences have been noted between races or genders. No environmental exposures or use of medications during pregnancy have been reported to increase the risk of having a child with aniridia.
- Photophobia (light-sensitivity)
- Poor vision (20/100-20/200)
- Nystagmus (shaking eye movements)
- Strabismus (eye misalignment)
- Color vision defects
- Dry eye disease
Patients with aniridia have impaired red-green and yellow-blue color vision.
Most cases of aniridia are diagnosed at birth or during infancy by six weeks old. An obvious iris/ pupil abnormality and nystagmus are often observed. An eye doctor may see small anterior polar cataracts with persistent pupillary membrane strands during the exam. Optical coherence (OCT), a type of ocular imaging, can be used to diagnose the underdevelopment of the fovea, the center of the macula.
Most individuals with aniridia can retain useful vision with ophthalmic management. Treatment depends on the ocular abnormality or condition. Vision can often be improved with spectacles and tinted lenses can help with light sensitivity. Low vision devices may aid those with significant impairment.
Patients with aniridia should be assessed yearly for glaucoma development. Contact lenses and artificial tears can be used to manage corneal complications. Topical glaucoma medications and glaucoma surgeries are effective treatments.
Current aniridia research is focused on corneal stem cells and gene therapy.