Aniridia

Aniridia is a rare, congenital eye disease in which the iris, the colored ring of the eye, is not fully developed. The name literally means "without iris," but most affected individuals still have a narrow iris remnant. As a result, the pupil is unusually large and often irregularly shaped. Typically both eyes are affected, though to varying degrees. The frequency is approximately 1 in 50,000 to 100,000.

Cause and inheritance

The disorder develops between the 12th and 14th week of pregnancy and is based in most cases on a mutation in the PAX6 gene on chromosome 11. This gene plays a key role in the development of the eyes, but also of the brain, spinal cord, and pancreas.

Autosomal dominant (approximately 2/3 of cases): One parent has aniridia, and each child has a 50% risk of inheriting the disease.
Sporadic (approximately 1/3 of cases): The mutation occurs for the first time – neither parent is affected. The recurrence risk for other children is low.
Autosomal recessive (rare): Both parents are carriers without being affected themselves. The risk per pregnancy is 25%.

How does aniridia affect vision?

The missing or severely reduced iris causes pronounced light sensitivity and glare. Furthermore, numerous other eye structures can be affected:

Corneal problems: Due to a lack of stem cells, corneal opacities, abrasions, and scarring occur.
Glaucoma (green star): Elevated intraocular pressure occurs in approximately half of patients and can damage the optic nerve.
Cataract (gray star): Lens opacity develops in 50–80% of affected individuals.
Foveal hypoplasia: The site of sharpest vision on the retina is underdeveloped, significantly reducing central visual acuity.
Nystagmus: Involuntary eye movements that further impair vision.

Visual acuity varies greatly from nearly normal vision to severe visual impairment. Prediction of visual development in infancy is barely possible.

Associated conditions and syndromes

Aniridia can occur in isolation or be part of an overarching syndrome:

WAGR syndrome: Wilms tumor (kidney tumor), aniridia, malformations of the urinary and reproductive organs, and developmental delay. Sporadic cases in particular with a PAX6 gene deletion have an increased risk.
Gillespie syndrome: Aniridia with balance disorders and developmental delay.

Regular ultrasound examinations of the kidneys (initially every three months) are important in children with sporadic aniridia to detect Wilms tumor early. Aniridia can furthermore be associated with diabetes, metabolic disorders, and neurological abnormalities.

Treatment

There is no cure, but targeted measures can preserve visual function and prevent complications:

Regular eye examinations: Lifelong necessary to detect glaucoma, cataracts, and corneal changes early.
Glasses and sunglasses: Correction of refractive error and protection from glare with tinted lenses.
Artificial tears and eye ointments: Care for the sensitive cornea.
Glaucoma therapy: Eye drops or surgical procedures to lower intraocular pressure.
Cataract surgery: For advanced lens opacity, possibly with an artificial iris-lens implant to reduce glare sensitivity.
Stem cell transplantation: Can prevent corneal scarring in corneal problems.
Special contact lenses: Painted soft lenses can reduce glare and improve cosmetic appearance. Caution is necessary for corneal problems.

School and everyday life

Most children with aniridia can attend regular school. The following adaptations help:

Seating with minimal glare, away from direct sunlight Magnified instructional materials and visual aids as needed Tinted glasses or sunglasses even in the classroom Collaboration with school health services and low-vision counseling Early support at home and in school

Genetic counseling

Genetic evaluation is highly recommended for affected families – both for assessing recurrence risk and for access to future therapies such as gene therapy, which is currently being researched.