Aniridia, meaning “without iris”, is a rare genetic disorder affecting vision, characterised by incomplete formation of the eye iris (the coloured part of the eye that surrounds the black pupil).
It may also cause other parts of the eye to be under-developed such as the optic nerve and the macula (the central part of the retina).
People with aniridia may also develop other eye conditions. Aniridia and these associated conditions affect everyone differently. So while some people with aniridia are partially sighted or blind, others may have near normal sight.
Aniridia is congenital (present at birth) and is caused by a disfunction of the PAX6 gene, situated on the 11th chromosome, that causes the eye to stop developing too early.
The disease is most often inherited as an autosomal dominant trait (familial aniridia). One in three cases may instead result from a de novo mutation, that is a genetic mutation that occurs in a child whose parents are not affected by the disease (sporadic aniridia).
Aniridia affects 1 : 40,000 to 1 : 100,000 people , and affects males and females equally.
People with aniridia may also experience secondary conditions; most people with aniridia will not develop all of these and some may not develop any at all.
- Photophobia: sensitivity to light that can dazzle and make it difficult to see. It can also cause discomfort, pain or headaches;
- Nystagmus: constant involuntary movement of the eyeball;
- Glaucoma: elevated pressure in the eyeball that may parmanently damage the optic nerve;
- Cataracts: clouding of the lens;
- Keratopathy: a variety of conditions that affect the cornea, the transparent front part of the eye that covers the iris and pupil, due to a deficiency of limbal stem cells.
Aniridia may occur as part of another genetic condition known as WAGR syndrome. It affects more than one gene on the 11th chromosome and the exact mutation can vary between patients. The acronym WAGR describes the four most common symptoms: Wilms’ tumor (kidney cancer affecting children), genitourinary abnormalities, aniridia and mental retardation.
When a newborn child is diagnosed with aniridia, there are some actions that need to be taken.
It is impossible to define very specific indications, since in each area of Europe access to healthcare and social assistance are regulated by different national health systems and policies.
Nonetheless, every child with aniridia should at least:
- be offered genetic investigation, to establish if aniridia is isolated or part of the WAGR syndrome and to identify the mutation on PAX6 when possible;
- perform regular ophtalmological checks, at a frequency established according to eye conditions;
- perform regular ultrasound tests of the kidneys, for an early detection of Wilms’ tumor;
- be followed, especially during the first years of life, by therapists specialised in visually impaired children, to help the best possible development of vision and to prevent problems associated with low vision that might affect other developmental areas (movement, speech, learning…).
It is very useful to contact local associations of visually impaired people to get specific information on healthcare and social assistance in each country.
Daily life with aniridia requires constant adaptation with the environment.
Some of the challenges are common to those with visual impairment: studying, working, using low vision aids, moving around, traveling and playing sport. Even the most common activities can be very difficult for a visually impaired child or adult in a world where most knowledge and information are conveyed through visual data. The exact causes and consequences of low vision are, in general, not fully understood; people with aniridia may share this difficulty with all visually impaired persons.
Other problems, however, are specific to aniridia. Nystagmus, if present, makes it difficult to maintain eye contact and may lead others to think that patients with aniridia are not paying attention. For children in school, this may lead their teachers to think that the child is absent-minded or uninterested, resulting in a wrong appraisal of the pupil’s attention.
People with aniridia usually find it difficult to adapt to rapidly changing light conditions They may be sensitive to intense light and reflections from windows, mirrors and wet, metallic or white surfaces and often have to adapt their home, work and school environments accordingly.
Glare caused by reflections may lessen the ability to see details or cause visual discomfort, dry sneezing and headaches. Moving from inside to outside, switching lights on and off, moving in foggy or cloudy days, and crossing in front of car headlamps produce a painful dazzling that reduces visual acuity and causes uncertainty in movement.
People with aniridia often need to wear sunglasses with highly protective lenses outdoors, which may also be needed on cloudy days or indoors.
Some people with aniridia can wear contact lenses with an artificial iris and fixed pupil that blocks out the light. Wearing contact lenses includes advantages such as correction of farsightedness or nearsightedness, greater comfort and greater discretion, but requires a constant monitoring of the corneal status. On the other hand, some keratopathies may take advantage from the use of therapeutic contact lenses.