Aniridia: causes, symptoms, eye complications and care

The iris controls how much light enters the eye by changing the size of the pupil. Fight for Sight explains that aniridia literally means "no iris", though in practice the iris is often partly rather than completely missing. This makes the pupils look very large or an unusual shape, and the signs are often visible soon after birth.

Aniridia is better understood as a condition of eye development as a whole. The gene involved is described by Fight for Sight as a master controller for how the eyes, brain, spinal cord and pancreas develop, and RNIB says that aniridia nearly always causes the optic nerve and the fovea, the very centre of the macula, to be underdeveloped.

RNIB says aniridia is caused by a change in a gene, most often PAX6, and that it can be inherited in two ways: a parent with aniridia can pass on the changed gene (familial aniridia), or the change can occur randomly when neither parent has the condition (sporadic aniridia).

Fight for Sight adds that a mutation in just one copy of PAX6 can cause aniridia, that a child of someone with aniridia usually has a 50/50 chance of having it, and that someone with sporadic aniridia can still pass it to their children.

Some people have aniridia as part of a wider syndrome. Fight for Sight describes WAGR syndrome, in which aniridia occurs with a risk of Wilms' tumour of the kidney, genitourinary problems and developmental delay, and says that between 13% and 30% of people with aniridia have WAGR syndrome. It also describes the very rare Gillespie syndrome.

RNIB says that because the iris tissue is missing, the eye cannot control the amount of light entering it, so people may experience dazzle in bright conditions, difficulty adjusting as light levels change and light sensitivity (photophobia) that can cause discomfort or headaches. Fight for Sight adds reduced vision from the underdeveloped fovea, difficulty focusing, a sore eye caused by a dry, easily damaged surface, and hazy vision from cataract or a cloudy cornea.

The effects vary. RNIB says some people with aniridia have quite a lot of sight loss while others have only mild blurred vision.

Fight for Sight says an ophthalmologist will usually diagnose aniridia by examining a baby's eyes at birth or soon after, looking for a missing or partially missing iris and other typical signs such as nystagmus, and checking for early signs of linked problems such as cataracts or glaucoma.

Genetic testing is often offered to confirm the diagnosis and look for changes in the PAX6 gene. Fight for Sight says this is especially important for children who are the first in their family to have aniridia, in case it is caused by WAGR syndrome, in which children are given regular kidney scans to check for a tumour.

Because many of the eye complications develop over time, diagnosis is the start of long follow-up rather than a single event.

RNIB says there is no treatment to cure aniridia at present, but treatments exist for associated conditions. Glaucoma treatment can lower eye pressure and protect the optic nerve; Fight for Sight says it often starts with eye drops and that many people eventually need an operation to control the pressure. Cataracts may need surgery if they affect vision a lot, although RNIB says they can be safely left for many years if vision is not badly affected. Keratopathy can make the eye feel dry and uncomfortable, and RNIB says lubricating eye drops may help; Fight for Sight adds that if it worsens, a stem cell transplant operation may be needed.

Glasses and contact lenses cannot improve sight problems caused by aniridia itself, according to RNIB, but RNIB says it is important for children to have any focusing problems corrected so that their sight can develop as fully as possible. Fight for Sight says that special cosmetic contact lenses with a coloured iris and fixed pupil can reduce light sensitivity, and that lifelong regular eye checks are essential so that glaucoma and keratopathy are found early.

RNIB says there are many things that can help people adapt and make the most of the vision they have, including low vision assessments and aids. RNIB says many people with aniridia find that sun hats, sunglasses, tinted glasses or sun blinds in cars help with light sensitivity, and Fight for Sight describes good-quality UV-blocking sunglasses and wide-brimmed hats as essential outdoors.

RNIB says it is completely understandable to be upset when you or your child is diagnosed, and that with the right help and support people with aniridia can lead full and positive lives. It also describes the Eye Care Liaison Officer (sometimes called a Vision Support Officer), a sight loss advisor in some hospital eye clinics who can give practical and emotional support, and it offers counselling and a helpline.

On the NHS, aniridia is diagnosed and followed by ophthalmologists, with lifelong regular appointments, as RNIB and Fight for Sight describe. Because it is rare, it is reasonable to ask whether your clinic has experience of aniridia and whether genetic testing has been offered.

Private ophthalmologists can offer additional appointments or second opinions. The monitoring involved is the same, so choose a clinician with experience of aniridia and make sure someone is coordinating glaucoma, cornea and genetic follow-up.