Aniridia, also known as iris hypoplasia, is a congenital eye condition in which the iris is partially or completely missing. The iris abnormalities cause the pupils to be abnormal or deformed. The hereditary eye disease occurs in isolation, but may be part of a syndrome. Patients with aniridia are often very sensitive to light (photophobia) and have problems with visual acuity, which usually results in visual impairment. Normally aniridia is congenital, but very sporadically it is acquired.
- Epidemiology aniridia
- Causes, heredity and types of the eye condition
- Symptoms: Visual acuity and photophobia
- Syndromes with aniridia as a symptom
- Diagnosis and examinations
- Therapy
- Prognosis Absence of the iris in the eye
Epidemiology aniridia
The representation of the incidence of aniridia is variable in scientifically based studies. The figures fluctuate between 1:47,000 to 1:100,000. The incidence also varies from region to region. For example, in countries where cousin marriage is permitted or encouraged, the recessive inheritance of aniridia is more visible, such as in India, Pakistan and Saudi Arabia. In 75% of patients, the disease is inherited in an autosomal dominant manner. Finally, aniridia occurs spontaneously in approximately 25% of patients.
Causes, heredity and types of the eye condition
Aniridia can be divided into hereditary and isolated forms.
Hereditary aniridia
The hereditary form of aniridia is usually inherited in an autosomal dominant manner (each offspring has a 50% chance of inheriting the disease). A genetic mutation (change) in the PAX6 gene is the cause of this condition. In rare cases, autosomal recessive forms have been reported.
Isolated aniridia
Sporadically, a patient acquires aniridia due to other eye disorders or due to eye trauma.
Symptoms: Visual acuity and photophobia
General
Aniridia is almost always bilateral, affecting both eyes. The eye condition occurs partially or completely. In complete aniridia, the iris is not visible. With partial aniridia, part of the iris is missing. Each patient has a different form of aniridia. For example, some patients do not suffer from visual problems, while others are visually impaired and still others are completely blind.
Visual acuity
Aniridia usually affects visual acuity, causing a patient to exhibit unsteady movements. Visual acuity largely depends on the extent of the condition and which parts of the eye are affected. Visual acuity in aniridia patients varies between 20/80 and 20/200. An average good eye sees 20/20 (1.00). With a visual acuity of 20/80 the visual acuity is 0.25, and with a visual acuity of 20/200 it is 0.10. If someone has a vision of 0.25, that person has to look at everything 4 times closer to see the same thing. With a vision of 0.10 that is 10 times.
Photophobia
Photophobia (increased sensitivity to light) is common in aniridia patients. The iris has a light-shielding effect and if the iris is (partially) missing, the patient suffers from dazzling and clouded vision. This often results in headaches and discomfort.
Other eye problems
Patients with aniridia sometimes have other eye problems. Glaucoma (increased eye pressure, which the ophthalmologist measures via tonometry) usually appears in late childhood or early adolescence. Cataract (clouding of the lens of the eye) occurs in 50 to 85% of aniridia patients. In approximately 10% of affected patients, the optic nerve structures are underdeveloped (the optic nerves carry information from the eyes to the brain). Nystagmus (medical term for “involuntary eye movements”) sometimes occurs. In addition, the region at the back of the eye is sometimes affected (foveal hypoplasia) , leading to a reduction or loss of sharpness of vision. Unfortunately, many of these eye problems are progressive and lead to vision loss.
Syndromes with aniridia as a symptom
Aniridia occurs as a symptom of a number of related genetic disorders:
- Gillespie syndrome: A rare congenital disorder characterized by partial aniridia, intellectual disability, and problems with motor balance and coordination (coordination problems).
- Miller syndrome: A condition that affects the development of the face and limbs.
- WAGR syndrome: Children born with this condition have an intellectual disability and behavioral problems in addition to aniridia, their genitals are abnormally shaped, and they also have an extremely high risk of a Wilms tumor (form of kidney cancer with abdominal pain).
Diagnosis and examinations
The pediatric ophthalmologist usually diagnoses aniridia. Typically, during a routine medical examination, he will notice that a baby with aniridia has little or no pupillary response to light. For diagnosis, the ophthalmologist performs a slit lamp examination and a CT scan of the eye socket and eyes.
Additionally, a geneticist performs a blood test to confirm the genetic mutation. When assessing a baby with aniridia, it is necessary to determine the family history, but even in the absence of a clear family history, the doctor will conduct an examination of the parents to detect the PAX6 gene. Geneticists are generally affiliated with universities and/or (children’s) hospitals.
Therapy
Aniridia itself cannot be cured, but treatment is available for other eye conditions.
A patient with aniridia regularly visits an ophthalmologist for a comprehensive eye examination to monitor vision. For glaucoma, the patient takes eye drops following correct eye drop guidelines. However, sometimes other treatment methods are required, such as laser treatment, a trabeculectomy or a drainage implant. For cataracts, an intraocular lens implant is sometimes necessary, such as a Symfony lens. The surgeon places an artificial iris after removing the cataract during cataract surgery. Finally, stem cell transplants help improve corneal scars. Regular kidney ultrasound is advisable to detect kidney cancer (nephroblastoma) in a timely manner (Wilms tumor).
On a practical level, aniridia patients often wear a sun hat or cap, or sunglasses with protective lenses outdoors, even on cloudy days. Some people find it more comfortable to wear sunglasses indoors.
Prognosis Absence of the iris in the eye
Aniridia often leads to other eye problems in the long term. For example, glaucoma often appears during adolescence, and more than half of aniridia patients eventually develop cataracts. Sometimes this leads to severe vision loss or even blindness. Children suffering from aniridia often look cross-eyed.
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