Aniridia is a rare congenital condition where a mutation of the PAX 6 gene on the 11th chromosome causes the under development of the eye and other body systems.
The most common form is the partial or complete absence of the iris which usually affects both eyes. The iris is the colored area of the eye surrounding the pupil and regulates the amount of light entering the eye. The word aniridia is derived from Greek meaning an- “without” and -iridia “iris”.
Unlike some other congenital defects, aniridia only requires the mutated gene be carried by just one parent for the condition to develop in the fetus. The gene remains dominant at that point with a 50% chance of being given to each child born to that parent carrying the mutation. Found in about 1 out of every 60,000 to 90,000 live births, parents often become concerned when the pupils of the child are very large, and do not constrict with changes in light intensity. Aniridia can be diagnosed with a simple eye examination by an ophthalmologist. A thorough dilated examination to include refraction, intraocular pressure, and a detailed look at the retina are all necessary to establish the presence of aniridia and to observe any other structures of the eye that are affected.
With the under development of the eye, patients are left prone to numerous ocular anomalies, which can have a profound effect on daily life and even cause permanent loss of visual capacity if not diagnosed, treated, and continuously monitored.
Nystagmus: an involuntary movement of the eyes. The intensity and direction of the movement can vary greatly in each individual who suffers from it.
Cataracts: a clouding of the lens of the eye. This condition can be treated with surgery, replacing the clouded lens with a new man made lens.
Glaucoma: an increase in the pressure of the eye, glaucoma can cause permanent vision loss if not treated due to damage to the optic nerve from the excessive pressure. Once glaucoma develops, the increase in pressure causes damage to an already undeveloped optic nerve. Treatments include drops, oral medication, and in some cases surgery where a drain is made or inserted to allow proper circulation and drainage of fluid in the eye.
Amblyopia: a loss of vision in the weaker of the two eyes.
Ocular hypoplasia: an under development of structures of the eye including, the fovea, retina, and optic nerve. The patient’s ability to process images correctly through the entire neurologic route is affected. For example, foveal hypoplasia will give the patient little or no ability to see details such as someone’s facial features.
Corneal opacifications: a clouding of the cornea, this can happen over time and requires surgical intervention in the way of a corneal transplant. Like other organ transplants, corneal transplants can fail due to rejection by the body.
Microcornea: is an unusual thin and flat cornea, which makes fitting and wearing of contact lenses very difficult.
As aniridic children age into adulthood, they will be faced with slowly declining vision as the condition progresses, along with the natural aging of the eye. This occurs not from the aniridia itself, but from the ocular complications that usually occur like the ones listed above. Although it varies with individuals, the visual acuity of an aniridic is commonly 20/200, monocular (in each eye) and considered legally blind. Use of low vision aids allows the patient to retain personal independence and self-sufficiency in the world. Numerous options are available with items such as Close Circuit Television (CCTV), large print books, and magnifiers, to name a few. Some feel that even learning to read Braille will maintain and encourage adaptation to everyday life activities. These services are available through several organizations on the local, state, and national levels. Many of these services are covered by government and some private insurance companies.
The condition of aniridia can also effect adequate development of other body systems, causing further medical complications. Many suffer from intellectual impairments like mental retardation and physical impairments such as glucose intolerance, leading to a predisposition for diabetes and the complications associated with diabetes.
It is extremely important that any complications stemming from systemic complications are treated promptly to prevent further decline of an already difficult medical status. Below average verbal and olfactory processing is a common finding in those with aniridia. With dysnomia, the patient is unable to recall common words from memory even though they thoroughly understand the meaning of the word.
In patients with dysosmia, they are unable to distinguish between different scents and in many instances the detected scent is conveyed incorrectly to the brain. It is crucial that patients be closely monitored for malignant tumors of the adrenal gland in the kidney, known as Wilm’s tumor. Generally these tumors often happen in children before the age of 5 years and are rare in adults. Careful monitoring is absolutely essential during childhood for this type of tumor. They are frequently tested, approximately every six months, by ultrasound to determine if tumors are present.
In some instances, the cornea has enough stability that a contact lens can be used. The lens can decrease the oxygen transfer and therefore should only be used if the health of the cornea can be maintained at a safe level. There is risk of abrasion of the cornea or conjunctiva with the use of contact lenses. This should also be carefully evaluated by the doctor to see if contact lenses are a possibility for the patient. If contact lenses are an option for the patient, many ophthalmologists opt for a tinted lens that will “black out” the pupil further.
The contact lens acts in the same capacity as a sunglass lens, controlling the amount of light entering the eye and giving much needed relief to chronic photophobia. These lenses are usually a special order from certain contact lens manufacturers and can be costly and are not always covered by insurance. Another type of contact lens can be used as a bandage. This means that the contact lens provides a protective layer on the cornea, allowing some relief for the patient. Bandage contact lenses are usually fit very flat to form a tight seal. Careful monitoring of the cornea with a bandage contact lens must be done to ensure that there is an adequate exchange of oxygen and tears.
A cure is not yet available for aniridia, but treatment options are numerous and range from glasses and contact lenses (for some) to medication and surgical intervention. Those with aniridia should have genetic testing soon after diagnosis; this will affect the opportunity of that child having their own children in later years. Artificial lens implants are being used to control the size of the pupil to alleviate photophobia, along with providing a more cosmetically appealing presence of the eyes. This biosynthetic implant is inserted into the stump of the iris and attached, thus producing a black iris and building a pupil that is more normal in appearance. The amount of light entering the eye is more controlled, allowing the patient some relief from photophobia.
There are ongoing studies in the UK where stem cells from patients, relatives, and even cadavers are harvested and grown into sheets within the laboratory. These cells are then implanted onto the cornea with the expectation of giving a resurgence of cell growth to thin corneas, allowing stabilization. Scientists are not completely sure how, but the results so far from this study are very promising.
The study has shown that the implanted cells motivated the growth of stem cells found in the patient’s own bone marrow. Through the bloodstream, the new cells are transferred to the limbic stem cells of the eye, located underneath the lids, where new growth was initiated. Limbic cells keep the cornea healthy and clear, thus allowing new development of cells take place. This development can give relief to the pain of an aniridic cornea due to thinning, erosion, and clouding. This possibly could be another alternative to the painful and sometimes unsuccessful corneal transplant that some aniridic patients are forced to endure.
The eye care professional should have a basic understanding of a patient’s condition to better assist the patient in making a sound choice in eye wear or in the fitting of contact lenses. It is important to know how the patient views the world around them and to have appropriate expectations. Most aniridic patients can wear glasses to assist with some retrieval of visual acuity. Glasses with a dark tint will also help the patient when venturing outside in sunlight and can also offer an added UV protection.