Have you ever seen a person with completely black eyes, having partial irises or none at all? He or she might have Aniridia, a hereditary condition that impairs the vision among other symptoms. Get complete information about the disorder, including its causes, symptoms and possible treatment options.
It is a type of eye abnormality characterized by the absence of the iris (colored part of the eye). This is a bilateral, hereditary and extreme form of hypoplasia of the iris that is generally present at birth (congenital). It causes various ocular problems apart from vision loss. This birth defect can lead to complete blindness in some rare cases.
The congenital disorder can be classified into the following subdivisions depending on its underlying cause:
- Familial Aniridia
- Gillespie Syndrome
- Sporadic Aniridia
- WAGR Syndrome
In most cases, this eye disorder is present when a baby is born. It occurs due to abnormality in the development of the eyes between the 12th and the 14th week of pregnancy. A defective 11p chromosome can cause the condition.
Mutation of the PAX6 gene is the main cause of this eye disease. This gene is responsible for providing instructions for the production of a certain protein which helps in developing the eyes, spinal cord and brain (central nervous system) as well as the pancreas. This protein also plays an important role in the development of the olfactory bulb (a specific brain cell group that helps to process the sensation of smelling) within the brain. The PAX6 protein regulates the functioning of other genes by attaching itself to some specific regions of the DNA. Due to this reason, this protein is referred to as a transcription factor. Once a child is born, the protein is responsible for regulating several genes that contribute to the formation and maintenance of various eye structures.
Aniridia and Genetics
The disorder is usually caused by mutations in the PAX6 gene (paired box gene) complex. This multifunctional complex plays an important role in the regulation of tissues of various developmental genes. Mutations in the PAX6 gene can result in foveal hypoplasia and hypoplasia of iris. The gene is also important in the development of the central nervous system. Various researches suggest that the PAX6 mutation may be the sole gene impairment that is responsible for this birth defect.
Aniridia Inheritance Pattern
It follows the autosomal dominant inheritance pattern, meaning that a single copy of the defected gene in every cell can cause the condition. In around two-thirds of all cases, the patients inherit a mutated gene from one parent who carries the altered gene. One-third of the total cases of the condition are caused by new genetic mutations in people who do not have any history of this disease in their family. In some very rare instances (Gillespie Syndrome), it can be inherited in the autosomal recessive pattern.
Its symptoms may vary greatly from one patient to another. The following symptoms are generally manifested in children having this eye disorder:
- Absence of the colored part of the eye (iris)
- Black eyes
- Abnormal pupils that can be dilated and fixed due to absence of the muscles that regulate them
- Low visibility due to the defect in the eyes
- Loss of normal luster in the corneas
- Photophobia or sensitivity of light
- Clouding of the entire eyes
- Development of cataract at a very young age
- Opacities can be noted in the eyes at birth of the patient
- Various corneal disorders, within 2 years of age
- Development of other eye conditions, like Glaucoma, at a later age
- Optic and macular nerve hypoplasia
It is often associated with various ocular complications including amblyopia, nystagmus and buphthalmos. In some individuals, it is associated with:
- Mental retardation
- Learning disabilities
- Genitourinary anomalies
- Gillespie syndrome (cerebellar ataxia)
- Wilms tumor (Kidney nephroblastoma)
These disorders may ultimately lead to the WAGR Syndrome.
There is no known way to prevent this inherited disorder. However, couples with a family history of the condition should consider genetic counseling and gene reviews before deciding to have a child. Genetic testing can be helpful to understand the chances of having a child with this eye abnormality.
The diagnostic test named slit lamp examination can be useful for detecting different eye abnormalities caused by the disease such as iris translucency, glaucoma and cataracts. Iris fluorescein angiography is another useful test but it is very rarely applied. Optical coherence tomography (OCT) or optical imagery are sometimes used for identifying symptoms of hypoplasia. OCT is very useful imaging test for diagnosing this genetic disease; however, this test is very difficult to be performed in case where nystagmus (involuntary eye movement) is present. High frequency UBM or ultrasound biomicroscopy examination has recently been found to be useful in displaying the absence of iris (hypoplasia) in infants with congenital glaucoma.
Serial renal ultrasound may be useful for detecting any iris abnormality in babies without any family history of this inherited type of iris hypoplasia.
In some cases, a diagnostic test for detecting a kidney tumor may be necessary once Aniridia has been diagnosed. Genetic tests of chromosomes are sometimes useful for determining the possibility of kidney tumor.
Aniridia Differential Diagnosis
The following conditions are characterized by symptoms that are similar to Aniridia:
- Congenital Cataract
- Juvenile Glaucoma
- Ectopia Lentis
- Congenital Nystagmus
- Iris Coloboma
- Rieger Anomaly
- Oculocutaneous Albinism (OCA)
- Gillespie Syndrome
The differential diagnosis for the disorder should aim at confirming that the symptoms are not the result of the aforementioned conditions.
Aniridia Treatment and Management
There are no medical treatments available for curing the disease. However, the associated conditions like corneal opacities, glaucoma and cataracts are treated to reduce the vision problems as much as possible. An ophthalmologist keeps patients under constant observation for controlling the light sensitivity and maximizing visual functioning. Eye drops are often used in cases where glaucoma is present.
Patients are often prescribed to wear glasses or contact lenses because their eyes are often extremely sensitive of light due to the absence of the iris. Glasses and sunglasses are also helpful for protecting the eyes from other external injuries. Soft painted contact lenses may also be prescribed to some patients as they help to improve cosmesis, reduce glare and improve the vision of the affected eyes. However, this treatment measure is not used if any cornea problems are present.
Cataract removal surgeries are often performed to improve the vision of an individual with this condition. At present, an artificial iris may be placed in the eye after removing the cataract. Various other surgical procedures can be used for treating the disorder including trabeculotomy, goniotomy, setons, cyclophotocoagulation, cyclocryotherapy and trabeculetomy. Recently, several cases of this disorder have been treated successfully with stem cell therapy. Laser therapy is another modern treatment option that can be used for dealing with it.
Individuals with this disorder require regular tests to detect any sign of cataract or glaucoma. Lifelong follow-up care is very important for these patients to maintain a reasonable visibility. Ophthalmologists should keep patients under constant observation to detect the slightest symptoms of any more serious condition.
It is not possible to cure this condition completely. However, proper management helps to minimize the vision problems in the patients. The visual prognosis is not usually positive in children suffering from bilateral optic nerve hypoplasia. Visual rehabilitation allows around 10% of the patients to have excellent vision. They can also participate in all normal social activities without any serious difficulty.
Aniridia Life Expectancy
This is not a life threatening condition. The patients generally live a long and normal life. However, the eye abnormalities and vision problems are often present for their entire lives.
The statistics regarding the incidence of the disease may vary in different parts of the world. On an average however, 1 out of every 50,000-100,000 people in the world is affected by this rare eye disorder.
Aniridia Support Groups
There are various foundations and support groups that help patients and their families to cope with this eye abnormality by providing useful guidance. These include:
111 E 59th Street
New York City, NY 10022-1202
1660 L Street, Northwest, Suite 301
Washington, DC 20036
National Association for Parents of Children with Visual Impairments or NAPVI
P.O. Box 317
Watertown, Massachusetts 02272-0317
NIH/National Eye Institute
31 Center Dr
Bethesda, Maryland 20892-2510
Although Aniridia causes various eye abnormalities, vision problems and other health issues, patients can have a relatively normal life with proper management of the disease.
Here are some pictures displaying the altered appearance of the eyes due to the absence of the irises.
Picture 1 – Aniridia
Picture 2 – Aniridia Image