Aniridia is a rare genetic vision disorder characterized by abnormal development of the eye's iris. The iris is the circular colored membrane in the middle of the eyeball. It is perforated in the center by an opening known as the pupil, which regulates the amount of light that enters the eye. Aniridia is characterized by partial or complete absence of the iris. Various forms of aniridia have been identified. Each can be distinguished by accompanying symptoms.
Aniridia is marked by partial or complete absence of the eye’s iris. Vision is preserved in some mild cases of aniridia. The iris fails to develop normally before birth in one or both eyes. At least four types of aniridia are thought to exist. One type is marked by incomplete expression of the disorder. Some people with this type of aniridia may be unaware of the eye problems because pupils appear normal and usually only one eye is affected with thinning of the iris. In a second type of aniridia, iris abnormalities may occur alone, or in combination with other disorders. Accompanying disorders may include cataracts (clouding of the crystalline lens of the eye), glaucoma (gradual loss of vision due to increased pressure inside the eyeball which may be accompanied by varying degrees of pain), or superficial clouding of the cornea (corneal pannus). Rapid involuntary movement of the eyeball (nystagmus), and underdevelopment of the fovea area of the retina (which controls acute vision) may also occur.
A third type of aniridia is associated with intellectual disability, and a fourth type occurs in conjunction with Wilms’ tumor, genitourinary abnormalities, and possible intellectual disability. (For more information on Wilms’ Tumor, please choose “Wilm” as your search term in the Rare Disease Database.)
A third type of aniridia is associated with mental retardation, and a fourth type occurs in conjunction with Wilms’ tumor, genitourinary abnormalities, and possible mental retardation. (For more information on Wilms’ Tumor, please choose “Wilm” as your search term in the Rare Disease Database.)
Until recently, it was thought that two separate genes were responsible for two distinct forms of aniridia. However, a review of the evidence revealed that what was thought to be two forms is actually one and that one gene is responsible. It is known as the PAX6 gene.
This condition is thought to follow an autosomal dominant pattern, and some patients appear to have a spontaneous genetic mutation. A second type of aniridia associated with intellectual disability and a third type occurring in conjunction with Wilms’ Tumor are also thought to follow an autosomal dominant pattern.
Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy. The risk is the same for males and females.
All types of aniridia affect males and females in equal numbers. This disorder is thought to occur in approximately one in 60,000 to 100,000 live births in the United States.
Treatment of aniridia is usually directed at improving and preserving vision. Drugs or surgery may be helpful for glaucoma and/or cataracts. Contact lenses may be beneficial in some cases. When a genetic cause cannot be identified, patients should be evaluated for the possibility of the development of Wilms’ tumor. (For more information on this disorder, please choose “Wilm” as your search term in the Rare Disease Database.)
In 2018, a surgically implanted device was approved to treat adults and children with aniridia. This device may help to reduce light sensitivity and glare, and improve the cosmetic appearance of the eye. The CustomFlex Artificial Iris is manufactured by Clinical Research Consultants, Inc.
Genetic counseling is recommended. Other treatment is symptomatic and supportive.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.
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FROM THE INTERNET
McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). Baltimore. MD: The Johns Hopkins University; Entry No:106200; Last Edit: 6/8/1994; Entry No: 106210; Last Update: 5/2/2000.
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