Aniridia

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By Mrinali Patel Gupta, M.D.

Aniridia and the Iris

The term aniridia is Greek for “without iris.” It is a congenital, bilateral (both eyes) condition characterized by the complete or partial absence of the iris.

The iris is the colored part of the eye surrounding the pupil. The iris contains muscles that allow the pupil to become larger (open up or dilate) and smaller (close up or constrict). The iris regulates the amount of light that enters your eye by adjusting the size of the pupil opening.

The iris also determines your eye color. People with brown eyes have heavily pigmented irises, while people with blue or lighter-colored eyes have irises with less pigment.

What Is Aniridia?

Aniridia is a genetic condition caused by a mutation in the PAX6 gene on chromosome 11:

In approximately 2/3 of people with aniridia, the condition is inherited in an autosomal dominant fashion, meaning that an individual has to inherit only one abnormal gene from either parent to manifest the disease.
In approximately 1/3 of people with aniridia, the genetic mutation is sporadic, meaning that it is not inherited from either parent but developed spontaneously in the person.
Rarely can aniridia be inherited in an autosomal recessive fashion, meaning that an individual has to inherit two abnormal copies of the gene, one from each parent, to exhibit the disorder. These individuals may also have other symptoms, including ataxia (problems with balance and movement) and cognitive disabilities.

Aniridia and Wilms’ Tumor

Approximately 30% of persons with sporadic aniridia can have WAGR syndrome. Wilms’ tumor is a rare kidney cancer that primarily affects children. WAGR is an acronym for a constellation of conditions that commonly occur together in this syndrome:

W: Wilms’ tumor
A: Aniridia
G: Genitourinary abnormalities, i.e., abnormalities in the reproductive and/or urinary organs
R: mental Retardation

Therefore, it is important for your eye doctor to evaluate your family history if you have aniridia. If you have sporadic aniridia, regular ultrasounds are necessary to screen for Wilms’ tumor.

How Does Aniridia Affect the Eyes?

While aniridia is named for its classic effect on the iris, the disorder actually involves widespread abnormal development of many structures inside the eye, all of which can impair vision.

The effects of aniridia can vary significantly from person to person. Some individuals exhibit only mild effects from the disorder, while others have profound ocular abnormalities:

Iris Development

Some persons have only minimal underdevelopment of the iris that is barely noticeable to the untrained eye while others have partial or total absence of the iris. Even in persons with “total” absence of the iris, there is usually a very rudimentary iris tissue remnant that can be seen during a careful eye examination under the microscope.

Light Sensitivity

Since the iris helps block and absorb some of the light entering the eye, people with aniridia may be very light sensitive (photophobic) and report symptoms of glare.

Glaucoma

Either abnormal development of the angle (the area of the eye responsible for draining aqueous fluid from the eye), blockage of the angle from the rudimentary iris stump, or narrowing of the angle can lead to glaucoma.

Corneal Problems

People with aniridia may have a deficiency in the limbal stem cells. These are stem cells that arise in the limbus. The limbus is an area at the border of the conjunctiva, which is the thin translucent tissue over the white surface of the eye, and the cornea, the transparent dome-shaped tissue that forms the front part of your eye, through which you can see the colored iris. These stem cells are responsible for maintaining the health and integrity of the cornea.

As a result of a deficiency in the limbal stem cells, the conjunctiva can grow over the cornea, the cornea cannot heal easily from injuries or scratches, and the cornea ultimately can undergo scarring or vascularization (growth of abnormal blood vessels into the normally clear cornea). These corneal changes can impair vision.

Lens Abnormalities

People with aniridia are also at higher risk of abnormalities in the lens, including cataracts and dislocation of the lens.

Retinal Problems

Individuals with aniridia often have foveal hypoplasia, meaning underdevelopment of the fovea, which is part of the retina responsible for fine visual acuity; they may also have hypoplasia of the optic nerve, which transmits visual information from the eye to the brain. “Hypoplasia” is a term that refers to a deficiency or underdevelopment of a tissue or body structure.

Nystagmus

Infants with anirida may exhibit abnormal, involuntary, rapid side-to-side or up-and-down movements of the eyes called nystagmus.

How Is Aniridia Treated?

Since aniridia can affect the eyes in a multitude of ways, aniridia treatment is similarly multifaceted:

Opaque or colored contact lenses can give the appearance of an iris to improve one’s appearance or for cosmetic purposes, as well as to improve vision and minimize glare/photophobia.
Absorptive sunglasses can also help with symptoms of photophobia and glare.
Some individuals also may be candidates for surgical placement of an artificial iris, though this procedure may be associated with complications.
Lubrication with artificial tears can help maintain the health of the cornea.
Significant corneal disease may require more aggressive surgery, including transplants and/or stem cell transplantation to replace some missing stem cells.
Individuals who have cataracts may require surgery to remove the cataract.
People with aniridia should be monitored closely for glaucoma, and those who develop it should be treated accordingly, with medications, lasers, and/or surgery.
A comprehensive low vision examination with optical, non-optical, and electronic low vision devices and vision rehabilitation services and training, can be helpful for some individuals with aniridia.

How Would You Describe the Eyesight of One with Aniridia and How Will My Child Function with It?

Discussed below are the functional implications of aniridia; remember, however, that aniridia seldom occurs in isolation. Review the following information in addition to the functional implications of each visual condition present in your child.

With undeveloped or “nonexistent” irises, the amount of light permitted into the eye is poorly controlled or unrestrained. In effect, there will be tremendous discomfort as well as limited vision in bright light and glare.

Tinted sunglasses (often red or blue) and use of a brimmed hat will provide relief to the eyes while outdoors; individuals with aniridia may also wear slightly tinted eyeglasses to improve vision indoors. Additionally, use of non-glare surfaces (such as a chalkboard instead of a whiteboard and matte wall paint) and use of thick curtains will aid in using vision indoors.

Your child should make the most of evening outdoor exploration, play, and social activities.

Furthermore, the child will need an orientation and mobility specialist to provide instruction on using a cane (to refrain from bumping into obstacles) and using public transportation while outdoors in the daytime.

Clarity of vision varies greatly in individuals with aniridia; some are considered to have “low vision,” while others are considered legally blind (having minimal useful vision). With diminished sharp/detailed vision, it will be difficult to recognize faces and facial expressions, access information from a classroom board or wall, view a speaker or performance, read print, and perform visual tasks of fine detail such as threading a needle. In order to best use remaining vision, your family can be taught to increase the contrast of the environment. Your child may be taught to increase the contrast of print by using a CCTV or screen-magnification software, increase print size by using a hand-held magnifier and distance-vision optical device such as a handheld telescope (called a “monocular”). Furthermore, your child should sit in a preferred seat of a room for optimal viewing, generally nearer to the speaker or chalkboard.

Your child’s teacher of students with visual impairments should perform a functional vision assessment to determine how your child uses his or her vision in everyday life and a learning media assessment to determine which senses your child primarily uses to get information from the environment. These assessments, along with an orientation and mobility assessment conducted by a mobility specialist, will give the team information needed to make specific recommendations for your child to best access learning material and his or her environment.