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lunes, 7 de noviembre de 2011

Aniridia

Aniridia

Last Modified: Sat, 18 Aug 2007


View other Common Causes of Vision Impairment

Aniridia describes the partial or complete absence of the iris of the eye and is also associated with cataracts, glaucoma, and macular hypoplasia. Aniridia is a congenital condition that causes blurred sight, sensitivity to glare and bright light (photophobia), and nystagmus (uncontrollable shaking of the eyes). Aniridia is a stable condition and patients generally do not become totally blind from aniridia, but they can lose their sight if they develop glaucoma and it is not treated. There is no cure for aniridia but medical treatments can frequently prevent further vision loss due to the secondary complications of aniridia. Patients with aniridia respond extremely well to optometric low vision aids and are typically able to use their vision to read, write, participate in sports, and many have received their driver’s licenses.



Diagram of Aniridia

The iris is a muscular tissue that normally forms a round pupil, the opening in the center of the eye. The iris regulates the amount of light that enters the eye and it also provides us with our eye color. Patients with aniridia do not have a fully developed iris and thus they are not able to regulate the amount of light that enters the eye normally, causing photophobia. In addition, the absence of the iris affects the cosmetic appearance of the eyes and patients with Aniridia tend to have eyes that appear black. Cosmetic contact lenses can improve the appearance of the eyes and provide color to the eyes. In addition, specialized colored contact lenses can regulate the amount of light entering the eye and reduce photophobia.

Aniridia also affects the development of other structures of the eye. The blurred sight that is associated with Aniridia is not due to the absence of the iris but is a result of the abnormal development of the macula, the centermost region of the retina that provides detailed sight, color vision, and daylight vision. As light enters the eye, it strikes the light sensing cells of the retina and sends the information to the brain. When the macula is not fully developed at birth, the brain is not able to perceive color, fine details, and images in the bright daylight. Consequently, many patients with Aniridia squint their eyes to reduce the glare and they tend to get closer to their reading materials to read. Their distance clarity of sight may range from 20/70 (able to read a 2 inch letter from 20 feet) to 20/200 (able to read a 4 inch letter from 20 feet).

In addition to the abnormal development to the macula, patients with Aniridia are at risk for developing other eye and medical problems. Cataracts (the cloudiness of the internal crystalline lens of the eye), glaucoma (increased intra-ocular pressure of the eye causing damage to the optic nerve), Wilm’s tumor (kidney tumor), abnormal blood sugar, reduced sense of smell, and dysnomia (difficulty naming familiar objects) are more common among children with Aniridia. Although these complications are associated with Aniridia, they are treatable when diagnosed early.

Most patients with Aniridia have nystagmus, the uncontrollable shaking of the eyes. Nystagmus does not cause images to appear to shake from side to side. Patients with Aniridia may turn their head or eyes to reduce the nystagmus. Eye muscle surgery and exercises are sometimes recommended but they generally do not completely eliminate nystagmus

Children and adults with Aniridia tend to have high levels of functional vision and respond extremely well to low vision aids. Specialized filters, high powered reading glasses, contact lenses, and bioptic telescopic spectacles can improve clarity of sight, reduce problems with glare, and increase their functional vision to a level that allows visual reading and sometimes to the level of vision allowing patients to take their drivers test. Assistive technology, computers, and software programs are extremely helpful for these patients.

Recommendations
•Children and adults with aniridia will benefit from a consultation by a low vision specialist and low vision aids. Patients should be evaluated for photochromic spectacles and tinted contact lenses to reduce glare and protect the eyes from the harmful rays of the sun.
•Low vision aids such as contact lenses, bioptic glasses, hand held telescopes, and video magnification systems can improve distance sight to 20/20 while specialized reading glasses, hand magnifiers, and closed circuit televisions can allow patients to read small print.
•Infants should be examined by the age of 6 months or younger. Glasses should be prescribed based on the visual developmental level of the children. For example, four-month-old infants should have their glasses prescribed to focus at their arms length rather than 20 feet.
•Infants will benefit from vision stimulation to maximally develop the visual cortex of the brain. For specific details, please see Developing Your Child’s Vision.
•Students will benefit from being positioned in the front portion of the class with their backs facing windows, doors, and glare sources. The use of a black chalkboard and bold architecture chalk are generally easier to see than dry erase boards due to the glare created by the white board. In the event that a dry erase board must be used, it is very helpful to only use bold black dry erase markers rather than colored markers.
•Tinted paper with bold lines, bold felt pens, and thick pencils will help students to perform writing tasks at school. Students who are bothered by glare will also benefit from placing their paper on a dark blotter or dark piece of construction paper to help them to see the edges of their paper.
•Students will benefit from having copies of material normally written on the board or presented on overhead transparencies. If PowerPoint presentations are used, a dark background with white letters written in Arial or Tahoma will improve readability for students with low vision.
•Students may have some difficulty seeing small objects such as a baseball while standing in the outfield. They may also have difficulty seeing in the direct sunlight and may prefer to wear their sunglasses and a hat. Students will benefit from additional time to adapt to the indoor lighting after entering the classroom from lunch or recess. Sports such as soccer, basketball, gymnastics, swimming, and golf may be easier to participate in rather than baseball or tennis.
•At home, the use of an incandescent light bulb hidden behind a dark torchierre floor lamp can provide excellent general lighting while reducing glare. A small desk lamp such as an OTT full spectrum lamp may provide a soft light for reading and writing. See Vision and Lighting.
•Computer users will benefit from changing the background of the display to a black or blue background with white letters. Enlargement of the font size will also increase readability. For information on how to modify the computer screen, see “Solutions To Help You User Your Computer.
•Students may benefit from using specialized computer software and technology such as Zoom Text magnification software, scanning programs such as Open Book and Kurzweil, and Video Magnification systems. For more information, see Computer and Assistive Technology.
•Teenagers with aniridia who are interested in learning whether they have sufficient vision for driving should have a low vision examination by an optometrist who specializes in fitting bioptic-driving glasses.
•Specific low vision aids that are often helpful to patients with aniridia include: ◦Cosmetic contact lenses
◦4x to 6x bioptic spectacles
◦DVI clear image aspheric reading glasses
◦Prescription CPF, Transitions, Melanin, and NoIR filters.
◦4x to 6x aspheric hand magnifiers for reading fine print.
◦ZoomText software magnification program to enlarge print on the computer screen and modify the contrast of the screen.

•For more information, please see Low Vision Rehabilitation

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