Aniridia


Aniridia

Description, Causes and Risk Factors:

Absence of the iris; when congenital, a rudimentary iris root is usually present. About 60% of cases are inherited as autosomal dominant, although somewhat irregularly manifested.

Aniridia is a rare congenital eye condition causing incomplete formation of the iris (the anterior division of the vascular tunic of the eye, a diaphragm, perforated in the center (the pupil), attached peripherally to the scleral spur; it is composed of stroma and a double layer of pigmented retinal epithelium from which are derived the sphincter and dilator muscles of the pupil). This can cause loss of vision, usually affecting both eyes.

Reserchers beleive aniridia is a genetic condition and in most cases is caused by damage to the PAX6 gene. This gene contains the genetic code for a protein also called PAX6 which plays an important role in the development of the eye. There is no single cause for this eye condition that falls roughly into two groups, one of which is hereditary and the other of unknown origin. Aniridia can result from autosomal dominant or autosomal recessive inheritance or may occur on its own.

Aniridia

Autosomal dominant individuals in this group will be unlikely to have additional health or developmental problems and may have normal or poor vision. Autosomal dominant problems result from one of a pair of matched genes being normal whilst the other carries the abnormality. There is a one in two chance of inheritance in each such pregnancy. Usually several individuals in successive generations will be affected.

Autosomal recessive inheritance carries a risk of accompanying learning disabilities. Autosomal recessive problems arise when both parents carry the abnormal gene although they are unaffected. There will be a one in four inheritance risk in each pregnancy. Usually this only affects siblings within a single generation.

Rarely aniridia may be associated with a tumour of the kidney called Wilms'. This type is sporadic although it has been associated with chromosomal disorder and may increase risk of other developmental flaws. Aniridia may also be associated with other eye conditions such as nystagmus, glaucoma, corneal disease, cataract, lens sublaxation (dislocation), macula and optic nerve disease.

At present, aniridia strikes 1 in 60,000 individuals; in Canada, this would represent only 475 individuals based on a present population of 28.5 million. In the United States, studies have shown the incidence to be 1 in 90,000. Based on a population of 265 million, this would represent 2945 people.

Symptoms:

The mostly found signs and symptoms of aniridia include:

    Absence of the iris.

  • Fading vision.

  • Nystagmus.

  • Cataract.

  • Loss of luster in corneas.

  • Glaucoma.

  • Vision impairment.

  • Absence of iris.

  • Partial presence of iris.

  • Blindness.

  • Absence of muscles regulating the pupil.

Diagnosis:

Aniridia can be diagnosed by an experienced ophthalmologist with a simple eye exam. There are genetic tests available as well but they are not yet perfected. For more information on genetic testing, contact a qualified genetic counselor. Genetic counselors are generally affiliated with universities and/or children's hospitals. Since aniridia is also associated with glaucoma, it is important that the ophthalmologist check an infant's eye pressure.

Chromosomal deletion is detected by cytogenetic testing with the use of high-resolution banding.Serial renal ultrasound examinations are indicated in patients through age 7 years, especially for those with a deletion of band 11p13 or for those with a negative family history of aniridia and normal chromosomes.

Treatment:

Babies with aniridia will need to be carefully and regularly examined to ensure no supplementary problems develop. Where treatment is offered this will relate to problems additional to the absent iris. In some individuals, loss of vision may increase risk of other problems and it is advisable, during the first five years of life, therefore careful attention will be paid to identify whether other complications develop which may require treatment.

There are several treatment options out there for people suffering from aniridia:

    Babies with aniridia will need to be carefully and regularly examined to ensure no supplementary problems develop.

  • Existing medical therapy for aniridia will be miotics, adrenergic agonists, beta- blockers and carbonic anhydrase inhibitors might even be tried however no medications have been approved by the FDA for the treatment of aniridic glaucoma.

  • Optical correction- spectacles, contact lens (Aniridia - tinted or iris contact, spectacle, intraocular lenses are out there for use).

  • There are several surgical procedures to deal with aniridic glaucoma but there is not convincing information as to which is preferable to the other procedure for example Goniotomy, trabeculotomy, trabeculetomy, setons, cyclophotocoagulation and cyclocryotherapy.

  • Laser therapies might be used to angle abnormalities.

  • The newest treatments posted on Aniridia Network are development of stem cell surgery, amniotic membrane transplantation, iris reconstruction, Morcher Innovations available in Australia.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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