Aniridia


The most common sign of children born with aniridia, a genetic eye condition known as underdeveloped eye, is that the child literally has no iris or partial absence of the iris. This condition results in the appearance of an overly large black iris, which is caused by a dysfunction of the gene PAX6. Gene PAX6 is responsible for a babies eye development and when the gene malfunctions it leaves the baby with only the outer edge of the coloured part of the iris showing, as the muscles used to open and close the eye are not in place.

Types of Aniridia

Aniridia falls into two categories one of which is hereditary and the other being unknown - occurs through natures own course. Autosomal dominant and autosomal recessive forms of aniridia are inherited and each have different effects on a newborn.

Babies born with the autosomal dominant form of aniridia ordinarily suffer from poor vision and are highly likely to have health or developmental problems. This form of aniridia has a 1 in 2 chance of being passed down the generations therefore affecting other siblings. The autosomal recessive form of aniridia occurs when gene PAX6 is carried by both parents, it is also possible that even though the babies’ parents carry the abnormal gene they may not be affected by it. This form of aniridia has a 1 in 4 chance of being passed down the generations therefore it normally only affects a single generation of siblings and may also result in the child suffering mental retardation.

Genetic counseling is available for parents who wish to be reassured of the implications of Aniridia and the affects it will have on their family members, not only the baby / babies affected but also their carer’s.

On rare occasions Wilm’s tumour (nephroblastoma) or Miller syndrome can occur, this is caused by what is thought to be a chromosomal disorder affecting the kidney and resulting in aniridia. Children are at risk of developing Wilm’s tumour before they reach the age of 5years and sometimes develop other problems during growth such as mental retardation and facial deformities’.

Symptoms of Aniridia

Symptoms of aniridia, vary considerably and parents may notice an abnormal pupil that may be fixed and dilated. Children with aniridia suffer from sensitivity to light (photophobia) and clouding of the eyes. Cataracts usually develop in a child’s first two decades and small opacities may even be noted at birth. These can be removed with surgery in later development. Corneal disease can occur in infants as young as 2 years and as it progresses to the entire cornea, it may be necessary to carry out a corneal transplant.

Careful attention to a babies development and health has to be taken during the first five years of his or her life, as there is a risk of loss of vision occurring and it is always advisable to seek regular expert medical advice once aniridia is diagnosed to ensure other development problems are spotted quickly.

Generally other eye conditions occur later in life resulting in vision deterioration, glaucoma being one of the major causes in patients with aniridia. Glaucoma is very rarely found in babies or infants. Some children may suffer from nystagmus or faulty development of the macula. Optic nerve disease is another condition which can cause nystagmus this results in poor vision. The lens in the eye may also become dislocated (sublaxation) in some cases also causing an affect on vision. It is therefore important that parents seek expert advice from an eye specialist about protecting their babies eyes.

Cause of Aniridia

Aniridia is a congenital disorder, which occurs during the 12th and 14th week of pregnancy and is apparent at birth. Aniridia is caused by an abnormality or mutation of the PAX6 gene, it has been noted that the abnormal gene occurs equally in both males and females

Eye Tests/Diagnosis of Aniridia

Children diagnosed with Aniridia will regularly need to have their vision tested throughout their life, the frequency depends entirely on what problems appear throughout the child’s development. Aniridia sufferers will also need to have regular checks for glaucoma or cataracts. Slit lamp examination can pinpoint various abnormalities of aniridia such as cataracts, and glaucoma, iris translucency and pupil abnormalities. Iris fluorescien aniography may uncover iris hypoplasia but this method is rarely used. Optical imagery or Optical coherence tomography may be used to look for typical cases of hypoplasia and although useful images can be obtained from OCT, it is difficult to perform where nystagmus is apparent. High frequency ultrasound biomicroscopy or UBM examination has been found to display iris hypoplasia or absence of the iris in infants suffering congenital glaucoma.

Treatment & Prevention of Aniridia

Whilst it is possible to help prevent the possible side effects of aniridia, it is unfortunate that aniridia cannot be treated. Tinted or photochromic lense spectacles can help to reduce glare from sunlight and to protect the eye from injury. Special soft contact lenses are available with either a dark tint or with a painted iris to stop the glare and make the eye appear normal. There is also evidence to support an improvement in nystagmus with the use of contact lenses. Cataracts in some cases are removed with surgery to improve vision, and Corneal disease can be treated with eye drops.

Glasses help to aid children with their poor vision and although youngsters with aniridia are able to attend a normal mainstream school, it is best to make the school aware of problems a child may encounter.


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