Aniridia or absence of the iris: what is it and why does it occur?

Aniridia was, until recently, a totally incurable pathology. Scientific advances are promising in this regard.

Last update: September 16, 2022

Aniridia is a rare pathology characterized by the total or partial absence of the iris. The latter is the diaphragm that surrounds the pupil and gives color to the eyes. Its basic function is to regulate the amount of light that enters the eye.

Aniridia is estimated to affect 1 in 100,000 people. Sometimes there is no iris at all; other times, this is incipient.

One could say that an eye without an iris is like a window without curtains. The light enters indiscriminately.

What is aniridia?

Aniridia is an eye disorder characterized by incomplete development of the iris. It usually affects both eyes. The absence of the iris can be total or partial, but in both cases it causes important alterations in vision.

Although aniridia refers only to the absence of the iris, the truth is that it is common for other parts of the eye to be affected when this condition occurs. It is common to be accompanied by corneal degeneration, lens dislocation, cataracts, glaucoma, nystagmus, strabismus or optic nerve atrophy..

In most cases, the disease is present from birth. It is almost always due to an inherited genetic mutation. It is considered a chronic pathology, but there are treatments to moderate its effects and even correct the problem.



Symptoms

Aniridia can be detected from the first days of life. It is recognized, in principle, because the newborn prefers to be in the dark and closes his eyes to light stimuli. The disease significantly diminishes vision and also gives rise to other eye pathologies.

The usual symptoms of aniridia are the following:

  • low vision
  • Glare.
  • Photophobia.

The most characteristic is the presence of a larger than normal pupil, which usually has an irregular shape. There is also decreased visual acuitywith associated defects, such as myopia, hyperopia or astigmatism.

Likewise, there may be amblyopia or decreased vision due to lack of sensitivity in the retina. Glaucoma is also present in up to half of aniridia cases. And it is not uncommon for pathology to generate cataracts.

Aniridia is present from birth. The baby has serious difficulties tolerating ambient light.

Causes

The direct cause is usually a mutation of the PAX-6 gene, which is located on chromosome 11. This is responsible for the formation of the eyeball during the first stage of pregnancy.

Although the most obvious manifestation is the total or partial absence of the iris, the mutation in this gene usually causes abnormalities in other parts of the eye. In about a third of patients there is sporadic aniridia; that is, the mutation occurs spontaneously and not inherited.

The disease has an autosomal dominant pattern of inheritance. A person with aniridia has a 50% chance of transmitting this pathology to their direct descendants.

There is no way to prevent pathology.

In rare cases, aniridia is associated with other systemic diseases, such as Wilms tumor. It is also possible that it is the effect of some trauma to the eye.



Diagnosis of aniridia

The diagnosis of aniridia is simple. Just look at the size and shape of the pupils to detect the partial or total absence of the iris. This is captured with the naked eye, without the need to do any extra testing.

However, it is important to perform some tests to determine the severity of the abnormality. In some cases, it can be confused with another disorder called iris colobomain which this organ is cracked.

For this reason, the following tests are usually requested:

  • Hybridization on-site fluorescent (FISH).
  • Chromosomal banding.
  • Images of the abdomen and brain.
  • Kidney ultrasound.

Treatment of aniridia

Until now, there is no specific treatment for aniridia. The usual thing is that an independent approach is made for each of the associated anomalies. That is, one for glaucoma, another for cataracts, etc.

During childhood there is the possibility of carrying out early visual stimulation. This helps to develop the maximum possible visual potential and to avoid motor problems.

It is common for many patients to use cosmetic contact lenses. They are a partial solution that help to overcome photophobia and solve the problem of the abnormal appearance of the eyes.

If the defect is partial, it may be possible to correct it with microsurgery.. This allows a reconstruction of the iris and the pupil. If the defect is very serious, in some cases it is possible to make an implant in the eye to form a complete iris.

Reconstruction of an incomplete iris is possible. In any case, it is not an easy surgery or always a favorable result.

Forecast

The prognosis of aniridia is very varied, since it depends on the severity and characteristics of each case. Sometimes it is possible to almost completely correct the problem, while at other times this is impossible.

Therefore, treatment must be individualized. The doctor in charge of doing it is the ophthalmologist, who will not only seek to improve or repair the condition, but also prevent possible complications.

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