Aniridia

What is Aniridia?

An eye disorder, Aniridia is a condition of complete or partial absence of the iris (colored part of the eye). In simple terms, it means “an eye without the iris.” Although a congenital disorder, a penetrant injury may be one of the causes. It also affects the pupil and other parts of the eye. In some cases, the iris is undeveloped or malformed, and at times this may affect other parts of the eye. Aniridia is a bilateral condition (affects both eyes) that affects both men and women in a ratio of 1:40,000 to 1:100,000 people respectively.

Other Names

  • Congenital aniridia
  • Irideremia
  • Iris hypoplasia

Types

  • Isolated Aniridia: One of the most common forms, reduced olfaction is the main functional deficiency. It affects:
    1. Anterior cingulate cortex
    2. Cerebellum
    3. Temporal & occipital lobes
    4. Corpus callosum
    5. Pineal gland
    6. Olfactory lobes
    Sometimes due to visual impairment, a person suffers from hearing deficit.
  • WAGR Syndrome: WAGR syndrome (a rare form of kidney cancer) is a combination of Wilms tumor, Aniridia, Genitourinary abnormalities and mental retardation. People suffering from this syndrome have higher chances of Wilms tumor.
  • Gillespie Syndrome: This syndrome is linked with Cerebellar ataxia (a disorder in cerebellum which controls voluntary movements of the body) and mental retardation. Due to its unidentified molecular basis and inheritance pattern G. syndrome is the rarest form of aniridia.

Causes

Aniridia (ANIRIDIA II, A2) is caused by the mutation in the PAX6 gene present in the shorter arm of the 11th pair of chromosomes (11p13). The PAX6 gene directs the production of a protein essential in the early development of eyes, brain, spinal cord and pancreas.

The PAX6 protein is called transcription factor because it gets attached to the specific regions of DNA and regulates the functions of other genes. Any shortage disrupts the formation and development of eyes at an embryonic stage. Hence, the deficiency of this gene expression leads to Aniridia. It inherits in an autosomal dominant pattern from the parental gene.

Symptoms

  • Photophobia: Eyes become highly sensitive to light
  • Nystagmus: Involuntary movement of eyeballs consistently
  • Cataracts: Clouding inside the lens, results in blurry vision
  • Gradual loss of vision
  • Abnormal pupil
  • Glaucoma
  • Optic and macular nerve hypoplasia
  • Corneal disorders

Clinical Diagnosis

  • Slit lamp examination: A crucial procedure, it evaluates the pupillary and iris aberrations. Corneal deformities, cataract, and glaucoma are also detectable through this technique.
  • Fundoscopy and indirect ophthalmoscope: Detects optic disc malfunctions as well as Foveal hypoplasia.
  • Optical Coherence Tomography (OCT): Used to determine the condition of foveal hypoplasia and nystagmus in young ones.
  • High-frequency Ultrasound Biomicroscopy (UBM): Analyzes corneal opacity and another corneal edema in infants. It can also detect the iris hypoplasia.

Genetic Diagnosis

In genetic diagnosis tracing of the family history and study of inherited traits are mandatory. The parents need to be diagnosed for the PAX6 mutated gene. Examination to study genetic anomalies and deletion of some inherited patterns are conducted through the following two techniques:

  • Multiplex-litigation probe amplification(MLPA)
  • Comparative genomic hybridization

Differential Diagnosis

There are some other disorders which are quite similar to Aniridia and hence, require differential diagnosis. They are:

  • Juvenile Glaucoma
  • Congenital Nystagmus
  • Ectopia lentis
  • Congenital cataract
  • Peters and Rieger anomalies
  • Iris Coloboma
  • Oculocutaneous Albinism (OCA)
  • Gillespie Syndrome
  • Rieger Anomaly
  • Oculocutaneous Albinism (OCA)
  • Gillespie Syndrome

Treatment

There is no specific treatment, but some associated diseases can be treated to enhance or balance the visual acuity. Treatment of amblyopia and refractive errors are important. Moreover, a patient suffering from Aniridia should undergo annual checkups for glaucoma, intraocular pressure, and visual field testing.

A prophylactic craniotomy is an effective cure for glaucoma while Aniridic Keratopathy (AAK) and Penetrating Keratopathy can be used to treat corneal disorders. Another technique that has grown in popularity over the past several years is Homologous Lamellarlimbokeratoplasty. Diagnosing and treating Aniridic Fibrosis syndrome is also important.

Prognosis

Proper management and follow-up treatment can reduce vision problems as this disease is non-curable. Prenatal diagnosis during pregnancy can control the risks of isolated Aniridia. A regular visit to the doctor facilitates a favorable prognosis.

References

  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3449076/
  2. https://www.aniridia.eu/what-is-aniridia/
  3. https://www.hindawi.com/journals/isrn/2014/305350/
  4. http://eyewiki.aao.org/Aniridia
  5. https://www.rnib.org.uk/eye-health-eye-conditions-z-eye-conditions/aniridia
  6. https://ghr.nlm.nih.gov/condition/aniridia#resources
  7. https://rarediseases.org/rare-diseases/aniridia/

Be the first to comment

Leave a Reply

Your email address will not be published.


*


This site uses Akismet to reduce spam. Learn how your comment data is processed.