What is Ocular Albinism?
Ocular albinism is a genetic disease associated with the deficiency of melanin pigment in the iris, the colored part of eye, and the retina, the light-sensitive tissue present at the rear end of eye.
The skin and hair color remains unaffected unlike oculocutaneous albinism where the hair and skin also shows reduced coloration along with the eyes.
Pigmentation is quite essential for normal vision of the eye.
Symptoms of Ocular Albinism
- The color of iris may change frequently from blue to green to brown. It may also darken with age.
- Ocular albinism is associated with acute impaired sharpness of vision due to which it results in inability to read and drive properly.
- The eye sensitivity towards glare and bright light is also increased significantly which is commonly known as photophobia.
- It is also characterized by stereoscopic vision in which eyes cannot perceive the depth.
- It shows strabismus where the eyes cannot look into the same direction.
- Also in this condition, the eyes show rapid involuntary movement, which is known as nystagmus.
- Some of the affected individuals also show abnormalities associated with optic nerves that carry the visual information from eyes to the brain. This is due to changed routing of optic nerves as in normal eye condition, the nerve fibers reach to both sides of brain whereas in ocular albinism, the nerve fibers stretch to opposite side of the brain crossing from the eyes.
Picture : Child having Ocular Albinism
Basically, the incomplete development of fovea, the small part of retina is responsible for ocular albinism as the eye lacks the ability to process the sharp light images in the absence of fully developed fovea.
This may be due to deficiency of melanin pigment, which is required for the growth of fovea that occurs before birth.
How ocular Albinism is inherited?
- Most commonly, ocular albinism is inherited in an X-linked pattern, as the gene responsible for this disease is located on X-chromosome .
- Basically, X-linked ocular albinism results from the mutation in GPR143 gene, which is responsible for the synthesis of protein that plays an important role in the pigmentation of skin and eyes.
- This gene also regulates the growth of melanosomes that produce and store the melanin pigment.
- Mutated gene prevents the protein from reaching the melanosomes to produce sufficient melanin required for pigmentation of skin and eyes .
- Since males have only one X-chromosome, the mutated gene drastically shows the characteristic features of ocular albinism whereas women are mildly affected with this disease as they have two X-chromosomes and second X-chromosome is sufficient to impart normal vision if one of them gets mutated. Hence, ocular albinism is almost exclusively found in males.
- This X-linked ocular albinism is also known as Nettleship-Falls ocular albinism or type 1 ocular albinism.
Types of Ocular Albinism
There are three types of ocular albinism that include the following types:
- Ocular albinism Type 1 (Nettleship-Falls syndrome), caused by mutation in GPR143 gene, is the most common kind of ocular albinism and is generally associated with rapid involuntary movement of the eyes (nystagmus).
- Ocular albinism Type 2, also known as Aland Island eye disease or Forsius-Eriksson syndrome (pp.447), is caused by mutation in CACNA1F gene (pp. 2498). It is frequently associated with the protanopic dichromacy, a form of color blindness and nyctalopia, night blindness.
- Ocular albinism sensorineural deafness (OASD), as the name implies, is accompanied with hearing loss (pp. 444). It is very rare form of ocular albinism and is supposed to be same as that of type 1.
Another less common variety of ocular albinism includes autosomal recessive that shows different pattern of inheritance (pp. 868).
In this kind of inheritance, both parents of affected child carry the gene responsible for this disease and hence, girls and boys are affected equally.
It is known to be mild variant of oculocutaneous albinism as slight reduced pigmentation is observed in hair and skin color of affected individual.
Analysis of Gene responsible for Ocular albinism (Genetics)
- Blood tests are required for analysis of gene responsible for ocular albinism but since, ocular albinism is accompanied with some but not all kinds of DNA defects, the genes responsible for ocular albinism are not identified with blood tests alone.
- Most of the times, the mottling of pigment in the retina of eyes is a significant indication of presence of X-linked ocular albinism.
- In case, the mottling is not very prominent, the skin biopsy or hair bulb can be used to identify the disease as it shows unusual large granules of pigment in the individual affected with X-linked ocular albinism but not with autosomal recessive ocular albinism.
Treatment of Ocular Albinism
- Environmental changes and the use of visual aids to magnify the limit of vision are the major considerations included in the treatment of ocular albinism.
- Surgery can be helpful sometimes in case of strabismus but usually does not result in fine harmonization of eyes.
- Contact lenses mounted with small telescopes may also provide additional correction for both close and distant vision.
- Social and emotional adjustment plays an important role in the treatment of individual affected with ocular albinism.