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Achromatopsia

What is Achromatopsia?

Achromatopsia is a non-progressive visual disorder which is characterized by decreased vision, light sensitivity, and the absence of color vision.

How common is Achromatopsia?

This condition affects approximately one in 40,000 live births. Its prevalence varies in different parts of the world. Because there is a genetic link, it is more common in regions where there is a high rate of consanguineous marriages (marriages between relatives) and in the eastern Pacific islands of Pingelap (see the book, ‘The Island of the Colourblind’ by Dr Oliver Sacks).

What causes Achromatopsia?

Achromatopsia is caused by an abnormality of the retina, that portion of the eye responsible for “making the picture”. It is analogous to the film in a camera. In the retina, there are three types of cells (cones) that are responsible for normal color vision. These are the red cones, the green cones, and the blue cones. A balanced distribution of these cells is necessary for normal color vision. If a child is born with non-functioning cones, they will have achromatopsia. Sometimes children have a reduced complement of the cones, in which case they will have partial or incomplete achromatopsia. Achromatopsia is an inherited condition and so far three genes (genetic markers found on chromosomes) are known to be associated with this condition: CNGA3, CGNB3 and GNAT2. The three chromosomes that may have changes associated with achromatopsia are chromosome 14, chromosome 8q21- q22 and chromosome 2q11.

What are the chances of having more children with Achromatopsia?

The achromatopsia gene is inherited from both the mother and father who carry the disease gene on one of two paired chromosomes. The parents do not develop the disease as this requires the genes on both of the paired chromosomes for the individual to be affected (autosomal recessive inheritance). This gives a family with one affected child a 25% (1in 4) risk of each pregnancy carrying an affected offspring.

How does Achromatopsia affect vision?

Achromatopsia is sometimes called ‘Day Blindness’, as these children see better in subdued light. Children with complete Achromatopsia will have reduced vision (20/200 or less) due to the abnormal cones of the retina. They also have no color vision, sensitivity to light (photophobia) and the presence of nystagmus (wobbly eyes). Children with incomplete or partial Achromatopsia will have better vision (20/120 to 20/80).

Fig. 1 Child with achromatopsia outdoors		Fig. 2 Same child indoors in dim light

How is the diagnosis made?

The diagnosis will be made by your eye doctor. The affected child may not be able to perform the screening tests to check for color blindness, but the presence of nystagmus, light sensitivity and reduced vision will provide clues essential to the diagnosis. The tests commonly performed in the clinic are the Ishihara pseudoisochromatic tests, H-R-R tests and the City University tests. The diagnosis can be confirmed by a specialized test called electroretinography (ERG).

What is the treatment is available for Achromatopsia?

Children should be checked for refractive errors (need for glasses). Prescribing glasses to correct refractive conditions such as far-sightedness (hyperopia), near-sightedness (myopia) and astigmatism can improve the vision somewhat but will not restore normal levels of vision. Magnifying devices (low vision aids) may be helpful for reading as may the use of large print books.

What type of glasses should my child wear?

Dark tinted glasses or red glasses will help reduce the sensitivity to light and enhance visual functioning.

How will this condition affect my child’s schooling?

With adequate help from teachers for the visually impaired, children with achromatopsia are usually able to attend mainstream schools. Front seat placement, large print books, and magnifying devices can be very helpful. More severely affected individuals may benefit from services available in schools specifically designated for the visually impaired.

Is there an Achromatopsia support group?

The Achromatopsia Network
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