Achromatopsia is a non-progressive and hereditary visual disorder which is characterized by decreased vision, light sensitivity, and the absence of color vision. In the U.S. it affects about 1 in every 33,000 people.
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 an abnormality of the retina. They also have no color vision, sensitivity to light (photophobia) and the presence of nystagmus (shaking of the eyes). Children with incomplete or partial Achromatopsia may have better vision (20/120 to 20/80).
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).
No, red-green color blindness is very common as it affects eight percent of all males. People with red-green color blindness have otherwise normal visual acuity and they do not have complete lack of color perception.
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 called 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. A child born with non-functioning cones 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 four genes (genetic markers found on chromosomes) are known to be associated with this condition. The four chromosomes that may have changes associated with achromatopsia are chromosome 14, chromosome 8q21- q22, chromosome 2q11 and chromosome 10q24.
The achromatopsia gene is inherited from both the mother and father who carry the diseased 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 (this is called autosomal recessive inheritance). This gives a family with one affected child a 25% (1 in 4) risk of each pregnancy carrying an affected offspring. There would also be a 50% chance that a child could be a carrier.
The diagnosis will be made by your ophthalmologist. Initially, symptoms such as light sensitivity and reduced vision will provide clues essential to the diagnosis. The retinal examination may in fact be normal. The color vision 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). Also, new advances in retinal imaging gives Ophthalmologists better tools to evaluate the condition.
Currently there is no cure for achromatopsia. Research on gene therapy is ongoing and may lead to clinical treatments in the future. Animal models of achromatopsia in dogs and mice have shown promising results in restoring some cone function in the retina. 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. Red colored lenses help reduce the sensitivity to light and thus enhance visual functioning. NoIR (injection-molded) plastic wrap-around glasses have a top ‘shield’ that covers the top of a prescription frame as well as broad side shields which is important since stray light can be disabling. Examples are Corning Lenses: CPF 550 lenses (5% transmission, darkened) and CPF 550XD lenses (4% transmission, darkened). These lenses are available through Winchester Optical (www.winoptical.com/medical/ecporder.htm). A newer device known as an eyeborg can help people with no color vision to perceive color through sound waves. Artist Neil Harbisson who suffered from achromatopsia was one of the first to use this device.
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. A low vision evaluation will be necessary before school begins. More severely affected individuals may benefit from services available in schools specifically designated for the visually impaired.
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