Achromatopsia

Wednesday, March 23, 2011

Also known as rod monochromatism, achromatopsia is a recessive inherited eye condition which is associated with color blindness, extreme light sensitivity, and visual acuity loss. It affects approximately 1 in every 33,000 Americans. Achromatopsia means without color and is defined as little or no function of the cone cells. In the retinas of normal eyes there are about 6 million cones (photoreceptor cells), which are sensitive to colors and located mostly in the fovea, at the center of the retina. Thus, this disorder affects the cones and the patients who suffer from achromatopsia do not have normal "cone vision."

There are two primary forms, the complete achromatopsia and incomplete achromatopsia.  

1) Patients with complete achromatopsia are only able to perceive black, white and shades of gray. Patients with complete achromatopsia have no real understanding of the concept of color. A color like red may be perceived as dark gray while yellow may be perceived as a light gray. The vision is much like that of a black and white photograph with varying shades of gray.

2) Patients with incomplete achromatopsia have profound color impairment, but do have a small residual amount of color vision and slightly better visual acuity due to the presence of some functioning cone cells in the retina.

Inheritance achromatopsia is a recessive inherited condition. It requires both parents to contribute a gene in order for the condition to occur. All the offspring of an achromat may carry one gene for achromatopsia.  In order to pass the condition onto their children, it would require having children with someone else carrying the same gene and passing a gene from each parent. This would be extremely unlikely in today's very mobile populations.