Achromatopsia :: Biology Essays Research Papers

Achromatopsia When I was young, I was told that "color blindness" did not mean that the person saw the world like an old movie, but rather it meant that they could not distinguish between green and red. I thought that this understanding was very advanced and would quickly share my knowledge with any less-informed children. After looking into the matter, I have been forced to reject this generalization in favor of a broader range of diseases resulting in very different types of inabilities to perceive color in a "normal" fashion. While the typical color blindness I was told about affects 8 percent of men and less than 1 percent of women in the United States (1), there are many other types. The most common types of color blindness, effecting red and green vision, are not too serious for the sufferers, who can function normally and do not have overly impaired vision other than an inability to distinguish between certain colors. There are, however, more serious forms of "color blindness", such as blue cone monochromatopsia, partial rod monochromatopsia, and total rod monochromatopsia (3). The rod monochromats are also known as achromats, meaning they see no color at all. Only about 1/33,000 Americans has this disease, and women and men are effected roughly equally (3). This most severe variety of color blindness has many interesting symptoms which reveal a lot about rod vision. Achromats have what can be called "night vision" or rod vision. This means that the only functioning receptors in their retina are rod photoreceptors. The cones are either absent entirely or are present but the signals are not being processed for some reason. There are two types of achromatopsia, one is congenital and the other can be caused by brain damage, called cerebral achromatopsia (3). There are also varying degrees of achromatopsia, with some sufferers being able to distinguish some color and others absolutely none. I will focus on the congenital version since cerebral achromatopsia varies in its symptoms and cause quite a bit, as well as being much more rare and so fewer cases have been studied. Congenital color blindness has more regular symptoms which can be used to demonstrate how rod-vision works. One of the most noticeable things about an achromat that reveals their vision deficiency is sensitivity to light (8). Cone vision is what most people use during the day, since cones have less light sensitivity, meaning they can absorb more light without discomfort, although they too can be overloaded with light (like looking into the sun).