Also known as Maskun, Achromatopsia is a rare form of color blindness where the sufferer is completely unable to perceive colors. This is caused by the cone cells (color receptors) in the retina not functioning. The lack of perceiving color isn’t the only problem caused by Achromatopsia however, as the rod cells (brightness perceivers) can become easily saturated with light, therefore sufferers of Achromatopsia can have problems seeing in bright lights or even on a bright day.
Achromatopsia sufferers see things in a very different way to people with full color vision, as they identify objects based on their brightness rather than color. People with full color vision only identify objects in this way when they use their eyes in very dark places as the rod cells become more predominant.
Achromatopsia is endemic of the Pohnpei island in the Federated States of Micronesia, which was described by Oliver Sacks as The Island Of The Colorblind, however Achromatopsia is found throughout the world. The reason Pohnpei is thought to suffer so much from Achromatopsia is their small gene pool.