Congenital Achromatopsia (Hereditary Achomatopsia)
This achromatopsia (color blindness) is inherited in which vision is characterized by a lack of cone vision (sight provided by the cone photoreceptors in the retina). People with achromatopsia (achromats) are completely or almost completely colorblind. They have poor visual acuity,
and their eyes do not adapt normally to higher levels of illumination and are very light sensitive (photophobic). At higher levels of illumination, the vision of achromats decreases unless they make use of tinted lenses. In moderately bright indoor spaces or outdoors just after dawn or just before dusk, some achromats adapt to their reduced level of visual functioning without resorting to tinted lenses, by using visual strategies such as blinking, squinting, or positioning themselves in relation to the light source. Others routinely wear medium tinted lenses in such settings. In full sunlight outdoors or in very bright indoor spaces, almost all achromats use very dark tinted lenses to have a reasonable amount of vision, since their retinas do not possess the photoreceptors needed for seeing well in such settings. In normal eyes there are some 6 million cone photoreceptors that are located mainly in the center of the retina. Lacking cones, persons with achromatopsia have to rely on their rod photoreceptors for vision. In the normal eye there are some 100 million rod photoreceptors. Rods are located mostly at the periphery of the retina. Rods saturate at higher levels of illumination. They do not provide color vision or good detail vision.