Genetics of Color Vision Defects

Abstract

The human retina contains two classes of photoreceptors, rods and cones. Rods are responsible for vision in dim light, whereas cones mediate vision in bright light and enable the perception of color. Individuals with normal color vision have three types of cone photoreceptors; the short wave-sensitive or blue, middle wave-sensitive or green and long wave-sensitive or red cones. Individuals with severe color vision defects usually either have nonfunctional red (protanopes) or green (deuteranopes) cone photoreceptors. Such individuals have dichromatic rather than trichromatic color vision. Those with milder color vision defects usually have either their red or green cone photoreceptor pigments replaced by an anomalous pigment with altered spectral sensitivity. Such individuals, therefore, have protanomalous or deuteranomalous trichromatic color vision. A wide variation in the ability to discriminate between colors exists among individuals with defective color vision. Subtle variation in color perception also exists among individuals with normal color vision. Significant advances have been made during the last 25 years toward understanding the molecular and genetic bases of variation in both defective and normal color vision. In this chapter, genotype to phenotype relationships in normal color vision and in the various classes of defective color vision will be reviewed. Emphasis will be placed on redgreen color vision defects since they are by far the most common. Recent reviews on this topic have been published and are recommended for additional reading.