(Usually and inappropriately termed “color blindness”)
(written some time ago)
The origin of the condition termed “color blindness” is indeed genetic which is a really obvious and often used statement to “explain” the condition! The mechanism involved (after genetic determination), however, does not produce “different types of cones” but rather must code for the protein that forms the inner segment of retinal receptors which in turn, sets the wavelength-defining interreceptor spacing of light interactive outer segments. If the ratio of the diameters of cones/rods is altered from a normal value of 1.8-2.0:1 this will shift the mid-band point of the visual band that this geometric premise uniquely defines, It will no longer lie at the normal approximately 7 1/2 degree retinal angle but will be shifted in one direction or the other. The refractive properties of the body of the eye however will not change so that the color determining mid-band will shift from a normal value of approximately 550 nanometers. This point on the retina is what Land termed the “fulcrum” and he demonstrated that any slight shift in this wavelength significantly altered color perception. I would propose that this is the mechanism involved in color blindness.
1.) From HUMAN COLOR VISION, Second Edition, by Kaiser and Boynton
