Different kinds of inherited color deficiencies result
from partial loss of function in one or more different
cone photo-receptors in the retina. The most frequent human
color vision deficiencies involve insensitivity to the middle
or long wavelength in the human cone systems. A person
with this deficiency has difficulty discriminating reds,
yellows, and greens from one another. Other color
deficiencies, such as discriminating blues from yellows, are
very rare. The rarest condition involves complete color
blindness, monochromacy, in which one cannot distinguish
any color from gray.
There are many eyeglasses