This form of complete color blindness is a very rare subtype of color vision deficiency among much more common ones like the the well known red-green color blindness. People suffering under monochromacy, perceive everything just in shades of gray.
Monochromacy, more commonly referred to as "total color blindness", is caused by the total absence of either 2 or 3 of
the pigmented retinal cones, reducing vision to one dimension. It comes in two forms:
Rod monochromacy is the condition where the rod cells of the retina are present and functional, but all types of cones are either non functional or missing. Even as the more common form of total color blindness, rod monochromacy is thought to only occur in around 0.003% of people or less.
Another name for rod monochromacy is achromatopsia, and it is not sex linked - men and women are equally as likely to suffer this disease. Those totally color blind as a result of rod monochromacy usually also suffer a number of other vision impairments including one or more of the following symptoms:
- Completely unable to distinguish colors.
- Amblyopia (reduced visual acuity)
- Hemeralopia (with the subject exhibiting photophobia - severe light sensitivity)
- Nystagmus: Involuntary eye movements
- Iris operating abnormalities
While cone monochromacy is less severe in that visual acuity remains normal, it is also significantly less common with only a handful of cases ever being identified. Total color blindness from cone monochromacy is the condition of having only a single type of cone in the retina. As a result, cone momochromacy can be categorized as follows:
- Blue cone monochromacy, also known as S-cone monochromacy
- Green cone monochromacy, also known as M-cone monochromacy
- Red cone monochromacy, also known as L-cone monochromacy