The two types of total colorblindness: Congenital and Cerebral

Congenital Colorblindness

Congenital colorblindness is the primary type since it is a sex-linked trait, inherited on the X chromosome. People who have congenital colorblindness have never experienced color and do not understand the concept of gray. Congenital colorblindness is much more common in males since males have one X and one Y chromosome and females have two X chromosomes. Females are typically carriers for the disease because only one of their chromosomes are infected. It is very rare that both X chromosomes in a sex-linked disease are mutated since both parents would have to have be infected and give the disease on both of the daugther's X chromosomes. (Web Exhibits).

Pedigree Chart

How can photoreceptors dysfunction?

There are two ways that they photoreceptors in the eye can dysfunction; either a type of cone is absent or a cone does not function properly. Typically, this is caused by defects on the X chromosome. The cones may detect, or absorb, the wrong light wavelength, which causes inability to perceive specific colors.

There are many variations of symptoms and severity due to the different gene expression in each person that may cause either total or almost total colorblindness. Partial colorblindness diseases that effect the long and medium cones are much more common than achromatopsia. These are often called red-green colorblindness since it is difficult for the person to detect those colors. That is as high as one out of twelve men and one out of two hundred women. People who are protans (red weak) and deutans (green weak) comprise 99% of this group. Protans have a difficult time detecting hues with wavelengths in the red range. Deutans have difficulty with green hues Web Exhibits. Approximately eight percent of men and less than one percent of women have typical red-green colorblindness. A more rare case of partial colorblindness is a defect in the short cones which causes yellow-blue colorblindness.

Doctors have developed a system of different plates with colors and number to help diagnose patients with colorblindness. The first photo is an introductory color plate that the majority of the population should be able to see. The number on the plate is 12. To people who are colorblind the top plate may look more like the bottom plate, where everything is basically the same color and it is very difficult to tell what the number is. (The bottom plate actually has the number 17 in because it is a different plate but it still illustrates the point.)

A very good test with 17 plates can be found is on this website administered by Dr. Mayers.

Rod monochromatopsia "Night Vision"

The most severe case of colorblindness is due to the absence or defect of cones, called complete rod monochromatopsia, that causes total colorblindness. They have “night vision,” or rod vision, because they inherited a trait from their mother's genes that prevents the production of cones or causes defects the cones in early development. Thus, only the rods are present and the easiest way for them to see is at night or in low light.

People with rod monochromatopsia cannot see color cannot detect detail or contrast between various colors and they have a difficult time adjusting to highly illuminated objects.

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