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Cone-specific measures of human color vision
Konan Medical is a corporate sponsor and supporter of AsMA Aerospace Medical Association
- Protan = L-cone (red) deficiency
- Deutan = M-cone (green) deficiency
- Tritan = S-cone (blue) deficiency
- Genetics Overview
Protan Factoids:
- L-cone deficiency
- Less discrimination of the red colors
- Similar functionally to Deutans
- Significantly more common in males (mutation on X-chromosome allele)
- Commonly genetic cause, but may be acquired
A person with “red deficiency” or “red weakness” is a Protan and the condition is called Protanomaly. The appearance of “redness” by a color normal observer is seen more weakly by the Protan viewer both in terms of its color power (saturation or depth of color) and its brightness. Red, orange, yellow, and yellow-green appear somewhat shifted in “hue” (another word for color) towards green and appear less intense that they do to a color normal observer. The redness portion of a violet or lavender color is also weakened with a Protan so what appears contains mostly the blue component of the color. Thusly, what a color normal calls “violet, may appear only as another shade of blue to the Protan.
Under poor viewing conditions, such as when driving in dazzling sunlight or in rainy or foggy weather, Protan observers may mistake a blinking red traffic light for a blinking yellow, or fail to distinguish a green traffic light from the “white” lights in store fronts, street lights or other general lighting.
Deutan Factoids:
- M-cone deficiency
- Less discrimination of the green colors
- Similar functionally to Protans
- Significantly more common in males (mutation on X-chromosome allele)
- Commonly genetic cause, but may be acquired
A person with a Deutan deficiency called Deuteranomaly (5% of males) is considered to be “green weak” This deficiency is similar to the Protan type as there is also difficulty in discriminating between red – orange – yellow – green portions of the color spectrum … they are confused as being very similar. These colors seemed similar to the red portion of the spectrum.
Deuteranopia (1% of males) has the same hue discrimination problems as the Protonope, but without the dimming.
Tritan Factoids:
- S-cone deficiency
- Less discrimination of the blue colors
- Typically an acquired condition (genetic basis is very rare)
- May be the most common color deficiency type
- No gender bias
- Many tests that have been commonly administered in the past (Ishihara as an example) do not test for S-cone deficiencies
- More common with age
- Pharmaceutical agent toxicity may cause
- Neurologic conditions, diseases and discorders may cause
- Changes to the crystalline lens (cataracts) may cause
Red-green color deficiencies are the most common type of genetic color vision deficiency, originating from an X-chromosome mutation which results in a color deficient allele.
This is a recessive trait, but females that are heterozygous (trait only on one X-chromosome) will not exhibit the inherited trait, rather it requires a homozygous condition where the trait is manifested on both chromosomes, i.e. inherited from both parents.
Males, that inherit trait on the single X-chromosome maternally, exhibit red-green color deficiency.