Colour blindness does not (usually) mean being unable to see colour.
Protanopia - reduced sensitivity to red wavelengths
Deuteranopia - reduced sensitivity to green wavelengths
Tritanopia - reduced sensitivity to blue wavelengths
Protanopia and deuteranopia are not wildly different in their effects, and together are known as red-green colour-blindness; tritanopia, sometimes known as blue-yellow colourblindness, is relatively rare.
All are genetic, and the proximal cause is the failure of the appropriate photoreceptors in the retina to develop.
The genes involved are on the X chromosome: as women have 2 copies of this chromosome, damage or mutation on one chromosome can be compensated for by a second, intact copy. Men have only one X chromosome, and are thus more likely to be affected by colour blindness.
This is what a person with normal colour vision sees:
Red-blind (protanopic) people see this:
Colours that containing red appear as the colour combined with red to create them - so orange looks yellowish, and purple appears blue.
Green-blind (deuteranopic) people see this:
This is what a person with normal colour vision sees:
Red-blind (protanopic) people see this:
Colours that containing red appear as the colour combined with red to create them - so orange looks yellowish, and purple appears blue.
Green-blind (deuteranopic) people see this:
Not a great deal of difference from red-blindness, just a bleaching of some shades.
Blue-blind (tritanopic) people see this:
Again, colours containing blue appear as the colour combined with blue to create them: the purple crayon looks dark red. Colours that contain yellow now look like the colour combine with yellow - the two green crayons appear blue, and the yellow crayon is off-white.
There is a form of colour blindness, achromatopsia, where no colour is seen, only shades of grey (including black and white). It is very rare indeed, and results from the developmental failure of all photoreceptor (‘cone’) cells.
They are thus reliant on their ‘rod’ (night-vision) receptors, which are on the periphery of retina.
There are lesser forms of achromatopsia, where one type of cone - usually blue - develops normally, but this is even rarer than full achromatopsia.
While colour blindness is usually genetic, it can be ‘acquired’ -
While colour blindness is usually genetic, it can be ‘acquired’ -
For Example:
Through retinal disease or brain damage. In the latter instance, the eye still encodes colour information correctly and passes it to the brain, but the brain can no longer interpret that information.
Interestingly, if asked to guess a colour, a brain-damaged achromat will usually be correct at a higher rate than chance, suggesting that colour information is being passed around the visual centres of the brain in some format.
-By Rachel Anderson, PhD Visual Psychophysics, University of Birmingham
*Will change the topic to different section soon
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