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protanopia) is a mild color vision defect, in which an altered spectral sensitivity of red retinal receptors (closer to green receptor response) results in poor red–green hue discrimination. Because of an abnormality in the visual pigment that absorbs long wave light subjects lack long-wavelength sensitive retinal cones, so those with this condition are unable to distinguish between colors in the green–yellow–red section of the spectrum.

Protanomaly a form of colour-blindness is the name for the clinical condition that arises form this defect

They have a neutral point at a cyan-like wavelength around 492 nm (see spectral color for comparison) – that is, they cannot discriminate light of this wavelength from white. Their matches are also outside the normal range of the Rayleigh equation

For a protanope, the brightness of red, orange, and yellow are much reduced compared to normal. This dimming can be so pronounced that reds may be confused with black or dark gray, and red traffic lights may appear to be extinguished. They may learn to distinguish reds from yellows primarily on the basis of their apparent brightness or lightness, not on any perceptible hue difference. Violet, lavender, and purple are indistinguishable from various shades of blue because their reddish components are so dimmed as to be invisible. For example, pink flowers, reflecting both red light and blue light, may appear just blue to the protanope. Very few people have been found who have one normal eye and one protanopic eye. These unilateral dichromats report that with only their protanopic eye open, they see wavelengths shorter than neutral point as blue and those longer than it as yellow. This is a rare form of color blindness.

It is hereditary, sex-linked, and present in 1% of males..[1]


Protanopia and its derivatives come from the greek 'protos' (first), relating to the first of the primary colours - red, green and blue *'anomalos' (uneven or inconsistent form 'an-' (without) = 'homalos' (even)[2]

See alsoEdit


  1. Cassin, B. and Solomon, S. Dictionary of Eye Terminology. Gainsville, Florida: Triad Publishing Company, 1990.
  2. Coleman,A F (2006). Oxford Dictionary of Psychology, 2nd ed. Oxford:OUP.

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