a type of anomalous dichromatism color deficiency in which the spectrum is seen in tones of yellow and blue with confusion of red and green and reduced sensitivity to monochromatic lights from the red end of the spectrum, due to a lack of (or lack of function of) “L-cone” photoreceptors sensitive to long (reddish) wavelengths of light

dichromacy characterized by lowered sensitivity to long wavelengths of light resulting in an inability to distinguish red and purplish blue

One of the two varieties of red-green color blindness (also known as red-dichromacy). Protanopia is thought to result from the loss of function of the L-cones. Protanopes display a marked loss of sensitivity to light at the long wavelength end of the spectrum. (See deuteranopia.)