colour blindness resulting from insensitivity to red light, causing confusion of greens, reds, and yellows. It is hereditary, and is the commonest form of colour blindness.Also called daltonism.Compare with deuteranopia, tritanopia.
early 20th century: from proto- 'original' (red being regarded as the first component of colour vision) + an-1 'lacking' + -opia
protanopia in other Oxford dictionaries
Definition of protanopia in the US English dictionary