Scoterythrous Vision

From scot- (greek skotos – darkness) and erythro- (greek erythros – red); meaning a darkening (less luminous) of the red portion of the visible spectrum, or likewise, a shortening of the visible spectrum on the red end. This is a symptom of all Protan defects, since the L-Opsin (red) is either missing or significantly shifted towards the M-opsin. It is also an important symptom of Blue Cone Monochromacy, where both L- and M-Cones are absent.

The symptom was a well known symptom of some colorblindnesses (“red blind” or “red weak”) in the very early days of color vision research, insomuch that Holmgren – creator of the infamous Holmgren’s Wool – assumed that it must also extend to “green blind” or “green weak” colorblindnesses – a theoretical “Scotochlorous Vision”. He thereby based his entire wool system on the assumption that Deutans also see green as black (Murray 1943). Of course, we now know that Deutans have very similar luminosity curves to color normals and therefore see green just as bright, albeit grayer at certain wavelengths (see Neutral Point).

Theoretically, the blue equivalent (“Scotocyanous Vision“), should exist and be a symptom of Tritanopia. However, because the S-Cones are so outnumbered by the other cones and contribute very little to the Luminosity Curve, the darkening of blues for Tritans is an almost negligible effect when compared to the Scoterythous Vision of Protans.