Schmidt’s Sign

An indicator discovered by Schmidt in [1955] that can identify female carriers of Protan CVD.

Protans exhibit Scoterythrous Vision (a darkening of red wavelengths) due to the shift or absence of the L-Opsin. Carriers of a protanopic or protanomalous allele will test as having normal color vision, but will have a Luminosity Curve that lies between a Protan Luminosity Curve and a normal Luminosity Curve. Measuring a female’s Luminosity Curve can therefore identify if she is a Protan Carrier.

Schmidt’s Sign cannot detect Deutan Carriers, and there is no equivalent that can.

Schmidt’s Sign has never been used to systematically screen for Carriers of CVD, and has only been rarely used in research. Protan Colorblindness does not pose a negative enough prognosis for a child to justify the ethical problems involved in routine screening.