Phenotypic diagnosis of protan and deutan heterozygosity.

The color vision of 18 women whose color vision genotype was known were tested on the Nagel anomaloscope. An amended examination procedure was used which allowed repeated brightness matches to be made. This procedure revealed that the spectral region of minimum average brightness settings was useful in determining heterozygosity for protan defects and that deutan heterozygous persons have a unique spectral region of minimum average variance of brightness settings.