Protanomaly without darkened red is deuteranopia with rods

Area of Science:

• Ophthalmology and Vision Science
• Genetics and Molecular Biology
• Psychophysics

Background:

• The Rayleigh match is a standard diagnostic tool for inherited red-green color vision defects.
• Variations in Rayleigh match ranges and luminance thresholds differentiate normal trichromacy from anomalous trichromacy (deuteranomaly, protanomaly).
• Unusual Rayleigh matches can complicate diagnosis, as seen in rare cases combining protanomalous range with normal luminance settings.

Observation:

• An observer presented with an atypical Rayleigh match, exhibiting a range typical of protanomaly but a luminance setting characteristic of deuteranomaly.
• This observer's condition defied clear diagnosis using conventional Rayleigh matching alone.
• Previous reports of similar cases predate advanced genetic and cone photopigment analysis.

Findings:

• Genetic analysis predicted the observer to be a deuteranope.
• Psychophysical testing, including Rayleigh matching with rod suppression, indicated the presence of a single L-cone photopigment, consistent with deuteranopia.
• The observer's Rayleigh match results were influenced by both L cones and rod contributions.

Implications:

• This case highlights the limitations of the Rayleigh match in diagnosing complex or atypical color vision deficiencies.
• Modern genetic and psychophysical methods are crucial for accurate diagnosis of rare color vision variants.
• Understanding these variants advances knowledge of human color perception and cone photopigment function.