Cone pigments in human deutan colour vision defects

Area of Science:

• Ophthalmology
• Visual Neuroscience
• Color Vision Research

Background:

• Red-green color vision deficiencies, including dichromacy and anomalous trichromacy, represent a significant portion of the population with impaired color perception.
• Understanding the underlying photopigment basis of these conditions is crucial for diagnosis and potential therapeutic strategies.

Purpose of the Study:

• To identify and characterize a population of red-green dichromats using psychophysical methods.
• To investigate the spectral sensitivity and photopigment characteristics in individuals with deuteranopia and deuteranomaly.
• To compare the spectral properties of cone pigments in dichromats with those of normal trichromats.

Main Methods:

• Utilized the Nagel anomaloscope and neutral points to identify seventy individuals with red-green color vision defects.
• Calculated relative action spectra from anomaloscope settings at red (645 nm) and green (535 nm) primary wavelengths.
• Performed retinal densitometry on the foveas of fifteen deuteranopes, comparing findings with trichromat measurements.

Main Results:

• The ratio of red to green primary action spectra showed a bimodal distribution, indicating distinct clusters of red-green dichromats.
• Deuteranopes exhibited significant variability in anomaloscope matches, as did protanopes.
• Retinal densitometry revealed a single photolabile pigment in the red-green spectrum of deuteranopes, contrasting with the two found in normal trichromats.
• Rushton's hypothesis of deuteranopes possessing erythrolabe but lacking measurable chlorolabe was confirmed.
• Deuteranomalous individuals displayed two red-green cone pigments, with extreme cases showing difference spectra similar to deuteranopia.

Conclusions:

• The study confirms that deuteranopes possess only one functional photolabile pigment in the red-green spectrum, supporting existing theories.
• Significant individual differences exist in the spectral properties and kinetics of photopigments even within diagnosed groups like deuteranopia.
• Further research is needed to elucidate the reasons behind the observed variations in photopigment characteristics among individuals with similar color vision deficiencies.