The Chemistry of John Dalton's Color Blindness

by D. M. Hunt, K. S. Dulai, J. K. Bowmaker and J. D. Mollon

Science 267, 984-988 (1995)

Two hundred years ago, the great chemist John Dalton described his own color blindness in a lecture to the Manchester Literary and Philosophical Society, and his condition has since been termed "daltonism". Dalton recognized only two main hues, one of which corresponded to the colors that normal individuals know as red, orange, yellow and green, and another that included the colors of blue and violet. Dalton instructed that, after his death, his eyes be dissected. He hypothesized that his condition was caused by abnormal blue tinting of his vitreous humor. However, the autopsy performed on Dalton showed his vitreous humor and lens to be completely normal. In a stroke of good fortune for future generations, Dalton's eye tissues were preserved and saved by the Manchester Literary and Philosophical Society.

The modern understanding of color vision is based on three types of photopigment opsin proteins (see Garrett and Grisham, Molecular Aspects of Cell Biology, Chapter 38), designated shortwave (SW), middlewave (MW) and longwave (LW), with respective wavelengths of maximum sensitivity of 420 nm, 530 nm and 560 nm. In this article, Hunt et al. describe their molecular biological analysis of the DNA extracted from Dalton's eye tissue.

Their analysis shows that Dalton lacked the MW photopigment opsin, and that Dalton's condition should therefore be described as "deuteranopia". (The condition of lacking the LW photopigment is known as "protanopia".) The figure below (taken from figure 3 of the referenced article shows the spectral sensitivities of the photopigments in each of these conditions.

Spectral sensitivity