Color blindness
About 8% of European men mix up some reds and greens. The first man to describe it left his eyes to science.
- Red-green deficiency
- ~8% of men, ~0.5% of women (N. European descent)
- First described
- John Dalton, 1794
- Dot-plate test
- Shinobu Ishihara, 1917
Most color blindness isn't blindness to color. One cone type is missing or shifted, so some colors that look different to most people look alike. The common kind blurs red, green, brown and orange. About 8% of men and 0.5% of women of Northern European descent have red-green color deficiency. Men are hit far more often because the genes for the long- and medium-wavelength cone pigments (loosely, 'red' and 'green') sit on the X chromosome. See how eyes see color.
The chemist John Dalton described his own case in 1794. He guessed the fluid inside his eyeball was tinted blue and asked for his eyes to be examined after his death. They were, and the fluid was clear. In 1995 scientists extracted DNA from his preserved eye and found he lacked the gene for the medium-wavelength (green) cone pigment, one of the three behind trichromacy. In French and Spanish the condition is still called daltonism.
Testing began on the railways. After two trains collided at Lagerlunda in Sweden in 1875, the physiologist Frithiof Holmgren blamed staff who misread colored signal lamps. He tested thousands of railway workers by asking them to sort colored skeins of wool, and testing spread to railways and ships. Historians who later reread the trial records doubt color blindness caused that crash at all. The familiar dot plates came later, from Shinobu Ishihara in 1917, hiding numbers among dots of easily confused colors like red, olive and brown.
What about the opposite, super color vision? Some women carry genes for a fourth cone type, and articles claim they see 100 million colors. Lab tests are far more sober: in a 2010 Cambridge study of 24 such carriers, only one behaved like a true four-color viewer. Rare confirmed cases exist; most tetrachromacy claims are hype. James Clerk Maxwell was among the first to measure color-blind vision with mixtures of colored light.
Swatches
- Often confused · red
- Often confused · brown
- Often confused · olive
- Often confused · green
Colors
Sources
- Hunt, D. M. et al. (1995). The chemistry of John Dalton's color blindness. Science 267(5200): 984–988.
- Birch, J. (2012). Worldwide prevalence of red-green color deficiency. Journal of the Optical Society of America A 29(3): 313–320.
- Mollon, J. D. & Cavonius, L. R. (2012). The Lagerlunda collision and the introduction of color vision testing. Survey of Ophthalmology 57(2): 178–194.
- Jordan, G., Deeb, S. S., Bosten, J. M. & Mollon, J. D. (2010). The dimensionality of color vision in carriers of anomalous trichromacy. Journal of Vision 10(8): 12.
Hex values are screen approximations. Every page lists its sources.