Wald, George (1906–1997)

US biochemist who was awarded a Nobel Prize for Physiology or Medicine in 1967 for work on the physiology and chemistry of vision. He discovered the role played in night vision by the retinal pigment rhodopsin, and later identified the three primary-colour pigments.

Wald was born and educated in New York. He spent his academic career at Harvard from 1935, becoming professor of biology in 1948. In the 1970s he spoke out against the US role in the Vietnam War.

Studying rhodopsin, which occurs in the rods (dim-light receptors) of the retina, Wald discovered in 1933 that this substance consists of the colourless protein opsin in combination with retinal, a yellow carotenoid compound that is the aldehyde of vitamin A. Rhodopsin molecules are split into these two compounds when they are struck by light, and the enzyme alcohol dehydrogenase then further reduces the retinal to form vitamin A. In the dark the process is reversed, but over a period of time some of the retinal is lost. This deficiency has to be made up from vitamin A, and if the body's stores are inadequate, night blindness results.

In the 1950s Wald found the retinal pigments that detect red and yellow-green light, and a few years later the pigment for blue light. All these are related to vitamin A, and in the 1960s he demonstrated that the absence of one or more of them results in colour blindness.