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Any of a class of purple, light-sensitive pigments similar to rhodopsin, found in the retinal rods of the eyes of freshwater fishes and certain frogs.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
Visual pigment found in the retinas of freshwater fish. It differs from rhodopsin in having its maximum absorption at about 522 nm. See visual pigment.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann