General overview of opsin function in vertebrates exemplified using the eye of a frog (Boana albomarginata, pictured here). 1) Light enters the eye and is focused on the retina. 2) Light reaches a photopigment (composed of an opsin and chromophore) embedded in the membrane of a light-sensitive retinal cell. The photopigment maximally absorbs a specific wavelength of light. In this example, the photopigment maximally absorbs blue light. 3) Absorption of light stimulates photoisomerization of the chromophore encapsulated within the opsin. 4) A neural signal is generated, processed in the retina and sent to the brain to be further processed and interpreted for visual or nonvisual purposes.