What is "photopigment"

n. Any pigment that is unstable in the presence of light; used especially of the chromophore pigments in the rod cells and cone cells of the eye

n. a special pigment found in the rods and cones of the retina

Photopigments are unstable pigments that undergo a chemical change when they absorb light. The term is generally applied to the non-protein chromophore moiety of photosensitive chromoproteins, such as the pigments involved in photosynthesis and photoreception. In medical terminology, "photopigment" commonly refers to the photoreceptor proteins of the retina.