Princeton's WordNet(0.00 / 0 votes)Rate this definition: 1  shimmer, play(verb) a weak and tremulous light. 2  shimmer(verb) shine with a weak or fitful light. 3  shimmer(verb) give off a shimmering reflection, as of silk.
Cats, like humans, have both rods and cones in the retina. Rods are the receptors that the eye uses for night time viewing and sudden movement. Cones are used during the daytime, and process color information. Cats have more rods than cones, as compared with humans, making cat night vision superior to humans.
To test visual sensitivity a more careful experiment must be performed. The retina at the back of the human eye has two types of receptors, known as cones and rods. The cones are responsible for colour vision, but are much less sensitive to low light than the rods. In bright light the cones are active and the iris is stopped down. This is called photopic vision. When we enter a dark room, the eyes first adapt by opening up the iris to allow more light in.