Cats' Eyes

Humans have better daylight vision than cats, but after duck the cat really comes into its own. Although it cannot see in total darkness, it has excellent vision in the dimmest of lights. The ability of the cat's pupil to expand and contract in order to control the amount of light available, explains why the cat's eye looks different each time we look at it. In dim light the iris become relaxed and the pupil widely dilated. The light passes through the curved cornea and lens to the retina at the back of the eye. It is then reflected by a special layer of iridescent cells called the tapetum lucidium, and thus causes the effect of the cat's eyes shining yellow, often seen at night. It is thought that either the tapetum or the retina itself may have a photomultiplying effect on the received light. The delicate mechanism in the back of the eye must be shielded from strong light, and this is effected during the day time by the contraction of the iris, closing down to form a slit-like pupil.