Cats cannot see in total darkness, but they require much less light than people and some of the animals they hunt because of the structure of their eyes.
A cat’s pupil is a vertical slit when it is constricted and becomes a large round or oval when it dilates.
The slit-shaped opening protects the eye in bright light, and the large opening lets in as much light as possible while the cat is hunting at night, anatomists say.
A cat’s eyes shine in darkness because there is a special reflective layer beneath the retina called the tapetum lucidum.
It is positioned mainly in the upper half of the eye. The function of the tapetum is to reflect any light not absorbed during its first passage through the retina back for a second opportunity to be absorbed.
A cat’s light sensitivity is estimated at nearly six times that of man’s, and this is probably mainly because of the tapetal reflection.
Both dogs and cats have better night vision than human beings because their retinas have a higher percentage of rods, cells for dark vision, as compared with cones, which are for day vision and sharp color vision.