Cat with Glowing Eyes, Mattes, Wikimedia Commons
Although cats’ eyes appear to glow in the dark, they are actually reflecting ambient light due to a reflective surface behind their retinas called the tapetum lucidum. Flash photography, car headlights, and any other available light may create the glowing effect.
The tapetum lucidum enhances a cat’s night vision by bouncing light back so that the photoreceptors in the eye have a second opportunity to use it if it didn’t hit them the first time. This enables a cat to see in dimmer light than humans can.
Humans, some other primates, squirrels, pigs, and kangaroos don’t have the tapetum lucidum, but many other animals do, including dogs, horses, deer, cattle,and ferrets. However, humans may appear to have glowing eyes at night if they have cataracts, which can create a white reflection, and via the “red-eye” effect in flash photography.
Animals with a tapetum lucidum may reflect different colours of light due to varying retina pigmentation, age, minerals such as zinc or riboflavin in the tapeum lucidum, and other factors.
For answers to more cat questions, see the main Cats page.