Why Do Cats’ Eyes Glow in the Dark?

The tapetum lucidum catches and reflects light back to the retina in the cat's eye.

The eyes are arguably one of the most beautiful features of the cat, and anyone with a cat has seen how their eyes shine in the dark.  Have you ever wondered what causes a cat’s eyes to have that mysterious glow, and what purpose it serves?

The cat has a special iridescent surface on the back of the eye called the tapetum lucidum. Located behind the retina, the tapetum lucidum is composed of an iridescent, reflective substance called guanine.  This surface works like a mirror to catch and reflect light back to the retina.  The more light reflected back onto the retina, the better the cat is able to see at night.  Since cats are nocturnal, this helps the cat with nighttime hunting.

The pupils are typically open wide at night and in dim light, so the distinctive glow of light reflecting back off the tapetum lucidum is most easily seen at night.  You may also see the distinctive reflective glow in flash photographs.  In most cats, the eyeshine is green or gold, but may be red in blue-eyed cats such as the Siamese.  Humans do not have this reflective layer, which is why, in dim light, cats are able to see about 6 times better than we can.

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