Why Do Cats' Eyes Glow?

Updated February 23, 2017 | Factmonster Staff

The Question:

Why do cats' eyes glow?

The Answer:

Cats, dogs, and many nocturnal creatures appear to have glowing eyes because the back of their eyeballs include a special reflective layer called the tapetum lucidum. This helps animals (cats in this case) see better in low light by working like a mirror on the retina to reflect the light back through the eyes, giving them a second chance to absorb the light. The colors seem more visible at night because the pupils are dilated wider than during the day, allowing more of the tapetum lucidum to be visible.

Humans don't have this layer. That partially explains why when you get your developed photographs back the subjects have red spots in their eyes. This is caused by the light from the flash traveling through the pupil and illuminating the blood-cell rich retina at the back of our eyes.

The secret behind so-called "red-eye-reducing cameras" is that they use two quick flashes instead of one. The theory being that the first flash will cause the subject's pupils to restrict and let in less light, while the second will be used for the actual picture.

Here is a link to more information about vision from Infoplease.

-The Fact Monster

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