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Why do a cat’s eyes appear to shine at night?

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A Maine Coon longhair cat with cream and white fur sits beside a tabby shorthair cat in a garden with green foliage in the background. — cat Two kinds of domestic cats.

Despite popular belief, a cat’s eyes do not actually glow in the dark. The phenomenon known as "eyeshine" occurs because of a specialized layer of cells located behind the retina called the tapetum lucidum.1

This structure acts as a mirror, reflecting light that passes through the retina back outward. By doing so, it provides the eye's photoreceptors a second chance to absorb photons that were missed on their first passage. This mechanism allows domestic cats, which are crepuscular hunters active at dawn and dusk, to utilize ambient light with high efficiency, requiring only one-sixth of the illumination levels that humans need to see well.231