Monday Medical: Why do cat's eyes glow?

Many of you have seen the recent article that's been making the rounds, where photographer Nickolay Lamm produced a series of photographs that are his visual interpretation of the way cats see differently from humans. It's hit all the major news outlets - Huffington Post, NBC, Wired.com, and others.

While I'm not completely convinced of its accuracy, it did spawn a lot of discussion.

So I thought I'd add to the discussion by re-running an article from last summer on why cats' eyes glow in the dark. It was a lot of fun to research and write. Enjoy!

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If you’ve taken many pictures of your dog, cat or ferret, then you’ve seen it: laser eyes!

It’s a phenomenon specific to only a handful of animals; other species like rabbits, guinea pigs – even humans – just don’t genetically have that "special glow."

Those that do are gifted with a unique surface in the eye behind the retina called the tapetum lucidum. This special surface is composed of 15 layers of glittery cells that combine to create a single reflective layer to capture and enhance light.

Any light that gets past the retina is bounced back at it, giving the photoreceptors in the retina more data - and a second chance - to resolve the image.

Basically it functions a bit like nature’s very own night vision goggles! Cool, huh?

Why do Siamese eyes
glow red instead of green?

I had never really paid any attention to the color of the boys' eyes when they glowed until someone mentioned this to me. The claim was that Siamese eyes glowed red while all other breeds glowed green.

Of course, I had to test this empirically. So out came the el-cheapo camera (you know, the one guaranteed to get the bad photos - and red eye - every time!).

Test Subject One: Allie

Yep, green!

Test Subject Two: Faraday

Look! Red eyes!

Test Subject Three: Maxwell

Seriously red eyes! We were shocked at how red, in fact.

Of course, that begs the question, what causes this?

Contrary to what Wikipedia states (you do know Wikipedia can be wrong, don't you?) Siamese cats do have that cool night vision layer behind their retinas. But unlike other breeds, there is a hereditary abnormality in Siamese that weakens the tapetum lucidum. So a Siamese cat probably won't see as well in the dark as other kitties.

Since Faraday is a Tonkinese (a blend of Siamese and Burmese), you'll notice his eyes are less red than Maxwell's. He probably sees better at night that Maxie.


So there you have it.
Cats: cool, built-in night vision goggles.
What's not to love?
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Sources:
"Hereditary abnormality in tapetum lucidum of the Siamese cats. A histochemical and quantitative study,"  Histochemistry, 1982;75(1):1-9. Published by National Institute of Health's PubMed site 

"Why do animals' eyes glow in the dark?" - NPR

"How Stuff Works"