Posts Tagged ‘why dogs eyes shine in the dark’

The Tapetum Lucidum: why dog’s eyes shine in the dark?

Tuesday, March 29th, 2011

My, what big eyes you have!

Have you ever been spooked by glowing eyes at the edge of the lawn at night?  “My, what big eyes that cat has.  Hmmm, maybe it’s a fox, hmmm, maybe it’s a coyote, perhaps a wolf?  I’d better go in now…”

The glowing eyes of animals at night are caused by a light enhancing layer of cells behind or near the retina called the tapetum lucidum (meaning “bright tapestry” in Latin) that reflects light back through the retina.  By augmenting light, the tapetum lucidum make it easier for animals to see at night.  Both predators and prey have them, so the balance is fairly equal.

Except humans… humans don’t have a tapetum lucidum.  And, just think, humans are the most dangerous predators of all!  But I digress…

Your pet, unless it’s a chimpanzee, probably has a tapetum lucidum in each eye, which also explains why his or her eyes are so creepy in most flash photographs.  You’ll have to learn some advanced photo techniques to fix that.  Again, I digress; what we want to bark about is some dogs and some cats  do not have the tapetum lucidum.

A somewhat common, mild, congenital defect some dogs can have is to be atapetal… meaning they do not have a tapetum lucidum.  The condition is not dangerous in any way and dogs born atapetal see just fine, even in the dark, just as you do.  (We assume you are not sending your dog out to hunt at night.)  Your dog’s eyes will still get that eerie glow when you take his pictures for some reason, but you will not be able to see him standing in the driveway as you drive home at night by locating his shining eyes. So be careful.

What is important for dog owners to know about this topic is that, when examined through an ophthalmoscope, atapetal eyes have different looking retinas.  An inexperienced or precipitous vet might tell you that your dog has cataracts since the view of the retinas is obscure.  Before accepting such a diagnosis, please see a veterinary eye specialist.  Cataracts require various kinds of medical intervention, but congenitally atapetal eyes see just fine and should cause no worries.

Siamese Cats are always born atapetal… which might explain why they prefer to be house cats rather than midnight stalkers.

The Hound of the Baskervilles from Sir Arthur Conan Doyle’s story of the same name had awesome tapeta lucida.

“A hound it was, an enormous coal-black hound, but not such a hound as mortal eyes have ever seen. Fire burst from its open mouth, its eyes glowed with a smouldering glare, its muzzle and hackles and dewlap were outlined in flickering flame. Never in the delirious dream of a disordered brain could anything more savage, more appalling, more hellish ….”   If you see anything like that in the driveway at night, stay in the car.