The other day I took pictures of these two Labradors using my flash. The pale dog’s eyes reflected brightly as one might expect but the other dog’s eyes merely glowed a dull red, and it reminded me of something I had once heard – that if his eyes didn’t reflect brightly, the dog may not have such good night vision. I looked into it a bit further.
The colour of the reflection comes from a layer of tissue at the back of the eye (the choroid) that contains blood vessels, brown pigment cells, and, in most dogs, a shiny cell layer (the tapetum). This tapetum may be yellow, green, blue, orange, or variations in between those colors and accounts for the brightness of a dog’s eye reflection.
Some dogs have very small tapeta or none at all so they show a very dull reflection or none at all (like this chocolate Labrador). Certain dogs, especially dogs with liver or orange-brown coat colour or with blue irises, have very little pigment in the back of the eye and the blood vessels that would normally be hidden by this pigment are visible and make the reflection glow bright red.
The tapetum is believed to be a nocturnal adaptation by increasing stimulation of the photosensitive cells of the retina – allowing a sort of double exposure.
The tapetum is absent in humans.
Science Daily says of dogs’ eyes compared to human eyes: ‘The canine’s biggest advantage is called the tapetum. This mirror-like structure in the back of the eye reflects light, giving the retina a second chance to register light that has entered the eye.
Here is what Melvin Pena has to say of dogs and night vision: ‘ A rough but poetic translation from Latin for “tapetum lucidum” is the “tapestry of light.” As the retinas draw in whatever light is available to dog eyes, and the rods process them as forms and movement, the tapetum lucidum reflects back whatever is left over for the dog to make use of again. Effectively, dogs can see in the dark because any available light is used twice, once coming in and again reflected back out’.
So here, put simply, is what could be happening in the Labrador’s case (scientifically there is a great deal more to the subject!):
Because this dog’s eyes appear a dull red they lack tapeta lucida and the result is the typical ‘red-eye’ seen in humans due to the appearance of the blood vessels of choroid and the underlying the cornea. Any available light is used just the once – coming in, and not reflected back out again as is the case with the majority of dogs.
For this reason, I conclude that what I had heard in the past about dogs not having such good night vision whose eyes don’t reflect a flash brightly, is true.
Here is my story of these two lovely dogs and the other two dogs they live with.