Wednesday, November 16, 2011
The Truth About Dog's Vision
I recently had a very interesting conversation with a veterinarian whose specialty is ophthalmology. He's been practicing veterinary medicine for decades, and was open to my myriad of questions regarding the vision of animals. I wanted to dispel rumor against myth, and he offered me some great information.
The largest myth to debunk is that dog's are color blind. What determines how we see shape, movement, color, etc. live in the cones and rods in our eyes. Dogs have both. They have less cones, which see color. He told me that the only color dogs are unable to see is red. He said the same goes for cats. Birds have way more of both, and can see ultra violet light, in addition to already having impeccable vision.
We always assume our dogs and cats have greater vision than us, and this is also not entirely true. While optimal vision for us is 20/20 vision, dogs have 20/70. This means all dogs are technically near-sighted. He explained that if I were to hang a seeing eye chart up, the dog would see that largest letter as being blurry. The difference, is that they retain that 20/70 vision in the darkness, unlike we who nearly go blind. So all things added up, perhaps their vision is better overall, but not in the light. He added that cats are virtually technically blind. Their vision would be more like 2200. When met with a disbeliever, he rolled a cotton ball in front of an eyeless cat, who quickly stomped the ball with it's paw. They rely on their other senses to make those amazing feats of hunting and agility.
The other myth I sought to debunk was that of dog's being able to watch television. I'd heard people in the past make claims that dogs cannot see anything other than 3 dimensional images. He explained to me that while a human has 1 nerve for each 1 retinal cell, dogs have more like 1 nerve per 5 retinal cells. This means that dogs, for lack of a better explanation, see slower. It takes longer for those complex images generated from your television to make sense. He explained that while dogs can indeed watch TV, the images likely appear to have lines running through them, as they are unable to receive all the information as fast as we do. He said the same is true for cats. While they can see the TV has images, he still insists that the dogs are likely paying more attention to the sounds from the TV than the images.
When I think of seeing talented dogs ability to retrieve very specific toys of varying colors, this all makes sense. Without some grasp of color, it'd be hard to ask them to bring back 1 stuffed toy that looks very much like the other, if we assume to take out the ability to see color. I'm also reminded of an episode of The Dog Whisperer where a woman insisted her dog loved to watch his show. While he wasn't truly seeing clear images of other dogs, he was still responding to all those fun barking sounds he was hearing!
As far as "seeing slower", I can imagine how a dog owner of a super agile breed may feel it doesn't add up. They catch frisbees mid-air, as if they can slow down time themselves! It all comes down to the amazing orchestra of senses they use for their day to day lives. Smell, sound, feel.. this is why we see so many visually impaired pets fairing so well when vision is diminished!
-by Shannon Murphy