Have you ever considered that your dog may need glasses? No, probably because you've never seen a dog wearing glasses. But if you think about all of the marvellous miracle cures we have for dogs - such as carts and prosthetics for amputee dogs and pills for epileptic dogs - isn't it strange that we haven't addressed the issue of poor sight in our dogs? If you've wondered, can dogs be short sighted? Read this.
If you think about it, before domestication poor sight would have eliminated a dog from the gene pool. An inability to see prey or predators would make a dog less likely to survive in the wild. Yet since domestication, it seems that there are no challenges to survival for dogs with poor vision. This has lead us as custodians of the breed to largely ignore the subject.
For all I know, my dog could be extremely short-sighted, there's no real way for me to tell without eye-tests. And how do you ask a dog to read the little letters on the bottom row?
Can dogs be short sighted?
Yes. In fact it may surprise you to know that not only are many dogs short-sighted, there are many breeds where short-sightedness is very common. Perhaps your dog is short-sighted...
Optical measurements of dogs' eyes have found a surprising incidence of myopia in some breeds. A study of about two hundred dogs by a veterinarian named Christopher J. Murphy and his colleagues found the average canine refractive error to be pretty close to normal (within a quarter of a diopter of perfect, an amount that would not provoke any person to get glasses).
What dog breeds are prone to short sightedness and long sightedness
Several breeds of sporting dogs, such as Chesapeake Bay retrievers, Golden Retrievers, Labrador Retrievers, Cocker Spaniels, and Springer Spaniels, were on average a bit farsighted. But two-thirds of Rottweilers and half of German shepherds and Miniature Schnauzers in this study were significantly myopic, by more than 1.5 diopters. The myopic Rottweilers were close to 3 diopters nearsighted on average.
Generally, people who have more than about 0.75 diopters of nearsightedness will complain of noticeable impairment and find they need to wear glasses or contact lenses to function in everyday life. The animals in this study population were all pets. Interestingly, when Murphy and his coworkers looked at a second population of German shepherds - animals kenneled at Guide Dogs for the Blind in San Rafael, California - they found that the guide dogs had average normal vision, with fewer than a third showing even as much as 0.5 diopters of nearsightedness.
The guide dog program did not specifically test dogs' vision in selecting animals, but they did flunk out any dogs that failed to perform well in training, which suggests that myopia results in a real impairment in getting the job done. The average farsightedness of sporting dog breeds suggests that there has likewise been selection at work in these breeds - that good distance vision has a demonstrable effect on making a good working dog.
The researchers noted a tendency for severe nearsightedness to run in families, which suggests a strongly inherited component. In breeds that are not expected to perform anything more demanding than lying on the carpet, walking on a leash, and finding their supper bowl, there has no doubt been little selection for good vision, which has allowed myopia to sneak into the gene pool.
Do different dog breeds have different vision?
There are distinct breed differences in peripheral vision and overall field of view as well. Human eyes look straight ahead, giving us just about a 180-degree field of vision, but with a lot of overlap between left and right eyes.
Animals can see in true 3-D vision only when they use both eyes together, and the overlap in the human visual field thus maximizes the region in which we can perceive depth by using this binocular vision. Canine eyes are slightly outwards pointing, which allows them to see a bit to the rear, with a wider overall field of vision.
With that in mind it's quite an eye-opener to learn just how common visual impairment in dogs is. But why wouldn't it be? They have eyes, the have genes and they have blood sugar - so all of the problems that afflict our eyes could just as easily do the same to theirs.
The main difference is that we need good eye-sight to function, otherwise we complain. We get headaches and we can't read car registration plates. Dogs are equipped with a rare determination (and inability to complain) that means short-sightedness is merely a reason to listen harder.
The dogs in this clip all varying vision and hearing problems. But can you tell who has what? I can't.