Most people are aware that there are various levels of impairment in human vision with the most common being nearsightedness (myopia) and farsightedness (hyperopia). A dog’s eyes are placed farther to the side of the head than the eyes on a human face, which does mean that vision is slightly different for a person than a dog, which much less overlap between the two eyes. Since the field of vision in the eyes of a dog don’t overlap as much, they have a smaller overall area with true depth perception. While this may be less three-dimensional vision than humans, the side positioning of the dog’s eyes ensures they can see much farther backwards than humans. Not surprisingly dogs can also have perfect vision, visual impairments or vision problems such as myopia and hyperopia, just like people. Since dogs with nearsightedness or myopia can see better up close than they can far away, there are some interested issues with regards to understanding how myopia may have developed within breeds and lines.
Generally speaking most owners of dogs that are companions and pets may not even realize if their canine friend has myopia. Most housedogs only need their vision for objects that are relatively close to them, without the need to be able to effectively and clearly see into the distance. Since the condition is not a concern for pet dogs or owners, some breeds have become more myopic in general with the condition being much more prevent in German Shepherds, about half the dogs tested, and Rottweilers, about two thirds, that were noticeable myopic. The German Shepherds were almost 1.5 diopters and the Rottweilers were 3 diopters off of normal. A diopter is a unit that measures the optical power of the lens and generally a human would require glasses with a measurement of 0.75 diopters. The researcher that tested the Shepherds and Rottweilers, Christopher J. Murphy, also tested various spaniels including Cockers and Springers as well as retrievers such as Labradors, Goldens and Chesapeake Bay and these breeds to be slightly farsighted, making them better able to see objects at a distance. Since this trait would be highly desirable in a hunting dog, it is likely that a genetic component for farsightedness has been favored through breeding programs without the breeders necessarily understanding why the particular line excelled in the field.
The same researcher then tested working dog populations, especially German Shepherds, that were used as seeing eye dogs. For this study he used guide dogs from a training facility and kennel and San Rafael, California. In this second study group Murphy noted that these working dogs uniformly had much less nearsightedness, with only about 1/3 of the working dogs having myopia. While the training program did not specifically test for eyesight and vision problems, it is highly likely that the myopic dogs were taken out of the program because they did not perform as well as their peers through the various trainings and tests that guide dogs must complete.
Article by John Costello of Oh My Dog Supplies, check for current specials on dog bowls online.
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