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Dogs &
Myopia (Nearsightedness)
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
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
Rottweiler 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.
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 view, 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. The eyes of dogs are turned a bit to the side, which
allows them to see a bit to the rear, with a wider overall field of
vision.
There are more
information articles on all aspects of basics dog training, dog health
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Dogs & Myopia
(nearsightedness)
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