Are Pet Dogs More Myopic Than Working Dogs?

The "Nearsightedeyes" web site reports on a study of about two hundred dogs by veterinarian Christopher J. Murphy and his colleagues who found that certain breeds of pet dogs were prone to myopia.

..... 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.

I would throw up a caution flag here: a pool of 200 dogs is pretty small, and not much can really be known about vision across breeds with a sample size so small.

How many Rottweilers, German Shepherds and Miniature Schnauzers were really in the sample, and how much genetic variation within these breeds did that sample really represent?

Not many and not much is my bet!

That said, an expanded and improved study might be a good project for some budding canine opthamologist to cut his or her teeth on.

A hat tip to Gina Spadafori at Pet Connection for sending the link my way!
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