Does Fido Need Glasses?

Scientists have long tried to find an answer to the question: what do animals see?  Do they see what we see?  Do they see colors?  Do they see shapes?  And if animals could drive, would they see the new stop sign they just put in at the corner of Fifth and Main?

How is the vision of animals tested, anyway?  Every time I ask our cat why she likes to get up on the kitchen counters, she stares at me blankly.  If I were to ask her to read the third line of my eye chart, I imagine she would do the same thing.

Vision in animals and small children who are too young to communicate or recognize letters is checked by use of a retinoscope. A retinocope, sometimes called a skiascope, is a handheld optical instrument that an eye doctor uses to see how light is refracted or bent by the eye. Essentially, a retinoscope allows the doctor to see how well or how poorly an animal or a small child can see. There are two types of retinoscope, the spot and the streak retinoscope. The spot retinoscope emits a spot or circular beam from a light source with a coiled filament whereas the streak retinoscope emits a streak or rectangular beam from a source that uses a linear filament. Basically, the streak retinoscope is more useful because it is easier to detect astigmatism. In most cases, the streak retinoscope has replaced the use of the spot retinoscope.

A while back, The School of Veterinary Medicine at the University of Wisconsin-Madison published an article titled "Yes, Your Dog May Need to be Fitted for Glasses", which reads in part (reprinted by permission):

"WHAT? FIDO NEED GLASSES? WHILE THAT’S PROBABLY NOT LIKELY TO HAPPEN, IT IS TRUE THAT DOGS CAN BE NEARSIGHTED"

"Is your dog nearsighted? If so, how does this defect affect its ability to function, at home or in the field?"

"In a recent study, Dr. Chris Murphy, a veterinary ophthalmologist at the UW School of Veterinary Medicine at Madison, found that Labrador retrievers indeed could be myopic, or nearsighted. Even more significant is the fact that myopia in Labradors is due to an elongation of the eyeball, just like in humans. This means that Labradors may be useful for the study of the kind of nearsightedness which affects people during childhood. To date, researchers have only been able to study artificially-caused nearsightedness in animal eyes."

How can it be that animals are nearsighted or farsighted? Basically, I believe that animals have refractive errors for the same reason that humans do.

Like humans, animals experience emotions, and anyone who doesn't believe this has never owned a cat or dog.  Likewise, animals are able to express these emotions by facial expressions via their facial muscles, and like human beings, much of an animals state of mind can be determined by looking at their eyes.

Over time, emotional and physical patterns of behavior emerge.  When these patterns veer away from consistent relaxation toward consistent tension, then refractive errors result.  Again, consistently tense muscles become chronically shorter than they ought to be, and this web of tension is spread over the entire body.  Ultimately, when this happens, the distorted muscle map of the body adversely affects the shape of the eye (specifically but not exclusively by way of the orbicularis oculi) and refractive errors are the end result.

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