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The Honolulu Advertiser
Posted on: Sunday, November 18, 2007

Fido, Fluffy, humans see things differently

Hawaiian Humane Society

Our world is a landscape of color full of shades and subtleties that we just can't share with our cats and dogs. Color nuances are intrinsic to our day-to-day life. Our ability to perceive these helps us shop for fruit and even cook a steak. Fortunately, our pets, who do see color but not as intensely, have to do neither!

Humans have about 1.2 million optic nerve fibers as opposed to dogs and cats that have about 150,000. Humans average one photoreceptor cell to each nerve cell, which enables excellent acuity. On the other hand, cats and dogs have multiple photoreceptor cells feeding into a single nerve cell, so their ability to see detail is much less.

If a dog could tell you what he sees, he'd probably describe a fuzzy world of blues and yellows in the daytime. Given the type and number of their color receptors, cats probably view the world in a pastel palette, and studies have shown that they see blue vividly. Veterinarian ophthalmologists and researchers believe that the holiday season is not as colorful as it is to humans, as our furry family members probably don't see reds and greens with the same saturation. These two colors likely appear as shades of gray. Distinguishing red and green is also the most common form of color perception deficiency in humans.

There are other differences in vision. A dog owner may think their dog is dimwitted for not being able to find his treat right in front of his nose. When in fact, human vision is just much better close up. Cats cannot see directly beneath their noses. If a treat is dropped directly beneath her nose, she can smell it but will probably have to hunt around a bit before finding it.

When it comes to vision, Fido and Fluffy do have a leg up on their owners in one way. Pet owners may have noticed when the lights are out, the cat and dog never walk into furniture at night. Their superior dim-light vision makes them the perfect navigators of the dark. Cats are nighttime hunters and can see clearly in conditions about six times darker than their owners. Vertical slit pupils allow a cat's eyes to take in more light at night.

Vision is determined by the number of cones (for color) and rods (for light) that the eye has. Human eyes have more cones than rods, which enable us to see color better than movement. A cat's eye has more rods than cones, which means they see motion better than color. This genetic wonder has enabled cats to be the excellent hunters that they are.

Cat eyes are also superior at judging distance. Cats have the ability to jump from as much as 6 feet onto a narrow window ledge without touching the window. This feat would require not only excellent balance, but also precise distance judgment.

No one knows exactly how a dog or cat sees color, but extensive research is shedding light on the matter.

One thing that veterinarians and ophthalmologists see eye-to-eye on is that what you feed your pets does matter. Just as nutrition plays a role in human eyesight, it's also important for the four-legged. Kittens that don't get the amino acid arginine are likely to develop cataracts. Cats without sufficient taurine daily (110 mg/kg) may become blind and develop heart problems. Deeply colored orange, red and green vegetables provide the antioxidants and nutrients that sensitive eye tissues need to stay healthy. Ophthalmologists recommend that pets receive a small amount of fresh or cooked vegetables that have been pureed or put into a blender to make them easily absorbed: sweet potatoes, carrots, spinach and broccoli.