Kids ask: How are dogs color blind?

Jordan Boucher, 10, a Wadsworth resident and a fifth-grader at O'Plaine School in Gurnee, asked, "How are dogs color blind?"

Peoples' eyes can see when light passes through the eye surface to the back of the eye, called the retina. Cells on the retina transform light into electrical impulses that are directed to the brain, and the brain figures out what you are seeing.

Dogs' eyes use the same process, but the cells on the retina are different. Human and dog retinas contain rod and cone cells. The rods help your eye to see in low light levels. The cones fill in the colors and details. Dog retinas have more rod cells than a human retinas, meaning they see much better in the dark than we do. While they can see much more at night, they have a poor ability to see color and detail.

Dr. Amber Labelle, a second year ophthalmology veterinarian resident at the University of Illinois at Champaign-Urbana College of Medicine Teaching Hospital, said, "Dogs definitely see color, in the blue-violet and yellow-red ranges. But not shades of green. That probably looks more like shades of gray. Their sight is probably close to a red-green colorblind in humans."

Even though dogs see differently than humans, dogs with good eye health can see everything we can, even television. "We believe that dogs are more sensitive to flickering light, and may see TV as a series of static images like a flip book," Dr. Labelle said.

It's difficult to accurately test a dog's vision, Dr. Labelle said. "Assessing vision in animals is one of the most difficult things to do, and one of the most frustrating parts of my job, because a dog can't tell you what it sees."

Testing dog vision is similar to how doctors test human vision. Skiascopy or retinoscopy exams are used to determine a dog's ability to see.

"What we do is look at the refractive error and see how much the light bends," Dr. Labelle said. Good vision for a dog generally means 20/75 as opposed to 20/20 for humans.

Vision is only one of the senses dogs use to understand their environment.

"Their sense of smell and hearing is exponentially more acute than a human's," Dr. Labelle said. "For a human, the loss of vision is devastating. We are visual creatures. Dogs and cats can function effectively with poor vision or no vision."

Some purebred dogs are prone to inherited eye illnesses. When selecting a puppy from a breeder, ask if the dog is CERF registered. The Canine Eye Registration Foundation provides certification for eye-disease-free dogs and also conducts research to improve eye health in purebred dogs.

Want to know how to care for pets like dogs, cats or iguanas, or even how to stop a horse from hiccupping? You can find out about animal care on the U of I Veterinary Medicine Web site at vetmed.illinois.edu/petcolumns/.

Check these out

The Warren Newport Library in Gurnee suggests these titles on dogs and vision:

• "How Smart is Your Dog?," by D. Caroline Coile

• "The True-Or-False Book About Dogs," by Patricia Lauber

• "The New Encyclopedia of the Dog," by Bruce Fogle

• "Dog," by Mathew Rayner

• "Understanding Man's Best Friend: Why Dogs Look and Act the Way They Do," by Dr. Ann Squire