What’s behind your cat’s eye color?

It’s not just the fur or the purr that cats use to hold us spellbound: It’s those eyes. Whether they are blue, green, gold, copper or some variation of those shades, a cat’s eyes are one of his most beautiful features.

Here’s how they come to be that way.

Eye color is genetically linked to coat color. Kittens are born with blue eyes, which may stay that way or change color as the kitten matures. For instance, all pointed cats have blue eyes. Cats who are solid white or mostly white may have blue, green, gold or copper eyes. The most common eye colors range from greenish-yellow to gold. You may have heard that white cats are always deaf. Not necessarily. Some are, and some aren’t.

White cats with blue eyes are more likely to be deaf, however, than white cats with gold or green eyes. Deafness is associated only with the dominant white gene, not the white spotting gene, says feline geneticist Leslie A. Lyons.

“There’s a high association of dominant white with deafness and dominant white with blue eyes, and if you are dominant white with blue eyes, you’re more likely to be deaf.”

Between 10 and 20 percent of white cats with eyes of other colors may be deaf. White cats with only one blue eye may be deaf only in the ear that’s on the same side as the blue eye. Eyes with the brilliant copper of a shiny new penny or the bright green of an emerald usually are the result of selective breeding, but genes don’t discriminate.

Those eye colors can appear in cats without a pedigree as well. Pedigreed cats noted for their distinctive eye color include the Burmese, with large, round gold eyes; the Tonkinese, with sparkling aqua eyes; the Egyptian mau, with gooseberry green eyes; and the Russian blue, with vivid green eyes.

Some cats have “odd eyes,” meaning one eye is blue and one is green or gold. The scientific term for this is heterochromia, from the Greek words “hetero,” meaning “different,” and “chromia,” referring to color. The difference in color might not be noticeable in a kitten, but changes gradually as the kitten moves toward adulthood.

We usually see odd eyes in white cats or cats with the white spotting gene, such as bicolor and tuxedo cats. Breeds in which odd eyes are common include Turkish angoras and Turkish vans. A description of angoras stated that the eyes should be “as green as the lake and as blue as the sky.” Other breeds that may sport odd eyes are Persian, sphynx, Oriental shorthair and Japanese bobtail cats.

Odd eyes occur when a dominant white gene (meaning it masks other colors) or a white spotting gene blocks the concentration and distribution of natural pigments within the iris tissues during development. It’s unusual to see odd eyes in cats who lack both the dominant white and the white spotting genes, but it can happen. An unusual and attractive look is the dichromatic, or dichroic, eye, usually seen in white cats. That’s one with two colors in one iris.

For instance, the eye might be half green and half blue or have a green iris encircled by yellow. One or both eyes can be dichromatic, sometimes with each eye mirroring the other. Even more rarely, only a section of the eye may be a different color. Think of a pie-sliced shape of brown in what is otherwise a blue or green eye. Those eyes aren’t just odd; they’re downright weird, but undoubtedly beautiful.

The buzz

Border collies, Labrador retrievers and other dogs are learning to help farmers with disabilities perform chores, thanks to a small group of volunteers called PHARM Dog USA: Pets Helping Agriculture in Rural Missouri. Founder Jackie Allenbrand evaluates farmers’ needs, assesses farms and makes placements. She and other trainers teach the dog-farmer teams to work together.

Tasks the dogs may perform include bringing or picking up tools, opening gates, carrying buckets, managing livestock, helping farmers brace themselves and going for help. The dogs, donated by breeders or acquired from shelters, are placed at no charge to farmers.

▪ Pet owners will spend nearly $16 billion on veterinary care this year, estimates the American Pet Products Association. If you’re considering purchasing pet health insurance, here are five things you should know:

1. Some insurers provide discounts to AARP or AAA members, active-duty and veteran military personnel or to customers who enroll two or more pets.

2. Some employers offer pet insurance as an employee benefit.

3. Policies are available for birds, reptiles and other exotic pets.

4. Older pets can be insured, usually until they are 12 to 14 years old, but policies may exclude coverage for age-related illnesses.

5. Policyholders can usually take pets to any veterinarian.

Can dogs benefit from cancer diet?

Q: My dog has been diagnosed with lymphoma. I’ve heard that there’s a cancer diet that may help. What can you tell me about it? Are there any other dietary changes I can make?

Via email

A: Many pet owners hope that a change in diet can help pets with cancer. So far, little published research has been done in this area, so I’m afraid I can’t tell you that there’s a “silver bullet” feeding regimen that will cure your dog.

But I can discuss cancer-related changes in metabolism and evidence-based approaches that are being looked at to help reduce or eliminate those problems. Dogs with cancer may lose weight or experience muscle wasting as a result of chemotherapy or radiation treatment. It’s really important to make sure they are able to take in nutrients and maintain a healthy weight as they undergo treatment.

This can mean continuing to feed your dog his regular food that he likes and does well on, or switching to a particular commercial or homemade diet recommended by a veterinary nutritionist.

You have probably heard that a low-carbohydrate diet is beneficial to cancer patients. There’s no strong evidence for that in dogs yet, but on the other hand, it can’t hurt to try it, as long as you choose an appropriate food that contains less than 20 percent of its calories from carbohydrates.

Bear in mind that a low-carb diet is not the same as a grain-free diet, which can still be high in carbohydrates, fat and calories. Ask your veterinarian to consult a veterinary nutritionist about appropriate choices.

We don’t currently have specific nutritional requirements for dogs with cancer. The best thing you can do to help your dog recover is to continue to feed a food that will maintain his body condition and meet his energy needs during treatment.

Dr. Marty Becker

Pet Connection is produced by a team of pet-care experts headed by veterinarian Dr. Marty Becker and Kim Campbell Thornton, author of many pet-care books. The two are affiliated with