My cat Kissy had the most amazing eyes I’d ever seen: If I caught her with her eyes open on a sunny day, they were a beautiful sea-green that I could never capture in a photo. Most of the pictures I have of her, like the one below, show her eyes with a golden tone. But whatever color your cat’s eyes are, there’s an amazing story behind how they got that way. Here’s the story on the way your cat’s eyes get their color.
The colored area around the pupil of the eye is called the iris. The iris has two layers, the stroma and the epithelium. Both of these layers contain pigment-producing cells called melanocytes. In the stroma, those melanocytes are loosely arranged, and in the epithelium, they are more tightly packed.
The pigment produced by the melanocytes is called melanin. A while back I wrote an article on the genetics of cat fur color, in which I explained that melanin plays an important role in determining how dark your cat’s fur coat will be. The same thing is true with cats’ eyes: The more melanocytes there are in your cat’s irises, the darker their color will be. But cats don’t get brown or black eyes like people do; the darkest color you’ll see in a cat’s eyes is a deep, rich copper.
When the melanin-producing cells are very active, a cat’s eye color will become more intense. For example, a cat with a medium amount of highly active melanocytes will have bright golden-yellow eyes, but a cat with a medium amount of less active melanocytes may have pale lemon-yellow eyes.
Because purebred cats are bred to meet a specific breed standard, which often includes eye color, breeders select for cats that have more intense colors or particular colors. For example, the Bombay cat breed standard requires copper-colored eyes; and the Tonkinese has aqua-colored eyes.
You know how window glass looks clear when you look straight through it, but it looks kind of blue or green around the edges? That’s because of the refraction of light through a clear surface. The same thing happens with blue-eyed cats: They have no pigment cells in their irises, and because the eye has a rounded shape, light refracts through that rounded surface and produces the blue color. Catster author Melvin Peña recently wrote about blue eyes and other eye color abnormalities; check out his article for more details.
Kittens are born with blue eyes because their melanocytes haven’t started working yet. As they grow, their melanocytes start to function and the true color of their eyes begins to appear. The adult eye color starts to appear between 4 and 6 weeks of age, and a kitten’s true eye color is usually apparent by the time he or she is 4 months old.
Different genes control fur color and eye color, so the melanocytes in the fur may be much more (or less) active than those in the eyes. Thus, a black cat like my Belladonna has pale hazel eyes, but a purebred orange Persian may have dark copper-colored eyes. The only exception to this rule is white cats. Because the epistatic white gene is a dominant and masks other colors, white cats are statistically more likely to have blue eyes than random-bred cats of other colors.
Is there anything else you’d like to know about cat eye color? Ask your questions in the comments!
About JaneA Kelley: Punk-rock cat mom, science nerd, animal rescue volunteer and all-around geek with a passion for bad puns, intelligent conversation, and role-play adventure games. She gratefully and gracefully accepts her status as chief cat slave for her family of feline authors, who have been writing their award-winning cat advice blog, Paws and Effect, since 2003.