A close-up of a blue eyed cat

How is eye color determined in cats?

Ever wondered how the color of a cat’s eye is determined? Join me for a short biology lesson as we discover how colors are created. Let’s assume that we got great news today: a kitten was born in our family. We’ll call her Layla.

The area of Layla’s eye that contains color is called the iris. This part has two layers of cells that produce a type of pigment called melanin. The cells themselves are called melanocytes.

Since the melanocytes are not active in young kittens yet, there is no melanin present either. This is why Layla is born with the same color in her eyes as all the other newborn kittens in the world. Indeed, all kittens have blue eyes. Simply because that is the default color that we see when there is no pigment present in the eyes yet.

Recommended: Dr. Greg’s tips for taking care newborn of kittens

So when will the real color show up?

A graph with various eye colors in cats and how they are determined
The color of the eye (left) is determined by the amount of pigment being produced inside the cells (right) – Image by HudsonAlpha

As Layla grows, those cells that we discussed earlier slowly start up their production of eye pigments. Over time, and if sufficient pigment is produced, the default blue that Layla had as a kitten will slowly be replaced as the matured color of the iris starts to emerge.

So how long does this process of eye pigmentation take? You should be able to notice the first changes about four to six weeks after birth. The entire transformation is usually completed by the fifth month in a kitten’s life.

Adult cat eye color

The type and amount of pigment determines the final color of the iris. Each shade is associated with a certain amount of pigment, depending on whether it’s a light or a dark color.

For instance, when your cat has green eyes, that means this cat’s melanocytes did not produce a lot of pigment. While not as light as blue, green is also a relatively light color that we see when there is little melanin present.

Tip: Want to know which cat breeds have green eyes? Here’s an overview

Black fur with green eyes is a stunning combination

Genetics

Eye pigmentation is heavily influenced by genetics. So, if mom and dad had the right genes, there’s a decent chance any offspring will possess that color too. Certain breeds possess the genetics to produce barely any pigment at all.

You’ve probably seen an adult cat with blue eyes before, Those specimens were born with a set of genes that codes for close to zero melanin production. In these cases, the eyes retain the same deep blue color throughout a kitten’s transition into adulthood.


Why do some cats have different colors in their left and right eye?

Not all cats have the same color in both eyes. This is what scientist refer to as heterochromia, a term which describes oddly colored irises. The phenomenon is most often observed in white and tuxedo cats. While this condition is usually a result of genetics, it may also result from damage to the melanin-producing cells during development.

Cats may also be dichromatic, which is another scientific term that’s used to describe eyes that contain two distinct colors instead of a single one (source). Some people find this look very aesthetically pleasing.

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