Before we can determine the reasons behind abnormal eye color in cats, we must first establish and understand what is considered normal. Let it be known that the vast majority of kittens are born with blue eyes, which typically settle into a specific color by the time they reach 3 months of age. Mature cat eyes take their hue from the amount of pigment cells in the iris, known as melanocytes, that are present during the processes of growth and development. Cat eyes that present with strange colors, different colors, odd patterns, or those that change color suddenly during adulthood may signal serious health issues.
What color are cat eyes? The general rule of thumb for cat eye color genetics is that the fewer melanocytes a cat has available, the lighter the shade of eye color, and the more there are, the darker and deeper they will be. From colors denoting the least pigment cells to most, and allowing for variations and shades, the basic range of colors goes something like this:
For its own part, “blue” is a misnomer. Cats with blue eyes have very little to no pigment whatsoever. What appears blue to us is simply a reflection of the transparent parts of a cat’s eyes. A similar phenomenon occurs when we look at a pane of glass from an edge. There is no inherent link between a cat’s eye coloration and health or lifespan, and none of the standard range of colors — from hazel to gold to amber — is considered particularly unusual. Let’s turn our attention now to why cat eye color can change or appear inconsistent.
While it is interesting and aesthetically intriguing, cats with different colored eyes are not unusual. What causes heterochromia in cats? The answer is genetic, and it’s tied to the white-spotting gene, which is associated with coat color. Because any cat might carry this gene, there is no specific breed or cat coat color that is necessarily associated with odd eyes.
Just as there is a range of cat eye colors, there are also a few varities of odd-eyed cats. The one we’re most familiar with is complete heterochromia, a condition in which one eye has more melanocytes than the other, leading to a mature cat whose eyes are each a different solid color.
There are two types of partial heterochromia in cats, a condition in which one or both of a cat’s irises contain two distinct colors. These are:
In cats, heterochromia or odd eyes may seem abnormal, but it’s usually no cause for specific concern. While old folk wisdom has long suggested that cats with blue eyes or cats with one blue eye are also deaf, it is not a valid generalization in practice. There is a higher reported incidence of blue-eyed, white-coated cats that have or develop hearing problems, and odd-eyed cats have a similarly higher rate of hearing issues than others, but neither blue eyes nor heterochromia necessarily mean that a cat’s ears are at risk.
A cat’s mature eye color tends to develop and stabilize over the first 3 months of life. Some cats certainly develop different colored eyes, while others may have one eye present with two distinct colors. Changing eye color as an adult or mature cat, on the other hand, is not only abnormal, but it can also be a sign of dangerous health issues. The uvea, the part of the eye that contains the pigment, is the source of the first of these. Uveitis, or inflammation of the uvea, can cause a cat’s eye color to change significantly and suddenly.
Uveitis in cats is rarely a problem of its own; it tends to be a symptom of any number of other conditions, all of which require veterinary attention and treatment. The eyes of a cat with uveitis may change to a different color abruptly, become cloudy, or turn red with irritation. Potential causes for this abnormal eye color change include, but are not limited to:
How a cat’s uveitis is treated and resolved depends on which of these larger problems is the cause. Eye color change is not always the most obvious symptom, either. A cat might start blinking rapidly, pawing repeatedly at the affected eye or eyes, or walk around with one eye shut. Uveitis is contagious only if the root cause itself is a transmissible disease.
Earlier, we established the range of standard eye colors. Nowhere among them did we find white, which is certainly an abnormal eye color in cats. Under normal circumstances, blood and other fluids circulate through your cat’s eyes. When these fluids are blocked or prevented from flowing normally, intraocular pressure begins to build up. This is a very basic explanation of glaucoma in cats. This disorder can affect not only a cat’s vision, but its mood, temperament, activity, and appetite. The classic symptom of glaucoma is white, cloudy, or milky eye color. Unsurprisingly, glaucoma is also a potential cause of uveitis.
It is a truism that the eyes are the windows to the soul, but we all know that cats are inscrutable creatures even in the best of times. My cat only really looks at me when she wants to be fed or groomed. Unlike humans, a cat’s physical growth and maturation tends to be accompanied by a change in their eye color. Some cat breed standards insist upon a specific eye color; for instance, a Russian Blue must have green eyes, while those of a Siamese must be blue. If your cat is fully grown and her eye color changes suddenly or without warning, it can be a sign of a serious health problem. Contact your veterinarian immediately.
About the author: Melvin Peña trained as a scholar and teacher of 18th-century British literature before turning his research and writing skills to puppies and kittens. He enjoys making art, hiking, and concert-going, as well as dazzling crowds with operatic karaoke performances. He has a one-year-old female Bluetick Coonhound mix named Idris, and his online life is conveniently encapsulated here.