Cat Vision

Cats are crepuscular, meaning they are active at dawn and dusk. That may be why they need such good night vision. Their eyes have six to eight times more rod cells, which are more sensitive to low light than humans do. They cannot see in total darkness, but they only need 1/6th of the light we need to function.

When their pupils open up in response to the decreasing light, they can increase so large they cover the entire surface of the front of their eyes. Cats are not colorblind, but they do have some difficulty distinguishing between certain shades. Compared to our own vision, cats see colors somewhat more muted than we do and not quite as crisp. For example, felines see blue the best but have trouble with darker shades of red.

Cat’s eyes open and close much quicker than ours. And cats have an exceptional membrane on the back of their eyes known as the tapetum lucidum^[1], meaning “bright carpet” that raises the amount of light trapped by the retina. The tapetum collects and re-radiates light back to the retina, donating the rods a second chance to absorb the image, expanding their sensitivity to low light levels.

While this light is reflected off the tapetum, the cat’s eyes appear to glow. Humans can see objects clearly at 100 to 200 feet away, but cats need to be no more than about 20 feet away to see those same things sharply. My cat can easily spot a spider, his favorite snack, across a 20-foot room.

Because cats lack the muscles necessary to change the shape of their eye lenses, they can’t see things clearly quite as close as humans can and need to be further away. Just like humans, the color of a cat’s eyes is determined by the amount of a pigment called melanin.

Both layers of a cat’s iris contain cells that produce melanin, called melanocytes. The more melanocytes a cat’s iris contains and the more active they are, the darker its eyes will be. The darkest cats’ eyes are a rich coppery color. They never get truly brown or black as people do. Blue-eyed cats don’t have melanin in their eyes as cats with copper, gold, yellow, or green eyes do.

Light refracts from their eyes’ rounded surfaces, causing the eyes to appear blue, much like the edges of clear windows look blue. Regardless of what color their eyes end up, all cats are born with blue eyes. That’s because the melanocytes in their eyes haven’t started producing the color-producing melanin yet. You’ll need to wait about four to six weeks to see any color in your kitten’s eyes and around four months to see its true adult color revealed.

It’s not unusual for some cats to have two eyes of different colors. Some cats even have multiple different colors within the same eye. No matter how the different colors appear, having eyes of different colors is called heterochromia. This occurs when the melanin that creates color either reaches just one eye or only certain parts of the eye. Heterochromia doesn’t impact a cat’s vision or health in any way.

Cats are subject to a host of diseases that can cause permanent damage to any or all of the eye’s components. These disorders include cataracts, in which the lens gradually clouds up—often impenetrably—and prevents light from entering the eye; glaucoma, a condition marked by excessive fluid pressure within the eyeball that can cause it to harden; progressive retinal atrophy, in which the retinal tissue degenerates and loses its ability to function correctly; and a variety of tumors—either malignant or benign—that develop within the eye or adjacent to it.

Many other feline eye diseases are attributable to viruses, bacteria, and fungal organisms that specifically target cats—such as the feline immunodeficiency virus (FIV), the feline leukemia virus (FeLV), the feline infectious peritonitis virus (FIP), feline herpesvirus (FHP), toxoplasma (a parasitic organism) and cryptococcus (a yeast-like fungus commonly found in soil).

The most frequently diagnosed feline eye disorder is conjunctivitis, an inflammation of the conjunctiva—the mucous membrane that lines the inner surface of the eyelid and the outer surface of the eyeball. This highly contagious condition, usually a by-product of an upper respiratory disease caused by either a bacterial or viral organism, is often observed in densely populated cat shelters, he notes. The disorder’s most apparent symptom is runny eyes, which are readily curable if treated promptly.

Cats’ eyes are also vulnerable to traumatic and potentially blinding injuries, such as corneal lacerations (cuts on the outer surface of the eye), which are common. As is the case with virtually all types of feline health problems, the earlier a cat’s vision impairment is diagnosed—whether the result of disease or injury—the better it may be treated. In some cases, unfortunately, an animal’s failing vision or blindness may have become irreversible by the time veterinary care is pursued.