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Eye Structure and Function in Cats—By Dr. Leslie Brooks

Eye Structure and Function in Cats—By Dr. Leslie Brooks

In the wild, cats are hunters that are typically most active at night. For this reason, their eyesight is definitely important.

Generally speaking, though, cats’ eyes function in much of the same way as humans’ eyes function. Cats can also develop many of the same eye disorders that we do.

In this article, we will discuss the function of the eye in cats and what eye disorders cats can develop. We will also touch on the common questions of whether cats can see colors and how well cats can see at night.

Eye Structure

We will start by discussing the structure of the eye. Eyes may appear small, but they are made up of so many different structures that work in tandem to provide one of the most basic senses- sight. After we describe what makes up the eye, then we can delve deeper into questions of sight in cats and common eye conditions of cats.

Orbit

The socket that the eyeball sits inside of is called the orbit. The orbit is made up of many small bones. Muscles, nerves, and blood vessels are also components of the orbit.

Sclera

The sclera is what we refer to as the white of the eye. It is the outer layer and is relatively tough.

Conjunctiva

The conjunctiva is a very thin membrane around the edges of the front of the eye. It is located just beneath and inside of the eyelids and is usually light pink in color when it is healthy.

Cornea

The cornea is the main structure of the eye you see when you are looking at your cat. It is the clear surface on the front of the eye. It is a protective layer and helps with focusing light to the back of the eye.

Iris

The colorful part of the eye is called the iris. Most cats’ have a green or yellow colored iris. Siamese cats or cats of Asian descent typically have a blue colored iris. The iris is actually able to control how much light enters the eye. It does this by making the pupil smaller or larger.

Pupil

The small, black area in the middle of the eye is called the pupil. In cats, the pupil is an elliptical shape standing in a vertical position. When your cat is in bright light, the pupil will appear more like a thin slit. When they are in dim light, the pupil will be in more of a round to oval shape. This is because when there is not much light around, the pupil becomes larger to let in more light to help with vision.

Lens

The lens sits behind the iris. You typically cannot see the lens unless there is something wrong with it, such as if your cat has cataracts, or if the lens has shifted out of place. The lens will become thicker or thinner, depending on what your cat is trying to look at.

Tiny muscles work to cause the lens to become thicker when your cat is focusing on nearby objects. These same muscles relax and cause the lens to become thin when your cat is focusing on objects far in the distance- like that little bird in the tree, or rabbit in your yard.

Retina

The retina sits behind the lens. It is what collects all of the light and information from what your cat is seeing and transmits this information up to the brain through the optic nerve. The retina, therefore, is very important for your cat’s ability to see.

The cells that make up the retina are photoreceptor cells, called cones and rods. Cone cells help cats judge speed and distance, which makes them great at hunting. Cone cells are also responsible for seeing in color. Rod cells help with seeing in the dark.

Optic Nerve

The optic nerve is a bundle of nerve fibers that travels all the way to the brain. It is essentially like the fiber optic cables that transmit information across computer networks. Or even, electrical cables that transmit electricity to your home. Once the information your cat sees with their eyes is transmitted to their brain, the brain will interpret that information into images for your cat.

Nictitating Membrane

You may have heard the nictitating membrane being referred to as the third eyelid. It is located underneath the eyelids in the inner corner of the eye, near the nose. It is essentially an extra layer of protection for the cornea and eyeball. You may only notice it during times when it is inflamed or thickened, such as if your cat has severe conjunctivitis.

Tear Glands

Tear glands are located in and around the upper and lower eyelids. Tears are so important at keeping the eye moist. If your cat’s eyes are healthy and functioning normally, you usually will not see their tears, as they normally drain through a small opening at the inner aspect of the eyelids and down into the nose.

If you have a brachycephalic breed cat, such as a Persian, you may notice their tears accumulating in between their eyes and nose, causing their fur to turn a light brown color. This is normal for these breeds, as their tear drainage tracts tend to get clogged up due to the structure of their face.

Can Cats See in Color?

We do not know for certain whether or not cats can see in color, at least to the degree that we can. Even though their retina’s cone cells provide cats with great visual acuity and binocular vision, we are not sure if they provide cats with the ability to see in a variety of colors. Their cone cells do give them the ability to judge speed and distance very well, which helps in their role as hunters.

We do know that humans have many more cone cells than cats do, suggesting that cats do not see as many color variations as humans do. Some scientists think cats can only see variations of gray and blue. Other scientists think cats can also see some degree of yellow.

Can Cats See in the Dark?

Cats do have much better eyesight than humans do in very dim light. Cats can see 6 times better than people can in dim light. While their eyes can adjust to darkness, much like our eyes do, we are not sure if they can see 100% in complete darkness. They do see much better in the dark than we can, though!

The reason cats can see better in the dark than we do is because of the rod cells within their retinas. Their rod cells are much better at collecting dim light than our eyes are. The rod cells in cats’ eyes also helps them detect motion much better than humans can. Your cat may pick up on a small rodent in the house sooner than you are able to notice its presence.

You may have noticed a bright reflection coming from your cat’s eyes at night. This is called the tapetum lucidum. It magnifies incoming light, helping cats to see better in dim light. It then gives off a blue or greenish-yellow reflection from their eyes if you look at them at the correct angle.

Eye Disorders Affecting Cats

Eye problems in cats can run the gamut from easily treatable, benign conditions, to life-threatening and expensive conditions. We will briefly discuss some of the more common conditions affecting the eye in cats.

Conjunctivitis

Conjunctivitis is a fairly common condition in cats. It is when something causes inflammation of the conjunctiva and can result in red, swollen, painful eyes. It is usually caused by a bacterial or viral infection, but can also happen due to trauma or if something gets stuck in the eye.

Corneal Ulcers

A corneal ulcer is usually the result of a scratch or trauma to the cornea. Sometimes this can happen if your cat is scratching their face with their own claws. Other times it can happen if they get in a scuffle with another animal.

Depending on the depth of the scratch, corneal ulcers will usually heal within 7 days. Your veterinarian will provide you with antibiotic drops to put in your cat’s eye to prevent it from getting infected while it heals. On rare occasions, corneal ulcers can be severe enough that they cause your cat to lose their vision in that eye.

Detached Retinas

Cats can become blind if the retina at the back of their eye becomes detached. The main cause of detached retinas in cats is untreated high blood pressure, or hypertension. Hypertension is fairly common in older cats. It can be due to underlying heart disease, kidney disease, or other conditions that affect older cats. This is why many veterinarians are now checking the blood pressure on cats over 8-10 years of age as part of regular health screens.

Lymphoma

Unfortunately, cancer is occasionally diagnosed in cats. One type of cancer that can directly affect the eyes of cats is Lymphoma. Lymphoma of the eye can take on many forms. You may notice a strange change to the color of your cat’s iris.

You may also notice your cat’s cornea appearing more of a red or purple color. Even though Lymphoma tends to affect the whole body, for some cats it shows up as a problem in the eye before they have any other symptoms.

These are just a few of the more common eye conditions we see in cats. There are many other things that can cause problems with their eyes, including cataracts, glaucoma, and dry eye.

Any eye condition in cats should not be ignored. If you notice your cat’s eye bothering them, tearing more than usual, or becoming swollen or inflamed, it is important to always make an appointment with your veterinarian.

What about Blind Cats?

Even though vision is very important to cats in the wild, if your cat loses their vision for one reason or another, it is not the end of their world. Cats are truly resilient creatures.

As long as you keep your cat indoors and provide their food and water in easily accessible locations, they will adapt just fine. Just try not to move the furniture around too much so as not to confuse them.

 

FAQ

Can cats see in color?

We are not 100% sure. Some scientists think cats can see variations of blue and gray. Other scientists think cats can also see some degree of yellow.

Can cats see in the dark?

Cats can see much better in the dark than we can. We are not sure that they can see 100% in complete darkness, but their eyes do adjust better to darkness than ours do.

Why do my cat’s eyes shine and seem to glow in the dark?

Cats’ eyes have a structure called the tapetum lucidum, which helps them see better in the dark. The shine or glow you see coming from your cat’s eyes in the dark is the reflection of light the tapetum lucidum gives off.

 

Conclusion

The eye is a very important organ in cats that is made up of many tiny structures. Cats can see much better in the dark than us and are much better at picking up on movement.

Even though they cannot see as many color variations as we can, they can still see some degree of color, though seeing color isn’t super important to their survival.

Even though vision is important, there are many cats who lose their vision or are even born blind. They can still have very good lives as long as they are given the proper care and conditions to thrive in.



Sources

 

Merck Veterinary Manual - Eye Structure and Function in Cats



 

Article by Dr. Leslie Brooks 👩‍⚕️
Veterinarian