Do you sit and watch your kitten play, chase a bug or stare intently out the window, and wonder how they see the world? Cat eyes have some similarities to human eyes but also have differences; for example, take the student. Cats have slit pupils, while ours are round.
But why do cats have slit pupils? What is the purpose? The reason our favorite felines have vertical slit pupils is because they are predators; think of this pupil shape as an evolutionary advantage. Here’s a closer look at the anatomy of the cat’s eye and how slit pupils help kittens hunt prey.
Structure of the Feline Eye
Before we discuss the pupil of the cat’s eye in detail, let’s briefly review the structure of the cat’s eye and how it works.
Actually, cats’ eyes have a lot in common with ours. Like us, they have a sclera (or the outer part of the eye, known as the white of the eye). They also have an iris with a pupil in the center. The iris is the colored part of the eye, and through the pupil, it controls how much light enters the eye.
Cats’ eyes also have lenses like ours. This lens, in both cats and humans, transmits light and focuses it on the retina to create a sharp image. However, there are some subtle differences in how the lens works in cats compared to humans. In humans, the lens changes its curvature to actively focus on objects at different distances. In contrast, the cat’s eye adjusts focus by moving the lens away from or toward the retina, depending on whether it is focusing on distant or near objects. Although the attentive power of the human eye is greater than that of a cat, this does not cause them any disadvantage.
Humans and cats also have retinas, although this part of the cat’s eye has some differences between the two species. You’ve probably heard of two types of cells called rods and cones in your eye, also known as photoreceptors. The cat and human retina have three types of cone cells, but cats are thought to see fewer colors and have less color vision than we do. In fact, scientists believe that they are likely to see colors similar to a person with red-green color blindness. Our feline friends also have more rods in their retinas than we do, which goes a long way in allowing them to see better in low-light conditions.
Speaking of night vision, a cat’s eyes have a layer called bright carpet which increases the amount of light reaching the retina, giving our feline friends a wonderful boost in their night vision.
Finally, the cat’s eye has a cornea like ours. This part of the eye is a protective layer and is also responsible for light refraction at the lens, which is then focused on the retina. However, the feline cornea is larger than ours, which means more light can enter.
Then, of course, there’s the student!
Why Do Cats Have Slit Pupils?
So, why do cats have slit eyes? Because they are hunters, and many features of the eye help in this purpose.
The pupil of the cat’s eye is a vertical slit and thanks to this, the pupil can change its shape from being a thin line to a wide round pupil, allowing more or less light depending on outdoor light conditions. This is why sometimes the cat’s pupil is a vertical slit, and sometimes it is large and wide. The amount of light allowed into the eye affects the way the brain creates images to understand the world around a cat. Of course, different lighting conditions will result in different images.
Think how big our pupils are when it’s dark; this is because our pupils are trying to get more light so we can see better. But when we are in brighter conditions, our pupils dilate to avoid being dazzled by sunlight. The same goes for cat eyes. However, cat eyes do that with more subtlety because of their vertical, slit-shaped pupils.
The vertical slit shaped pupil allows the cat’s eye to have more control over the amount of light entering. Since cats are crepuscular and do their play and hunting in low light conditions, this gives them a great advantage while hunting. Their pupils can dilate so much to let in even the tiniest amount of light that they can see their prey in the dark. During the day, their pupils retract into small vertical slits to prevent excessive light from entering. Having a vertical slit shape also means that cats can better estimate where their prey is by sharpening their depth perception.
Interestingly, big cats such as tigers and lions do not have slit-shaped pupils but round ones. The reason for this is not exactly defined, but it is thought to be due to their higher height from the ground, their behavior as active foragers rather than ambush predators, or differences in their circadian rhythms compared to cats.
Final Thoughts
The reason why cats have vertical slit pupils is because they are predators. This pupil shape gives them the best dynamic range to allow full dilation during the night and good constriction to avoid glare in daylight, resulting in cats being able to find and chase prey during of high and low light. The vertical slit eye shape gives the cat’s eye more control over how much or how little light is allowed in when it changes shape. This shape also helps a cat better focus on their prey and reduces the amount of blur of horizontal contours. Just call it an evolutionary advantage!
Featured Image Credit: photosbelkina, Shutterstock
