Tag Archives: nictitating membrane

QQ: Night Vision and Kitty Winks

This week we have a few questions about cats’ eyes and vision!

Q: How can cats see so well without much light?

A: Cats can see in 6x less light than we can. Cats have a wider field of view of 200 degrees, and they have a greater range of peripheral vision, which helps with hunting and avoiding threats.

Cats are crepuscular, meaning they are active at dawn and dusk. There are many creatures, not all benign, that are also active at that time. Their eyes have 6–8x more rod cells than we do, which are more sensitive to light and motion. So, if something is slithering toward them in the gloaming, they will be able to jump out of the way before it strikes.

In addition, cats’ elliptical eye shape, larger corneas, and tapetum, a layer of tissue that may reflect light back to the retina, help gather more light as well. The tapetum may also shift the wavelengths of light that cats see, making prey or other objects silhouetted against a night sky more prominent.

 Anatomy of the Eye

Here’s an image of what a nighttime landscape might look to us (top) vs. how it looks to a cat (bottom).

Night Vision

Image Credit: Nickolay Lamm and Space.com Feline Vision: How Cats See the World Click to see the original, larger image.

More images showing how cats see the world: This Is How Cats See the World

Q: Did my cat just wink at me?

A: Cats have a third eyelid, called a nictitating membrane (AKA haw or, more formally called the palpebra tertia). It is translucent, and moves diagonally from the inner corner of the eye up across the eye to keep it moist and this membrane can also cover the eye and allow them to still see since it is semi-transparent.

Nictitating Membrane

The membrane moves so fast that we rarely catch them blinking with the third eyelid. However, one eye may become drier than the other, or may get a strand of fur or something in it, and that is when they will blink with their regular eyelids. Since this usually only happens in one eye, it appears as if they are winking at us.

So, yes, it’s normal for a cat to blink one eye at a time, but it is not the same as what we think of as winking.

Want to know more? This article at Scientific American has all the details you’d ever want to know about the nictitating membrane.