Cat Eyes

If you've been in close contact with a cat before, you may have noticed that their eyes are not like yours.  Wondering what I'm talking about?

Dilated pupils

Constricted pupils

Dilated pupil

Constricted pupil

For one thing, cat pupils can dilate way more than human pupils can.  And when their pupils do constrict, cat eyes constrict into vertical slits whereas human ones constrict into pinpoints.

But why?

It turns out that cats are naturally more active at dawn, dusk and nighttime and therefore need to be able to see well with very little light.  But on sunny days, they have to be able to protect their retina and shut their pupil as tight as possible!  In humans, the ciliary muscle in the eye is circular, but cats have two ciliary muscles that act as shutters.

In addition to dilating their pupils so that the iris is barely visible, cat eyes have a layer of reflective tissue behind the retina to allow light that passes the retina to be reflected back to the sensory cells.  Have you ever taken a picture of a cat?  The flash makes their eyes look something like this:

Creepy eyes

Now, you may have heard of Cat Eye Syndrome...it is a triplication or quadrupling of part of chromosome 22 in humans which leads to an abnormal development of the iris such that there is an abnormally shaped pupil, often making it look like a keyhole:

Depending on the severity of the chromosomal abnormality, those with the syndrome can also have abnormalities in the development of their heart, kidneys, facial bones, and even the brain.

You might be wondering why there aren't any pictures of Finn in this post.  He rarely has his eyes open  because he naps a LOT: