Cat's Eyes: A Look at the Science of the Feline Eye

Since cats are naturally a nocturnal animal, their eyes must function well in very lowlight conditions, while still functioning in daylight as well. Cat's eyes are still able to function in the darkness with only one sixth of the light that humans need to see. How are the cat's eyes able to change to suit the light conditions?

The structure and size of a cats eyes is what allows the cat to see well both in the light and dark. In low light conditions the cat's pupils must be able to open as wide as possible to allow the maximum amount of light to enter the eye. In bright sunlight, the pupils need to be able to contract to protect the retina. In our eyes this function is controlled by a circular muscle called the ciliary muscle, but there is limited size variation. In cat's eyes, there are two ciliary muscles that act like shutters, resulting in a slit-like appearance in daylight and a more circular pupil when dilated in low light conditions.

Compared to our eyes, cat's eyes are also relatively larger, therefore allowing more light to enter the pupil. The eye lens is also more curved in a cat allowing sharper focusing. In cat's eyes, the cornea is also more curved and the anterior chamber is larger, resulting in more light being refracted onto the retina.

To increase the amount of light hitting the retina, cat's eyes also have a feature called the tapetum lucidum located at the back of the eye. This feature reflects light, similar to a mirror, back on to the retina hitting the light sensor cells. This feature is what gives cat's eyes that nighttime glow when light hits their eyes.

Just like humans, cat's eyes have rods which are sensitive in low light and cones which are sensitive in high levels of light. However cat's eyes have a higher concentration of rods then humans giving them better nighttime vision.

Cat's eyes also have a third eyelid, a membrane which closes from the sides. This eyelid can be seen when the cat is sick but is also often seen when the cat is sleepy and contented. Cats can also see some colors and can differentiate between red and green lights as well as red, yellow and blue lights. Cats can distinguish between blues better then they can colors at the red end of the spectrum.

Cats do not need to blink very often to keep their eyes moisturized like humans do which can be an advantage during hunting. When cats do blink it is slow and often only one eye at a time giving the impression they are winking. Cats also often squint as a means of communication, usually indicating pleasure. Cat's eyes also vary widely in color from blue to orange. The most common colors are green, orange and golden.

Sources:

Cat's Eyes

Cat Senses - Wikipedia, the free encyclopedia