Monday, September 22, 2014

Feline Sense and Scents-ability: Part 4: Sight




SIGHT

Despite those huge, luminous eyes that sometimes seem to glow in the dark, a cat’s sense of sight is probably its least important sense next to taste! Cats can thrive with only one eye or even no eyes! Without sight, a cat relies on its sense of touch and hearing to map out the world, just like a human would.

The glow that you see in your cat’s eyes is light reflecting off a membrane lining the retina that collects and amplifies light called the tapetum lucidum. Because of this membrane, cats can see in as little as 1/6th the light that humans need to see – but they still can’t see in complete darkness. Cats have many more rod light receptors than cone light receptors in their retina. Rod receptors are good at sensing motion and seeing in low-light conditions. Cones are the light receptors that sense color variation. What this means is that in order to see so well in so little light, cats sacrifice some clarity of vision, but they are much more skilled at sensing tiny motions, have extremely well-developed depth perception and much more acute low-light vision. They also have 200 degrees of visual field vs. human 180 degrees but their field of binocular vision is slightly narrower than ours. What a human can see clearly at 100 feet, a cat can only see clearly as far as 20 feet.

People often wonder if cats can see colors. They can, but their perception of color is much more limited than ours. They have dichromatic vision, meaning that they have two types of cone light receptors in their eyes - yellow/green and blue. Humans have trichromatic vision, meaning that in addition to the color receptors that cats have, we also have receptors that sense the color red. Cats can tell the difference between green, blue and yellow, but probably have difficulty distinguishing between red and green. Cats are able to distinguish between colors at the blue end of the spectrum (long wavelengths) better than between colors near the red end of the spectrum (short wavelengths).

Photo interpretation by Nicolay Lamm (http://www.wired.com/2013/10/cats-eye-view/)

While color and field of vision are limited, a cat seems to be exquisitely sensitive to sensing motion, or changes within the field of vision. It is thought by some that instead of seeing fluid motion, cats may see a "stop-motion" view of the world, giving their brain time to compare each "scene" to the one before and process minute differences between each image.




A cat’s eyes can indicate a lot about its mood – the cat’s pupils dilate up to five times their normal size when it is frightened or threatened, or about to pounce. When cats are content, they squint their eyes.

This alert kitten's dilated eyes mean it is likely going to pounce
This cat's dilated eyes mean it is ready for a fight, with ears tucked back protectively
Cats have a third eyelid or nictitating membrane that closes across the eye from the inner corner. This third eyelid is whitish in color and is usually retracted when the cat is awake. When a cat is ill, the third eyelid often becomes visible as it relaxes and covers part of the eye. Sometimes, this is due to an eye infection or injury, but it can also mean that the cat doesn't feel well in other ways.

Besides eye disorders, third eyelid elevation can also commonly be caused by fever and vestibular (inner ear) problems
Because cats don’t see well close up, it seems that cat food and toys that come in fun shapes and colors are designed more for humans enjoyment than for cats – smell, sound and motion are much more fun to them.Instead of using sight for close-up encounters, cats point their whiskers forward and use the sense of touch to guide them.



So, to better understand your cat, instead of taking a “cat’s eye view” of the world, perhaps it would be better to take a sniff and a listen, instead?