How a Cat's Eyes Help Them Hunt

Are you curious why, along with its other keen senses and directional ear movement, cat eyes work so well for cats! Felines are obligate carnivores which means they need to consume protein in the form of fresh meat to survive. Peripheral visual acuity (movement detection) and night vision separate hunters from the hunted in the wild. If a cat needs meat to eat; they certainly need the eyes of a predator to endure.

Peripheral Vision
Ever try to sneak up on your cat? You were probably unsuccessful because, aside from keen hearing and smell, your cat has a very wide visual field. Even though a cat's peripheral visual acuity extends approximately 186 degrees on either side of its head, there is a minor tradeoff. Your cat can see sideways (laterally) and stereoscopically (in 3 dimensions) but can't see its own nose or focus on anything placed immediately in front of its face! Maybe that's why it has such a keen sense of smell and whiskers!

Night Vision
A similar tradeoff exists with night vision. The ability to see clearly in very dim light typically reduces the same ability in daylight because of the anatomy and physiology of the mammalian eye. The cellular connections in a cat's eyes (more light-sensitive "rod" cells converging on one or two nerve cell) have the same disadvantage as high-speed film; the brighter the light the more grainy or blurred the picture clarity. Primates have poor night vision; they have fewer rods and thus, see less light in the dark. Cats also have an especially reflective layer of cells in the back of their eye called the "tapetum lucidum" that "re-reflects" light back onto the rods. This specialized tissue greatly enhances photosensitivity especially in dim light. Felines need only about one-sixth of the illumination a human or primate would need to see prey at dusk or in the dark. A cat's distinctive vertically-slitted elliptical pupils open fully in dim light too. Is this why we call cats nocturnal?

Color Vision
Bright light and color vision however, are entirely different issues. Primates often have only a single color sensitive "cone" cell in their eyes converging on a neuron; cats can have a four-to-one ratio. Primates thus see many colors quite clearly. Cats alternatively see a narrower range of purple and blue. But at dusk or in the dark, does the color of one's fur or feathers really matter?

Visual Acuity
Finally, a cat has 20/100 visual acuity. This means that a cat needs to be within 20 feet to see an object as clearly as you can see it (without your glasses!) at 100 feet. But are cats likely to track prey running 100 feet away from them? It might be more adaptive to pay attention only to movement that is closer at hand (or paw)! Does it make sense consequently that visual acuity has been traded away for keener peripheral acuity and night vision? Cats stalk, they pounce, and they kill! Even though they often play with their prey, a cat can't sit and (visually) examine their food like a monkey or a human would. They smell and they eat... sometimes. Cat eyes work perfectly for cats. It might however, be a different story, if in the future, they grew opposable thumbs!

References:
Doctors Foster and Smith - pet education.com
Fundamentals of veterinary ophthalmology