Cats see better in the dark than they do during the daylight hours. Since most cats hunt at night, they need to see better at night than humans do. There are three reasons why.
A cat’s retina are predominated by rod-type photoreceptors. Cats have three times more rods in their eyes than humans. Cats have 100 rods to I cone, while humans have 20 rods to 1 cone. Rods are responsible for detecting and processing movement and short wavelength light. Cones are responsible for providing more detail and longer wavelengths of light. Therefore, cats cannot detect colors in the dark, but can detect movement.
Cats have elliptical shaped pupils to allow more light to be directed toward their retinas. Finally, cats have an area full of specialized cells behind their retinas called the tapetum lucidum. When the light reaches the tapetum it is reflected back to the retina and allows the eye to absorb more light. It is the tapetum that is responsible for the “glow” of a cat’s eyes in the dark.
During the day or night, cats aren’t able to see colors as well as humans. This is due to a difference in the cone. Humans can see a large spectrum of colors because they have three types of cones in their eyes. Cats only have two. Cats do see the world in world, but it’s not in as much vibrancy. Dogs are red/green colorblind and it’s thought that cats are the same since both dogs and cats have similar photoreceptors.
Human cones detect green, red and blue. The two cones in the feline eye detect blue and green with red spectrum being the least detectable. (Red objects likely appear gray to them.) Blue or purple objects are most easily detectable for them.
Cats have a third eyelid. (So do dogs, birds and a multitude of other animals.) The third eyelid moves from the corner of the eye and across the cornea. It is believed to provide the eye with an additional protective layer, especially when cats are hunting prey through tall grass or get into a fight with another feline. The eyelid helps to spread tears across the entire surface of the eye and to remove particles, such as dirt, dust or other debris. When a cat is ill or has sustained damage to the eye, the third eyelid can become visible and protrude. When a cat is ill, if the eyelid does protrude, it usually occurs in both eyes.
Does the eye color play a role in a cat’s vision? For the most part, no, but about 67% of blue-eyed cats are deaf. This is not caused by the eye color itself, but from genetics. Blue-eyed cats have a greater capacity to carry one or more defects that can cause deafness.