CATS' EYES

All cats big and small – along with many other animals that are active in darkness - have a reflective layer behind the retina of the eye, called the tapetum lucidum (latin: “bright carpet”).

This structure increases the sensitivity of the eye to low light levels. However, in brighter daylight conditions the reflected light may blur the image, reducing visual acuity. This is why truly diurnal animals, such as humans, lack this part of the eye. In fact, though their eyesight is better than ours in the dark, human vision is superior in the daytime. Cats are often described as "nocturnal" animals. This is not entirely correct, as in the wild they principally hunt in the twilight hours; the correct term for this type of lifestyle is "crepuscular". 

Like humans, cats adapt to high levels of light by constricting their iris. This is a different shape, more of a slit than a round hole, due to differences in the muscles of the iris - the spincter and dilator pupillae.

Cats do not need to blink. They have a third eyelid, called the "nictating membrane". This lubricates and protects the eyes of certain animals, especially hunters. A good example is the Great White shark, which closes this membrane when it lunges for its prey. Domestic cats may appear to blink when they squint their eyes. Normally this is for communication and may indicate submissiveness.

The fovea is a spot in the centre of the human retina. It has the highest density of cones and rods (the colour and light-sensitive cells that we use to see), and also has fewer blood vessels (which would reduce the amount of light reaching this area. This means that the fovea looks pale. The equivalent of the fovea in cats is called the "central streak", and is relatively larger.