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.