Do you know that some animals have much better eyesight than humans? Birds of prey have the keenest vision of all animals. Their big eyes let in the maximum amount of light and contain two foveae: one fovea for sideways vision and the other for seeing straight ahead.
Each spot contains three times as many sensitive cells as that of human eyes! Have you ever seen a cat's eyes shining in the dark? This reflection of light from an animal's eyes is called 'eyeshine' and is an adaptation to help nocturnal animals see. Behind the retina is a reflecting 'mirror', called the tapetum. Animals with a tapetum see twice as well in the dark than those without one.
A chameleon is the only animal which can look both backwards and forwards, or upwards and downwards, at the same time. Each of its eyes can swivel about independently in almost any direction. Only a fly that is perched on the top of a chameleon's head can possibly escape being detected by its all- seeing eyes.
Humans have good colour vision, but they cannot see beyond the ends of the visible spectrum - infrared and ultraviolet light.