The fastest muscle in human body, the eye has the capacity to see nearly colors of 2.7 million. The eyes can weigh just 28 grams in the body. The eyes of the different species have different features. The flies cannot focus because of the lack of pupils and can see only up to a yard, but can have a 360 degree view. Snakes have day eyes, and can recognize prey only by the movements, which means still preys escape. The ability to sense vibrations substitutes the poor eyesight in snakes.
Hawks and eagles have the capacity to look at things in the front and the side simultaneously. They have sharp eyesight, which is as good as 4 times of a perfect person’s eyesight. They can see even the smallest animals because of the light sensitive cells. Horses see the colors of grey mostly, and only can see with the side of the heads. Unlike humans, horses cannot merge the visions of the two eyes. Fishes can move the lenses to and fro and see through this movement. Fishes have no need to retain moisture in the eyes and the absence of eyelids is not an issue. Also, the fishes can sleep with their eyes open.