Tuesday, January 12, 2010

Amazing Eyes !!!!!!!

Sight- the ability to see- is most important of our five senses. It gives us the most information about the world around us. The eyes are organs for our sense of sight. They let in light and form image of the scene before us and send the message to the brain to translate this view into a picture.

Most familiar animals such as dogs cats and horses have eyes like ours. But the eyes of some creatures are totally different. Simple animals like flatworms have eyes without lenses, consisting of hollows lined with light sensitive cells. Insects have highly complicated eyes containing literally thousands of lenses each of which forms a separate Image. The complicated eye is called a compound eye, because it is a combination of very many different elements called ommatidia, each one is effectively a tiny separate eye. It has a lens at the top and light sensitive cells lower down, Together the lens form the outer surface of the eye.

Like most insects the bee has two of these compound eyes one on each side of its head. They give it all sound vision. Each eye is made up of about 5000 lenses but the image produced by these lenses is not very sharp. The compound eyes are most useful for detecting movement.

The eyes of more advance animals, such as mammals produce sharply formed images like our own eyes do. But there are differences for example Horses do not have round pupils like ours instead horizontal ones. Cats are creatures of the night, and their eyes are well adapted for seeing in the dark. Behind the retina cats have layer called the tapetum .Cats eyes shine in the dark because the tapetum reflects back any light that passes through the retina.

The eyes of many nocturnal creatures have a tapetum to improve their night vision. Others have large eyes with particularly big pupils which can let maximum amount of light. Owls have eyes like this.

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