What Is The Eye Made Of?
The human eye is like a camera. The opening is adjustable to admit light (the pupil); alens which focusses the light waves to form an image; and a sensitive film (the retina) on which the image is recorded.
There are about 1,30,000,000 light sensitive cells inside each human eye. When the light fells on one of these cells, it causes a quick chemical change with in the cell. In the nerve fiber this change starts an impulse. This impulse is, so to say, a message that travels through the optic nerve to the “seeing” part of the brain. The brain has understood what this message is about, arid what it means, so We know to have seen.
The shape of our eye is like a ball. It has a slight bulge in the front. There is a hole at the centre of this bulge and we call it the ‘pupil’. It looks black because it opens into the dark inside of the eye. Light passes through the pupil to the lens. The light is focused by lens. The picture is formed at the back of the eye-ball. Instead of film as in the case of a camera, there is a screen of light-sensitive cells, called the retina.
There is iris around the pupil. It is a doughnut-shaped ring coloured blue, or green or brown. The iris can change in size like the diaphragm of a camera. In bright light, tiny muscles expand the iris, so that the opening of the pupil is smaller and less light passes into the eyeball. In dim light, the pupil is opened wider and more light is admitted.
There is a strong membrane surrounding the eyeball. This is called ‘sclera’. The whites of the eye are part of the sclera. In front, where the eyeball bulges, selera is transparent. This part is called ‘Cornea’. The space between the iris and the cornea is filled with a clear, salty liquid and is called the ‘aqueous humour’. The space is lens shaped. It is in fact a liquid lens.
Other lens of eye is behind the pupil. Whatever happens can be seen, with the change in shape of the lens. When looking at near things the lens attains thickness. The lens becomes thinner while looking at distant objects.
