The eye is usually likened to a superbly designed camera when people want to explain how we can see. However, to understand fully how the outside world can be viewed inside the tiny chamber of the eye one has to go back to basics.

Light

The fact that we can all see is, as most people instinctively realize, due to light.

One of the most important thing to understand about light is, it can be bent if it passes through certain substances such as the specially shaped glass, or the lens made from tissues in a human eye.

The cornea

The thin, transparent covering of the outer eye, forms the powerful, fixed focus lens of the eye. The optical power of the cornea accounts for about two-thirds of total eye power, yet the cornea is only 0.5 mm thick at the center and 1 mm thick where it joints the white of the eye, called the sclera.

The anterior chamber

after passing through the cornea, a ray of light enters the outer of two chambers within the eye, properly called the anterior chamber. This is filled with a watery fluid called the aqueous humour that is constantly drained away and replaced.

The iris and the lens

Forming the back of this first chamber are the iris, and just behind it, the lens.

The iris is a circular, muscle diaphragm, in the other words, a disc with an adjustable hole in the center. This hole is called the pupil, and alteration of its size is done by two sets of muscles.

Just behind the iris is the soft, elastic lens, whose job is the fine focusing of light rays. For this reason, the lens is adjustable. It is held round its edges by the ciliary muscle, which can change the shape of the lens.