The eye is shaped like a ball. The tough white outer coat is called the sclera and its surface is covered by a thin skin layer called the conjunctiva. The outer coat is clear at the front of the eye and is called the cornea which is covered by the tear film. Behind the cornea is the iris - the coloured part of the eye - with the pupil forming a hole in its centre.
Structure of the Eye
The space between the cornea and the lens is filled with a clear fluid, called aqueous humour; this fluid maintains the pressure in the eye (the intraocular pressure).
The pressure is determined by the balance between the fluid production inside the eye and its drainage out of the eye.
On the inside of the back of the eye is the retina, which is the light sensitive layer onto which an image of what is being seen is focused by the cornea and the lens working together.
The central area of the retina, where the most detailed vision is to be found, is known as the macula and has a very high density of light-sensitive cells. Further away from this central detailed-vision area is the area of the retina which also provides our peripheral vision.
Immediately under the retina is the choroid, which is the layer of the eye that provides the blood supply to the cells of the retina and onto which the retina is attached. Light that has passed through the front of the eye and is focussed onto the retina is finally converted into a series of complex electrical impulses by retinal photoreceptor cells known as rods and cones. These signals pass along the optic nerve to the back of the brain, where the final image is processed.