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How the Eye Works
To understand how refractive surgery works, it is important to have a basic understanding of how the eye works.
The eye works like a camera. Light enters the eye through the cornea (the front surface of the eye), which provides most of the focusing power for the eye. Light then travels through the lens of the eye, which provides further fine tuning of the focusing.
The light rays are then focused on the retina at the back of the eye. The retina works like the film in a camera, converting the light rays to electrical signals, which are transmitted to the brain through the optic nerve.
In the brain the actual process of seeing occurs. In order to see clearly, all parts of the eye must function normally.
If you have a refractive error, the light rays are not focused correctly on the retina. This can be, and has historically been, corrected with prescription glasses or contact lenses, and can now also be corrected with laser refractive surgery.
Refractive disorders of the eye
Anatomy of the Eye
Cornea
The cornea is the clear part on the front of the eye. It provides most of the focusing power for the eye and is reshaped by the laser during laser refractive surgery.
Iris
The iris is the coloured part at the front of the eye, lying just behind the cornea. The main function of the iris is to control the size of the pupil. It does this by contracting and relaxing muscles around the pupil.
Pupil
The pupil is the black circle in the centre of the iris. Its function is to control the amount of light that enters the eye. It does so by expanding or contracting in response to varying light levels entering the eye.
Lens
The lens is a clear structure that lies behind the iris. Its main function is to provide fine focusing adjustment for looking at different distances. It does so by changing shape. With increasing age the lens is less able to change shape and after the age of 40 to 50 years it is more difficult to focus at close distances. This condition is known as presbyopia. When a cataract is present, the lens has become cloudy, obscuring vision.
Vitreous
This is a clear jelly-like substance that fills up the back of the eye. It is normally perfectly clear, and provides nutrition and support to the other structures within the eye. Sometimes the vitreous jelly can degenerate and develop lumps that the patient may experience as floaters. Floaters are more common in short sighted people and may still develop after refractive surgery has been performed to correct short sight.
Retina
The retina is a very complex tissue that lines the back of the eyeball. It is composed of a fine nerve network and is really an extension of the brain. Its function is to convert light rays to electrical signals, which are transmitted to the brain through the optic nerve. In order to see clearly light rays must be focused sharply on the retina.
Optic Nerve
The optic nerve connects the eye to the brain and transmits electrical signals from the retina to the brain, allowing seeing to take place.
Sclera
The sclera makes up most of the wall of the eyeball and is the white part of the eye that can be seen behind the cornea. With some types of short sight the sclera stretches, making the eye too long and causing the light rays to be focused in front of the retina.
Read about refractive disorders of the eye.