Laser treatment has become very popular in recent years to permanently correct short-sightedness (myopia) and long-sightedness (Hypermetropia). This article describes the procedures involved and the principles that underpin them.
Glossary of Terms Used in Laser Treatment
- Retina - the "screen" at the back of the eye onto which light is focused
- Cornea - the outer part of the eye that is normally in contact with air. It is this that is re-shaped during eye laser surgery
- Keratome - a very sharp blade that is used to open a flap in the cornea
- Laser - a high energy light beam that may be controlled very accurately
- Diopter - the dgree of vision that needs to be corrected
How Laser Eye Treatment Works
Figure 1 shows what happens when a person is short-sighted (near-sighted), and Figure 2 shows what happens when he is long-sighted (far-sighted). The eye of a short-sighted person makes the light focus before it reaches the retina. The focusing is done mostly by the cornea, and partially by the lens. Laser surgery works by adjusting the shape of the cornea to make it focus light just at the retina. In a short-sighted person, the cornea is made to focus the light less by removing material in the centre of the cornea (See Figure 3). In a long-sighted person, the cornea is made more rounded to make it focus the light more quickly, and this is done by removing material from the edges of the cornea. (See Figure 4).
What Happens During Eye Laser Surgery
To achieve the shaping of the cornea that will improve eyesight, a mild pain-killer is applied to the cornea. After a short time, the patient opens their eye wide so that the eyelids may be taped open. A device called a speculum is used to keep the eyelids apart. A small, almost invisible mark is made on the cornea, and the automatic laser device uses this to track the correct movements. A flap of cornea is opened using either a keratome or a laser. The laser is then used to remove the internal cornea material by a process known as ablation. The laser process takes only a few minutes, after which the cornea flap is replaced. All of this procedure is virtually painless, although there may be some minor discomfort.
Who is Suitable For Eye Laser Correction
Most people in good general health and with healthy eyes may be treated. Some eye conditions such as glaucoma may not be suitable. It is also important that the patient has had stable vision (eye-sight not getting worse) for a reasonable period. This often means that younger patients are not suitable. Finally, the surgeon will calculate how much cornea material needs to be removed to achieve the correct focus. If the patient has a thin cornea, or needs to have more corneal material removed than they have available, then surgery may not be possible. This may be the case with extreme near-sight (below -10 dioptre), but the eye surgeon will advise on this.
Summary of Laser Eye Surgery
Eye laser treatment is a proven method to permanently correct vision, so that glasses and contact lenses are no longer needed. It is virtually painless, and has a very high success rate. Some patients may be entitled to free surgery if their condition is severe enough, but laser surgery is not usually covered by health insurance, as it is an optional procedure.
Although sight may be corrected, as patients get older they will almost always develop long-sightedness due to the aging process.
This article is for information only, and is not a substitute for professional medical advice.
Martin Bell - Martin holds a B.Sc. degree in chemical engineering, and an M.Sc. degree in electronics and computing. He has spent more than 25 years ...
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