This information is provided to help you make an informed decision about Excimer Laser procedures called PRK (Photo Refractive Keratectomy) and LASIK (Laser-in-situ Keratomileusis). With the advancement of technology in the correction of Myopia or short-sightedness, Astigmatism and long-sightedness, this new generation of Excimer Laser (flying spot) is available in Malaysia in the year 2000. These two procedures do not involve any injection or hospitalization.

These procedures have been designed to allow patient with short-sightedness, Astigmatism and long-sightedness to discontinue the use of corrective lenses (contact lens or spectacles) or reduce their reliance on corrective lenses due to a total correction in short-sightedness (Myopia), Astigmatism or long-sightedness, or reduction of power.

The word “Excimer” is an acronym of “Excited” and “Dimer”. Atoms of inert gas are excited to form unstable molecules. These unstable molecules only exist for a short period of time and when they breakdown, they emit photons of ultra-violet light, which are used in the Excimer Laser (LASER is yet another acronym from Light Amplification by the Stimulated Emission of Radiation).

The Excimer Laser is a “cool” laser, unlike conventional lasers, which usually generate heat that can cause substantial damage to the surrounding tissues. When the photons of ultra-violet light hit the surface of the cornea, they break the chemical bonds that hold molecules of the corneal tissue together. This results in the gentle removal or ablation (also called “corneal sculpting”) of the cornea. There is virtually no damage to the cells that surround the ablated tissue. This absence of damage is the major reason why the Excimer Laser is suitable for delicate procedures on the eye.

Comparison Between PRK and LASIK:

Anatomy of Eyeball	Normal Vision

How does your eye work in normal vision?

In order for us to see clearly, the image of the scenery should be focused on the retina. In optical terminology, the parallel light rays should focus precisely onto the retina when the eyes are looking at a distant scenery (see diagram of normal vision).

How Does the eye focus the light rays?

The eyeball acts like a camera, the cornea (transparent front surface of eyeball) and the crystalline lens are the two powerful focusing lenses in the eyeball which focus light rays onto the retina (similar to negative film).

The pupil adjusts the amount of light entering into the eyeball automatically like the aperture of the camera. Too much light will glare or whitewash the focused image, whereas too little light on the focused image will make it too dark to see.

Once the light rays are focused onto retina (with proper amount of light), clearer images are sent through nerve impulse by the retina to the occipital lobe of the brain, via the optic nerve of the eyeball.

In refractive errors, the parallel light rays are focused in front or behind the retina as in the case of short–sightedness (myopia) or long-sightedness (hyperopia) respectively or focused onto the retina in one axis only in the case of astigmatism.

Children with refractive error, usually watch TV with half-closed eye, or superior gaze (head turned down) or side gaze (head turned to one side) or copying wrongly from the blackboard in school. They may even complain of eyeache or headache.

It is important for children below 10 years of age to have the full eye check-up by an eye specialist due to the fact that children have not yet acquired the capability of differentiating between clear object and blur object. In addition, it is necessary to paralyse the focusing power temporary (with the use of eyedrop) to obtain a correct measurement of spectacle power. This is because children may not be cooperative enough to maintain a fixed focus as in adult.

Long-Sightedness (Hyperopia)

• Person suffering from Hyperopia will have the focus of the light rays entering the pupil behind the retina instead of precisely on the retina in the eye.
• Eyeball of the person is too short or smaller than it should actually be, in relation to the focusing power of the eyeball.
• In lay person’s term, long-sightedness person can see distant image clearer than near object.
• Long-sightedness seldom occurs among the Chinese and even if it does, the power is usually relatively low.
• If happen during childhood, the long-sightedness usually improve over the years and may slowly disappear as the child grows.
• Headache and eyeache is common complaints in children with long-sightedness.
• Children are usually able to see well during normal eye sight checking.

Astigmatism

• Person suffering from astigmatism will have the focus of the light rays entering the pupil, on the retina except along one particular axis. Along this axis the focus is either in front or behind the retina.
• The focus is usually at two different axes with one focused at one axis at right angle to another.
• In lay person’s term, no matter at what distance the object is, it will still appear blur to a person with astigmatism.
• Astigmatism commonly occurs together with short-sightedness, where the power of short-sightedness is usually higher than that of the astigmatism.
• Astigmatism usually appears quite stable and does not increase accordingly with the power of short-sightedness during childhood and puberty.
• It is a common misconception that astigmatism will lead to blindness.
• Children with astigmatism usually can see almost normally during eyesight testing by straining the eyes.

Short-Sightedness (Myopia)

• Person suffering from myopia will have the focus of the light rays entering the pupil in front of the retina, instead of precisely on the retina in the normal eye.
• Eyeball of the person is too long or larger than it should actually be, in relation to the focusing power of the eyeball.
• In lay person’s term, short-sighted person can see clearer near image than distant image, that is, distant image is blur.
• Short-sightedness usually make its appearance during childhood – the younger the age of onset, the higher will be the final permanent power after puberty.
• Once short-sightedness is diagnosed, the initial power will increase gradually over the year at a rate of about half to one dioptre or 50 to 100 degrees per year before and during puberty.
• The short-sightedness will become stable at around 16 to 18 years of age, except in the case of pathological myopia where it may increase slightly after 21 years of age.
• Retinal degeneration or other complication of shortsightedness is usually associated with pathological myopia.
• The correction of short sightedness may be through glasses, contact lenses or LASIK or PRK depending on the need of the individual.
• Pathological myopia is a subgroup of shortsightedness with spectacles power of over 1000 degrees or 10 dioptres.

Background on the Excimer laser

All laser refractive surgery is performed with an Excimer laser. The development of the Excimer laser is the key element that has made eye laser surgery possible. Created by IBM, Excimer lasers (the name is derived from the terms excited and dimers) use reactive gases, such as chlorine and fluorine, mixed with inert gases such as argon, krypton or xenon. When electrically stimulated, a pseudo molecule (dimer) is produced that eventually emits laser light in the ultraviolet range.

The Excimer laser is a cool laser, which means that it does not heat up the surrounding air or surfaces. Instead, a very tightly-focused beam of ultraviolet light is produced. The ultraviolet light is absorbed by the upper layer of the cornea surface that it come into contact. The sheer amount of ultraviolet light is too much for most organic materials (such as the cornea of the eye) to absorb, resulting in the breakdown of the molecular bonds of the material. The ultraviolet beam of light only penetrates a microscopic amount, less than a micron (millionth of a meter), into the surface of the cornea. The heat created from the energy released by the laser is dissipated along with this microscopic layer of the cornea. This process is known as photoablation.

Conclusion

This information is intended to provide individuals with an overview of the Excimer laser PRK and LASIK procedures. It is important that you should first discuss in depth with your ophthalmologist (eye specialist) of the other options for refractive correction such as the use of corrective lenses (spectacles or contact lens) and other refractive surgical procedures (radial keratotomy and intraocular lens implantation), for the correction of your short-sightedness, Astigmatism and long-sightedness.