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The Light at the End of the Tunnel

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Eyeglasses, followed by contact lenses a few decades ago, have been the most common vision correction option; however, over the past 25 years, surgical techniques, tools, and procedures for vision correction have evolved rapidly. If you are tired of wearing eyeglasses or contact lenses, laser eye surgery is now the most commonly practiced procedure to correct vision problems caused by refractive errors, including myopia (nearsightedness), hyperopia (farsightedness), and astigmatism (distorted vision when looking at objects at any distance).

In the 1980s, laser eye surgery was made possible when a new type of laser called the excimer laser was being used at an IBM research facility. The researchers discovered that this laser could incise animal tissue precisely without leaving scar tissue. After years of clinical trials and improvements, corrective eye surgeries such as LASIK, PRK, LASEK, and Epi-LASIK became approved around the world.

Using the excimer laser, all laser vision correction surgeries, also known as refractive surgery, reshaping the cornea, the clear front part of the eye, so that light traveling through it is properly focused onto the retina located at the back of the eye.

If you are an eye correction surgery candidate, you should have reached an age when your eyes stopped growing so that the refractive error would have stabilized. The doctor should examine the thickness of the cornea because large corrections require more tissue removal. Eyes should be free of any diseases or conditions that might affect the cornea’s stability, clarity, or ability to heal well.

LASIK (Laser-Assisted in situ Keratomileusus) is the most commonly performed laser vision correction procedure; however, it is not the only option and may not be the right vision correction procedure for everyone. Depending on the patients’ circumstances and the doctors’ recommendation, other laser vision correction options may be better suited to the patient.

During LASIK surgery, vision is corrected by reshaping corneal tissue, so that it can properly focus light into the eye and onto the retina. The surgery starts with the creation of a thin protective flap to access the inner corneal tissue. Once the flap is created, the excimer laser is used to reshape the cornea, and then the surgeon carefully repositions and aligns the flap to its original position. During the healing process, protective shields are placed over the patient’s eyes to prevent accidental rubbing for the flap to heal naturally.

LASIK is used to flatten a cornea that is too steep for nearsighted people. Farsighted people will have LASIK to achieve a steeper cornea. LASIK can also correct astigmatism by shaping an irregular cornea into more normal shape.

Like LASIK, Photorefractive Keratectomy (PRK) laser eye surgery works by reshaping the cornea using an excimer laser, but the main difference is that during PRK surgery, the eye surgeon does not create a flap of corneal tissue. Instead, the doctor uses the laser to remove the outer thin layer of the cornea or epithelial tissue, changing the cornea’s refractive power, thereby changing the way the eye focuses light.

The initial PRK recovery is slower because it takes a few days for new epithelial cells to regenerate and cover the surface of the eye. PRK is preferable to correct mild to moderate nearsightedness, farsightedness, and/or astigmatism.

LASEK (Laser Epithelial Keratomileusis) is similar to LASIK and PRK, but it starts with the application of alcohol to the corneal epithelium. This loosens the outermost corneal cells and allows the surgeon to move them out of the way, without removing them to help him reach the stroma, a mid-layer of cornea, then comes the laser procedure to reshape the cornea. Once done, the surgeon replaces the epithelium to protect the eye while it heals; a LASEK patient will need to use a special contact lens for a couple of days to protect the eye while it heals.

Epi-LASIK (Epithelial Laser In Situ Keratomileusis) surgery starts just as the LASIK surgery, except that the flap is thinner and made only of epithelial tissue. Once the flap is created, it is moved aside, to give space for the surgeon to reshape the strome underneath with the excimer laser. The flap of epithelium is then replaced and covered with a contact-lens bandage to heal. Some surgeons believe that Epi-LASIK is a better option than LASIK because the flap exists only in the epithelium layer, and because there is no alcohol used during the procedure.

If you are tired of forgetting or breaking your eyeglasses, or if your day is ruined when your contact lenses are torn while wearing them, other options are here. Check with your doctor and go for the eye surgery that suits you.

References
health.howstuffworks.com
allaboutvision.com


*Published in SCIplanet, Autumn 2014 Issue "How Things Work".

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