Advice and Procedures on Laser Vision Correction
Laser vision correction or laser eye surgery is a type of refractive surgery for correcting myopia (nearsightedness), hyperopia (farsightedness) and astigmatism. The surgery eliminates or reduces the patient’s dependence on glasses by using a laser to reshape the cornea.
The history of refractive surgery goes back to the 1950’s when ophthalmologist Jose Barraquer developed the microkeratome and keratomileusis techniques to surgically reshape the cornea. In the 1970’s Russian ophthalmologist Svyatoslav Fyodorov developed Radial Keratotomy (RK) which changed the shape of the cornea and corrected myopia by using a diamond knife to cut tiny radial lines into the surface of the cornea.
By the 1980’s Rangaswamy Srinivasan discovered that an ultraviolet excimer laser could precisely sculpt living tissue with no damage to adjacent areas, a process he called ablative photo decomposition.
In 1985, Steven Trokel applied the excimer laser to radial keratotomy at the Edward S. Harkness Eye Institute in New York. He also cofounded VISX USA. In 1989, Marguerite MacDonald performed the first human VISX refractive laser eye surgery.
LASIK (Laser Assisted in Situkeratomileusis) and PRK (Photorefractive Keratectomy) are the two most common types of laser vision surgery. For nearsighted (myopic) individuals corneal tissue is removed or ablated from the center of the cornea to flatten the corneal surface. For farsighted (hyperopic) people corneal tissue is removed from the periphery to steepen the corneal surface. The underlying corneal tissue is referred to as the residual stromal bed.
Average corneal thickness ranges from 500 to 600 micrometers. The FDA (Food and Drug Administration) recommends that the residual stromal bed must be at least 250 micrometers thick. This is essential since it preserves the integrity of the eye and prevents corneal ectasia which occurs if the corneal tissue is too thin to support the eyeball resulting in bulging of the cornea and severe visual distortions. Most ophthalmologists prefer to leave up to 300 microns for added safety. Potential side effects include halos, starbursts, night vision loss and dry eyes.
LASIK was first approved in 1999. In Lasik, a surgical blade is used to create a hinged flap of corneal material usually about 100 to 180 microns thick. This flap is now often cut with a laser. The flap is folded over exposing the tissue beneath. A laser is then used to remove or ablate an amount of corneal tissue commensurate with the amount of correction required. The more nearsighted or farsighted the patient is, the more tissue is removed. When the laser has finished its work, the flap is carefully placed back into its original position. One of the key advantages of Lasik is the speed of recovery with little discomfort and lower risk of side effects including haze, glare and halos. I’ve had friends who were out and about the day after their Lasik surgery with no problems.
Candidates for Lasik must have sufficient corneal thickness do undergo the procedure. The more correction required, the thicker the cornea must be. To maintain the integrity and strength of the eye, there must be sufficient depth of the cornea (residual stromal bed) after the flap is pulled back and the interior corneal material is removed.
I was not a good candidate for Lasik because of my extreme myopia. Instead, I underwent PRK in 2003. PRK is actually an older and simpler procedure. A laser is used to ablate or remove corneal tissue from the surface of the eye rather than the interior. This procedure does not require a hinged flap to be cut from the cornea.
PRK sometimes known as Advanced Surface Ablation became popular in the mid 1990’s particularly after the Excimer laser was approved by the FDA. A laser beam of cool light is utilized to remove surface corneal tissue. A soft contact lens is then applied as a bandage for five to seven days. Recovery usually takes two to three weeks. In my case, I was functional in a couple of weeks, but it was probably four to six weeks before I was comfortable with the results. I had a great deal of tissue removed since I was so nearsighted and this resulted in a longer recovery time. The first week to ten days is the most difficult. During the first few days my vision was very cloudy and hazy like looking through thick fog. I was also extremely sensitive to light and couldn’t do anything that required using my eyes. As my eyes healed, the side effects slowly dissipated, but it was several months before my vision was restored to the point where I was completely satisfied with it.
The main advantage of PRK is its simplicity. There is no cutting or surgical flap creation, so less can go wrong. This aspect of Lasik always bothered me. I wasn’t comfortable with a device cutting my cornea and pulling a flap back. I was actually delighted when I was told I wasn’t a candidate for Lasik. If I wanted laser correction, I would have to undergo PRK. Another advantage of PRK is that it’s somewhat better at preserving the integrity and strength of the eye. Tissue is removed from the surface of the cornea instead of a flap being cut and tissue ablated from the interior requiring a minimal thickness of the residual stromal bed. For most people this probably wouldn’t matter, but if you’re extremely myopic or hyperopic then it could matter if your cornea isn’t thick enough.
In PRK the outer layer of the cornea or epithelium is removed. This layer can rapidly replace itself in a matter of days. The healing process is uncomfortable but bearable. In Lasik where the deeper layers of the cornea are ablated there is a much reduced regenerative capacity, but recovery time is much faster with less inflammation.
Another huge improvement in laser refractive eye surgery is the addition of Wavefront customized technology. Wavefront compares the distorted light waves leaving the eye to flat waves of light that would have returned in a perfect optical arrangement. This information is converted into a three dimensional map by a computer which then guides the laser while reshaping the cornea. The surface of the cornea has many irregularities including microscopic hills and valleys which distort light rays as they pass through. Wavefront technology uses the laser to smooth out these imperfections and provides much sharper vision. Wavefront technology can also sharply reduce unwanted visual effects such as glare, halos and night vision loss.
The addition of Wavefront technology to laser eye surgery can provide vision quality to patients superior to anything that could be achieved with glasses or contacts. Fortunately, wavefront technology was included with my PRK laser surgery providing outstanding results. My left eye was 20/1000 before the surgery and 20/15 afterwards - a result better than anything I had ever known even before I began wearing glasses. My right eye went from 20/800 to about 20/25. Some of the visual acuity was reduced by minor scarring due do to infiltrates, a rare complication treated with antibiotics and steroids. My eyes are also slightly drier than they used to be. I only notice this in the morning and it’s easily remedied with a saline drop in each eye.
Lasik is generally favored by most people because of the fast and easy recovery. If your vision correction isn’t too extreme, Lasik is probably the better solution for vision correction. If you’re extremely near or farsighted, I would go with PRK. PRK is simpler, but the recovery process is much longer. I was very happy with the results of my PRK refractive surgery. I no longer need glasses or contacts except for occasional close work and would definitely recommend the surgery. The only thing I might have done differently was to have surgery done on one eye at a time. Most people have both eyes done at the same time. Doing one eye at a time takes longer to complete the process, but if there’s a problem or complication like the infiltrate problem I experienced, it’s confined to one eye instead of risking both. The only drawback is that the more extreme your pre surgery vision is the more awkward it is to function with one eye corrected and the other eye not corrected. I would also highly recommend including the customized Wavefront technology in any laser procedure. The additional cost is well worth it. Don’t be cheap when it comes to your eyesight!