Dede is just one of the eight hundred-fifty-thousand people who have undergone a procedure by the name of LASIK or Laser In-Situ Keratomileusis. If surgical procedures were movies, LASIK would be this years box office smash as it has received much media coverage and many praises; however, not that many people know what LASIK is, what the advantages and disadvantages are, and most importantly if LASIK is right for them (Buratto, 1).
LASIK is basically a type of laser surgery which can help correct nearsightedness (myopia), which is the inability to see distant objects, farsightnedness (hyperopia), which is the inability to see close, and astigmatism, the inability to focus light waves evenly. LASIK has grown greatly in the last year, mostly because of 4 reasons; it is fast (procedure takes about 5-10 minutes), safe, painless, and the results are almost always prolific.
The eye is just like a camera because it works by focusing light waves that pass through it. Light rays that enter the eye must first pass through the most outer layer of the eye called the cornea. The cornea performs 2/3 of the focusing process, the remainder of is then completed by the crystalline lens which further focuses the light on the retina. This requires extreme precision in that the focused light must fall exactly at the level of the retina (Gallo, 126).
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The retina is a nerve tissue that carpets the inner surface of the eye, much like wallpaper covers all aspects of a wall. The retina converts the light into electrical signals, which are transmitted to the brain by the optic nerve. Just as a camera cannot produce clear photographs of the image if the incoming light is not focused on the film, we cannot produce a clear vision if the cornea and crystalline lens do not focus the light precisely on the retina. This is where LASIK steps in.
A laser is a device that creates a very special kind of light energy that is usually invisible to the human eye (Caster, 16).
In LASIK, ophthalmologists use a certain type of laser called the excimer. By using invisible ultraviolet light, the excimer is able to break covalent bonds between molecules. What sets excimer aside from other lasers used in medicine is the wavelength used. At one-hundred ninety-three nm (nanometers), excimer lasers remove tissue by breaking the covalent without creating much thermal energy (Slade, 25).
This allows for precise removal of tissue with minimal surrounding tissue damage. The very thin layer of the cornea that is removed, changes the curvature of the cornea ever so slightly, thus then results in a change in the light focusing ability. In nearsightedness (myopia), light rays from distant objects are not focused on the retina, but instead they are focused in front of the retina (See Figure 1).
Therefore to correct nearsightedness in a LASIK procedure, the curvature of the cornea must be decreased or in another words made flatter by removing corneal tissue in a disc-shaped pattern, or from the central cornea. A computer determines the exact pattern and number of pulses that are needed to do this. In farsightedness (hyperopia), light rays from distant objects are focused not onto the retina, but behind it (See Figure 1).
To correct this, the central portion of the cornea must be made steeper; and this is accomplished by removing corneal tissue in a donut shaped pattern, or in another words more from the peripheral areas. Eyes with astigmatisms focus light waves unevenly because of the irregular shape of the cornea; football shaped as opposed to the usual round, basketball shaped corneas. The excimer laser can remove corneal tissue asymmetrically, and so the end result is a round, symmetrical surface (Sloat, 90).
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LASIK, did not just develop suddenly overnight in some ophthalmologist’s mind; however, LASIK is part of an evolved procedure (Gallo, 127).
Today’s vision correction revolution dates back decades through the sheer genius, persistence, and ingenuity of Professor Jose Barraquer (Slade, 8).
Refractive surgery, which is the type of surgery LASIK is characterized as, started in Bogota, Columbia in 1948 when Barraquer started performing a procedure called Freeze Keratomileusis. This procedure involved adding a disc of corneal tissue (donated from another person) with a predetermined curvature in the cornea giving it structure. In a journal found 2 decades after this procedure, it stated that patients who had myopia could see better after the procedure; however he stated a few months after the surgery, that some patients would lose their eyesight due to infection. The reason for this was that Barraquer used an unsterilized shaver to cut the cornea. It was not until the late 1970’s that refractive surgery resurfaced when US surgeons visited the Soviet Union. The surgeons brought back a procedure called Radial Keratotomy (RK) which made spokelike incisions in the cornea by using a handheld diamond scalpel. The results were good, but scientists noticed that the incisions structurally weakened the eye.
Soon after PRK was introduced, surgeons began testing a procedure called Laser In-Situ Keratomileusis, which was first partially introduced by the father of ophthalmology, Barraquer in 1950 (Slade, 8).
Keratomileusis is derived from the Greek root keras (horn-like cornea) and mileusis (carving) and basically it is a procedure that involves slicing and peeling back the outer layer of the cornea (anterior cornea), leaving a hinge on one side, while the laser sculpts the tissue underneath (corneal stroma).
After the excimer laser is done, the flap is placed back to where it was before, and no stitches are needed because the corneal flap heals by itself when left to dry. You are probably wondering if they still used the diamond scalpel, and the answer thankfully is not. Surgeons use a very precise instrument called the microkeratome (See Figure 3) which makes LASIK very unique compared to other surgeries. This device is a mechanical shaver that has a sharp blade, which moves back and forth at very high speeds (See figure 2).
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After a suction ring has been placed on the cornea, the microkeratome is place on top of the cornea and advances across it at very small increments creating a flap that is only 1/3 inch in diameter. This instrument cuts the cornea at a uniform thickness and creates a portion of the cornea uncut. After the suction ring and the microkeratome have been removed, the corneal flap is folded back (See Figure 4), exposing the middle portion of the cornea. Also in LASIK surgery, the excimer laser can be used at different frequencies and therefore produce different desired results in the same patient. Each laser pulse in a LASIK procedure removes ten-millionths of an inch of corneal tissue in twelve-billionths of a second while in a PRK procedure, the laser removes about twice as much in about the same time. The amount of corneal tissue removed depends on how nearsighted or farsighted the patient is (Gorman, 60).
The more nearsighted a patient is the more tissue must be removed to obtain a flatter cornea, and the same goes with farsightedness, except the cornea has to be made steeper.
While the recovery period of LASIK is remarkably short, forty-percent of people who had the procedure see halos or starbursts around bright lights for several months (Buratto, 5).
Ophthalmologists believe this effect seems to be caused by the edge created between the treated and the untreated part of the cornea which bends and distorts the light as it enters the eye. Seeing halos or starbursts usually occurs during night, when the pupil dilates and the edge of the cornea falls right into view and for this reason, people with exceptionally large pupils should not undergo LASIK. These starburst effects, as ophthalmologists call it, usually go away after a few months.
Little research is available on LASIK’s long-term safety and effectiveness, but there is information available on PRK. Last year, a review in ophthalmology traced eighty-three British patients who underwent PRK in 1990, and found no serious complications in any of them. This is attributed to the amount of untouched, deep cornea (approximately fifty percent of the entire cornea), which maintains the eyes original overall shape. This is opposite of RK which left only 10% of the untouched cornea (Voelker, 1494).
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Despite its increasing popularity, LASIK is not for everyone. People with extra-thin corneas are not good candidates of this surgery because the surgeon does not have enough tissue to work with. Ophthalmologists also turn away people who have rheumatoid arthritis and diabetes because they have problems with dry eyes, and are hence poor healers.
