Refractive Surgery: LASIK or PRK

chillibreeze writer — Jayitha Ganguly

Sometimes it is the little things that matter the most in making a difference to people's lives such as waking up in the morning and seeing the alarm clock without glasses or going to the beach and playing with one's children without the fear of losing one's spectacles or contact lenses in the water. Refractive surgery has made these things possible.

WHAT IS REFRACTIVE SURGERY?

Refractive surgery is a procedure that changes the shape of the cornea to correct visual impairment due to refractive errors like myopia, near sightedness; hypermetropia, far sightedness; and some types of astigmatism, irregular curvature of the cornea. It changes the curvature of the cornea, thus changing the way images focus on the retina. It can eliminate or reduce the need for glasses or contact lenses.

WHAT ARE THE DIFFERENT TYPES OF REFRACTIVE SURGERY?

In all the methods the end result is the same - correction of refractive errors. But the surgical procedure involved in changing the corneal curvature is different. They are

1) Radial keratotomy (RK)
2) Photorefractive keratotomy (PRK) LASER IN SITU KERATOMILEUSIS (lasik)
3) Intracorneal rings (INTACS)
4) Epikratophakia
5) Keratophakia
6) Conductive keratoplasty

Out of these various methods the ones in vogue today due to their superior results are

1) Photorefractive keratotomy (PRK)
2) Laser in situ keratomileusis(LASIK)

The advent of the excimer laser as an instrument for use in reshaping the cornea was a leap forward in refractive surgery. Laser energy can be delivered on the corneal stromal surface with PRK or deeper on the corneal stroma by means of lamellar surgery and creating a corneal flap in LASIK procedure.

WHAT is PRK?

In PRK the outer layer of the cornea (corneal epethelium) is removed either mechanically, with or without the aid of chemicals or by laser.

a) MECHANICAL REMOVAL - a spatula or rotating brush is used to remove the anaesthetized epithelium. The epithelium may be "softened" by soaking it with certain anesthetic drops or diluted ethyl alcohol.

b) In excimer laser removal the outer layer is removed in a process called transepethelial ablation. A cold laser beam is then applied to sculpt the cornea. A soft contact lens is placed over the eye as a bandage for the epithelium to grow back.

WHAT IS LASIK?

LASIK involves the combination of 2 separate procedures:

1) Making a corneal flap
2) Sculpting the corneal stroma under the flap with excimer laser.

In the first step, a hinged corneal flap is created by using:

a) traditional microkeratome or more recently
b) femtosecond laser or Intralaser- bladelaser lasik, a type of high energy laser.
The corneal flap is folded back exposing a bed of cornea.

In the second step, a cold laser beam is used to sculpt the curvature of the exposed corneal stroma by evaporating tissue corneal. Then the corneal flap is repositioned and it adheres without the need for stitches.

Currently LASIK is the dominant procedure in practice all over the world.

LASIK enjoys several benefits over PRK-

1) Rapid recovery- In most cases, driving vision is present the next day whereas in PRK it takes about 3 -5 days for the blurred vision to clear. This is the time required for the corneal epithelium to grow back. Driving vision takes 4-14 days to recover.

2) Pain -The flap seals within hours and brings an end to the typical scratchiness and irritation following surgery. No removal of corneal surface epithelium is required. Therefore post operative pain is substantially reduced. There is minimal discomfort, described as pressure sensation while creating the corneal flap, which very few describe as pain

3) Stability occurs within 1-3 months. In the long term, corneal scarring is much less. Therefore there is less change due to healing (regression) and greater stability of the correction.

4) Bowman`s membrane is preserved.

5) Haze- Tears carry cells and other substances that promote inflammation after surgery. In PRK, the treated layer of cornea is very close to the tear film layer. As a result, a stromal haze may develop. In LASIK, the treated layer is protected by the corneal flap, so haze is not a concern. Mild haze is not a problem, but sometimesit may be quite stubborn and take months of therapy with steroid eyedrops or surgical application of MMC before it subsides.

6) Infection- Although extremely uncommon, chances are slightly more in PRK than in LASIK as the epithelium (the protective barrier) is removed in PRK.

7) Delayed epithelial healing- The epithelium, which normally grows back in a few days in PRK, may take longer to heal resulting in discomfort to the patient and may require special treatment. But, with LASIK, this is never a problem.

8) PRK is good for correcting low to moderate myopia or hypermetropia with or without astigmatism. But LASIK can correct a greater range. FDA limits on approved procedures exclude those with more than -14D myopia, more than 6D of hypermetropia and more than 6.00d of astigmatism.

When we weigh the benefits of LASIK over PRK it might appear that LASIK is a superior procedure to PRK. But LASIK has a significant list of potential risks and complications.

1) More surgeon dependent- Due to the importance of the corneal flap and the incidence of flap related complication, the surgeon’s experience becomes a major factor in the surgery’s outcome. But with the advent of the LASIK INTALASE procedure, flap related complications can be reduced.

2) Eye trauma concerns- Despite the fact that LASIK seals quite firmly there is still a remote possibility that extreme trauma to the eye may dislodge the flap. Susceptible people, like police officers or martial arts persons, should consider PRK.

3) Incomplete correction- eye retreatment with laser

4) Decentred ablation- visual aberration-eyedrops' retreatment with laser

5) Oversize pupil(pupils wider than treatment zone)- visual abberation-eyedrops, retreatment with laser

6) Irregular flap(folds, wrinkles, striae)- visual aberration- eyedrops, surgical correction, second LASIK procedure

7) Diffuse lamellar keretitis- eyedrop.retreatment.

8) Epithelial ingrowths- visual aberration- eyedrop, retreatment with laser, surgical correction

Visual aberration includes symptoms like glare, halo, ghosting, double vision, starburst, loss of contrast sensitivity and problems with low light or night vision. Not all patients experience all symptoms and some patients with these complications experience no symptoms and require no treatment.

Nevertheless, in the hands of a good surgeon the advantages of LASIK far outweigh that of PRK. So if you were to get rid of your spectacles, LASIK should be the preferred choice.

 

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—About our writer: Jayitha writes for chillibreeze.

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