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Whenever I see a LASIK proponent trying to dance on PRK's grave, I think of the history of intracapsular cataract extraction. During my residency, I learned that intracap was the greatest ophthalmic breakthrough of the twentieth century. We all agreed that no one would perform extracap anymore, especially with the development of advances like alpha chymotrypsin and cryophakia. Now, of course, intracap is all but extinct, and that maligned "dinosaur" extracap has been resurrected in the form of phacoemulsification.
The rumors of PRK's death are likewise greatly exaggerated. Right now, the hyperbole surrounding LASIK is at an all-time high, and one has to question the motives behind calling for the complete abandonment of a procedure that has provided--and continues to provide--very good results. Maybe some surgeons think using a microkeratome guarantees optometrists will be unable to perform laser refractive surgery, or that LASIK is perceived as "separating the men from the boys" in terms of surgeon skill. No matter. As new developments take hold in surface PRK, and surgeons and patients begin to see the potential complications of LASIK, I believe surface ablation will be around for well into the future. Here's why:
The hyperbole on the street is that LASIK produces much better results than PRK. It's just not true. The results of the modern PRK technique we use are excellent in all ranges of myopia, especially when used on myopes under 6 D, the population that makes up the bulk of any refractive surgery practice.
Many physicians are under the incorrect impression that PRK commonly causes excessive pain, slow, unpredictable healing, haze and regression. This may have been true of early PRK, with 5-mm ablation zones, manual debridement and single-pass ablation. Larger ablation zones, "no touch" debridement with the excimer laser and a multi-pass approach yields very predictable healing responses.
As for healing, in a study I performed on 320 myopes ranging from -1 D to -25 D, 80 percent of patients saw 20/40 by day three, and we didn't hear complaints of how patients had to miss work or otherwise suffer post-op "downtime" because of epithelial healing. Our retreatment rate is under 4 percent.
As for accuracy, in another study of 201 low myopes from -1 D to -6 D, at six months 96 percent saw 20/40 or better uncorrected, and three quarters saw 20/20. Around 96 percent are within +/- 1 D of the intended correction.
The incidence of haze is also very low. No patient from a study of 363 no-touch patients developed haze greater than grade one. At six months post-op, 82 percent of patients have totally clear corneas, and around 18 percent have some minor haze, running from trace amounts to grade one.
Pain is also not the significant problem it's made out to be by LASIK proponents. With modern PRK techniques such as multizone and no-touch epithelial removal, pain is only a significant issue in 2 percent of patients. I would argue that LASIK isn't pain free, since any epithelial abrasion caused by repositioning the flap or using the microkeratome could result in post-op discomfort.
Ultimately, neither surgery has reached its full potential in terms of technique or results. Declaring either "dead" at this point would be irresponsible.
Admittedly, the recovery period for LASIK may be a day shorter than that for modern PRK. With today's busy patients, that's a sought-after benefit. But for this small convenience, patients and surgeons pay a very big price.
To me, the No. 1 issue is safety. PRK is quite safe. In a study of 330 patients, including high myopes, only three (0.9 percent) lost two lines of vision, and no one lost more than two lines. Overall, our adverse effect ratio, including halos, glare or symptoms from haze or an irregular corneal surface, is around 0.5 percent.
The same is not true for LASIK. Because of manual manipulation of the cornea, LASIK poses a much higher risk of flap and healing complications than does surface PRK. Following are just a few of the complications that can occur:
A 1,013-patient study of LASIK done by researchers at Emory University yielded a 4.8 percent adverse event rate. Two percent derived from intraoperative flap complications and around 3 percent occurred because of post-op flap problems.
These types of complications are a particular risk in the hands of beginning surgeons. Many LASIK surgeons will tell you that it will take anywhere from 500 to 1,000 procedures for a beginning surgeon to feel comfortable with using the microkeratome, and for his complication rates to subsequently decrease.
I invite those surgeons who say PRK is dead--or who wish it were--to come see my results. Far from deceased, PRK is a time-proven procedure that provides excellent outcomes with a minimum of complications for the patient, or surgical difficulty for the ophthalmologist.
Dr. Johnson specializes in refractive surgery. His "no touch" technique is patented in the U.S. and 50 countries.
References
1. Fiander DC. How to avoid and manage LASIK complications. Review of Ophthalmology, Nov 1996. pp. 82.
Once upon a time, the best option for patients with cataracts was intracapsular surgery. But then the concept of extracap surgery with phacoemulsification emerged, and soon surgeons were able to provide their patients a procedure that was less traumatic, had fewer complications and offered better visual results with a shorter recovery time.
Although not everyone has realized it yet, the same sort of evolution has taken place in the field of refractive surgery. At one time, PRK was the best option for patients with ametropia. But technology has marched on, and today the best option is LASIK. Like extracapsular cataract surgery, it offers better visual results, less physiological damage, fewer complications and a shorter recovery time. I stopped recommending PRK as a primary procedure three years ago, and most of the high volume refractive surgeons I know have also stopped or minimized the use of PRK. If you are now doing PRK, you will soon join us. Here's why:
Pain. The epithelial debridement necessary for PRK results in moderate to severe post-op pain, a major negative for an elective procedure like this one. Pain in LASIK is usually negligible.
Visual recovery. Even though corneas which have undergone PRK re-epithelialize in a few days, the restructured epithelium is initially irregular on the surface, leaving patients with limited quality of vision during the initial post-op period. With LASIK, however, depending on such factors as surgical technique, surgeon experience and beam quality of the laser, most patients see better than 20/40 uncorrected on the first post-op day. Many actually see 20/25 or better at that time.
In most cases, LASIK reaches a stable refraction quicker than PRK, as well. In our study, we found that most of our patients (93 percent) have refractions that are stable within one diopter at three months. With PRK, this can take upwards of six months to achieve.1
Predictability. LASIK is more predictable than PRK. In one study comparing LASIK and PRK, 71 percent of the LASIK group was within +/- 0.5 D of emmetropia at one year, whereas 61 percent of the PRK group met these criteria.1 Also, 4 percent of the PRK eyes lost two lines of best corrected acuity, while only 1 percent of the LASIK eyes lost this much. The differences in predictability are especially dramatic in higher myopes. Greek researchers found that for high myopia, the predictability of LASIK is three times that of PRK.2 One major reason is corneal wound healing. Corneal wound healing after PRK can be unpredictable. In one study, researchers found that the epithelium in the treated eyes of PRK patients was 21 percent thicker than that in the untreated eyes, and that there was a statistically significant relationship between refractive regression and epithelial hyperplasia after PRK.3
Results. LASIK also yields excellent results. At six months, 96 percent of the lower (less than -7 D) myopes in the second cohort of our study saw 20/40 or better and 94 percent were within +/- 1 D of the intended refraction. This compares favorably with one large study of PRK in a similar range of myopia (less than -6 D), in which 94 percent of eyes were 20/40 or better, and only 83 percent were within +/- 1 D.1
Risk of infection. Although the incidence of infection in PRK is relatively low, I'm still bothered by the fact that we are creating a large epithelial defect, without the normal protection of Bowman's membrane. With LASIK, only a small amount of epithelium is removed, and the cornea usually reepithelializes in a few hours, not a few days.
Steroid complications. Another problem with PRK is the procedure's dependence on relatively long post-op courses of steroids to reduce pain and inflammation. Patients need qid dosage for as long as one month, with as much as four months of tapered dosing. Chronic steroid use can lead to elevated IOP and induced glaucoma, and induced cataracts. With LASIK, steroids are necessary for only four days.
Haze. Another byproduct of the PRK healing process is corneal haze. Though most PRK haze resolves, the haze that doesn't is almost always in the optical zone, necessitating aggressive steroid use or even a retreatment. Haze can also occur in LASIK, but it's typically confined to a ring corresponding to edge of the flap, outside the visual axis.
Physiological change. PRK destroys two important structures: the basal nerve plexus and Bowman's membrane. The nerve plexus eventually recovers somewhat, but the risk of corneal anesthesia is present. Bowman's membrane never returns. Though we're not sure of the exact effect of removing this protective layer of the cornea, it doesn't make sense to remove it if we don't have to.
Over the years, PRK has taught us much about refractive surgery and how the cornea responds to the excimer. It's now time to pass the torch to newer procedures that offer more accurate correction, without all the pain, unpredictability and sloppy healing that surface ablation inevitably brings.
Dr. Kremer has performed a variety of refractive procedures, including what is believed to be the first U.S. LASIK.
References:
1. Wang Z, Chen J, Yang B. Comparison of laser in situ keratomileusis and photorefractive keratectomy to correct myopia from -1.25 to -6.00 diopters. J Refract Surg 1997;13:528-534.
2. Pallikaris IG, Siganos DS. Excimer laser in situ keratomileusis and photorefractive keratectomy for correction of high myopia. J Refract Corneal Surg 1994;10:498-510.
3. Gauthier CA, Holden BA, Epstein D, Tengroth B, Fagerholm P, Hamberg-Nystrom H. Role of epithelial hyperplasia in regresion following photrefractive keratectomy. Br J Ophthalmol 1996;80:545-548.
In my experience, PRK works much better when surgeons observe two principals. First, keep cold steel away from the cornea. Second, impart gentle rather than harsh curvatures to the eye. I call this technique "No Touch."
The no-touch debridement technique consists of two steps. First, the surgeon performs a 6.5-mm myopic ablation right on the tear film, creating a central depression. He or she then performs an ablation in PTK mode, which provides a greater peripheral removal of tissue. This two-step technique is balanced to give a uniform epithelial removal. When fluorescence stops, it's the sign Bowman's membrane has been reached. We've found this technique makes healing much more predictable.
The multi-pass, multi-zone technique involves three different passes with the laser at three different optic zones: 4 mm, 5 mm, and 6.5 mm. The dioptric power of the ablations is distributed so that the initial central 4 mm receives half of the total treatment power. Even for relatively low myopia, such as five or six diopters, these ablations can result in smoother contours along the corneal surface. I believe it's this contour, rather than the absolute optic zone diameter, that determines whether the patient will see well at night or not. Gentler curves induce fewer night-vision problems, in my experience. This technique also induces less of a healing response, enhancing predictability, and makes PRK more patient friendly, appealing to patients who feel uncomfortable with instruments touching their eyes.