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LASIK, PRK go eye-to-eye in Saudi clinical trial
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Jeddah, Saudi Arabia—Clinical results from a study in Saudi Arabia point to laser in situ keratomileusis (LASIK) as preferred over photorefractive keratectomy (PRK) in treating myopia, according to George O. Waring III, MD, of the El Maghraby Eye Hospital here.
Waring, along with Saudi surgeons Akef M. El-Maghraby, MD, and Tarek Salah, MD, studied 33 myopic patients who received LASIK in one eye and PRK in the other eye. One-year results were collected for 91% of the patients.
The randomized study found nearly identical refractive results from both procedures. About 90% of the eyes treated were within 1 D of emmetropia after a year. But visual acuity at the 20/20 level was better in the LASIK eyes. Also 90% of patients were highly satisfied with the LASIK treatment while only half were equally pleased with the PRK results.
"In terms of visual acuity," said Waring, "we prefer to report 20/20. We think reporting 20/25 is sort of a sleight of hand, and 20/40 is not an adequate criterion for successful results. We use 20/20 for adequate fitting of glasses and contact lenses, so we should report 20/20 results for refractive surgery."
Better uncorrected visual acuity
At the one-year mark, two-thirds of the LASIK eyes saw 20/20 or better without correction compared with half of the PRK eyes. "The uncorrected visual acuity is better with LASIK than it is with PRK," Waring said. "The refractive results are similar in this bilateral study design. The recovery of vision is faster with the LASIK procedure. The LASIK eyes see faster, better and more comfortably."
The Saudi team used a Summit Omnimed system with a 6-mm diameter ablation, and the Summit algorithm for PRK. "The only real variation, then, could be the different response in the two eyes," Waring said.
Differences in patient satisfaction and postoperative visual acuity, he added, can be attributed to the wound-healing process and the resultant topography. "With PRK," he said, "we are accustomed to seeing the subepithelial haze, but with LASIK there is not any subepithelial or interface haze."
The key to the superiority of LASIK is the corneal topography, noted Waring. Stephen D. Klyce, PhD, at the Louisiana State University Eye Center in New Orleans, did an analysis of the topography measured with the Tomey TMS. The topography "is quantitatively better after LASIK," Klyce said. In fact, postoperative corneal topographical analysis of 13 of the patients revealed more central corneal variability following PRK than following LASIK. Likewise, central islands of 3 D or 4 D were apparent in PRK eyes. But, said Waring, "we did not have central islands in the LASIK eyes."
Moreover, recovery is faster with LASIK. "Rapid recovery is more characteristic with LASIK because Bowman’s layer is intact, and because the epithelium does not have to heal," Waring said.
The Saudi clinical trial was not without its difficulties. In the LASIK eyes, two cases had displaced flaps with epithelium in the bed. With PRK, there were two cases of scarring and subepithelial haze.
Not surprisingly, the refractive outcome after PRK initially showed overcorrection, with vision improving during a three-month wound-healing process. The LASIK eyes stabilized after about six weeks.
More complicated procedure
The study attributes a trend toward residual myopia in the PRK eyes to "wound healing and fill-in." Over-correction with the LASIK procedure was blamed on the use of a PRK algorithm even though there is no subepithelial wound healing.
"LASIK is a more complicated procedure," Waring said. "[But] one big advantage with LASIK is that there is very little pain after surgery." In fact, 80% of patients in the Saudi study reported "little or no pain" after LASIK, while 70% said they had "severe pain" after PRK.