Wavefront-guided PRK may be superior to standard

December 15, 2004

San Diego-Wavefront-guided PRK using the CustomVue S4 laser (VISX) was found to be safe and effective and to induce fewer higher-order aberrations when compared with standard PRK, according to Steven C. Schallhorn, MD.

San Diego-Wavefront-guided PRK using the CustomVue S4 laser (VISX) was found to be safe and effective and to induce fewer higher-order aberrations when compared with standard PRK, according to Steven C. Schallhorn, MD.

He and his colleagues are conducting a multicenter, prospective, randomized study being carried out at the Navy Medical Center, San Diego, and the Wilford Hall Medical Center, Lackland Air Force Base, San Antonio, TX. The investigators are planning to enroll 300 patients in the primary cohort after determining the need for a nomogram adjustment.

Three-month results Dr. Schallhorn reported the preliminary 3-month results from a group of 100 eyes of 50 patients who had received nomogram-adjusted treatment. One eye of each patient received customized PRK (50 eyes) and the contralateral eye standard PRK (50 eyes). Emmetropia was the goal for each patient.

"The wavefront-guided PRK resulted in slight undercorrection and there was a reversal of the undercorrection between 1 and 3 months after the surgery. The results of the standard PRK were also good and slightly hyperopic, which is desirable in the early postoperative period after PRK," said Dr. Schallhorn.

"In the customized PRK group, the uncorrected visual acuity (UCVA) improved significantly between 1 and 3 months postoperatively, reflecting the hyperopic shift in the refraction," he said. "More than 90% of eyes had 20/20 vision or better. There was also a slight improvement in the standard PRK group, which is commonly observed. The results between the two groups were similar.

"In the customized group, 94% of eyes were within 0.5 D of emmetropia, which was slightly higher and more predictable than in the standard PRK group (81%); this was also reflected in the standard error of the manifest spherical equivalent," he continued.

When the investigators evaluated the quality of vision in the first cohort of patients, they found that in both the wavefront-guided and the standard PRK groups there was a slight improvement in the best-corrected visual acuity (BCVA) and a slight improvement in the contrast sensitivity 3 months after the procedure.

However, in the customized group there was a slight trend toward improvement in 5% contrast sensitivity and in 25% contrast sensitivity.

"We saw a trend suggesting that wavefront-guided PRK is superior to standard PRK, although more data are needed to confirm that impression," Dr. Schallhorn reported.

Also at 3 months postoperatively, the investigators found that there were significantly fewer higher-order aberrations with wavefront-guided PRK compared with standard PRK, which is similar to wavefront-guided LASIK compared with standard LASIK.

"Our preliminary findings with VISX surface ablation indicate that there are no safety concerns with the procedure-no loss of BCVA. There was a slight undercorrection initially. The predictability of the procedure is very good and approaches some of the best predictability data that we have. There is less induction of higher-order aberrations; however, the numbers are still small," Dr. Schallhorn stated.

He and his colleagues will begin using the new VISX 3.5 software, which requires that they carry out a small safety and efficacy study initially before using the software to treat the primary cohort.