Used as an enhancement after refractive surgery, wavefront-guided LASIK and wavefront-guided PRK result in similar outcomes, according to Lisa Y. Chen, MD.
“We found that LASIK and PRK resulted in similar improvements in uncorrected distance visual acuity [UDVA],” said Dr. Chen, clinical instructor, Department of Ophthalmology, Stanford University, Stanford, CA. “Both procedures were safe, resulting in no adverse outcomes.”
Previous studies have found similar outcomes in LASIK and PRK as a primary treatment for refractive error. But few prospective trials compare the two procedures as enhancement surgery, she noted.
Dr. Chen and co-author, Edward E. Manche, MD, followed 34 eyes of 30 patients whose prior refractive surgery had left them with residual refractive error. Eyes had a mean spherical equivalent power of -0.36 D (range -1.125 to 1.625 D) and a mean cylinder of 0.53 D (range 0 to 1.25 D).
They re-treated 12 eyes with wavefront-guided LASIK and 22 eyes with wavefront-guided PRK using an excimer laser (AMO VISX S4 CustomVue IR, Johnson & Johnson Vision).
Making the decision
“The decision whether to perform a LASIK or PRK enhancement was determined by the type of original refractive surgery the patient underwent and the amount of time since the initial procedure,” Dr. Chen said.
Most patients had chosen LASIK as their primary treatment due to increased familiarity with the procedure and the greater speed and ease of recovery, Dr. Chen said.
The majority of these patients underwent LASIK enhancements, with the exception of those whose primary treatment occurred more than 1 year ago due to the increased risk of epithelial ingrowth with late enhancements.
Epithelial ingrowth has been reported to occur in up to 25% of LASIK enhancements, she said.
“Lifting the flap can cause epithelial disruption and open a conduit for these cells to grow under the flap,” Dr. Chen said.
To avoid this problem, researchers recommended PRK to patients who had undergone LASIK as their primary treatment at least a year earlier. Those who had PRK as their primary treatment chose it because their corneas were too thin or irregular in shape to make them good candidates for LASIK, she explained.
All of these patients also received PRK surgery as an enhancement.
Researchers found no statistically significant differences in UDVA, spherical equivalent power, or higher-order aberration (HOA) among the groups.
UDVA in those receiving LASIK enhancements improved from a mean logMAR 0.2 to -0.07. In those receiving PRK, it improved from logMAR 0.25 to -0.06. The differences between the groups were not statistically significant.
Spherical equivalent power improved in eyes receiving LASIK from a mean of -0.3 to -0.094 D. It improved in PRK eyes from -0.39 to -0.059 D.
HOAs were similar between the two groups as well, with no statistically significant differences. After treatment, LASIK eyes had a mean coma of 0.28 compared with 0.22 for PRK eyes. Mean trefoil was 0.13 for LASIK and 0.13 for PRK. Mean spherical aberration was 0.18 for LASIK and 0.27 for PRK. Mean RMS error was 0.47 for LASIK and 0.45 for PRK.
The safety profile of the two groups was also comparable. No eyes developed epithelial ingrowth. Among the LASIK eyes, 17% lost 1 Snellen line of corrected distance visual acuity; 8% gained 1 line; 8% gained 2 or more lines, and 67% were unchanged. Among the PRK eyes, 9% lost 1 line; 32% gained 1 line, and 59% were unchanged.
All of the eyes re-treated with LASIK and 90% of those re-treated with PRK were within ±0.50 D of emmetropia, Dr. Chen said. The researchers followed up for about 6 to 12 months with most patients, but in a few cases, the follow up was as little as 1 month, she noted.
“So it’s possible that a smaller percentage of the PRK cases achieved emmetropia because visual recovery is slower,” Dr. Chen said.
In any event, this difference was not statistically significant.
Guiding patients
“There isn’t a ton of prospective data out there comparing these two procedures for enhancements, but anecdotally or just talking to other providers, there is a perception that PRK is less predictable,” she said. “At least in our hands, the outcomes appear to be comparable.”
This study may prove useful to refractive surgeons guiding patients in their choice of enhancement procedures, Dr. Chen added.
“Maybe for those who are concerned about the risk of epithelial ingrowth with a LASIK enhancement—but are hesitant to perform PRK surgery over a primary LASIK—this might give them more confidence in choosing PRK as their surgical technique,” she said.