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.