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A COMPARISON study of leading LASIK systems demonstrates differences between wavefront aberrometers with respect to how and what they measure, which may reflect differences in clinical outcomes. Researchers at the Magill Research Center, Storm Eye Institute are conducting a prospective, randomized clinical trial of several available systems for conventional and customized LASIK. Helga P. Sandoval, MD presented the design and early findings from the study at the XXI Congress of the European Society of Cataract and Refractive Surgeons. The investigation will involve a total of 120 eyes of 60 patients who will undergo conventional LASIK with the LADARVision (Alcon), Technolas 217z (Bausch & Lomb), or the S4 (VISX) systems, or custom ablation with CustomCornea (Alcon), CustomVue (VISX), or Zyoptix (Bausch & Lomb) systems. The LADARWave (Alcon), WaveScan (VISX), and Zywave (Bausch & Lomb) aberrometers are being used to measure higher order aberrations (HOAs) in all patients pre- and postoperatively. Baseline and follow-up assessments also include contrast sensitivity testing (Optec 3500, Stereo Optical) at spatial frequencies of 1, 3, 6, 12, and 18 cycles/degree, and determination of subjective vision quality with a questionnaire. The preliminary results presented at the ESCRS included 16 patients who reached the one-month postoperative visit. Two of those patients had conventional treatment with the Visx S4, three with the Alcon LADARVision lasers and one with the Bausch & Lomb Technolas 217A laser. Ten patents had custom ablation, half with the Visx CustomVue system and or half with the Alcon CustomCornea system. Dr Sandoval reported an apparent benefit for custom versus conventional treatment when comparing the two Alcon systems. Patients receiving the custom ablation procedure had significantly fewer HOAs at the one month follow-up.
She also noted improvements in contrast sensitivity and driving vision following the custom treatment relative to conventional LASIK. So far, use of CustomVue has not been associated with a benefit for minimizing induction of HOAs relative to conventional LASIK with the S4, although that may coincide with the finding that conventional LASIK with the S4 laser seems to induce less HOA than conventional treatment with the LADARVision system. "There has been a paradigm shift in evaluating outcomes of refractive surgery to consider not just attainment of 20/20 or better Snellen acuity, but also the quality of vision. Therefore, it is important to understand the effects of our treatments on lower and higher order aberrations and aim to reduce or at least avoid inducing higher-order aberrations. This study is designed to evaluate the potential benefits of custom ablation for achieving those goals and to compare different lasers. However, we want to emphasize that these findings are just preliminary and from a small sample size, and it remains to be seen if they are maintained or change as more patients are enrolled and our follow-up continues," said Dr. Sandoval. The preliminary comparisons of measurement of HOA RMS values presented were based on data from the 32 eyes that have completed one month. Data for all three instruments were standardized for a 6.0 mm pupil size. At baseline, mean values were lowest with the WaveScan and highest with the Zywave, and while all systems demonstrated an increase in both mean total HOA and mean spherical aberration RMS after surgery (Figure 1), there were also differences between devices in the amount of change measured. "With the WaveScan, aberrations are measured without pupil dilation, and since pupil size is not 6.0 mm in all eyes, this reduces the sample size for comparison," Dr. Sandoval observed. Comparison of total HOA measured with the LADARWave aberrometer showed that the ten eyes undergoing CustomCornea treatment and six undergoing conventional LADARVision LASIK had comparable levels of mean total HOA RMS at baseline. However, total HOA RMS increased almost 100% after conventional LASIK versus only 10% following CustomCornea treatment. (Figure 2). Measurements performed with the WaveScan aberrometer in a smaller cohort of eyes yielded different results. Comparing data from six eyes treated with CustomCornea and four eyes treated with conventional LADARVision LASIK showed that the mean total HOA was lower in the conventional LASIK group at baseline and increased more than 100%. By comparison, WaveScan aberrometry indicated that the mean total HOA in the CustomCornea group decreased slightly from baseline. (Figure 3). The researchers also measured total HOAs before and one month after LASIK in four eyes undergoing conventional LASIK with the Visx S4 and seven eyes undergoing custom ablation with the WaveScan aberrometer. At baseline, mean total HOA was about 0.1-microns lower in the conventional ablation group, 0.3 vs. 0.4-microns. But at one month total HOAs were essentially unchanged in both groups. Using the LADARWave aberrometer to measure total HOA in the same patients showed baseline values were the same as those measured with the WaveScan. However, the LADARWave results indicated both treatments increased total HOA with the increase being greater with conventional LASIK. Contrast sensitivity studies performed with low illumination and no glare showed CustomCornea treatment was associated with an improvement of at least 25% at all spatial frequencies tested, while contrast sensitivity was generally unchanged after conventional LADARVision treatment or following CustomVue or conventional treatment with the VISX S4. Consequently, the preliminary comparison of the effects of the Alcon and VISX customised ablation treatments showed a slight difference between CustomCornea and CustomVue. When testing was performed under low illumination with a glare source, contrast sensitivity was still improved by about 25% at all spatial frequencies after CustomCornea treatment whereas it was relatively unchanged or worsened after conventional LADARVision and CustomVue treatment. Consistent with those findings, results from the questionnaire responses showed a significant benefit for improved driving vision after CustomCornea treatment compared with conventional LADARVision, which was associated with no change in driving vision score. (Figure 4). Glare also improved after CustomCornea treatment, while it worsened after conventional LADARVision treatment. The difference between treatments showed only a trend to statistical significance. While these findings are some of the first to compare LASIK systems head to head, the results are preliminary and part of an ongoing study. More comprehensive results will be presented as the study proceeds. Helga P. Sandoval, MD Magill Research Center for Vision Correction Storm Eye Institute, Medical University of South Carolina, Charleston SC sandoval@musc.edu |
