Vector Analysis of Myopic Astigmatism Comparing Wavefront-Guided and Wavefront-Optimized Excimer Platforms for Photorefractive Keratectomy
Purpose
To compare the astigmatic outcomes of photorefractive keratectomy (PRK) with a wavefront-guided (WFG) and a wavefront-optimized (WFO) excimer laser.
Methods
70 eyes of 35 patients underwent PRK for compound myopic astigmatism. One eye underwent WFG-PRK with the AMO VISX Star S4IR platform, and the fellow eye underwent WFO-PRK with the Alcon Wavelight Allegretto Eye-Q 400 laser platform. Preoperative and postoperative assessments were performed and included manifest refraction, vector analysis, topographic analysis, and wavefront aberrometry analysis. Eyes were stratified for subgroup analysis based on preoperative manifest astigmatism: 0.25-1, 1.25-2.25, and 2.5-3.5 diopters. Statistics were calculated using t-tests.
Results
Preoperatively, mean spherical equivalent (SE) was -4.7±2.3 vs -4.5±2.3 diopters(D) (p=0.77), and mean cylindrical error(CE) was 0.9±0.7 vs 0.7±0.7D (p=0.29) in the VISX-WFG and Alcon-WFO groups, respectively. At postoperative month 12, mean SE was -0.2 ±0.4 vs -0.2±0.4D (p=0.85), and mean CE was 0.2±0.2 vs 0.2±0.2D (p=0.53), respectively. Alpins vector analyses for the VISX-WFG and Alcon-WFO groups, respectively, were: surgically-induced-astigmatism (0.9±0.7 vs 0.8±0.7D, p=0.43), error-magnitude (0.1±0.2 vs 0.1±0.2D, p=0.98), error-angle (11±32° vs 27±51°, p=0.02), [BT1] correction-index (1±0.4 vs 1±0.4, p=0.85), success-index (0.3±0.5 vs 0.4±0.5, p=0.3), and flattening-index (1±0.7 vs 0.8±0.8, p=0.29). Subgroup analysis by preoperative astigmatism showed no significant differences.
Conclusion
Minimal difference in outcomes between VISX-WFG and Alcon-WFO platforms based on objective Alpins analysis of astigmatism.