# Comparison of Refractive Outcomes Between Small Lenticule Extraction Using a 500 KHz and a 2 MHz Femtosecond Laser

## TL;DR

This study compares two femtosecond lasers for correcting myopia and finds that the 2 MHz laser offers better accuracy in astigmatism correction.

## Contribution

The study provides a direct comparison of refractive outcomes between 500 KHz and 2 MHz femtosecond lasers in SMILE surgery.

## Key findings

- Both lasers achieved high postoperative visual acuity, with 99% and 97% of eyes reaching 20/20 UDVA.
- The 2 MHz laser showed significantly better correction of astigmatism axis and lower residual myopia.
- The 2 MHz laser had a smaller mean absolute angle of error compared to the 500 KHz laser.

## Abstract

Background/Objectives: The aim of this study was to compare the efficacy of correcting myopia and myopic astigmatism between small incision lenticule extraction (SMILE) surgery performed using VisuMax 500 and that using VisuMax 800. Methods: Patients who underwent myopia correction using either VisuMax 500 (493 eyes of 249 patients) or VisuMax 800 (169 eyes of 85 patients) employing the nomogram of VisuMax 500 were enrolled in this retrospective case–control study. At 2 months after the operation, the percentage of eyes achieving a postoperative uncorrected distance visual acuity (UDVA) of 20/20 and residual refractive error were compared between the two groups. Additionally, the percentage of eyes with refractive astigmatism angle of error within ±15° and the mean absolute angle of error were analyzed. Results: In the VisuMax 500 and 800 groups, 99% and 97% of eyes achieved a postoperative UDVA of 20/20, respectively. Postoperative residual astigmatism was similar between the two groups, but residual myopia was significantly lower in the VisuMax 800 group (−0.09 ± 0.50 cylinder diopters [CD]) compared to the VisuMax 500 group (−0.21 ± 0.49 CD; p-value = 0.005). Additionally, 84% of eyes in the VisuMax 800 group achieved astigmatism correction within ±15° of the intended meridian, significantly outperforming the 71% in the VisuMax 500 group (p-value = 0.002), with a significantly smaller mean absolute angle of error (8.3 ± 12.2° and 14.1 ± 20.1°; p-value < 0.001). Conclusions: Both VisuMax 500 and VisuMax 800 effectively corrected myopia. However, in terms of the accuracy of astigmatism axis correction, VisuMax 800 demonstrated superior precision compared to VisuMax 500. This study may be limited by perceived bias associated with evaluating two platforms from the same manufacturer.