Comparative Assessment Of Cap Geometry In Keratorefractive Lenticule Extraction Using Visumax 500 And Visumax 800 And Its Association With Clinical Outcomes

To quantitatively compare corneal cap thickness accuracy and uniformity after keratorefractive lenticule extraction (KLEX) using the VisuMax 500 (500 kHz) and the VisuMax 800 (2,000 kHz) femtosecond lasers.

Onnuri Smile Eye Clinic, Seoul, South Korea

This retrospective comparative study analyzed the right eyes of patients who underwent KLEX using the VisuMax 500 or VisuMax 800 systems. Cap thickness was measured at nine predefined horizontal points across the 6-mm optical zone using anterior-segment optical coherence tomography at 1 month postoperatively. Cap accuracy was defined as the difference between achieved and intended thickness, and cap uniformity was quantified as the intra-subject standard deviation (SD) across the central 2-mm zone (central SD) and the full 6-mm zone (total SD). Correlations between cap uniformity and clinical outcomes were also assessed.

Both groups did not show a significant difference in cap accuracy and demonstrated minimal central deviation from the intended thickness with increasing discrepancy toward the periphery. However, the VisuMax 800 group exhibited significantly greater central cap uniformity. The central SD for the VisuMax 800 group was 2.5 ± 1.2 µm compared to 3.5 ± 1.6 µm for the VisuMax 500 group (p = 0.010). While there were no significant differences in clinical outcomes between the groups, in the VisuMax 800 group, total SD correlated significantly with postoperative sphere, SE, and changes in SA, and central SD correlated with changes in other higher-order aberrations. No significant correlations were observed for the VisuMax 500 group.

Both femtosecond laser platforms exhibited comparable cap accuracy, yet the VisuMax 800 produced significantly better cap uniformity. In the VisuMax 800 group, greater cap uniformity was associated with distinct patterns of postoperative optical and refractive outcomes, suggesting that the higher-frequency platform provides more consistent corneal modification during lenticule creation.