Lenticule Thickness Readout for Small Incision Lenticule Extraction Compared to Artemis Three-Dimensional Very High-Frequency Digital Ultrasound Stromal Measurements

PURPOSE: To evaluate the accuracy of the lenticule thickness readout for small incision lenticule extraction (SMILE) with the VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany). METHODS: Artemis very high-frequency digital ultrasound (ArcScan, Inc., Morrison, CO) measurements were obtained before and 3 months after SMILE in 70 eyes of 37 patients. The Artemis measured lenticule thickness was calculated as the maximum difference in stromal thickness before and after treatment. Comparative statistics and linear regression analysis were performed between the VisuMax readout lenticule thickness and Artemis measured maximum stromal change. Central epithelial thickness was measured and a similar analysis was performed using corneal thickness. Variability of the data were compared to ablation depths for a matched group of eyes from a previously published LASIK population treated with the MEL80 excimer laser (Carl Zeiss Meditec). RESULTS: The mean maximum myopic meridian treated was -7.81 +/- 2.33 diopters (range: -2.25 to -12.50 diopters). On average, the VisuMax readout lenticule depth was 8.2 +/- 8.0 mu m thicker (range: -8 to + 29 mu m) than the Artemis measured stromal change (P <.001). On average, central epithelial thickness was 15.0 +/- 5.2 mu m thicker (range: 5 to 30 mu m) after the procedure. The VisuMax readout lenticule thickness was 23.2 +/- 10.9 mu m thicker (range: + 5 to + 49 mu m) than the Artemis measured corneal thickness change. The R-2 of 0.868 for the SMILE group was higher than 0.738 for the LASIK group (P=.015). CONCLUSIONS: The accuracy of SMILE lenticule thickness was found to be higher than actual measured stromal thickness change; however, predictability for SMILE lenticule thickness appeared higher than predictability for excimer laser ablation depth. The VisuMax readout lenticule depth was found to be 8 mu m thicker than the achieved stromal change. This can be partly explained by alignment errors between preoperative and postoperative scans. However, this appears to show some biomechanical changes occur after SMILE.