Accuracy and reproducibility of cap thickness in small incision lenticule extraction

To evaluate the accuracy and reproducibility of cap thickness for small incision lenticule extraction (SMILE) with the VisuMax femtosecond laser (Carl Zeiss Meditec, Inc., Jena, Germany).

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 with intended cap thickness between 80 and 140 μm. True cap thickness at the time of creation was calculated as the addition of the preoperative epithelial thickness and the postoperative stromal component of the flap and mapped for the central 5-mm diameter zone. Cap thickness accuracy was calculated as the difference between the mean and intended cap thickness. Reproducibility was evaluated as the cap thickness standard deviation between eyes. Accuracy and reproducibility of cap thickness were calculated for all eyes and grouped by intended cap thickness. Within-eye variation in cap thickness was calculated as the standard deviation of all data within the central 5-mm diameter zone.

Mean cap thickness accuracy was between -2.3 and 6.5 μm and was -0.7 μm centrally (range: -11 to +14 μm), including all eyes. Cap thickness reproducibility was 6 μm or less for the majority of the central 5-mm diameter zone and was 4.4 μm centrally. Cap thickness accuracy and reproducibility were similar for different intended cap thicknesses. Average within-eye variation in cap thickness was 4.3 μm.

SMILE cap thickness using the VisuMax femtosecond laser was found to be accurate and reproducible across the central 5-mm diameter zone for intended cap thicknesses over the range of 80 to 140 μm.