Accuracy of lower and upper SMILE lenticule interface depth

Session Details

Session Title: SMILE for Myopia II

Session Date/Time: Wednesday 17/09/2014 | 08:00-09:30

Paper Time: 08:54

Venue: Capital Hall B

First Author: : K.Pradhan NEPAL

Co Author(s): :    D. Reinstein   G. Carp   T. Archer   M. Gobbe     

Abstract Details

Purpose:

To evaluate the accuracy and reproducibility of cap thickness and lenticule thickness for small incision lenticule extraction (SMILE) with the VisuMax femtosecond laser.

Setting:

London Vision Clinic, London, UK

Methods:

Artemis very high-frequency digital ultrasound 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. 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. 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.

Results:

Including all eyes, mean cap thickness accuracy was between -2.3 and 6.5 µm and was -0.7 µm centrally (range: -11 to +14 µm). Cap thickness reproducibility was <6 µm 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. The mean maximum myopic meridian treated was -7.81±2.33 D (range -2.25 to -12.50 D). On average, the VisuMax readout lenticule depth was 8.2±8.0 µm (range: -8 to +29 µm) thicker than the Artemis measured stromal change (p<0.001). The R2 of 0.868 for the SMILE group was higher than 0.738 for the LASIK group (p=0.015).

Conclusions:

SMILE cap thickness using the VisuMax femtosecond laser was found to be highly accurate and very reproducible across the central 5 mm diameter zone for intended cap thicknesses over the range 80-140 µm. The accuracy of SMILE lenticule thickness was found to be comparable, if not superior, to that of excimer laser ablation. The 8 µm difference between intended and readout lenticule thickness can be partly explained by alignment errors between pre and postoperative scans. However, this appears to show some biomechanical changes occur after SMILE.

Financial Interest:

One or more of the authors... has significant investment interest in a company producing, developing or supplying product or procedure presented, One or more of the authors... receives consulting fees, retainer, or contract payments from a company producing, developing or supplying the product or procedure presented