Cap Lenticular Adhesion During Small Incision Lenticular Extraction Surgery: Causative Factors and Outcomes

PURPOSE: To study the factors causing cap lenticular adhesion (CLA), a rare complication of small incision lenticule extraction (SMILE) surgery, and its effect on surgical outcomes. DESIGN: A prospective, observational, cross-sectional study involving 550 eyes of 285 subjects. METHODS: SMILE was performed using the VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany) with a minimum of 3 months follow-up. Preoperative visual quality assessment, measurement of corneal biomechanics, and Bowman membrane imaging were performed. Based on the mean refractive spherical equivalent (MRSE), subjects were classified into mild, moderate, and high myopes. Causes of CLA and postoperative outcomes were evaluated. RESULTS: CLA was seen in 1.8% of patients, in whom the median preoperative MRSE was -1.5 (-2.75 to -1.38), deformation amplitude was 1.13 (1.10 to 1.21), and lenticular thickness was 46.2 (39.9 to 54.31). They had microdistortions in the Bowman layer and poor quality of vision. A median Strehl ratio of 0.08 (0.07 to 0.11) and modulation transfer function of 9.88 (8.98 to 13.34) were noted on the first day after surgery, which gradually improved to 0.17 (0.15 to 0.18) and 33.90 (27.27 to 38.94), respectively. On observing the surgical videos, a distinct shining reflection, "the shimmer sign," was seen around the dissector in patients with CLA when the posterior plane was dissected before the anterior. CONCLUSIONS: Cap lenticular adhesion was associated with a low preoperative MRSE and thin lenticules. The shimmer sign serves as an indicator for identification of the correct plane of dissection.