Contralateral Eye Comparison Between 2 Cap Thicknesses in Small Incision Lenticule Extraction: 110 Versus 130 μm

PURPOSE To evaluate the posterior corneal elevation (PCE) and biomechanical changes after small incision lenticule extraction (SMILE) at depths of 110 μm and 130 μm. METHODS One hundred sixteen eyes from 58 consecutive patients who underwent SMILE were included in this prospective study. Each patient underwent SMILE in one eye to a depth of 110 μm and in the other eye to a depth of 130 μm. A Scheimpflug camera and Hartmann-Shack WASCA aberrometer were used to assess the PCE and wavefront aberrations, respectively, before SMILE and at 1 and 3 months after surgery. The PCE was analyzed along 3 optical zones (apex and 2 and 4 mm diameters) as a function of the meridian. Dynamic Scheimpflug imaging was used to evaluate the biomechanics preoperatively and at 1 day, 1 month, and 3 months postoperatively. RESULTS No significant difference was found in either vision correction or corneal biomechanics between the 2 groups. In both groups, the PCE became significantly flattened at the apex and at 2 mm annulus 1 month postoperatively, especially for the 110-μm cap group. Three months postoperatively, the 110-μm cap group was still flattened significantly, whereas the displacement at the apex in the 130-μm cap group had disappeared. There was no significant difference in wavefront aberrations between the groups after surgery, except in the vertical coma (P < 0.001). CONCLUSIONS The differences in corneal biomechanics between the 110-μm cap group and 130-μm cap group were small; however, the superficial lenticule might cause displacement of the PCE to be more persistent in one eye than in the other.