Quantitative Evaluation of Microdistortions in Bowman's Layer and Corneal Deformation after Small Incision Lenticule Extraction

Purpose: To quantitatively evaluate microdistortions in Bowman's layer and change in corneal stiffness after small incision lenticule extraction (SMILE). Methods: This was a prospective, longitudinal, and interventional study. Thirty eyes of 30 patients were screened preoperatively and underwent SMILE for treatment of myopia with astigmatism. Visual acuity, refraction, optical coherence tomography (OCT, Bioptigen, Inc., Morrisville, NC) imaging of the layer and air-puff applanation (Corvis-ST, OCULUS Optikgerate Gmbh, Germany) was performed before and after surgery (1 day, 1 week, and 1 month). The Bowman's Roughness Index (BRI) was defined as the enclosed area between the actual and an ideal smooth layer to quantify the microdistortions. A viscoelastic model was used to quantify the change in corneal stiffness using applanation. Results: Uncorrected distance visual acuity improved (P < 0.001) and refractive error decreased (P < 0.0001) after SMILE. BRI increased from preoperative levels (1.81 X 10-3 mm(2)) to 1 week (3.14 X 10(-3) mm(2)) after SMILE (P < 0.05) and then decreased up to a month (2.43 X 10-3 mm 2; P < 0.05). Increase in the magnitude of the index correlated positively with refractive error (P = 0.02). However, corneal stiffness reduced after SMILE (105.86 +/- 1.4 N/m versus 97.97 +/- 1.21 N/m at 1 month, P = 0.001). The decrease in corneal stiffness did not correlate with refractive error (P = 0.61). Conclusions: BRI correlated positively the magnitude of refractive error. However, decrease in corneal stiffness, assessed by air-puff applanation, may not be related to microdistortions after SMILE.