Association Between Corneal Deformation and Ease of Lenticule Separation From Residual Stroma in Small Incision Lenticule Extraction.

To study the association between corneal deformation (CD) and ease of lenticule separation from the stroma in small incision lenticule extraction. Thirty-six myopic eyes of 36 patients underwent small incision lenticule extraction. Preoperative refraction, intraocular pressure, central corneal thickness, and CD were evaluated with Scheimpflug imaging and air-puff applanation. Fourier transform of CD waveform was also performed. The surgeon also graded the ease of separation of lenticule surfaces from the residual stroma intraoperatively as grades 1 (low effort), 2 (moderate effort), and 3 (high effort). All the procedures were performed by the same surgeon. CD values were concealed from the surgeon. Differences between the grades were assessed with 1-way analysis of variance and analysis of covariance. Mean preoperative refraction, intraocular pressure, central corneal thickness, lenticule thickness, and incision width were similar among the grades (P > 0.05). A total of 5 of the 10 analyzed CD variables were significantly different among the grades. Among them, deformation amplitude (1.20 vs. 1.13 vs. 1.07 mm in the order of increasing grades, P = 0.001), velocity of the corneal apex at the second applanation point (-0.47 vs. -0.43 vs. -0.40 m/s, P = 0.02), peak distance (5.33 vs. 5.25 vs. 5.07 mm, P = 0.006), area under the deformation amplitude (13.40 vs. 12.84 vs. 12.06, P = 0.04), and root mean square of Fourier coefficients (0.12 vs. 0.12 vs. 0.11 mm, P = 0.005) decreased from grades 1 to 3. CD was inversely correlated with the ease of lenticule separation from the residual stroma and may assist in customization of the energy parameters of the laser.