Effect of femtosecond laser cutting parameters on the results of small-incision lenticule extraction

Femtosecond laser pulse energy setting can affect postoperative interface light scattering, visual and refractive outcomes, and cap thickness. Purpose: To determine the effect of femtosecond laser cutting parameters on small-incision lenticule extraction (SMILE) results by evaluating cap thickness, interface light scattering, and visual and refractive outcomes. Setting: SynsLaser Clinic, Oslo, Norway. Design: Retrospective. Methods: 58 right eyes treated with SMILE using a programmed cap thickness of 130 μm were divided into 2 groups according to laser settings: Group 1: 165 nJ pulse energy and 4.5 μm spot separation (n = 36); Group 2: 125 nJ pulse energy and 4.2 μm spot separation (n = 22). The cap thickness was measured within the central 5 mm of the horizontal meridian using spectral-domain optical coherence tomography. Postoperative interface light scattering was graded based on the percentage area showing light scattering: 0: no scattering; 1: ≤25%; 2: 26% to 50%; 3: 51% to 75%; and 4: >75%. Results: At 3 months postoperatively, cap thickness was 138.9 ± 6.2 μm in Group 1 and 149.4 ± 3.5 μm in Group 2 (P < .001). Interface scattering was 0.9 ± 1.0 in Group 1 and 0.3 ± 0.9 in Group 2 (P < .05), with no scattering in 33.3% and 86.4% of the eyes, respectively. The postoperative spherical equivalent refraction was −0.03 ± 0.44 diopters (D) in Group 1 and −0.04 ± 0.31 D in Group 2. In Group 1, 83.3% of the eyes were within ± 0.5 D of the desired outcome, and 69.4% achieved an uncorrected distance visual acuity of 20/20 or better. In Group 2, these values were 95.5% and 86.4%, respectively. Conclusions: Lower pulse energy with tighter spots seems to reduce interface light scattering and improve refractive outcomes while also significantly increasing cap thickness.