Corneal biomechanical characteristics following small incision lenticule extraction for myopia and astigmatism with 3 different cap thicknesses

Abstract

Background The design of cap thickness for small incision lenticule extraction (SMILE) plays a role in post-laser vision correction (post-LVC) corneal biomechanics. This study aimed to compare the corneal biomechanical characteristics following SMILE with different cap thicknesses of 110 μm, 120 μm, and 130 μm for myopia and myopic astigmatism correction. Methods Seventy-five patients (146 eyes) who underwent SMILE with designed cap thickness of 110 μm, 120 μm, and 130 μm were recruited at the Eye Center of Beijing Tongren Hospital between August 2020 and November 2021. Visual acuity, refraction, and corneal biomechanical parameters were measured preoperatively, 1 week and 1, 3, 6 months postoperatively. One-way analysis of variances (ANOVA) with Bonferroni correction or Kruskal-Wallis test was performed to compare the parameters among different groups. Repeated-measures analysis of variance with Bonferroni correction or Friedman test was applied for comparing the parameters within different follow-up times. Results Uncorrected distance visual acuity of 110-μm group was better only at 1-week and 1-month postoperatively (P = 0.012, 0.037). There were no significant differences in spherical equivalent, nor in Corvis biomechanical index-laser vision correction (CBI-LVC). All the parameters reached stability at 3-month postoperatively. Integrated radius (IR) and deformation amplitude ratio 2 mm (DA ratio 2 mm) in 120-μm and 130-μm groups were higher than 110-μm group at 1-month postoperatively (P = 0.019, 0.002). So was Ambrósio relational thickness (ARTh) at 6-month postoperatively (P = 0.011). Stiffness parameter at applanation A1 (SP-A1), stress-strain index (SSI), biomechanically corrected intraocular pressure (bIOP) and central corneal thickness (CCT) were highest in 130-μm group, followed by 120-μm group, then 110-μm group at 3-month (P<0.001, P = 0.030, P = 0.027, P = 0.008) and 6-month (P<0.001, P = 0.002, P = 0.0023, P = 0.001) postoperatively. Conclusions The corneal stiffness following SMILE was greatest with 130-μm cap, followed by 120-μm cap, then 110-μm cap. 130-μm cap might have advantages in terms of corneal biomechanics and retreatment option. The SMILE-designed protocol should be customized in practice.

Corneal subbasal nerve plexus reinnervation and stromal cell morphology with different cap thicknesses in small incision lenticule extraction

“…Other studies [ 30 ] claimed that a thicker corneal cap may not correct refractive errors effectively because of less flattening of the anterior curvature through their ex vivo experiments. This is partly consistent with our results of refractive outcomes and another previous study [ 15 ]. Although the UDVA was slightly better in the 110 μm group, especially in the early period after surgery, we should note that the UDVA result was easily affected by the examination environment subjectively, and there was no statistically significant difference in MRSE.…”

“…Third, it is believed that different corneal cap thicknesses may affect postoperative corneal biomechanics. Our previous study showed that the 130 μm group had the most stable biomechanics [ 15 ]. This finding is consistent with the corneal biomechanical characteristics anatomically and theoretically.…”

“…The optical zone diameter was 6.5 mm, cap diameter was 7.6 mm and the transition zone diameter was set as 0.1 mm. The surgical procedures and the management of the perioperative period were carried out following standard clinical protocols [ 15 ].…”

Comparison of the accuracy of 9 intraocular lens power calculation formulas after SMILE in Chinese myopic eyes

“…Fang et al found no in uence of different ap thicknesses on CBI after SMILE, while another study showed signi cant differences in CBI and stiffness parameters at rst applanation between 110 µm cap and 145 µm cap 38 . Lv et al also found differences in CBI between 110 µm, 120 µm, and 130 µm caps 39 . Several studies have shown that the application of historical data improves calculation accuracy in patients after LASIK 25,40 , but the limitation lies in the di culty of obtaining such data due to long intervals between cataract surgery and refractive surgery.…”

Corneal biomechanical changes following small incision lenticule extraction (SMILE) with variable cap thickness in management of mild to moderate myopia

“…This residual stromal bed thickness difference explains the variation regarding the DA ratio as well as integrated inverse radius changes between both groups [21] . In contrast, Lv et al (2023) conducted a prospective comparative study to examine the corneal biomechanical characteristics following SMILE for myopia as well as astigmatism, utilizing three various cap thicknesses (110, 120, and 130 μm). The corneal biomechanical parameters went through assessment before the surgery as well as at 1 week, 1, 3, and 6 months postoperatively.…”