Comparison of corneal biomechanics after myopic small-incision lenticule extraction compared to LASIK: an ex vivo study

Abstract

PurposeTo investigate ex vivo potentially different corneal biomechanical properties after small-incision lenticule extraction (SMILE) versus LASIK for myopic correction.MethodsThirty human donor corneas were subjected to either myopic SMILE or femtosecond laser-assisted LASIK. Donor corneas were assigned to six investigative groups: Group A, −3.00 D (diopters) SMILE; Group B, −8.00 D SMILE; Group C, −3.00 D LASIK; and Group D, −8.00 D LASIK. Additionally, two control groups were formed: Group E, SMILE and Group F, LASIK. All groups consisted of five corneas, randomly allocated. The corneas in the control groups were subjected to the corresponding femtosecond-laser lamellar cuts but not to tissue removal. Evaluation of biomechanical tensile strength was conducted by biaxial force application. Primary outcome measures were stress at 10% and 15% strain, and Young’s modulus at 10% and 15% strain.ResultsIn SMILE, the average relative difference (Δ) of the four outcome measures was −34.46% for −3.00 D correction versus control Group E and −49.34% for −8.00 D correction versus control Group E. In LASIK, average Δ was −24.88% for −3.00 D correction versus control, and −52.73% for −8.00 D correction versus control. All these differences were statistically significant; SMILE compared to LASIK for the same myopic correction appears to result in more biomechanical reduction for −3.00 D corrections by −26%, while a nonstatistically significant difference was noted in −8.00 D corrections.ConclusionBoth SMILE and LASIK procedures do substantially alter corneal biomechanical properties, and the degree of tensile strength reduction is statistically significantly correlated to the extent of myopic correction. Additionally, SMILE procedure seems to result in more tensile strength reduction in lower myopic corrections compared to LASIK, and similar tensile strength reduction to LASIK in higher myopic corrections when compared to LASIK.

Application of Decellularized Porcine Sclera in Repairing Corneal Perforations and Lamellar Injuries

“…Biaxial stress–strain measurements were superior to corneal strip tensiometry. − Previous studies have also shown that sclera exhibited a stress-hardening response when subjected to gradual tensile loads, demonstrating nonlinear characteristics. , The present study also indicated that the sclera is elastic and exhibits an obvious hysteresis phenomenon. This further indicates that the whole sclera exhibits major mechanical anisotropy.…”

Survival analysis of myopic regression after small incision lenticule extraction and femtosecond laser-assisted laser in situ keratomileusis for low to moderate myopia

“…The similarity of the biomechanical effects after SMILE and FS-LASIK might sustain this parallel occurrence of myopic regression. Kanellopoulos [ 18 ] showed that the SMILE procedure reduces the tensile strength in lower myopic corrections while retaining a similar tensile strength in higher myopic correction compared with LASIK. Magallanes et al [ 19 ] proved that the significant loss of corneal strength following large myopic corrections might lead to refractive regression.…”

Changes in Corneal Morphology and Biomechanics in Cases of Small Incision Lenticule Extraction with Prophylactic Accelerated Collagen Cross-Linking

“…Although this scoring system was developed for LASIK, it was also applied here given that a modified version does not yet exist for SMILE. Moreover, we believed that the risk factors for ectasia should be applied uniformly to both procedures although the biomechanical superiority of SMILE over LASIK is attributed to the stromal tissue removal at the deeper layers [ 30 ]. Hence, the results of the Randleman scoring system may be used as a supplementary reference for the ectasia risk after SMILE, and moderate-to-high risk patients should be treated with caution.…”