Comparison of the posterior corneal elevation and biomechanics after SMILE and LASEK for myopia: a short- and long-term observation

Manrong Yu,Jinhui Dai,Minjie Chen

doi:10.1007/s00417-018-04227-5

Abstract

PurposeThis study compares the posterior corneal elevation and corneal biomechanics after small incision lenticule extraction (SMILE) and laser-assisted subepithelial keratomileusis (LASEK) for myopia correction in a short- and long-term observation.MethodsThis prospective study included 32 patients in the SMILE group and 32 patients in the LASEK group. Corneal posterior central elevation (PCE), posterior mean elevation (PME), corneal back power (Kb), and anterior chamber depth (ACD) were evaluated with Pentacam, and intraocular pressure (IOP), corneal hysteresis (CH), and corneal resistance factor (CRF) were evaluated with the ORA at pre-operation and 3 months and 3 years post-operation.ResultsThree months post-operatively, CH, CRF, and IOP decreased significantly and central posterior surface shifted backward in both groups (p < 0.05). CH was lower in the LASEK group (p = 0.03) and change of CH and CRF per unit corneal tissue removed (ΔCH/ablation depth (AD) and ΔCRF/AD) was lower in SMILE than in LASEK (p = 0.01, 0.03). Three years post-operatively, the PME shifted more posteriorly in LASEK (p = 0.04), but was stable in SMILE (p = 0.06). Kb flattened and ACD was shallower in both groups (compared to preoperative data, p < 0.001). CH in the LASEK group increased and is comparable to that in the SMILE group at 3 years post-operative.ConclusionBoth SMILE and LASEK can change the posterior surface and corneal biomechanics. SMILE may have less influence on corneal biomechanics than LASEK at an early stage post-operative in terms of per unit corneal tissue removed, but the effect became comparable in a long-term observation.

Highlights

Laser refractive surgery corrects a person’s refractive error by removing a portion of cornea tissue
posterior central elevation (PCE) decreased in both groups (p < 0.001) and even smaller in the Laser-assisted subepithelial keratomileusis (LASEK) group (p = 0.01), while ΔPCE remained no difference between the two groups (p = 0.06), so did posterior mean elevation (PME) and ΔPME
The change of the corneal posterior surface is of great assistance in predicting early corneal ectasia after ablation, as the posterior elevation is independent of the axis and orientation and not affected by tear film [12, 13]

Summary

Introduction

Laser refractive surgery corrects a person’s refractive error by removing a portion of cornea tissue. A study using Pentacam (Oculus, Inc., Wetzlar, Germany) to evaluate the PCE found that there was no significant change after laser surface ablation [4]. As another flapless procedure, small incision lenticule extraction (SMILE) may have biomechanical benefits over FS-LASIK as it leaves the cap overlying the stroma intact. Small incision lenticule extraction (SMILE) may have biomechanical benefits over FS-LASIK as it leaves the cap overlying the stroma intact This hypothesis can be confirmed in that posterior corneal elevation change was greater after FS-LASIK than after SMILE [5]. Another study demonstrated that PCE decreased over time in moderate and high myopia post-SMILE [6]

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