Impact of ablation ratio on 5-year postoperative posterior corneal stability after refractive surgery: SMILE and FS-LASIK

Meiyan Li,Peijun Yao,Xue Lin,Jianmin Shang,Dong Yang,Xueyi Zhou,Yu Zhao,Danjuan Yang,Weiming Yang,Xingtao Zhou

doi:10.1186/s40662-020-00218-y

Abstract

BackgroundTo investigate the impact of the ablation ratio on 5-year postoperative posterior corneal stability in myopic eyes after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery.MethodsA prospective, nonrandomized, cohort study: 80 eyes of 43 patients underwent SMILE surgery and 63 eyes of 32 patients underwent FS-LASIK surgery at the EYE & ENT Hospital, Fudan University. Ablation ratio was defined as lenticule thickness (SMILE cases) or ablation depth (FS-LASIK cases) divided by central corneal thickness (CCT). Posterior corneal elevation changes were recorded as posterior central elevation (PCE), posterior corneal surface at thinnest point (PTE) and posterior corneal mean elevation (PME). Patients were followed up at 6-month and 5-year interval to investigate the impact of the ablation ratio on posterior corneal elevation after SMILE and FS-LASIK surgery.ResultsPCE dropped at the 6-month follow-up for both SMILE (decreased by −1.11 ± 2.93 μm, P < 0.05) and FS-LASIK groups (decreased by −0.46 ± 3.72 μm, P < 0.05). PTE also dropped in SMILE (reduced by −2.04 ± 3.02 μm, P < 0.05) and FS-LASIK group (reduced by −1.28 ± 4.21 μm, P < 0.05) at the 6-month follow-up. Stable PCE (elevation change: SMILE −0.28 ± 4.03 μm; FS-LASIK 0.79 ± 4.13 μm, P > 0.05) and PTE (elevation change: SMILE −0.08 ± 4.28 μm; FS-LASIK 1.42 ± 3.85 μm, P > 0.05) for both groups were recorded at the 5-year follow-up compared to the 6-month visit. Ablation ratio was strongly correlated with 5-year postoperative PCE (β = 2.68 ± 1.05, P < 0.01) and PTE (β = 2.35 ± 1.17, P < 0.05). Cut-off value for 5-year postoperative raised PCE and PTE was 27.3 and 27.1%, respectively.ConclusionsAblation ratio was strongly correlated with postoperative posterior corneal elevation in a 5-year follow-up in both SMILE and FS-LASIK groups. PCE and PTE underwent slight backward displacement 6-month postoperatively and remain stable at the 5-year follow-up. Threshold of the ablation ratio for resisting forward displacement of posterior corneal surface was 27.3 and 27.1% for SMILE and FS-LASIK groups, respectively.

Highlights

To investigate the impact of the ablation ratio on 5-year postoperative posterior corneal stability in myopic eyes after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery
Small incision lenticule extraction (SMILE) surgery is a flap-free, small-incision refractive operation introduced in 2011 by Sekundo and Shah in correcting myopia with stable visual outcomes in both the short- and long-term and is believed with better post-operative corneal stability compared with femtosecond laser-assisted in situ keratomileusis (FS-LASIK) [1,2,3,4]
This study aims to record a 5-year follow-up of posterior corneal elevation change and reveal the correlation between an individualized metric “ablation ratio” and postoperative posterior corneal stability

Summary

Introduction

To investigate the impact of the ablation ratio on 5-year postoperative posterior corneal stability in myopic eyes after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery. Small incision lenticule extraction (SMILE) surgery is a flap-free, small-incision refractive operation introduced in 2011 by Sekundo and Shah in correcting myopia with stable visual outcomes in both the short- and long-term and is believed with better post-operative corneal stability compared with femtosecond laser-assisted in situ keratomileusis (FS-LASIK) [1,2,3,4]. Previous studies reported that risk factors of ectasia post LASIK and photorefractive keratectomy (PRK) surgeries include residual bed thickness (RBT), preoperative corneal thickness, abnormal corneal topography, age and high myopia state [10]. Risk factors of forward posterior corneal displacement post SMILE and FS-LASIK surgery in the long term remain unknown

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