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. 2021 Dec;105(12):1656-1660.
doi: 10.1136/bjophthalmol-2020-316601. Epub 2020 Sep 26.

Evolution of corneal thickness and optical density after laser in situ keratomileusis versus small incision lenticule extraction for myopia correction

Jorge Luis Alio Del Barrio  1   2 , Alberto Parafita-Fernandez  3   4 , Mario Canto-Cerdan  1 , Jorge L Alio  1   2 , Miguel Teus  5   6
Affiliations

Evolution of corneal thickness and optical density after laser in situ keratomileusis versus small incision lenticule extraction for myopia correction

Jorge Luis Alio Del Barrio et al. Br J Ophthalmol. 2021 Dec.

Abstract

Purpose: To compare the thickness and stromal optical density (OD) evolution of the flap and cap after femtosecond (FS-LASIK; Visumax) and small incision lenticule extraction (SMILE), respectively, for myopia correction.

Methods: A prospective study comprising 78 eyes (n=39 per group) was performed. Anterior segment optical coherence tomography (MS39) images were collected at each postoperative visit (1 day, 1 week and 1 and 3 months) and flap/cap thicknesses were measured. Using ImageJ software, three regions were defined to measure OD (in grayscale units: flap/cap stroma, residual stromal bed (RSB) and all stroma (including flap/cap-stroma, surgical interface and RSB).

Results: Mean central thickness significantly increased during the 3-month follow-up in both LASIK (5.43±4.23 μm; p=0.0118) and SMILE (2.76±5.61 μm; p=0.0118), with differences between both techniques statistically significant (p=0.020). All OD values showed a statistically significant reduction during SMILE follow-up: cap 48.96±5.55 versus 44.95±5.41 (p=0.19×10-6), RSB 50.26±7.06 versus 45.42±7.53 (p=0.00005), total stroma 50.34±6.49 versus 45.46±6.96 (p=0.5×10-5) at 1 day and 3 months, respectively, whereas no statistically significant changes were found during LASIK follow-up. No significant differences were observed in OD values between both techniques at any time point, although SMILE showed a tendency for higher OD values than LASIK within the first postoperative month. Visumax presented a tendency for thicker caps than target (11.48±7.85 μm), but not for flaps (2.73±8.93 μm) (p=0.00003).

Conclusions: Both LASIK flaps and SMILE caps show a significant postoperative rethickening. SMILE corneas present higher optical densities than LASIK corneas in the early postoperative period, with a significant decrease thereafter and up to 3 months. These findings correlate with the delayed visual recovery observed after SMILE.

Keywords: Cornea; Treatment Lasers.

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Conflict of interest statement

Competing interests: JLAdB is part of the medical advisory board of CSO. The rest of the authors, their families, their employers and their business associates have no financial or proprietary interest in any product or company associated with any device, instrument or drug mentioned in this article. The rest of the authors have not received any payment as consultants, reviewers or evaluators of any of the devices, instruments or drugs mentioned in this article. The study has been carried out in the framework of the Red Temática de Investigación Cooperativa en Salud (RETICS), reference number RD12/0034/0007 and RD16/0008/0012.

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