The study was done to compare the thickness and stromal OD evolution of the flap and cap afterFS-LASIK; Visumax and SMILE, respectively, for myopia correction.

A prospective study comprising 78 eyes was performed.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).

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).

The study concluded that LASIK flaps and SMILE caps show a significant postoperative rethickening.