Corneal stromal thickness changes after myopic laser corneal refractive surgery

Abstract

Purpose: To evaluate the postoperative behavior of the central corneal stromal thickness after myopic femto-laser-assisted in-situ keratomileusis (LASIK) and small-incision lenticule extraction (SMILE) by using combined anterior segment optical coherence tomography and a Placido disk topographer and to compare the accuracy of both laser machines in predicting the real stromal change.Setting: Vissum Miranza, Alicante, Spain.Study design: Prospective, observational, comparative study.Methods: The VisuMax 500 kHz femtosecond laser (FS) and the Amaris 750 excimer laser were used for the correction of myopia with or without myopic astigmatism. Central and paracentral stromal thicknesses (ST) and 6.0 mm corneal aberrometry were obtained with the MS39 topographer. Laser-predicted stromal consumption was recorded (maximum lenticule thickness for SMILE and central ablation depth for LASIK). Visual and refractive outcomes were also evaluated. Total follow-up was 6 months.Results: 77 LASIK eyes were matched with 77 SMILE eyes. Mean preoperative spherical equivalent (SE) was -3.92 ± 1.67 diopters (D) for LASIK and -4.02 ± 1.63 D for SMILE (P = .356). After LASIK, ST parameters showed significant rethickening between months 1 and 3 (+4.38 μm for central ST; P < .001), remaining stable thereafter. After SMILE, all ST parameters remained stable from month 1. Stromal ablation prediction was higher for SMILE compared with LASIK for all SE ranges, although postoperatively such differences were significant only for ametropias ≤4 D. At 6 months, mean SMILE laser prediction error was -13.21 ± 7.00 μm, whereas LASIK prediction showed better accuracy (+0.92 ± 8.16 μm; P < .001).Conclusions: The accuracy of the Amaris 750 excimer laser in predicting the stromal consumption after LASIK was better than the VisuMax FS laser for SMILE. Although SMILE ST remained stable from month 1, after LASIK, mild stromal rethickening was observed up to the third month.