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Evaluation of morphological features: femtosecond-LASIK flap vs. SMILE cap, and the effects on corneal higher-order aberrations

  • Refractive Surgery
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Abstract

Purpose

The aim of this study is to evaluate morphological features of corneal flap/cap and the correlations with corneal higher-order aberrations (HOAs) changes after femtosecond laser in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE).

Methods

This was a retrospective study. Pre- and postoperative (1 and 3 months) corneal HOAs were assessed with Pentacam HR. The corneal flap/cap thickness at 32 points (± 1.5 mm, ± 2 mm, ± 2.5 mm, and ± 3 mm from the corneal vertex on meridian 0°/45°/90°/135°) were measured using anterior segment optical coherence tomography at 3 months postoperatively. Morphological features of corneal flap/cap including predictability (P), uniformity (U), and symmetry (S) were calculated and used for correlation analysis with corneal HOAs changes.

Results

Eighty-six eyes (44 patients) and ninety-six eyes (50 patients) were involved in FS-LASIK and SMILE groups, respectively. Significant thicker corneal flap/cap than the predicted was observed at each measuring point and meridian in both groups (difference > 2.225 μm, the within-subject standard deviation over 6-mm optical zone). There was no statistically significant difference in predictability of corneal flap/cap thickness, while U6 mm (P < .0001), U0 (P < .001), U45 (P = .002), U90 (P < .0001), U135 (P = .004), S6 mm (P < .0001), S0 (P < .001), and S90 (P < .0001) over 6 mm zone were less in SMILE than in FS-LASIK. The changes of corneal tHOAs, Z (3, − 1), Z (3, 1), and SA were significantly correlated with morphological features of corneal flap/cap.

Conclusion

Both FS-LASIK and SMILE had good predictability in flap or cap thickness, while the uniformity and symmetry of SMILE cap were better than FS-LASIK flap. The quality of flap/cap was closely associated with the changes of corneal HOAs.

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Author notes

  1. Xiaoying He and Qin He contributed equally to this work and should be regarded as co-first authors.

Authors and Affiliations

  1. Department of Ophthalmology, Eye Center of the Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, People’s Republic of China

    Xiaoying He, Minjie Yuan, Zhi Fang, Kai Zhang, Tiepei Zhu & Wei Han

  2. Department of Ophthalmology, The First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, People’s Republic of China

    Qin He

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Correspondence to Wei Han.

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Supplementary file1

Supplemental Fig. 1 Predictability (a & b), uniformity (c & d), and symmetry (e & f) over 4- and 6-mm zone in different postoperative corrected distance visual acuity (CDVA) groups (including ≥0.00, -0.08, and -0.18 groups). The P-value is shown when there is significant difference between groups. FS-LASIK = femtosecond Laser in situ keratomileusis, SMILE = small incision lenticule extraction. (PNG 495 kb)

High resolution image (TIF 4693 kb)

Supplementary file2

Supplemental Fig. 2 Total higher-order aberrations for 4 mm (a) and 6 mm (b) analytical zones. The P-value is shown when there is significant difference between preoperative data and postoperative data. FS-LASIK = femtosecond Laser in situ keratomileusis, postop = postoperative, preop = preoperative, SMILE = small incision lenticule extraction, tHOAs = total higher-order aberrations. (PNG 724 kb)

High resolution image (TIF 9368 kb)

Supplementary file3

Supplemental Fig. 3 Individual Zernike terms of the total cornea (a), anterior (b), and posterior (c) corneal surface for 4 mm analytical zones. The P-value is shown when there is significant difference between preoperative data and postoperative data. FS-LASIK = femtosecond Laser in situ keratomileusis, postop = postoperative, preop = preoperative, SMILE = small incision lenticule extraction. (PNG 876 kb)

High resolution image (TIF 7868 kb)

Supplementary file4

Supplemental Fig. 4 Individual Zernike terms of the total cornea (a), anterior (b), and posterior (c) corneal surface for 6 mm analytical zones. The P-value is shown when there is significant difference between preoperative data and postoperative data. FS-LASIK = femtosecond Laser in situ keratomileusis, postop = postoperative, preop = preoperative, SMILE = small incision lenticule extraction. (PNG 877 kb)

Supplementary file5 (DOCX 16 KB)

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He, X., He, Q., Yuan, M. et al. Evaluation of morphological features: femtosecond-LASIK flap vs. SMILE cap, and the effects on corneal higher-order aberrations. Graefes Arch Clin Exp Ophthalmol 260, 3993–4003 (2022). https://doi.org/10.1007/s00417-022-05841-0

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