Comparison Of Corneal Epithelial Thickness After Small Incision Lenticule Extraction And Femtosecond Laser-assisted In Situ Keratomileusis

Objective To comparatively investigate the corneal epithelial thickness changes for 6 months postoperatively between small incision lenticule extraction(SMILE)and femtosecond laser-assisted in situ keratomileusis(FS-LASIK),study the possible factors related to it and analyse the relationship between the changes in corneal epithelial thickness and corneal aberration.Methods Epithelial thickness was obtained in nine zones(central,superior,superonasal,nasal,inferonasal,inferior,inferotemporal,temporal,superotemporal)with fourier-domain optical coherence tomography across 5-mm diameter centered by pupil center before surgery and at 1 week,1 month,3 and 6 months postoperatively.The observed changes were analysed with the central corneal thickness decrement and ablation rate.Postoperative average epithelial thickness alterations were analysed with corneal total higher orders aberration,spherical aberration and coma.Results Thirty-eight eyes underwent SMILE and 26 eyes underwent FS-LASIK for low-moderate group(manifest refraction sphere equivalent[MRSE]>0.00 to-6.00 diopters[D]),meanwhile 30 eyes underwent SMILE and 24 eyes underwent FS-LASIK for high group(MRSE≥-6.00 to-10.00 D).There was no significant difference in corneal epithelial thickness of nine zones between SMILE and FS-LASIK of low-moderate,high groups respectively(P>0.05).At 1 month,no significant difference in nine zones of corneal epithelial thickness increment between FS-LASIK and SMILE of low-moderate group(P>0.05),a larger increase was observed in superior,superonasal and nasal zones following FS-LASIK than SMILE of high group(P<0.05).At 3 months,a larger increase in corneal epithelial thickness increment was observed in the superior zone following FS-LASIK than SMILE of low-moderate group(P<0.05),the same increase was observed in central,superior,nasal,inferonasal,inferotemporal and superotemporal zones of high group(P<0.05).At 6 months,a larger increase in corneal epithelial thickness increment was observed in the superior and nasal zones following FS-LASIK than SMILE of low-moderate group(P<0.05),the same increase was observed in superior and inferonasal zones of high group(P<0.05).The central corneal thickness decrement of SMILE were much more than FS-LASIK both in low-moderate and high group(P<0.05).The average corneal epithelial thickness increment correlated positively with central corneal thickness decrement and ablation rate at 1 month,3 and 6 months postoperatively(P<0.01).For SMILE,the total higher orders aberration and spherical aberration were less than FS-LASIK at 1 month,3 and 6 months postoperatively(P<0.05),furthermore the corneal aberration increment correlated positively with average corneal epithelial thickness increment(P<0.05).Conclusions For SMILE,the corneal epithelial thickness increment was less than FS-LASIK.SMILE has better uniformity of the corneal epithelial thickness increment at the observed zone which may explain following finding that the postoperative corneal aberration of SMILE was less than FS-LASIK.