AIM: To compare the changes in corneal densitometry after small incision lenticule extraction(SMILE)and femtosecond laser in situ keratomileusis(FS-LASIK)and investigate the effect of corneal interface haze on vision after SMILE.

METHODS: Prospective cohort study. A total of 93 patients(186 eyes)who were scheduled to undergo refractive surgery at the Ophthalmic Refractive Surgery Center of the Affiliated Hospital of Nantong University from May 2020 to October 2021 were included in the study, and there were 48 patients(96 eyes)in the SMILE group and 45 patients(90 eyes)in the FS-LASIK group. The changes in corneal densitometry, spherical equivalent(SE), and uncorrected visual acuity(UCVA)were observed and compared between the two groups before and at 1d, 1wk, 1, 3 and 6mo after surgery.

RESULTS: The 93 patients all successfully completed the surgery, and there were no related complications during and after the surgery, and there were no lost cases. The UCVA of FS-LASIK group was 0.044±0.064 and -0.001±0.065 respectively at 1d and 1wk after surgery, which was better than that of SMILE group(0.102±0.077 and 0.023±0.064; all P<0.05). There was no statistical difference in the SE between the two groups at the postoperative follow-ups(P>0.05). The corneal densitometry values at 0-2 and 2-6 mm from corneal vertex and total corneal densitometry at 1d postoperatively in the FS-LASIK group were 18.0(17.5, 18.6), 16.2(15.6, 16.7)and 16.7(16.1, 17.3), which were lower than those of SMILE group \〖18.6(18.1, 19.3), 16.8(16.4, 17.4), 17.2(16.6, 17.8)\〗(all P<0.05); The corneal densitometry values at 0-2 and 2-6 mm from corneal vertex and total corneal densitometry at 1wk postoperatively in the FS-LASIK group were 17.2(16.7, 17.6), 15.5(15.0, 15.9)and 15.9(15.3, 16.7), which were lower than those of SMILE group \〖17.6(17.1, 18.3), 16.0(15.6, 16.5), 16.6(15.9, 17.1)\〗(all P<0.05).

CONCLUSIONS: The transient interface haze after SMILE is responsible for the early higher corneal densitometry than FS-LASIK. The presence of interface haze is probably a factor for the quality of vision.