Posterior corneal elevation after small incision lenticule extraction (SMILE) in eyes of different myopia severity

To investigate the changes in posterior corneal elevation after small incision lenticule extraction (SMILE) surgery in eyes of different myopia severity.

A total of 141 eyes of 86 patients were recruited and followed at 1 month, 3 months, 6 months, and 12 months after SMILE surgery. The eyes were divided into four groups according to the spherical equivalent (SE): low myopia (LM, -3.00 D≤SE<-0.50 D, 35 eyes), moderate myopia (MM, -6.00 D≤SE<-3.00 D, 54 eyes) and high myopia (HM, -10.00 D≤SE<-6.00 D, 52 eyes). Posterior corneal elevation was measured by Pentacam HR. Posterior corneal apex elevation (PCAE), posterior maximum elevation (PME), and posterior elevation at the thinnest point of the cornea (TPC) in the central 4-mm area were recorded and compared among different examination time points in the same group or among different groups at the same time point.

Uncorrected distance visual acuity (UDVA) at 12 months was 20/20 or better in 100.00 % of eyes in LM group, 100.00 % in MM group and 96.15 % in HM group (P > 0.05). There were significant reductions of post-operative PCAE compared to baseline in the LM group (P = 0.038) and HM group (P<0.001), and the reduction was marginally significant in the MM group (P = 0.076). No statistically significant changes in PME were observed after SMILE surgery in the three groups (all P > 0.05). TPC was significantly decreased after the surgery in the MM group (P = 0.022) and the HM group (P<0.001), and was marginally significantly decreased in the LM group (P = 0.063). There was no significant difference in PCAE and PME among the three groups at baseline or any postoperative timepoint (all P > 0.05). TPC was significantly different among the three groups at 3 months, 6 months and 12 months (all P < 0.05), but not at baseline (P = 0.066) or 1 month (P = 0.080).

In the first year after SMILE surgery, PCAE was decreased in both LM and HM eyes, and TPC were decreased in MM and HM eyes, but PME was stable after the surgery.