To investigate the changes in posterior corneal elevation within 6mo after small incision lenticule extraction (SMILE) surgery for myopia and myopic astigmatism in patients with thin corneas.

A prospective study included patients with thin corneas (preoperative thinnest corneal thickness ranging from 480 to 520 μm) who underwent SMILE for myopia or myopic astigmatism. Corneal topography and posterior corneal elevation were assessed using Pentacam HR at three time points: preoperatively, 1mo, and 6mo postoperatively. The measured parameters included thinnest point elevation (PTE), posterior maximal elevation (PME), posterior central elevation (PCE), and 24 additional reference points.

A total of 106 eyes from 106 patients (age range: 18-34) were included in the study. Uncorrected distance visual acuity (UDVA) improved significantly, with a mean logMAR value of -0.07±0.06 at the final follow-up visit. Measurements of posterior corneal elevation showed no significant changes in most points, hemispheres, and meridians at 6mo postoperatively. Notably, only two points, ∆E_2mm-45° and ∆E_2mm-90°, exhibited statistically significant elevation changes: the elevation of ∆E_2mm-45° increased from -2.3±4.99 to -1.0±5.9 μm (P=0.0037), and that of ∆E_2mm-90° increased from -16±7.53 to -15±7.4 μm (P=0.016). However, these changes were within the measurement error range of the Pentacam HR (±5 μm in a 5 mm area).

SMILE surgery is a safe and stable procedure for correcting myopia or myopic astigmatism in patients with thin corneas, as evidenced by the stability of posterior corneal elevation.

To assess early visual outcomes and corneal stability following small incision lenticule extraction (SMILE) in eyes with a pre-planned residual stromal thickness (RST) ranging from 280 to 300 μm.

This retrospective study was designed to evaluate 82 eyes from 82 patients, all of whom had a pre-planned RST of 280 to 300 μm and normal corneal topography prior to undergoing SMILE surgery. The mean preoperative spherical equivalent (SE) was -4.82±1.30 D. A standard follow-up protocol was conducted between 1 to 6mo postoperatively. Visual outcomes were recorded using uncorrected visual acuity (UCVA) and subjective refraction. The curvature of the anterior and posterior corneal surfaces, as well as the posterior elevation at the thinnest point (PTE) were derived from the Pentacam system.

At the final follow-up, the efficacy index was 1.14±0.15, the safety index was 1.20±0.13. The mean preoperative UDVA was 0.78±0.16 logMAR, which improved significantly to -0.07±0.06 logMAR postoperatively (P<0.001). The preoperative mean SE was -4.82±1.30 D, which decreased to -0.14±0.30 D by the last visit. The curvature of the anterior cornea at the flat meridian (AK1) were 42.62±1.02 D preoperatively, 38.56±1.37 D and 38.59±1.39 D at 1 and 6mo after operation, respectively. Corresponding measurements at the steep meridian (AK2) were 43.55±1.14 D preoperatively, 39.18±1.46 D and 39.22±1.50 D at 1 and 6mo after operation, respectively. Both AK1 and AK2 remained stable at 1 and 6-mo postoperative intervals (P=0.126 and 0.082, respectively). There were no observed changes in the curvature of the posterior cornea at the flat meridian or at the steep meridian, or the PTE before and after surgery.

SMILE represents a safe and effective procedure for the correction of myopia and astigmatism in eyes featuring a pre-planned RST ranging from 280 to 300 μm accompanied by normal corneal topography, on the premise of strict control of surgical indications.