What was measured

After SMILE, investigators compared predicted lenticule thickness with change in central corneal thickness. This retrospective study included 77 patients, or 146 eyes, measured at one and three months.

Difference from plan Mean deviation was −7.11 µm at one month and −13.37 µm at three months. Negative deviation occurred in 137 of 146 eyes at month three.

Factors linked to deviation

  • Baseline refraction and attempted correction.
  • Corneal curvature, central thickness and posterior elevation.
  • At month three, total higher-order aberrations, spherical aberration and coma.

How to interpret it

Pachymetric change is an indirect estimate of removed tissue, not a direct lenticule measurement. Hydration, epithelial remodeling and measurement error can contribute. Correlation with aberrations also does not prove that a difference of several micrometers causes noticeable symptoms.

The study is mainly a signal for refining nomograms and interpreting pachymetry, topography and wavefront data together. It did not validate a threshold for changing a surgical plan.

Limitations

The study was retrospective, single-center and limited to three months. Both eyes of some patients were included, and multiple correlations increase false-positive risk. SMILE was not compared with LASIK or PRK.