The Achieved Central Corneal Stromal Thickness Reduction Less Than the Planned in SMILE: A Retrospective Study

To evaluate the differences between the planned and achieved central corneal thickness (CT) reduction after small incision lenticule extraction (SMILE).

This retrospective study included 426 eyes (426 patients) treated with SMILE. The central CT and corneal epithelial thickness (CET) were measured using the RTVue XR 100 optical coherence tomography device preoperatively and more than 6 months postoperatively. The central corneal stromal thickness (CST) was obtained by central (CT - CET). The planned and achieved thickness reductions were compared and the difference was defined as the planned-achieved difference (PAD).

The achieved central CT reduction was 75.80 ± 16.24 µm, which was smaller than the planned (100.20 ± 20.46 µm, P < 0.001). Similarly, the central CST reduction, which excluded the influence of corneal epithelial proliferation, was overestimated by 19.91 ± 6.53 µm. Furthermore, the PAD of central CST reduction showed a positive correlation with preoperative manifest refraction spherical equivalent (MRSE) and with planned central CST reduction (R² = 0.906, P < .001). However, the PAD of central CST reduction did not influence postoperative visual acuity. When removing the nomogram adjustment, the overall overestimation of central CST reduction was narrowed to 12.09 ± 8.09 µm.

Over 6 months postoperatively, the achieved central CT reduction after SMILE was less than the planned reduction. The difference was due to the overestimation of CST reduction, rather than corneal epithelial proliferation. Moreover, there was a greater disparity between the planned and achieved central CST reduction with higher MRSE, attesting to the safety of SMILE for patients with relatively high MRSE. [.