Corneal Ablation Depth Predictions Often Inaccurate in Refractive Surgeries

Corneal ablation depth predictions developed using a corneal topography device are likely to have significant inaccuracies, according to research presented at the American Society of Cataract and Refractive Surgery (ASCRS) 2023 meeting, held in San Diego, CA, May 5 to 8. The study compared preoperative corneal ablation depth predictions with postoperative optical coherence tomography findings in patients who underwent either small incision lenticule extraction (SMILE) or laser in-situ keratomileusis (LASIK).

Researchers incorporated findings from 27 pairs of myopic eyes of 27 patients. All patients were treated with the LASIK procedures in 1 eye and the SMILE procedure in the fellow eye. Central corneal thickness was measured preoperatively and again at 1 month postoperative. The difference between both measurements was calculated to yield the actual corneal ablation depth. Researchers defined the difference between actual and predicted depth as Δ-AD. 

Preoperatively, the central corneal thicknesses averaged 565±31 µm in eyes that underwent LASIK and 566±32 μm in the eyes that were treated with the SMILE procedure (P =.983). In the eyes treated with LASIK, the predicted corneal ablation depth was lower than their actual, postoperative ablation depth measurements (56±23 vs 67±27 μm; P =.002). This differenced yielded a Δ-AD (actual minus predicted) of 11±16 μm. In eyes treated using the SMILE procedure, the actual AD was 66±29 μm, significantly more shallow than the mean predicted AD of 71±28 μm (P =.002), yielding a Δ-AD of -7±13 μm. 

However, researchers reported no significant differences between postoperative spherical refractions in eyes that received LASIK vs eyes that received SMILE (-0.26±0.32 vs -0.48±0.47, P =.096).

These corneal ablation depth findings were significantly less than predicted in patients who underwent the SMILE procedure, and significantly more in those who underwent LASIK, the researchers reported. The eyes treated with SMILE were more myopic postoperatively, although this difference was not statistically significant in this cohort.