Risk of raised posterior corneal elevation associated with cornea and sublayer thicknesses 5 years post keratorefractive lenticule extraction

Objective To evaluate the risk of posterior corneal forward shift associated with central corneal thickness (CCT), residual bed thickness (RBT), cap thickness and lenticule thickness after keratorefractive lenticule extraction (KLEx) over 5-year follow-up period, providing evidence for preoperative assessment to improve safety. Methods and analysis Retrospective cohort study that included patients (n=165) who underwent KLEx surgery. Changes in posterior central elevation (PCE) were measured at 3 months, 6 months, 1 year and 5 years post-KLEx. Elevation measurements were obtained at 27 prespecified points and separated into central, peripheral zones and nasal, temporal, superior and inferior quadrants for analysis. Risk ratios for raised PCE were compared across thickness groups. Results Overall, posterior corneas exhibited a slight forward shift over the early postoperative period and ultimately returned to their original state within 5 years. Central cornea shifted backward, whereas peripheral cornea shifted forward at each follow-up examination. Preoperative CCT had a significant effect on PCE (p<0.05), whereas cap thickness did not (p>0.05). RBT had a weakly negative correlation with PCE (β=−0.12, p=0.01), whereas lenticule thickness was positively correlated (β=0.02, p=0.03). Each 10 µm loss of CCT resulted in up to 3.5 µm forward shift of the PCE (p<0.001). CCT <500 µm increased the risk ratio of postoperatively raised PCE by 2.9–5.6 (p<0.05). Conclusions Intended sublayer thicknesses were strongly correlated with posterior corneal shift post-KLEx. Although long-term PCE remained stable, a preoperative CCT <500 µm was associated with greater forward displacement of the posterior cornea and a higher likelihood of elevated tomographic parameters, suggesting a need for cautious preoperative assessment.