Intraoperative OCT-Based Stromal Topography in Phototherapeutic Keratectomy

Objectives: This study aims to investigate whether anterior corneal curvature can be reliably measured by combined Placido–optical coherence tomography (OCT) during phototherapeutic keratectomy (PTK) despite intraoperative stromal swelling, and to quantify the immediate smoothing effect of PTK on anterior stromal higher-order aberrations (HOAs). Methods: In this prospective study, 20 eyes with epithelial basement membrane dystrophy (EBMD) undergoing PTK were examined using the MS-39ã (CSOã) at four timepoints: preoperatively (t1), after epithelial debridement (t2), after PTK ablation (t3), and at 3-month follow-up (t4). Anterior curvature, corneal and stromal thickness, and epithelial thickness were analyzed across 17 corneal sectors within an 8 mm zone using two-way repeated-measures analysis of variance (ANOVA) (timepoint × sector). Anterior Zernike HOAs were computed globally, and the smoothing effect of PTK ablation was assessed by paired comparison of t2 and t3, both obtained on de-epithelialized stroma. Results: Mean central sagittal anterior curvature remained stable across intraoperative timepoints (t1: 44.27 ± 2.32 D; t2: 44.83 ± 2.75 D; t3: 45.01 ± 2.48 D; p = 0.490), despite substantial stromal swelling: Central corneal thickness increased by 114.4 ± 53.0 μm from t2 to t3 (p < 0.001), exceeding preoperative values. At 3-month follow-up, a significant flattening of −1.13 ± 1.38 D was observed (t3→t4; p = 0.002). Stromal HOA analysis revealed a significant smoothing effect of PTK ablation: total HOA root mean square (RMS) decreased from 2.28 ± 2.14 to 0.99 ± 0.46 μm (t2→t3; p = 0.001), with coma RMS showing the most consistent reduction (Δ = −0.38 ± 0.33 μm, p < 0.001; 19/20 eyes). Epithelial thickness distribution narrowed at t4 (interquartile range (IQR) −52.2%), consistent with epithelial remodeling after stromal surface regularization. Conclusions: Anterior corneal curvature remains stable during PTK despite intraoperative stromal swelling, supporting the feasibility of OCT-based intraoperative topographic assessment. In contrast, pachymetric readings are rendered unreliable by stromal hydration. Anterior stromal HOA, particularly coma RMS, may serve as a quantitative intraoperative marker of the smoothing effect achieved by PTK.