Preoperative Oct Thinnest Stromal Thickness As A Predictive Tool For Corneal Thickness Progression During Cross-Linking In Keratoconus Patients

To evaluate the effectiveness of preoperative Optical Coherence Tomography (OCT) with virtual epithelial removal for predicting corneal thickness progression during corneal collagen cross-linking (CXL) in keratoconus patients. The study aimed to assess if OCT-derived thinnest stromal thickness can serve as a safer and more reliable alternative to traditional pachymetry and to compare central corneal thickness (CCT) measurements obtained by OCT and manual pachymetry to enhance treatment planning and safety.

Retrospective analysis conducted at the Galilee Medical Center Corneal Unit, Nahariya, Israel, involving 24 keratoconus patients who underwent standard corneal collagen cross-linking (CXL) using RiboCare riboflavin and the C-eye cross-linking device. Corneal thickness was measured preoperatively with OCT (Anterion) and intraoperatively with manual pachymetry at multiple stages: pre-epithelial removal, post-epithelial removal, post-riboflavin loading, and post-UV irradiation.

Retrospective analysis of 24 keratoconus patients undergoing standard CXL. Corneal thickness was measured at four stages: preoperatively using OCT (Anterion) with virtual epithelial removal, post-epithelial removal, post-riboflavin loading with RiboCare, and post-UV irradiation using manual pachymetry. Thinnest stromal thickness and CCT measurements were compared between OCT and manual pachymetry. Correlations and predictive accuracy of pre-op OCT measurements for post-UV thickness were evaluated using linear regression.

Preoperative OCT thinnest stromal thickness showed a strong correlation with actual post-epithelial removal measurements (r = 0.98, p < 0.0001), validating its accuracy. CCT increased by 60.50 µm post-riboflavin and by 2.00 µm post-UV irradiation, with a total net increase of 30.33 µm. Manual pachymetry consistently measured higher CCT values than OCT-derived CCT, potentially overestimating safety margins. A predictive nomogram based on pre-op OCT measurements was developed to estimate post-UV CCT using the regression equation: Post-UV CCT = 0.77 × (Pre-op OCT Thinnest Stroma) + 182.79 µm (R² = 0.82). This model supports using pre-op OCT as a safer tool for CXL planning.

Preoperative OCT-based thinnest stromal thickness measurements with virtual epithelial removal offer a safer and more accurate alternative to manual pachymetry for assessing corneal thickness during CXL in keratoconus patients. The developed nomogram enables precise estimation of post-UV CCT based on pre-op OCT measurements, ensuring safety margins are maintained without the risk of sub-400 µm thinning. By minimizing operator dependency and reducing the risk of overestimation associated with manual pachymetry, pre-op OCT can significantly enhance treatment planning and safety in CXL procedures. Further studies with larger cohorts are needed to validate these findings across different riboflavin solutions and cross-linking devices.