Beyond the Cornea: Early Changes in Scleral, Iris, and Corneal Parameters After Corneal Collagen Cross-Linking

Background/Objectives: To evaluate early postoperative changes in scleral and iris thicknesses together with corneal layer thicknesses and tomographic parameters following corneal collagen cross-linking (CXL) in eyes with progressive keratoconus. Methods: This retrospective study included 94 eyes of 94 patients with progressive keratoconus who underwent standard epithelium-off CXL using the Dresden protocol. Corneal tomography (Pentacam) and anterior segment optical coherence tomography (AS-OCT) measurements were obtained preoperatively and at the early postoperative follow-up (3 months ± 2 weeks). Thickness measurements of the tear film, corneal epithelium, Bowman layer, stroma, Descemet-endothelium complex, sclera (1-3 mm from the limbus), and iris (1-2 mm from the pupillary margin) were analyzed. Pre- and post-CXL values were compared using paired statistical tests, and effect sizes were calculated. Results: In the early postoperative period, scleral thickness showed a significant increase at all measured distances from the limbus, with medium effect sizes, while iris thickness demonstrated a significant decrease at all measurement points with large effect sizes (p < 0.001). Tear film, epithelial, and stromal thicknesses decreased significantly after CXL, whereas Bowman layer and Descemet-endothelium complex thicknesses remained unchanged. Pachymetric measurements revealed significant thinning at the pupil center, corneal apex, and thinnest point. No significant changes were observed in Kmax or anterior chamber depth, indicating stabilization rather than progression in the early postoperative period. Conclusions: Corneal collagen cross-linking was associated with measurable early structural changes in corneal layers and extra-corneal anterior segment tissues during the postoperative period. The observed increase in scleral thickness and decrease in iris thickness suggest that structural alterations may occur in extra-corneal anterior segment tissues following CXL. These findings support the concept that CXL influences anterior segment biomechanics in a tissue-specific manner and that extra-corneal parameters may serve as complementary markers for early postoperative assessment.