Corneal Higher-Order Aberrations and Posterior Segment Changes in Keratoconus: A Multimodal OCT and OCTA Study

Background/Objectives: To evaluate the associations between corneal topographic irregularity, higher-order aberrations (HOAs), and posterior segment structural and microvascular parameters in keratoconus using optical coherence tomography (OCT) and OCT angiography (OCTA). Methods: In this cross-sectional study, 81 eyes with keratoconus and 60 healthy control eyes underwent corneal topography and wavefront analysis, spectral-domain OCT with enhanced depth imaging, and OCTA. Retinal layer thicknesses, choroidal thickness and area metrics, choroidal vascularity index (CVI), and OCTA-derived vascular parameters were analyzed. Associations were assessed using Spearman correlation analysis with false discovery rate (FDR) correction. Results: Compared with controls, keratoconus eyes showed significantly increased corneal curvature, corneal irregularity indices, and HOAs (all p < 0.001). Structural OCT analysis demonstrated preserved inner retinal layers, whereas outer nuclear layer thickness was reduced (p < 0.001) and overall outer retinal layer thickness was increased (p = 0.005). Choroidal thickness and both total and luminal choroidal areas were significantly greater in keratoconus eyes (all p ≤ 0.011), while CVI did not differ between groups (p > 0.05). OCTA revealed reduced superficial capillary plexus vessel density at the whole image and perifoveal regions (all p < 0.001), whereas deep capillary plexus and foveal avascular zone metrics were largely preserved. Correlation analyses identified only weak and inconsistent associations between corneal parameters, HOAs, and posterior segment measurements, none of which remained statistically significant after FDR correction. Conclusions: Despite pronounced anterior segment deformation and optical degradation, posterior segment structural and microvascular alterations in keratoconus are limited and weakly related to corneal disease severity. These findings support a predominantly anterior segment centered pathophysiology of keratoconus and highlight the importance of stringent multiple-comparison control in multimodal imaging studies.