Peripapillary Vessel Density Mediates the Relationship Between Axial Length and Visual Field Damage in Glaucoma

Objectives: Axial myopia is a risk factor for glaucoma, yet the mechanism(s) linking axial length (AL) to visual field (VF) damage remain unclear. This pilot study investigates to what extent peripapillary vessel density (pVD) mediates the relationship between AL and VF outcomes in patients with primary open-angle glaucoma (POAG). Methods: This cross-sectional pilot study included a primary cohort of 26 POAG eyes with directly measured AL, with an exploratory expanded cohort of 71 POAG eyes used to assess the consistency of findings. Optical coherence tomography angiography quantified pVD across eight sectors. VF outcomes included mean deviation, pattern standard deviation, and visual field index. Mediation analyses used ordinary least squares regression adjusted for age, intraocular pressure, and scan quality. Indirect effects were assessed via bias-corrected bootstrap confidence intervals. Results: In both primary and expanded cohorts, inferior-temporal pVD mediated the relationship between AL and all VF outcomes. Additional sectors emerged as mediators in the expanded cohort, suggesting broader vascular involvement. Conclusions: Peripapillary microvascular compromise significantly mediates the impact of AL on glaucomatous VF loss, supporting a possible biomechanical-vascular model of POAG eyes across a range of axial lengths.