Optic Nerve Head Parameters and Their Associations With Axial Length and Refractive Status in Cynomolgus Macaques

Purpose: Optic nerve head (ONH) morphology in relation to refractive status remains incompletely characterized in nonhuman primates (NHPs). We established reference values for ONH parameters in cynomolgus macaques and examined their associations with age, sex, axial length (AL), and spherical equivalent (SE). Methods: Fundus photographs and spectral-domain optical coherence tomography (SD-OCT) images from 302 eyes of 302 macaques were analyzed. Measurements included Bruch's membrane opening distance (BMOD), disc ovality, torsion angle, central retinal vein trunk (CRVT) position ratio, disc-fovea distance (DFD) ratio, and β- and γ-peripapillary atrophy (PPA). Multivariable linear, Firth logistic, and AL-based segmented regression analyses with bootstrap inference were performed, together with two-part sensitivity analyses. Results: Longer AL was associated with larger BMOD, greater disc ovality, a higher DFD ratio, and a lower CRVT position ratio, indicating a more nasal CRVT location, after false discovery rate correction. Highly myopic eyes showed larger BMOD, greater ovality, a higher DFD ratio, and higher prevalence and larger areas of β- and γ-PPA. Estimated AL breakpoints were 18.17 mm for ovality, 18.30 mm for γ-PPA area, and 18.86 mm for β-PPA area. Two-part analyses associated longer AL and more negative SE with both β-PPA presence and larger positive β-PPA area. The γ-PPA and β-PPA were present in 56.0% and 9.6% of eyes, respectively. Conclusions: ONH morphology in cynomolgus macaques varies with AL and refractive status and shows nonlinear cross-sectional associations. These reference values and AL-based estimates may inform future longitudinal and experimental studies of myopia-related ONH variation.