Girard, Michaël J. A.

Abstract In this study, we quantified differences in iris stiffness between female and male subjects in healthy and postlaser peripheral iridotomy (post-LPI) groups using an image-based inverse modeling approach. We analyzed anterior segment optical coherence tomography (AS-OCT) images from 25 participants across four groups. Finite element models were created using **solidworks, **abaqus, and a custom C program, modeling the iris as a neo-Hookean material. We found that post-LPI females had significantly higher normalized elastic modulus (E′=3.81±1.74) than healthy females (E′=0.92±0.31,p=0.004), while no significant difference was observed in males. Post-LPI females also showed significantly higher stiffness than post-LPI males (p=0.003). Here, p denotes the probability value, with p<0.05 considered statistically significant. Our findings suggest that sex-based differences in iris biomechanics may contribute to the higher susceptibility of females to primary angle-closure disease. Despite the small sample size, this preliminary study highlights the need for larger, sex-stratified investigations into glaucoma pathophysiology.

The aim of this study was to quantify connective tissue fibre orientation and alignment in young, old and glaucomatous human optic nerve heads (ONH) to understand ONH microstructure and predisposition to glaucomatous optic neuropathy. Transverse (seven healthy, three glaucomatous) and longitudinal (14 healthy) human ONH cryosections were imaged by both second harmonic generation microscopy and small angle light scattering (SALS) in order to quantify preferred fibre orientation (PFO) and degree of fibre alignment (DOFA). DOFA was highest within the peripapillary sclera (ppsclera), with relatively low values in the lamina cribrosa (LC). Elderly ppsclera DOFA was higher than that in young ppsclera ( p < 0.00007), and generally higher than in glaucoma ppsclera. In all LCs, a majority of fibres had preferential orientation horizontally across the nasal–temporal axis. In all glaucomatous LCs, PFO was significantly different from controls in a minimum of seven out of 12 LC regions ( p < 0.05). Additionally, higher fibre alignment was observed in the glaucomatous inferior–temporal LC ( p < 0.017). The differences between young and elderly ONH fibre alignment within regions suggest that age-related microstructural changes occur within the structure. The additional differences in fibre alignment observed within the glaucomatous LC may reflect an inherent susceptibility to glaucomatous optic neuropathy, or may be a consequence of ONH remodelling and/or collapse.