The retinal nerve fibre layer thickness slope: a localised biomarker of the structure-function relationship in early glaucoma.

Abstract

To describe the relationship between the novel biomarker retinal nerve fibre layer thickness slope (RNFL-S), and visual field sensitivity (VFS) in healthy and early glaucoma eyes. This prospective cross-sectional study of 50 early glaucoma and 139 healthy eyes analysed RNFL-S locally along retinal nerve fibre trajectories that were automatically traced and centred on 24-2 and 10-2 visual field (VF) test points. Corresponding virtual B-scans were extracted from stitched wide-field polarisation-sensitive optical coherence tomography images. A linear mixed-effects model (LMM) assessed the association between VFS and the factors RNFL-S, glaucoma status and age. The average VF mean deviation was -3.11±1.51 dB in glaucoma (mean age: 63.0±9.3 years) and -0.36±1.10 dB in healthy eyes (mean age: 47.9±16.3 years). In healthy subjects, VFS and the corresponding RNFL-S were 31.8±2.4 dB (12.5±2.9 µm/mm) in the upper hemisphere and 32.4±2.2 dB (12.5±2.5 µm/mm) in the lower hemisphere. In glaucoma patients, these values were significantly lower: 27.5±7.0 dB (8.6 ± 3.9 µm/mm, p<0.001) in the upper hemisphere and 30.1±4.3 dB (10.5±3.3 µm/mm, p<0.001) in the lower hemisphere. Significant point-wise Spearman correlation coefficients (up to r=0.61) were observed, particularly in the upper VF hemisphere within the central 10° and close to the optic nerve head. The LMM showed a positive association between VFS and RNFL-S (β=0.0415, SE=0.0023, p<0.001, R²=0.1885). Glaucoma was significantly associated with lower VFS (β=-2.468, SE=0.069, p<0.001). Age negatively correlated with VFS (β=-0.048, SE=0.002, p<0.001). Local RNFL-S is significantly correlated with VFS, highlighting its potential as a biomarker for focal glaucoma damage.