Comparing the Speed of Glaucoma Progression at Various Stages as Measured by Function, Structure, and Perfusion

Abstract

Purpose : To compare the speed of glaucoma progression as measured by visual field (VF), optical coherence tomography (OCT), and OCT angiography (OCTA).

Methods : This is a prospective, observational study. Pre-perimetric glaucoma (PPG) and perimetric glaucoma (PG) patients are followed up every 6 months for at least 18 months (average: 30.4±11.0 months). One eye of each participant was scanned using 4.5x4.5-mm OCTA centered on the disc with the AngioVue system (Optovue). The nerve fiber layer plexus capillary density (NFLP CD) was deefined as the percentage area occupied by flow pixels excluding large vessels. The nerve fiber layer (NFL) thickness was measured from ONH scan. The NFLP mean deviation (NFLP MD) and NFL MD were visual field (VF)-equivalent dB-scale quantities based on sectorwise nonlinear regression of NFLP CD and NFL thickness with VF deviation. The speed of glaucoma progression was measured by linear regression trend slope over time. A linear mixed model was used to calculate the P values of the slopes.

Results : Forty-one patients were analyzed. Twelve had PPG (average VF MD -0.55 dB), 29 had PG (average VF MD -5.13 dB; range -0.84 ~ -18.35 dB). Reproducibility, on dB scale, was best for NFL MD, followed by NFLP MD and VF MD (Table 1). The trend slope in VF MD was not significantly different from zero in either group. In the PPG group, progression as measured by NFL MD was significantly (P<0.007, Wilcoxon test) faster compared to NFLP MD and VF MD. In the PG group, NFLP MD progression was significantly (P<0.001) faster than NFL MD and VF MD. NFLP CD and NFLP MD had significant decrease only in the PG stage, not the PPG stage. While NFL thickness loss was twice faster (P<0.001, Mann-Whitney test) in the PPG stage compared to the PG stage.

Conclusions : VF MD is not suitable for measuring progression over such a short follow-up period due to the high measurement variability of this functional parameter. NFL thickness and its derivative NFL MD may be useful in monitoring progression in PPG patients as these structural parameters decreased faster in this early stage. NFLP CD and its derivative NFLP MD may be useful in monitoring PG patients as these perfusion parameters decreased faster in this later stage.

This is a 2021 ARVO Annual Meeting abstract.