Abstract
Purpose :
Glaucoma pathogenesis has been explained by mechanical and vascular theories; the interplay between these factors, however, is poorly understood. This prospective, interventional study was conducted to determine the effect of intraocular pressure (IOP) reduction on the vessel density (VD) in the peripapillary and optic nerve head (ONH) regions in eyes with glaucoma or ocular hypertension using optical coherence tomography (OCT) angiography.
Methods :
Thirty-eight eyes of 28 patients with glaucoma or ocular hypertension were studied. The median age was 59 years (inter-quartile range, IQR= 56-68) and 19 were male. The inclusion criterion was eyes requiring anti-glaucoma medications due to an IOP over target. All participants underwent spectral domain OCT and OCT Angiography (Optovue Inc., Fremont, CA) prior to, and following treatment with IOP-lowering medications. Scans were taken less than 10 weeks apart. Multi-level mixed effect modelling was used to determine the effect of IOP on the peripapillary and ONH VD after accounting for the effect of change in signal strength index (SSI) of the scans.
Results :
Median IOP at the time of initial scan was 25 (IQR=23-32) mmHg and after IOP reduction was 16 (IQR=14-18) mmHg (p<0.001). Mixed effect modelling showed that change in SSI had no effect on neuro-retinal rim (NRR) and retinal nerve fiber layer (RNFL) thickness parameters but a significant positive effect on the peripapillary and ONH VD in most sectors (coefficient 0.26 to 0.83; p<0.01) as shown in Figure 1. Although, change in IOP had no effect on RNFL thickness, the global and sectoral NRR area showed a significant negative association (r = -0.001 to -0.01, p<0.02). Similarly, the change in IOP had no effect on the peripapillary VD (p>0.05), but a small, statistically significant effect on the average ONH VD (-0.11, 95% confidence intervals -0.20 to -0.02, p =0.02) and the vessel densities in the temporal, supero-nasal and supero-temporal sectors of the ONH (r = -0.22 to -0.16, p≤0.05).
Conclusions :
Interpretation of alterations in VD should factor in the SSI of the images. Reduction in IOP does not affect the peripapillary VD, but does result in a small increase in the VD within the ONH.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.