Abstract
Purpose :
Alterations of intraocular pressure (IOP) result in corresponding changes to optic nerve head (ONH) blood flow. Further, eyes with glaucoma have reduced ONH blood flow. This study aimed to determine differences in blood flow response to acute changes in IOP in nonhuman primates (NHP) with early experimental glaucoma.
Methods :
Data were collected from the right eye of 6 healthy NHPs, with laser-induced experimental glaucoma. Before the first laser session and a month following the last laser session, the anterior chamber was cannulated for pressure adjustment (10, 25, 40, 55 and back to 10mmHg) with a pressure control system. Three laser speckle flowgraphy (LSFG-LITE, Softcare) videos centered on the ONH were acquired at each pressure exposure. LSFG parameters of Mean Blur Rate (MBR), Resistivity Index (RI), Blow Out Score (BOS), Beat Strength (BS), BS over MBR (BOM), Blow Out Time and Acceleration Time Index were used for statistical analysis. ONH morphology was determined at the initial 10mmHg setting using an isotropic optical coherence tomography (OCT) raster scan centered on the ONH at both pressure challenge sessions (Spectralis, Heidelberg Engineering).
Results :
The second cannulation experiment was done 29±1.5 days from the last laser session (mean IOP = 33.3±7.9mmHg). Reduction in ONH minimum rim width at this time point ranged from 24µm to 147µm, and circumpapillary retinal nerve fiber layer thickness from 2µm to 43µm. The MBR at baseline was 17.2±4.6, and 15.5±1.8 at second cannulation (P<0.05). Based on two-way repeated measures ANOVA, there was no difference in how eyes responded to pressure increase for each of the LSFG parameters. Above 25 mmHg, there was a reduction in MBR, and an increase in RI (P<0.05). An increase above 10mmHg resulted in a decrease in BOS (P<0.05), and BS increased with an increase in pressure up to 40mmHg (P<0.05). Each LSFG parameter returned to baseline when pressure was changed from 55mmHg to 10mmHg, except MBR, which was greater than baseline in eyes before induction of experimental glaucoma, and less in early-stage eyes (P<0.05).
Conclusions :
Changes in LSFG blood flow metrics with increased anterior chamber pressure are similar in early experimental glaucoma compared to baseline measures. The observed differences in the return of MBR with pressure reduction likely reflect changes in vascular anatomy or autoregulation.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.