Abstract
Purpose :
It is known that retinal blood flow is reduced in glaucoma. We asked whether pulsatile hemodynamics alter, consistent with changes in vascular resistance, as glaucoma progresses.
Methods :
378 eyes of 189 participants with glaucoma or glaucoma suspects were tested using Laser Speckle Flowgraphy (LSFG-Navi, Softcare Co. Ltd) and optical coherence tomography (Spectralis OCT2, Heidelberg Engineering GmbH), every six months. LSFG measures flow within the optic nerve head (ONH) at 30 frames per second for 4 seconds, to quantify and parameterize the pulsatile cycle. Beat Strength Over Mean (BOM), defined as the magnitude of the pulsatile waveform divided by its mean, is calculated separately for the major vessels in the ONH that supply the retina, and other tissue containing capillaries that supply the ONH itself. Higher BOM is believed to refect higher vascular resistance. OCT was used to measure average retinal nerve fiber layer thickness (RNFLT) within a 6° radius circular scan centered on the ONH. BOM was compared cross-sectionally against RNFLT; and rates of change of BOM over 6 visits were compared against the mean RNFLT from those visits.
Results :
BOM in both vessels and ONH tissue was highest in eyes with RNFLT 80-100μm, and lower in eyes >100μm or <80μm (Fig 1). Among 52 eyes of 44 individuals with RNFLT thinning faster than -1μm/y over 6 visits, BOM increased over that period in early/suspected glaucoma eyes, but decreased over time in more advanced glaucoma (Fig 2). The relation between BOM rate and mean RNFLT was significant for both vessels (p=0.004, GEE regression) and tissue (p=0.003), and remained significant after adjusting for IOP (p=0.004 for both).
Conclusions :
Vascular resistance, both within ONH tissue and in the wider retina supplied by major vessels traversing the ONH, appears to increase in early glaucoma, before decreasing as damage continues to progress. It might be affected by biomechanical tissue remodeling in response to chronic IOP elevation; effects of neuroinflammation; constricted flow due to failing autoregulation and/or neurovascular coupling; and/or reduced demand secondary to axon loss. The non-monotonic relation with RNFLT suggests that the relative contributions of those elements of pathogenesis change with disease stage. Altered vascular resistance is part of the pathophysiology of glaucoma, potentially linking the mechanical and vascular hypotheses of glaucoma development.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.