Associations Between Retinal Microvasculature, Orbital Blood Flow, and Cerebral Blood Flow in Healthy Adults

The purpose of this study was to assess whether retinal microvascular structures reflect orbital and cerebral perfusion in healthy adults across the lifespan.

Arterial spin labeled (ASL) perfusion magnetic resonance imaging (MRI) and ocular coherence tomographic angiography (OCTA) data acquired from 93 healthy adults (ages = 21-85 years) across two sites were analyzed to quantify orbital blood flow (OBF; retinal and choroidal), cerebral blood flow (CBF) and retinal vessel density (VD) in the superficial plexus (SVP), deep vascular plexus (DVP), and total vascular network (RVN) via fractal analysis. Correlations among retinal VD, OBF, and CBF were evaluated. The reproducibility of OBF was also assessed in a subset (N = 21) of participants.

OBF showed good reproducibility (intraclass correlation coefficient [ICC] = 0.836, P < 0.001) and correlated positively with gray matter (GM) CBF (r = 0.24, P = 0.034) and its anterior circulation territories (r = 0.26, P = 0.020). OCTA VD in DVP also showed a positive correlation with anterior circulation CBF (r = 0.40, P = 0.0039) and a trend with OBF (r = 0.27, P = 0.052). OBF, GM CBF, and OCTA VD declined with age, and their associations were age-dependent.

Associations among VD, OBF, and anterior circulation CBF suggest that there are associations between retinal microvascular density and both OBF and CBF in healthy aging, supporting OCTA and ASL as complementary tools to assess orbital and cerebral microvascular health across aging and, more broadly, the notion of the eye as a window to the brain with respect to vascular integrity.