Purpose: To investigate differences in ocular blood flow between people of African (AD) and European descent (ED) with healthy eyes.Methods: Retrobulbar and retinal capillary blood flow was assessed in one eye of 58 participants (24 AD, 34 ED) with healthy eyes with systemic blood pressure lower than 140/90. Retrobulbar blood flow was measured in the ophthalmic artery (OA), central retinal artery (CRA), nasal (NPCA) and temporal posterior ciliary arteries (TPCA). Peak systolic velocity (PSV), end diastolic velocity (EDV) and resistive index (RI) were assessed. Retinal capillary blood flow was assessed using mean retinal flow and avascular space defined as the percent of area measured with no blood flow. Groups were compared using t-tests and Pearson correlations were compared using Fisher r-toz transformation.Results: Compared to people of ED, people of AD had significantly lower EDV in the NPCA (p=0.01), and higher RI in the CRA (p=0.04) and TPCA (p=0.01). No significant differences were observed in mean retinal capillary flow or avascular area. In the CRA, a significant positive correlation was observed between pattern standard deviation (PSD) and PSV (p=0.02) and this correlation was significantly different from that observed in the ED group (p=0.01). A significant correlation was also observed between PSD and EDV (0.04) in the AD group. Conclusion:This study suggests that retrobulbar blood flow is lower in healthy eyes in persons of AD compared to ED. This may provide a mechanism through which people of AD are at increased risk for ophthalmic diseases such as glaucoma.

Purpose: This study aimed to assess differences in the relationship between structural parameters and ocular blood flow between persons of African (AD) and European descent (ED) with healthy eyes.Methods: The relationship between structural and ocular blood flow parameters was assessed in 46 participants (20 AD, 26 ED) with healthy eyes. Disc area (DA), rim area (RA), and retinal nerve fiber layer (RNFL) thickness were measured. Retrobulbar blood flow was assessed in the ophthalmic (OA), central retinal (CRA), nasal (NPCA) and temporal short posterior ciliary arteries (TPCA). Peak systolic velocity (PSV), end diastolic velocity (EDV) and resistive index (RI) were assessed. Retinal capillary blood flow was also evaluated. Differences between the correlations were determined using the Fisher r-to-z transformation.Results: Significant differences in correlations were observed between the AD and ED groups in the CRA, where PSV and DA were positively correlated in AD (r=0.43) and negatively correlated in ED (r=-0.36) (Δr=0.79; P=0.01). A similar finding was observed for PSV and RA (AD: r=0.39; ED: r=-0.23; Δr=0.62; P=0.04). In the inferior hemifield for ED group only, percentage of avascular space and RNFL thickness were positively correlated (r=0.51, P=0.01) and mean retinal flow and RNFL thickness were negatively correlated (r=-0.50, P=0.01).Conclusion: The relationship between structural parameters and the blood supply to the superficial layer of the retina was significantly different in the healthy eyes of AD compared to ED. More research is required to show how these differences may affect glaucomatous risk.