Study finds, Diurnal Variation of Retinal Vessel Density in
A small increase in optic nerve head vessel density (VD), but not macular VD, in the evening compared to the morning is observed in healthy subjects.

Researchers aimed to evaluate the diurnal variation of the macular and optic nerve head (ONH) vessel density (VD) in healthy eyes as measured with optical coherence tomography angiography (OCT-A).

In this prospective study of healthy individuals older than 18 years old, VD parameters, including macular whole image vessel density (wiVD), parafoveal vessel density (pfVD), ONH whole image vessel density (ONH-wiVD), ONH whole image capillary density (ONH-wiCD), circumpapillary vessel density (cpVD), and circumpapillary capillary density (cpCD), were measured with OCT-A at four time points throughout the day (8 AM, 12 PM, 4 PM, and 8 PM).

--29 healthy eyes were included from 15 subjects (mean age: 30.9 years).

--After adjustment for age and mean ocular perfusion pressure (MOPP), a significant positive rate of change was found for cpVD (0.05%/hour).

--In contrast, macular VD changes were not significantly different. When comparing morning (8 AM and 12 PM) and evening (4 PM and 8 PM) measurements, there were small, but statistically significant, increases for all ONH measurements.

--The greatest increase was found for cpVD (0.58%). Significant but small increases in mean arterial pressure and MOPP were also observed.

In the evening, compared to morning with healthy human eyes, the ONH VD, increased somewhat. Because of the difference seen within the measurement variability, these results shows the timing of an OCT-A test that does not alter measurements of retinal VD.