Changes in Optical Coherence Tomography Angiography metrics over 24 hours in healthy adults

Abstract

Purpose : Diurnal variations have been observed in a range of posterior eye structures, yet the pattern of diurnal variation in retinal vasculature over 24 hours has not been established. We performed a prospective observational study to explore the magnitude and pattern of diurnal variation in retinal vasculature over 24 hours using optical coherence tomography angiography (OCT-A) among healthy myopes and non-myopes.

Methods : Healthy young adult participants (n=44, 23.2±4.1 years (range:18-35)) underwent measurements every 4h for 24h starting at 9 AM. AngioPlex OCT-A macula images were captured to determine a range of retinal vascular metrics including foveal avascular zone (FAZ) metrics (area, perimeter, and circularity) as well as the vessel, and perfusion density in the 3mm ETDRS central, and inner subfields. Blood pressure, intraocular pressure (IOP) and axial length were also assessed. Acrophase and amplitude of diurnal variation for each measurement were calculated and compared between 24 myopes and 20 non-myopes.

Results : Vessel and perfusion density showed significant variations over 24h (ANOVA, p<0.05) whereas none of the FAZ metrics changed significantly (ANOVA, p>0.05). Central vessel and perfusion density had their minima phase at 4:48 AM ± 4.44h and 5:45 AM ± 4.14h respectively, with a diurnal amplitude of 1.09±0.65 mm^-1 and 1.95±1.25 %. The inner vessel and perfusion density peaked around 5 PM. Myopes and non-Myopes showed different 24h variation patterns for inner vessel density (Figure 1) and perfusion density (with a significant time of day and refractive groups interaction; p=0.04 for both) but not in the central subfield. The myopes and non-myopes had minima at 4:35 AM and 6:06 AM, respectively however, the amplitude of daily variations was not significantly different (p>0.05) between them. The minimum pulse pressure was also in the morning (5:56 AM). Axial length and IOP both demonstrated an acrophase in the afternoon at 2:24 PM and 12:22 PM respectively.

Conclusions : This study, for the first time, demonstrates that significant diurnal variation exists in OCT-A metrics of macular retinal vasculature when evaluated over a full 24h duration while the FAZ does not exhibit any significant variations

This is a 2021 ARVO Annual Meeting abstract.

 

Figure 1: Inner vessel density over 24 hours between the two refractive groups (*p=0.012). Error bar represents standard error mean.