Siegfried F, et al. - Researchers examined 22 normal eyes from 22 participants for diurnal changes of choroidal sublayer perfusion. In addition, they sought for the influencing factors using optical coherence tomography angiography (OCTA). Subfoveal choroidal thickness (SFCT), as well as perfusion of Sattler's layer (SLP) and Haller's layer (HLP), showed a significant pattern of diurnal variation. A linear decrease in SFCT was observed, it was thicker in the morning (348 μm) and thinner in the evening (310 μm). They noted a quadratic relation to the time of day of both, SLP and HLP, increasing from morning (64% and 76%) to afternoon (66% and 77%), before decreasing again in the evening (64% and 76%). Fluctuations of mean arterial pressure were observed in significant correlation to HLP changes. Older participants (≥60 years) demonstrated fewer diurnal changes. These findings highlight the importance of accounting the time of day when comparing longitudinal OCTA data.