Twenty-four hour diurnal variation in retinal oxygen saturation.

Retinal oxygen saturation is influenced by systemic and local vasculature, intraocular pressure (IOP), and individual cellular function. In numerous retinal pathologies, early changes take place at the level of the microvasculature, thereby affecting retinal oxygenation. The purpose of this study was to investigate diurnal variations in retinal oximetry measures and evaluate the relationship with other ocular and systemic physiological processes. Healthy adults (n = 18, mean age 27 ± 5.5 years) participated. Ocular and systemic measures were collected every four hours over 24 h and included retinal oximetry, IOP, optical coherence tomography (OCT), OCT-angiography (OCTA), biometry, blood pressure, and partial pressure of oxygen. Amplitude and acrophase for retinal oxygen saturation, axial length, retinal and choroidal thickness, OCTA parameters, and mean arterial and ocular perfusion pressure (MAP, MOPP) were determined were determined using cosine fits, and multiple regression analysis was performed to compare metrics. Retinal oxygenation saturation demonstrated a significant diurnal variation with an amplitude of 5.84 ± 3.86% and acrophase of 2.35 h. Other parameters that demonstrated significant diurnal variation included IOP, MOPP, axial length, choroidal thickness, superficial vessel density, heart rate, systolic blood pressure, and MAP. Diurnal variations in retinal oxygen saturation were in-phase with choroidal thickness, IOP, and density of the superficial vascular plexus and out-of-phase with axial length and MOPP. In conclusion, retinal oxygenation saturation undergoes diurnal variations over 24 h. These findings contribute to a better understanding of intrinsic and extrinsic factors influencing oxygenation of the area surrounding the fovea.