Past studies have explored daytime variations in the OCT-A indexes of superficial and deep retinal layers among healthy participants between 7 AM and 8 PM (Penteado R, et al.
IOVS 2018;59:ARVO E-Abstract 2856; Rommel F, et al.
IOVS 2018;59:ARVO E-Abstract 2860).
7–15 Most of these studies did not detect significant variations during the day, except for one study that reported a significant increase (
P = 0.048) in parafoveal perfusion density between 12 PM and 8 PM using linear spline model analysis (Penteado R, et al.
IOVS 2018;59:ARVO E-Abstract 2856). Other ocular measurements also showed significant diurnal variations. Retinal thickness, axial length, and intraocular pressure (IOP) demonstrate a reduction at night whereas choroidal thickness and mean ocular perfusion pressure (MOPP) demonstrate peaks during the night or early morning.
16–18 Additionally, significant fluctuations exists in systemic blood pressure, vascular resistance, and heart rate during nighttime.
19, 20 These ocular and systemic measurements also show significant associations with OCT-A indexes and contribute to the regulation of ocular blood flow.
21–25 Therefore it is expected that retinal OCT-A indexes may also demonstrate significant variations over 24 hours. However, to the best of our knowledge, no previous studies have evaluated OCT-A measurements over a complete 24-hour period. In addition, OCT-A indexes are also affected by axial length and refractive error.
26–28 Myopes had lower superficial and deep vessel/perfusion density and higher vascular resistance index than emmetropes in a number of previous studies.
19,20,22,26–36 However, the role of these factors in diurnal variation of OCT-A indexes over 24 hours is not known.