Diurnal variations in blood flow at optic nerve head and choroid in healthy eyes: diurnal variations in blood flow

Abstract

To investigate the diurnal variations of the ocular blood flow in healthy eyes using laser speckle flowgraphy (LSFG), and to determine the relationship of the diurnal variations between the ocular blood flow and other ocular parameters.This prospective cross-sectional study was conducted at Nagoya University Hospital. We studied 13 healthy volunteers whose mean age was 33.5 ± 7.6 years. The mean blur rate (MBR), expressing the relative blood flow, on the optic nerve head (ONH) and choroidal blood flow was determined by LSFG (LSFG-NAVI) every 3 hours from 6:00 to 24:00 hours. The intraocular pressure (IOP), choroidal thickness measured by enhanced depth imaging optical coherence tomography, systolic (SBP) and diastolic (DBP) blood pressure, and heart rate (HR) in the brachial artery were also recorded. We evaluated the diurnal variations of the parameters and compared the MBR to the other parameters using a linear mixed model.The diurnal variations of the MBR on the ONH varied significantly with a trough at 9:00 hours and a peak at 24:00 hours (P < 0.001, linear mixed model). The MBR of choroid also had significant diurnal variations with a trough at 15:00 hours and a peak at 18:00 hours (P = 0.001). The IOP (P < 0.001), choroidal thickness (P < 0.001), SBP (P = 0.005), DBP (P = 0.001), and HR (P < 0.001) also had significant diurnal variations. Although the diurnal variation of the MBR on the ONH was different from the other parameters, that on the choroid was significantly and positively correlated with the DBP (P = 0.002), mean arterial pressure (P = 0.023), and mean ocular perfusion pressure (P = 0.047).We found significant diurnal variations in the ONH and choroidal blood flow. Although the ONH blood flow had its own diurnal variation because of strong autoregulation, the choroidal blood flow was more likely affected by systemic circulatory factors because of poor autoregulation.

FIGURE 1

Composite color maps using the mean blur rate (MBR) as measured by laser speckle flowgraphy (LSFG). The red color indicates high MBR and the blue color indicates low MBR. To measure MBR on the optic nerve head (ONH) blood flow and choroidal blood flow, a circle was set around the ONH (A) and a rectangle was set at the macula (B). The MBR was measured every 3 hours from 6:00 to 24:00 hours to evaluate the diurnal fluctuations.

FIGURE 2

The ONH blood flow in healthy subjects had significant variations with a relative nadir MBR at 9:00 hours and progressive increase during the day to a relative peak at 24:00 hours (P < 0.001) (A). The best fit curve was a cubic polynomial curve (red line). The choroidal blood flow had significant diurnal fluctuations with a relative trough at 15:00 and peak at 18:00 hours (P = 0.001). The phase of the choroidal blood flow is different from that of ONH blood flow (B). MBR = mean blur rate, ONH =  optic nerve head.

FIGURE 3

Diurnal variations in the intraocular pressure (IOP), subfoveal choroidal thickness (SFCT), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), mean ocular perfusion pressure (MOPP), and heat rate (HR) measured every 3 hours from 6:00 to 24:00 hours. The SBP, MAP, and MOPP had a peak at 18:00 hours, which was the same as that of the choroidal blood flow. The HR increased in the evening and the IOP was high in the morning and low at night.