Longitudinal stability of retinal blood flow regulation in response to flicker stimulation and systemic hyperoxia in mice assessed with laser speckle flowgraphy

Abstract

This study aimed to evaluate longitudinal changes in retinal blood flow in response to flicker stimulation and systemic hyperoxia in mice using a laser speckle flowgraphy (LSFG-Micro). The retinal blood flow in vascular area surrounding the optic nerve head was measured in 8-week-old male mice every 2 weeks until age 20-week. The coefficient of variation of retinal blood flow under resting condition was analyzed every 2 weeks to validate the consistency of the measurement. On day 1 of the experiment, retinal blood flow was assessed every 20 s for 6 min during and after 3 min flicker light (12 Hz) stimulation; on day 2, retinal blood flow was measured every minute for 20 min during and after 10 min systemic hyperoxia; and on day 3, electroretinography (ERG) was performed. Body weight, systemic blood pressure, and ocular perfusion pressure increased significantly with age, but the resting retinal blood flow and ERG parameters remained unchanged. Retinal blood flow significantly increased with flicker stimulation and decreased with systemic hyperoxia, independent of age. The LSFG-Micro provides consistent and reproducible retinal blood flow measurement in adult mice. Longitudinal assessments of retinal blood flow in response to flicker stimulation and systemic hyperoxia may be useful indexes for noninvasive monitoring of vascular function in retinas.

Retinal blood flow dysregulation precedes neural retinal dysfunction in type 2 diabetic mice

“…The mean arterial BP (MABP) was derived from the standard formula: MABP = DBP + (SBP-DBP)/3. Ocular perfusion pressure (OPP) was calculated using the formula OPP = MABP − IOP 64 , due to the animals' prone position during the experiments.…”

“…Retinal blood flow was measured with the LSFG-Micro system (Softcare Co., Ltd., Fukutsu, Japan), which is designed for small animals 64 . The LSFG-Micro system is equipped with a standard charge-coupled device camera (700 × 480 pixels) and a diode laser (830-nm wavelength) attached to a stereomicroscope (SZ61TR, Olympus Corporation, Tokyo, Japan).…”

“…The LSFG-Micro system is equipped with a standard charge-coupled device camera (700 × 480 pixels) and a diode laser (830-nm wavelength) attached to a stereomicroscope (SZ61TR, Olympus Corporation, Tokyo, Japan). The underlying principle of the LSFG-Micro is the same as that of LSFG, which has been used in humans 65 and animals 64 for quantitative estimation of ocular (optic nerve head, choroid, and retina) blood flow. In brief, the mean blur rate (MBR) represents a relative index of blood velocity and is generated from the blurring of the speckle pattern formed by the backscattered light of the coherent laser by moving blood cells.…”

“…Systemic hyperoxia was induced by inhalation of 100% oxygen over 10-min, as described in our previous studies 11 , 64 . The baseline value was determined as the mean of three consecutive flow measurements, obtained at 1-min intervals for 3 min before the initiation of hyperoxia.…”

“…The baseline value was determined as the mean of three consecutive flow measurements, obtained at 1-min intervals for 3 min before the initiation of hyperoxia. Retinal blood flow measurements were made every minute for 20 min during hyperoxia (10-min stimulation) and after the termination of hyperoxia (10-min recovery) 64 .…”