Retinal tissue oxygen tension and consumption during light flicker stimulation in rat

Abstract

Light flicker stimulation has been shown to increase inner retinal oxygen metabolism and supply. The purpose of the study was to test the hypothesis that sustained light flicker stimulation of various durations alters the depth profile metrics of oxygen partial pressure in the retinal tissue (tPO) but not the outer retinal oxygen consumption rate (QO). In 17 rats, tPO depth profiles were derived by phosphorescence lifetime imaging after intravitreal injection of an oxyphor. tPO profile metrics, including mean inner retinal tPO, maximum outer retinal tPO and minimum outer retinal tPO were determined. QO was calculated using a one-dimensional oxygen diffusion model. Data were acquired at baseline (constant light illumination) and during light flicker stimulation at 10 Hz under the same mean illumination levels, and differences between values obtained during flicker and baseline were calculated. None of the tPO profile metrics or QO differences depended on the duration of light flicker stimulation (R ≤ 0.03). No significant change in any of the tPO profile metrics was detected with light flicker compared with constant light (P ≥ 0.08). Light flicker decreased QO from 0.53 ± 0.29 to 0.38 ± 0.30 mL O/(min*100 gm), a reduction of 28% (P = 0.02). The retinal compensatory responses to the physiologic challenge of light flicker stimulation were effective in maintaining the levels of oxygen at or near baseline in the inner retina. Oxygen availability to the inner retina during light flicker may also have been enhanced by the decrease in QO.

Increased Retinal Metabolism Induced by Flicker in the Isolated Mouse Retina

“…In the retina, the increase in blood flow may be a little smaller than the metabolic change based on the observation in the rat that PO 2 sometimes decreased by a few millimeters of mercury during steady or flickering illumination ( Lau and Linsenmeier, 2012 ), whereas a matched increase in supply and demand should lead to no PO 2 change. Blair et al (2018) , using a phosphorescence lifetime method, could not detect a difference in inner retinal PO 2 between steady light and flicker, also suggesting that flow and metabolism were well matched when flicker causes an increase in metabolism, and with the more sensitive microelectrode methods, the difference in PO 2 between steady light and flicker is indeed rather small ( Fig. 3 ).…”