Alterations in retinal tissue oxygen tension due to light flicker stimulation in rat

Abstract

Purpose : Light flicker stimulation increases the neural activity of the retina and alters vascular caliber and oxygen extraction fraction. The purpose of this study is to characterize depth-resolved alterations in retinal tissue oxygen tension (PO₂) due to light flicker stimulation.

Methods : A palladium porphyrin phosphor was injected intravitreally in 10 rats. Using our established optical section phosphorescence lifetime imaging system and methods, depth-resolved phosphorescence images of the retinal tissue were acquired the next day. The light stimulus was at a wavelength of 570 nm and frequency of 10 Hz. Three depth-resolved images were acquired without and then with light flicker between 60 and 110 seconds in 5 rats (Group 1) and between 60 and 240 seconds in another 5 rats (Group 2). Images were analyzed to determine phosphorescence lifetime and generate PO₂ maps. From each PO₂ map, a PO₂ profile through the retinal depth was derived from a 500 by 30 µm region of the retina. Three PO₂ profiles under each condition were used to generate mean PO₂ profiles. The following metrics were determined from each mean PO₂ profile: mean inner retinal PO₂ (PO_{2_meanIR}), minimum PO₂ (PO_{2_min}), maximum PO₂ (PO_{2_max}), gradient of the outer retinal PO₂ (PO_{2_gradOR}), and the percent depth location of the PO₂ profile minimum (PO_{2_minLoc}). Metric differences (indicated by Δ) were calculated by subtracting the metric values obtained without light flicker from those obtained with light flicker. Data were analyzed by paired and unpaired t-tests.

Results : Light flicker did not alter any of the metrics in Group 1 (P>0.1). ΔPO_{2_meanIR}, ΔPO_{2_min}, and ΔPO_{2_max} were significantly negative in Group 2 (P<0.03), while ΔPO_{2_gradOR} and ΔPO_{2_minLoc} did not differ from zero (P>0.4). ΔPO_{2_meanIR} were 0.3 ± 4.7 and -8.5 ± 5.0 mmHg in Groups 1 and 2, respectively (P = 0.02). Similarly, ΔPO_{2_min} were -0.4 ± 3.8 and -9.9 ± 6.6 mmHg in Groups 1 and 2, respectively (P = 0.02). Again, ΔPO_{2_max} were -2.8 ± 4.0 and -9.4 ± 3.5 mmHg in Groups 1 and 2, respectively (P = 0.03). ΔPO_{2_gradOR} were -0.8 ± 1.0 and -0.3 ± 1.2 mmHg/µm in Groups 1 and 2, respectively (P = 0.5). ΔPO_{2_minLoc} were 0.4 ± 14 and -4.8 ± 12% in Groups 1 and 2, respectively (P = 0.5).

Conclusions : The findings suggest that light flicker stimulation deceases retinal tissue PO₂ over a period of several minutes.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.