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Norman P Blair, Michael Robert Tan, Anthony E Felder, Pang-yu Teng, Justin Wanek, Mahnaz Shahidi; Alterations in retinal tissue oxygen tension due to light flicker stimulation in rat. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3750.
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© ARVO (1962-2015); The Authors (2016-present)
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.
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 (PO2_meanIR), minimum PO2 (PO2_min), maximum PO2 (PO2_max), gradient of the outer retinal PO2 (PO2_gradOR), and the percent depth location of the PO2 profile minimum (PO2_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.
Light flicker did not alter any of the metrics in Group 1 (P>0.1). ΔPO2_meanIR, ΔPO2_min, and ΔPO2_max were significantly negative in Group 2 (P<0.03), while ΔPO2_gradOR and ΔPO2_minLoc did not differ from zero (P>0.4). ΔPO2_meanIR were 0.3 ± 4.7 and -8.5 ± 5.0 mmHg in Groups 1 and 2, respectively (P = 0.02). Similarly, ΔPO2_min were -0.4 ± 3.8 and -9.9 ± 6.6 mmHg in Groups 1 and 2, respectively (P = 0.02). Again, ΔPO2_max were -2.8 ± 4.0 and -9.4 ± 3.5 mmHg in Groups 1 and 2, respectively (P = 0.03). ΔPO2_gradOR were -0.8 ± 1.0 and -0.3 ± 1.2 mmHg/µm in Groups 1 and 2, respectively (P = 0.5). ΔPO2_minLoc were 0.4 ± 14 and -4.8 ± 12% in Groups 1 and 2, respectively (P = 0.5).
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.
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