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J. M. Wanek, T. Wu, N. P. Blair, M. Shahidi; Measurement of Retinal Tissue Oxygen Consumption in Rats by Phosphorescence Lifetime Imaging. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1031.
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© ARVO (1962-2015); The Authors (2016-present)
The metabolic function of the retinal tissue is likely altered due to disease, therefore measurements of retinal tissue oxygen tension and consumption may be beneficial in assessment of retinal health. The purpose of this study is to report measurements of outer retina oxygen tension (PO2) and oxygen consumption (Q) by a phosphorescence imaging technique in rats under hypoxia and normoxia.
Retinal tissue PO2 maps were generated in rats using our optical section phosphorescence lifetime imaging system. A narrow vertical laser line at 532 nm was projected at an angle on the retina after intravitreal injection of an oxygen-sensitive molecular probe. Phosphorescence lifetime and PO2 were calculated at each pixel on the depth-resolved retinal tissue image. Three repeated retinal PO2 maps were generated in each of 9 and 10 rat eyes under hypoxia (10% O2 breathing) and normoxia (30% O2 breathing), respectively. Retinal PO2 profiles through the retinal depth were derived by plotting PO2 values vertically averaged over 100-micron segments along the image. For each profile, the outer retina Q was calculated by fitting the curve to a steady-state one-dimensional oxygen diffusion model. Coefficients of variation (COV) for maximum outer retinal PO2 (PORmaxO2), minimum outer retinal PO2 (PORminO2), and outer retinal Q were calculated. Statistical t-test and ANOVA were performed to compare measurements.
The systemic arterial PO2 measurements under hypoxia and normoxia were 44 ± 10 mm Hg (mean + SD, N = 9) and 106 ± 18 mm Hg (N = 10), respectively and were significantly different (p<0.001). The COV of repeated measurements of PORmaxO2, PORminO2, and Q were on average 9%, 11% and 15% under normoxia, respectively, and not significantly different (p > 0.09). PORmaxO2 and PORminO2 measurements were 16 ± 5 and 10 ± 4 mm Hg under hypoxia and 59 ± 15 and 39 ± 13 mm Hg under normoxia, respectively. Outer retinal Q measurements were 0.31 ± 0.12 and 0.75 ± 0.28 ml O2/100g-tissue-min under hypoxia and normoxia, respectively (p < 0.001). Outer retina Q was linearly correlated with PORmaxO2 (r = 0.84, p < 0.0001; N = 19). The COV of PORmaxO2, PORminO2, and Q measurements along the image were on average 16%, 21%, and 32%, respectively, and significantly different (p < 0.001).
An imaging method was utilized to measure outer retina oxygen tension and oxygen consumption and report alterations under hypoxia and normoxia in rats. This technique may be of value for quantitative mapping and monitoring of retinal metabolic function over time.
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