Outer retinal oxygen consumption of rat by phosphorescence lifetime imaging

Since the metabolic function of the retinal tissue is altered due to physiologic changes or disease, measurements of outer retinal oxygen consumption (Q(OR)) may be beneficial in assessment of retinal status. The purpose of this study was to report measurements of Q(OR) in rats using a phosphorescence lifetime imaging technique.

Phosphorescence lifetime imaging was performed and retinal PO(2) maps were generated in 10 rats under a light-adapted condition. Depth-resolved retinal PO(2) profiles were derived from the PO(2) maps. From the profiles, the maximum outer retina PO(2) (P(max)O(2)) was obtained and Q(OR) was calculated using a one-dimensional oxygen diffusion model. Repeatability, inter-location variability, and inter-subject variability of P(max)O(2) and Q(OR) measurements were established.

Intraclass correlation coefficients of repeated measurements of P(max)O(2) and Q(OR) were 0.89 and 0.70, respectively (P < 0.001). Inter-location variability of P(max)O(2) and Q(OR) measurements at superior to inferior contiguous locations on the retina were on average 9 mmHg and 0.22 ml O(2)/100 g-tissue-min, respectively. Mean and standard deviation of P(max)O(2) and Q(OR) measurements averaged over all rats were 60 ± 16 mmHg and 0.73 ± 0.28 ml O(2)/100 g-tissue-min, respectively. Inter-subject variability of P(max)O(2) and Q(OR) measurements was on average 2.3 and 1.5 times inter-location variability, respectively.

Measurements of outer retinal oxygen consumption can be made by phosphorescence lifetime imaging and may be of potential value for detecting changes in retinal oxygen metabolic activity due to altered physiological and pathological conditions over multiple locations and time points.