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AC Kight, RD Shonat; Imaging of Oxygen Tension in the Mouse Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2577.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Retinal hypoxia and inadequate oxygen delivery have been implicated as causal for the development of several eye diseases, including diabetic retinopathy, glaucoma, and retinopathy of prematurity. The imaging of oxygen tension (PO2) in the retina, generated from a measure of the phosphorescence lifetimes of injected palladium-porphyrin probes, has been used successfully for nearly a decade to study retinal oxygen dynamics in the cat, miniature pig, and monkey; however, the specific parameters for applying this technique in the mouse have not been thoroughly investigated. As the number of transgenic and knockout mouse models displaying characteristics of human retinal diseases rapidly increases, an ability to image PO2 in these very small eyes will likely be of great benefit. In this study, we investigate the refinement of a technique for generating PO2 maps in the mouse retina using our recently constructed phosphorescence lifetime imaging system. Method: To accurately measure retinal PO2 in this animal, it was necessary to optimize a number of important acquisition parameters, including excitation power, intravascular probe concentration, camera exposure time, and camera intensifier gain settings. Measurements were made using both an in vitro calibration system and in vivo experiments in mice. Appropriate ranges for the stated parameters were determined using relationships between camera signal-to-noise values and the coefficient of determination (R2) generated from the least-squares analysis used to produce the PO2 maps. Results: R2 decreased with increasing intensifier gain (at the same signal-to-noise ratio), with the highest gain setting for the camera (255) producing unacceptable fits. Intensifier gain settings of 10 and 100 yielded R2 values above 0.90 with exposure times of 440 ms and 43 ms, respectively. Thus moderate intensifier gain (near 100) reduced exposure time dramatically without significantly affecting the fits. The determined ranges for these parameters are currently being applied to the in vivo experiments, where excitation power and intravascular probe concentration will also be varied to study the effects of probe excitation on mouse retinal physiology. Conclusion: Determination of these parameters permits a more efficient and effective method for creating oxygen maps in the mouse retina. Investigation of how changes in retinal oxygen tension correlate with ocular disease progression in cases where abnormalities in the delivery and consumption of oxygen are thought to be contributing factors, such as diabetic retinopathy, now becomes possible in the mouse.
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