Optical mapping of inner retinal tissue PO2.

Abstract

A high resolution optical mapping procedure was developed to visualize oxygen concentration levels topographically within the tissue of the inner retina in vivo. The novel optical mapping procedure has the potential for describing oxygen metabolism in retinal and other body tissues and elucidating the coupling of metabolism to function. The method is based upon the fluorescence quenching by molecular oxygen of a lipid soluble probe substance which accumulates within the lipid bilayers of tissue cells. The optical mapping system can provide more than 300,000 values of tissue PO2 in space with millisecond time resolution. Optical maps of inner retinal tissue PO2 were imaged under conditions of normoxia, hyperoxia, and for a retina which received restricted panretinal photocoagulation. Moreover, the effects of transient increases in intraocular pressure were also investigated. An O2 consumption rate of 5.48 +/- 0.50 (SEM) x 10(-3) ml O2/ml tissue/min for the light-adapted rat inner retina was estimated from the application of a Krogh cylinder diffusion model to tissue PO2 gradients measured in the capillary-free zone around arterioles. Similarly, arterioles oxygenated a surrounding cylinder of tissue with a mean radius of 144.73 +/- 5.52 (SEM) microns. Histograms of PO2 values within inner retinal tissue (mean PO2 = 25.03 mm Hg, median = 24.58 mm Hg) showed remarkable correspondence to those determined invasively in brain by others, using O2 microcathodes, possibly suggesting a similarity in the underlying capillary architectures of the two neural tissues.(ABSTRACT TRUNCATED AT 250 WORDS)