Abstract
The retina requires adequate oxygenation to maintain cellular metabolism and visual function. Inner retinal oxygen metabolism is directly related to retinal vascular oxygen tension (PO2) and inner retinal oxygen extraction fraction (OEF), whereas outer retinal oxygen consumption (QO2) relies on oxygen availability by the choroid and is contingent upon retinal tissue oxygen tension (tPO2) gradients across the retinal depth. Thus far, these oxygenation and metabolic parameters have been measured independently by different techniques in separate animals, precluding a comprehensive and correlative assessment of retinal oxygenation and metabolism dynamics. The purpose of the current study is to report an innovative optical system for dual oxyphor phosphorescence lifetime imaging to near-simultaneously measure retinal vascular PO2 and tPO2 in rats. The use of a new oxyphor with different spectral characteristics allowed differentiation of phosphorescence signals from the retinal vasculature and tissue. Concurrent measurements of retinal arterial and venous PO2, tPO2 through the retinal depth, inner retinal OEF, and outer retinal QO2 were demonstrated, permitting a correlative assessment of retinal oxygenation and metabolism. Future application of this method can be used to investigate the relations among retinal oxygen content, extraction and metabolism under pathologic conditions and thus advance knowledge of retinal hypoxia pathophysiology.
Highlights
Several techniques have become available for quantitative assessment of oxygen content within the retinal vasculature or tissue
A novel optical imaging method for near-simultaneous imaging of retinal vascular PO2 and tPO2 was demonstrated by phosphorescence lifetime imaging of dual oxyphors delivered intravenously and intravitreally
Inner retinal oxygen extraction fraction (OEF) was 0.58, on average, indicating 58% of the oxygen delivered by the retinal circulation was extracted for metabolism by the inner retinal tissue
Summary
Several techniques have become available for quantitative assessment of oxygen content within the retinal vasculature or tissue. Information about the metabolic activity of the retinal tissue has become available by calculation of inner retinal oxygen extraction fraction (OEF) based on retinal vascular oxygen content[5, 16] and by estimation of outer retinal oxygen consumption (QO2) from retinal tPO2 depth profiles[14, 17, 18] To date, these parameters of retinal oxygenation and metabolism have been measured independently in separate animals. The purpose of the current study is to report an innovative optical system for dual oxyphor phosphorescence lifetime imaging to near-simultaneously measure retinal vascular PO2 and tPO2 in rats, derive OEF and QO2, and determine associations among these parameters
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