A Method for Combined Retinal Vascular and Tissue Oxygen Tension Imaging

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 PO ₂ , tPO₂ through the retinal depth, inner retinal OEF, and outer retinal QO ₂ 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.