A Method for Combined Retinal Vascular and Tissue Oxygen Tension Imaging

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.

Biocompatible Ir(III) Complexes as Oxygen Sensors for Phosphorescence Lifetime Imaging

“…Biochemical processes in living aerobic organisms in many aspects are critically dependent on oxygen, which is a key substrate of energy metabolism [ 1 ] and an important indicator of cell/tissue physiological status under healthy and diseased conditions. Misbalance of oxygen demand and supply is associated with many pathologies, such as cancers [ 2 , 3 , 4 ], neurological diseases [ 5 , 6 ], retinopathy, glaucoma, and nuclear cataracts [ 7 , 8 , 9 ], that inevitably stimulates the study of organs, tissues, and cell compartments’ oxygenation, see for example Chapters 4 and 12 in book [ 10 ], Chapter 17 in [ 11 ], and research articles [ 12 , 13 , 14 ]. Noteworthy that in vitro and in vivo real time monitoring of O 2 concentration with high spatial and temporal resolution is one of the challenging tasks in medicine and biology, the solution of which can provide invaluable information related to metabolic status of cells and tissues in normal and diseased states.…”

Retinal tissue oxygen tension and consumption during light flicker stimulation in rat

“…(Felder et al, 2015; Hammer et al, 2011; Shakoor et al, 2006; Teng et al, 2014) Recently, we described a method in which dual phosphors with different spectral characteristics were used to measure tPO 2 and intravascular PO 2 simultaneously. (Felder et al, 2017b) Further modifications of this method to also measure retinal blood flow and MO 2 is expected to contribute to elucidating the relationships among these factors and their time courses in response to light flicker stimulation.…”

“…The instrument and methods for retinal tPO 2 imaging have been described. (Felder et al, 2017b; Felder et al, 2018; Shahidi et al, 2010; Wanek et al, 2012) Briefly, the illumination light of a slit lamp biomicroscope was fitted with a 570 nm filter to illuminate a 30 degree retinal field of view, centered on the optic nerve head. Prior to image acquisition, the rats were under constant illumination for approximately 10 minutes during image alignment.…”

“…Second, the inner retina can change the rate at which oxygen is removed from the blood, thereby altering the arteriovenous oxygen concentration difference,(Hammer et al, 2011; Shakoor et al, 2006) and the oxygen extraction fraction (OEF). (Felder et al, 2015; Teng et al, 2014) While several groups have measured tPO 2 ,(Braun et al, 1995; Felder et al, 2017b; Felder et al, 2018; Linsenmeier, 1986; Pournaras, 1995; Shahidi et al, 2010; Wanek et al, 2012; Yu and Cringle, 2005) to the best of our knowledge, the only information available on how effective these compensatory mechanisms are in terms of stabilizing the retinal tPO 2 during light flicker stimulation is from Lau and Linsenmeier(Lau and Linsenmeier, 2012) in rats. In their study, oxygen sensitive microelectrodes that had been positioned within the inner retina (9 - 18% of the retinal depth from the internal limiting membrane) were used to measure tPO 2 during light flicker stimulation.…”

Imaging of Hypoxia in Retinal Vascular Disease

“…This technique was modified for use in vivo to measure PO 2 in the retinal and choroidal vasculature of large animals such as cats and pigs [95][96][97], and later for smaller animals such as mice and rats [98][99][100][101][102][103][104]. More recently Shahidi et al have made significant advances by using phosphorescence-lifetime to image oxygen tension within the retinal tissue itself [105,106]. This minimally invasive technique requires an intravenous injection of a phosphor that can be imaged using an intensified CCD camera to provide a clear image of retinal arteries, veins and even some capillaries with good spatial resolution.…”