A method for volumetric retinal tissue oxygen tension imaging

ABSTRACT

Purpose: Inadequate retinal oxygenation occurs in many vision-threatening retinal diseases, including diabetic retinopathy, retinal vascular occlusions, and age-related macular degeneration. Therefore, techniques that assess retinal oxygenation are necessary to understand retinal physiology in health and disease. The purpose of the current study is to report a method for the three-dimensional (3D) imaging of retinal tissue oxygen tension (tPO₂) in rats.

Methods: Imaging was performed in Long Evans pigmented rats under systemic normoxia (N = 6) or hypoxia (N = 3). A vertical laser line was horizontally scanned on the retina and a series of optical section phase-delayed phosphorescence images were acquired. From these images, phosphorescence volumes at each phase delay were constructed and a 3D retinal tPO₂ volume was generated. Retinal tPO₂ volumes were quantitatively analyzed by generating retinal depth profiles of mean tPO₂ (M_tPO2) and the spatial variation of tPO₂ (SV_tPO2). The effects of systemic condition (normoxia/hypoxia) and retinal depth on M_tPO2 and SV_tPO2 were determined by mixed linear model.

Results: Each 3D retinal tPO₂ volume was approximately 500 × 750 × 200 μm (horizontal × vertical × depth) and consisted of 45 en face tPO₂ images through the retinal depth. M_tPO2 at the chorioretinal interface was significantly correlated with systemic arterial oxygen tension (P = 0.007; N = 9). There were significant effects of both systemic condition and retinal depth on M_tPO2 and SV_tPO2, such that both were lower under hypoxia than normoxia and higher in the outer retina than inner retina (P < 0.001).

Conclusion: For the first time, 3D imaging of retinal tPO₂ was demonstrated, with potential future application for assessment of physiological alterations in animal models of retinal diseases.

KEYWORDS:

• Rat
• retina
• tissue oxygen tension
• three-dimensional imaging
• phosphorescence lifetime imaging

Acknowledgment

The authors would like to acknowledge the contributions of Tara Nguyen and Marek Mori for animal care and data acquisition.

Declaration of interests

None (AEF, JW, PT, NPB); patent (MS).

Funding

This study was supported by NIH grants EY017918 and EY001792, Senior Scientific Investigator award (MS) and an unrestricted departmental grant from Research to Prevent Blindness.

Additional information

Funding

This study was supported by NIH grants EY017918 and EY001792, Senior Scientific Investigator award (MS) and an unrestricted departmental grant from Research to Prevent Blindness