Retinal oxygen extraction during systemic hypoxia assessed with laser-speckle flowgraphy and retinal oximetry

Aims/Purpose: Retinal oxygen extraction has been found to be altered in several ocular and systemic diseases, such as diabetic retinopathy, glaucoma or neurodegenerative diseases. However, measurement techniques for the assessment of retinal oxygen extraction are limited because most of them are based on time-consuming and custom-built devices. In the present pilot study, we assessed retinal oxygen extraction during systemic hypoxia with a combination of two commercially available devices: Laser-Speckle Flowgraphy (LSFG) and retinal oximetry.

Methods: Retinal blood flow and retinal oxygen saturation were measured in each vessel around the optic nerve head at the same position. Arterial and venous oxygen content was estimated from the measured retinal oxygen saturation parameters and the difference between these two parameters was calculated (cO₂,_DIFF). By using mean vessel flow rate (MV) for retinal blood flow and cO₂,_DIFF, retinal oxygen extraction was determined. For each healthy study participant, baseline measurement and measurement during inhalation of 88% nitrogen in 12% oxygen were performed.

Results: Ten (10) healthy subjects (4 females, 6 males) with a mean age of 27 ± 3 years were included in this study. During systemic hypoxia, a significant decrease in arterial oxygen content occurred (p = 0.046) while venous oxygen content did not change, leading to a decrease in cO₂,_DIFF. As expected, this was accompanied by a significant increase in MV (p = 0.014). No change in retinal oxygen extraction was observed (46 ± 8 a.u. at baseline vs. 46 ± 5 a.u. during hypoxia, p = 0.997).

Conclusions: Breathing of 88% nitrogen in 12% oxygen caused a significant decrease in retinal arterial oxygen content. This was compensated by an increase in retinal blood flow in order to keep retinal oxygen extraction constant. This was physiologically expected, and these findings are consistent with the literature. Therefore, the presented approach for measurement of retinal oxygen extraction appears to be feasible.