Age-Related Decline of Retinal Oxygen Extraction in Healthy Subjects

Abstract

PURPOSE. To investigate the age-dependence of total retinal blood flow and total retinal oxygen extraction in healthy subjects and determine their possible correlations with structural optical coherence tomography (OCT) parameters. METHODS. This observational cross-sectional study consisted of 68 healthy subjects (mean 6 SD age, 45.6 6 16.3 years; 47% female). Total retinal oxygen extraction was calculated based on measurement of total retinal blood flow using bi-directional Doppler OCT and measurement of oxygen saturation using spectroscopic reflectometry. Retinal nerve fiber layer thickness was measured using OCT, and the total number of retinal ganglion cells was estimated based on a previous published model. Correlation of these parameters with age was studied and the association between structural OCT parameters and hemodynamic vascular parameters was calculated. RESULTS. Both structural and vascular parameters showed a significant decline with increasing age. The correlation coefficients were between r ¼ À0.25 and r ¼ À0.41. Furthermore, structural and vascular parameters were significantly correlated with each other. The strongest association was found between the level of total retinal oxygen extraction and the number of retinal ganglion cells (r ¼ 0.75, P < 0.001). CONCLUSIONS. We showed that there was an age-related decline of retinal oxygen extraction. Levels of retinal oxygen extraction are correlated to retinal nerve fiber layer thickness and number of retinal ganglion cells. Our data partially explain the wide inter-individual variability in retinal blood flow values in healthy subjects. Longitudinal studies are required to study the time course of vascular and neuronal loss in humans.

Repeatability and Reproducibility of Total Retinal Blood Flow Measurements Using Bi-Directional Doppler OCT

“…Previous studies have indicated an age-related decline in retinal blood flow. 32,48,49 In this study we did, however, include only healthy young subjects, and the age range was narrow. Whereas some studies indicate higher retinal blood flow in women, 50 data are controversial, and no clear evidence for gender differences exists.…”

“… 46 We have previously presented a method for calculating total retinal oxygen extraction by coupling the dual-beam Doppler OCT system to a fundus camera. 7 , 31 , 32 Although we have not explicitly studied the repeatability and reproducibility of this approach, it can be estimated based on our previous results on the variability of oxygen saturation measurements 47 and the data obtained in this study.…”

“…The system and analysis of data have been described in a number of previous publications and will therefore only be summarized shortly here. 7 , 26 , 27 , 30 – 32 The technology is based on the illumination of the target tissue with two laser beams separated by an angle Δα being the difference between the Doppler angles α i of the two measurement channels (Δα = α 1 – α 2 ). Hence, given by the different Doppler angles, the phase changes that are detected in the two detection units are different.…”

The Various Oximetric Techniques Used for the Evaluation of Blood Oxygenation

“…The simultaneous measurement of oxygen saturation in a pair of retinal artery and vein can assess the arteriovenous difference of oxygen saturation and oxygen content, CaO 2 -CvO 2 (See Equation (1)). The latter provides information on the retinal oxygen consumption in the tissue supplied by the artery and drained by the vein, an important parameter, which is related to the metabolism rate of the retinal cells [ 78 , 79 ]. The arteriovenous difference of oxygen saturation or oxygen content decreased during breathing of 100% oxygen relative to breathing air in measurements on healthy subjects [ 78 , 80 ], but was unchanged in COPD patients [ 75 ].…”

“…Non-invasive retinal oximetry has been used in physiological studies on healthy persons [ 68 , 70 , 74 , 78 , 79 , 80 ] and on patients with ophthalmic and a number of systemic diseases [ 70 , 75 , 81 , 82 , 83 , 84 , 85 , 86 ]. The increase in arteriovenous difference of retinal oxygen saturation is generally due to ischemia, while the decrease in that difference might originate from atrophy, which is associated with lower metabolism of retinal cells.…”