Aging affects retinal oxygen and blood flow metrics in mice

Purpose: Aging affects the eyes and is a major risk factor for ocular diseases. The purpose of this study was to determine the effect of age on retinal oxygen and blood flow metrics in mice. Methods: Forty-seven C57BL/6 mice were included in four age groups (3-month-old (m): N = 18, 9m: N = 13, 15m: N = 8, and 21m: N = 8). Retinal arterial and venous diameters (DA, DV), venous blood velocity (VV), and arterial and venous oxygen contents (O2A, O2V) were measured by our established multimodal imaging system. Average blood flow (BF), oxygen delivery (DO2), metabolism (MO2), and extraction fraction (OEF) were calculated. ANOVA, and Tukey post-hoc analyses were performed to determine the effect of age on variables. Results: We found significant differences in VV, BF, O2A, O2V, and DO2 among the age groups. VV was significantly lower in the 21m (p = 0.004) and marginally lower in 15m (p = 0.06) compared to the 3m group, representing reductions of 41% and 30%, respectively. BF was lower in the 21m than the 3m group (p = 0.007), a 42% reduction. Additionally, O2A and O2V were significantly lower in 21m compared to the 9m group (p <= 0.05), indicating reductions of 30% and 65%, respectively. DO2 was significantly decreased in the 21m compared to 15m (p = 0.05) and 9m (p = 0.04) groups, representing reductions of 46% and 44%, respectively. Differences in MO2, OEF, DA, and DV did not reach statistical significance (p >= 0.07). Conclusions: Our results showed that retinal vascular oxygen content, oxygen delivery rate, and blood flow were significantly reduced in older mice and established baselines for retinal physiological biomarkers according to age.