Aging decreases CO₂ reactivity in the retinal artery, but not in the ocular choroidal vessels; A cross-sectional study

BACKGROUND: The CO₂ reactivity is often used to assess vascular function, but it is still unclear whether this reactivity is affected by aging. OBJECTIVE: To investigate the effects of aging on the CO₂ reactivity in ocular and cerebral vessels, both of which are highly sensitive to hypercapnia, we compared the CO₂ reactivity in the retinal artery (RA), retinal and choroidal vessels (RCV), optic nerve head (ONH), and middle cerebral artery (MCA) between young and middle-aged subjects. METHODS: We measured the CO₂ reactivity in 14 young and 11 middle-aged males using laser-speckle flowgraphy during a 3-min inhalation of CO₂-rich air. RESULTS: The CO₂ reactivity in the RA and ONH were lower in the middle-aged group than in the young group, but no significant effect of age was observed in the RCV or MCA. The CO₂ reactivity in the RA and ONH were correlated significantly with age, whereas those in the RCV or MCA were not. CONCLUSIONS: These findings suggest that there are regional differences in the effect of age on the CO₂ reactivity among not only ocular and cerebral vessels, but also the retinal and choroidal vessels, even though these vessels are in neighboring areas.