Purpose: To determine the vascular reactivity (VR) capacity and visual function (VF) response to potent vasoconstrictor and vasodilatory provocations of retinal arterioles in healthy subjects. Methods: One hyperoxic hypocapnic and two graded hypoxic hypercapnic stimuli were administered. VR in response to gas provocation was assessed using the Canon Laser Blood Flowmeter. VF was assessed using high and low contrast ETDRS logMAR charts, Medmont C-100, and H.R.R. Pseudoisochromatic Plates. Results: Flow reduced by 23% (p=0.0001) during hyperoxic hypocapnia and increased by 18% (p=0.0129) during hypoxic hypercapnia. During hyperoxic hypocapnia, high contrast VA improved by -0.026 (p=0.0372). During hypoxic hypercapnia, high and low contrast VA were reduced (+0.033, p=0.0110; +0.025, p=0.0058, respectively). Colour vision was unaffected. Conclusions: The retinal arterioles demonstrated a greater capacity for vasoconstriction than vasodilation in response to the stimuli used in our study. Hyperoxic hypocapnia improved high contrast VA while hypoxic hypercapnia reduced high and low contrast VA.

Purpose: To determine the vascular reactivity (VR) capacity and visual function (VF) response to potent vasoconstrictor and vasodilatory provocations of retinal arterioles in healthy subjects. Methods: One hyperoxic hypocapnic and two graded hypoxic hypercapnic stimuli were administered. VR in response to gas provocation was assessed using the Canon Laser Blood Flowmeter. VF was assessed using high and low contrast ETDRS logMAR charts, Medmont C-100, and H.R.R. Pseudoisochromatic Plates. Results: Flow reduced by 23% (p=0.0001) during hyperoxic hypocapnia and increased by 18% (p=0.0129) during hypoxic hypercapnia. During hyperoxic hypocapnia, high contrast VA improved by -0.026 (p=0.0372). During hypoxic hypercapnia, high and low contrast VA were reduced (+0.033, p=0.0110; +0.025, p=0.0058, respectively). Colour vision was unaffected. Conclusions: The retinal arterioles demonstrated a greater capacity for vasoconstriction than vasodilation in response to the stimuli used in our study. Hyperoxic hypocapnia improved high contrast VA while hypoxic hypercapnia reduced high and low contrast VA.