Caffeine is the most commonly used stimulant drug with well documented effects on cerebral
vascula-ture. Caffeine is known to non-specifically bind to adenosine receptors in the brain
and to reduce resting blood flow while improving attention and cognitive function, which
suggests that it may allow a more efficient dynamic blood flow regulation through
neurovascular coupling. This study will use standardized dose of caffeine to test its effect
on NVC responses in cerebral and retinal arterioles.