Optic nerve head blood flow response to increase of arterial blood pressure in humans

Purpose Autoregulation in ocular tissues allows a constant blood flow despite variations in ocular perfusion pressure and may be impaired in ocular diseases. The purpose of this study was to investigate the effect of increased blood pressure (BP) and ocular perfusion pressure (OPP) during isometric exercise on the optic nerve head blood flow (FONH). Methods In 21 healthy subjects, aged 18 to 40 years, BP was measured using a pneumatic transcutaneous sensor Nexfin™ and blood flow was measured using LDF. OPP was defined as (0.74 × mean BP) – intraocular pressure. Handgripping consisted of static contraction of the finger flexors at 30% of maximum contraction force using a hand dynamometer during two minutes. Results Data was analyzed in 15 healthy subjects, exhibiting a homogeneous response of BP to handgrip (linear regression of BP versus time, R> 0.8). A large increase in OPP during exercise up to 50% was not associated with a proportional increase in FONH, vascular resistance increased about 30%. The blood flow‐pressure relationship showed blood flow significantly increased by approximately 30%, mainly due to the rise of velocity. Conclusion This new data strongly supports the notion of autoregulation in ocular blood flow, protecting the eye from over‐perfusion. However the increase in OPP is not completely counterbalance despite the regular increase of vascular resistance. This blood flow regulation is possibly due to a vasoconstriction, taking place outside of the sampled volume, probably in the arterioles proximal to the capillary bed of the neuroretinal rim. In the future, real time measurements of vascular resistance during handgripping could be investigated in glaucoma patients.