Role of Nitric Oxide in Optic Nerve Head Blood Flow Regulation During Experimental Increase of Intraocular Pressure in Healthy Humans

Summary

Autoregulation is defined as the ability of a vascular bed to adapt its vascular resistance to changes in perfusion pressure. In the eye, several studies have reported that retinal blood flow is autoregulated over a wide range of ocular perfusion pressures. Large scale studies have shown that reduced ocular perfusion pressure is an important risk factor for the prevalence, the incidence and the progression of primary open angle glaucoma.

Former studies that investigated ocular blood flow autoregulation focused mainly on choroidal blood flow. For the optic nerve head only few data are available, although it seems likely that it underlies similar autoregulatory mechanisms.

A previous study investigating choroidal blood flow has shown that nitric oxide (NO) plays a key role in choroidal autoregulation. The present study is designed to test the hypothesis that NO plays a role in optic nerve head autoregulation during increased intraocular pressure (IOP). Therefore, IOP will be experimentally increased using a suction cup device in the absence of presence of either a nitric oxide synthase inhibitor (L-NMMA), an α-receptor agonist (phenylephrine) or placebo. Optic nerve head blood flow will be continuously measured during the procedure.

Conditions

• Healthy

Interventions

DRUG

NG-monomethyl-L-arginine (L-NMMA)

bolus 6mg/kg over 5 minutes followed by a continuous infusion of 60µg/kg/min over 15 minutes

DRUG

Phenylephrine

1µg/kg/min, infusion period 20 minutes

DRUG

Physiological saline solution (as placebo)

infusion period 20 minutes

DEVICE

Laser Doppler Flowmetry

Measurements will be performed at the neuroretinal rim to assess ONH blood flow.

DEVICE

Goldmann applanation tonometer

intraocular pressure measurements

DEVICE

Suction cup

Experimental stepwise increase of intraocular pressure while measurement of optic nerve head blood flow.

Sponsors & Collaborators

• Medical University of Vienna

  lead OTHER

Principal Investigators

• Gabriele Fuchsjaeger-Mayrl, MD, Univ.Doz. · Department of Clinical Pharmacology, Medical University of Vienna

Study Design

Allocation

RANDOMIZED

Purpose

BASIC_SCIENCE

Masking

TRIPLE

Model

CROSSOVER

Eligibility

Min Age

18 Years

Max Age

35 Years

Sex

ALL

Healthy Volunteers

Yes

Timeline & Regulatory

Start

2010-10-31

Primary Completion

2011-07-31

Countries

• Austria

Study Locations