Short-Term Increase of Intraocular Pressure Does Not Alter the Response of Retinal and Optic Nerve Head Blood Flow to Flicker Stimulation

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PURPOSE. We compared the response of choroidal and optic nerve head blood flow (ChBF, ONHBF) in response to an increase in ocular perfusion pressure (OPP) during isometric exercise and during a decrease in OPP during an artificial increase in intraocular pressure (IOP). METHODS.We included 96 healthy subjects in our study. In 48 subjects OPP was increased by 6 minutes of squatting, and either ONHBF (n ¼ 24) or ChBF (n ¼ 24) was measured continuously. In 48 other healthy subjects either ONHBF (n ¼ 24) or ChBF (n ¼ 24) was measured continuously during a period of artificial increase in IOP using a suction cup. All blood flow measurements were done using laser Doppler flowmetry. RESULTS.During all experiments the response in blood flow was less pronounced than the response in OPP, indicating for flow regulation. During isometric exercise ChBF regulated better than ONHBF (P ¼ 0.023). During artificial IOP increase ONHBF regulated better than ChBF (P ¼ 0.001). Interindividual variability in blood flow responses was high. During squatting ONHBF decreased considerably below baseline ONHBF when OPP fluctuated in 3 subjects, although OPP still was much higher than at baseline. This phenomenon was not observed in the choroid. CONCLUSIONS.Our data indicate that regulation of ChBF and ONHBF during changes in OPP is different and complex. In some subjects performing squatting, considerable ONHBF reductions were observed during OPP fluctuations, although OPP still was high. Whether this predisposes to ocular disease remains unclear. (Invest Ophthalmol Vis Sci. 2012;53:4337-4346)

Section: Discussionsupporting

confidence: 70%

Section: Discussionmentioning

confidence: 99%

Comparison of Choroidal and Optic Nerve Head Blood Flow Regulation during Changes in Ocular Perfusion Pressure

Schmidl¹,

Boltz

Kaya³

et al. 2012

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“…Studies supporting the autoregulatory capacity have been performed in healthy humans, nonhuman primates, cats, and rabbits. [17][18][19][20][21][22][23][24][25] The mechanisms that mediate this autoregulatory response in the ONH are unclear. Nitric oxide (NO) is a potent vasodilator that is involved in the maintenance of basal vascular tone, in tonic blood pressure regulation, and in the distribution of blood flow.…”

Section: Methodsmentioning

confidence: 99%

Role of Nitric Oxide in Optic Nerve Head Blood Flow Regulation during Isometric Exercise in Healthy Humans

Schmidl¹,

Boltz

Kaya³

et al. 2013

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PURPOSE. We determined whether administration of a nitric oxide synthase (NOS) inhibitor alters optic nerve head blood flow (ONHBF) regulation during isometric exercise in healthy subjects. METHODS.Our study was done in a randomized, placebocontrolled, double-masked, three-way crossover design. A total of 18 healthy subjects was randomized to receive either placebo, phenylephrine, or an inhibitor of NOS (L-NMMA) on three different study days. ONHBF was measured with laser Doppler flowmetry while the study participants performed isometric exercise (squatting). This was done before drug administration and during infusion of the study drugs. Mean arterial pressure (MAP) and IOP were measured noninvasively, and ocular perfusion pressure (OPP) was calculated as 2/3 MAP À IOP.RESULTS. The response in ONHBF to isometric exercise was less pronounced than the response in OPP, indicating for some autoregulatory capacity in the ONH. Administration of L-NMMA significantly decreased ONHBF at rest (P < 0.01). In contrast, inhibition of NOS did not alter the pressure-flow relationship in the ONH during an experimental increase in OPP compared to phenylephrine and placebo (P ¼ 0.37 between groups).CONCLUSIONS. The data of our study support previous findings that ONHBF is autoregulated during an experimental increase in OPP. Nitric oxide has an important role in basal ONHBF regulation, but seems not to be involved in the autoregulatory response during an increase in OPP induced by isometric exercise. (ClinicalTrials.gov number, NCT00806741.) (Invest Ophthalmol Vis Sci.

“…A large number of studies have been performed to assess vessel diameter changes during stimulation with diffuse luminance flicker in healthy subjects under normal conditions 9,11 or during oxygen breathing, 15 as well as in patients with diabetes, 16,17 glaucoma, 18,19 or systemic hypertension. 19,20 However, the interpretation of the latter experiments is limited by the fact that only data about retinal vessel diameter, but not about volumetric blood flow, are available.…”

mentioning

confidence: 99%

Effect of Diffuse Luminance Flicker Light Stimulation on Total Retinal Blood Flow Assessed With Dual-Beam Bidirectional Doppler OCT

Aschinger

Schmetterer

Fondi

et al. 2017

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METHODS. In six healthy subjects, TRBF was measured before and during stimulation with diffuse luminance flicker. Blood flow velocities in retinal vessels were measured via dual-beam bidirectional Doppler Fourier-domain optical coherence tomography (FD-OCT), retinal vessel diameters were assessed based on FD-OCT phase data. This allowed for the calculation of TRBF before and during visual stimulation. Additionally, a mathematical flow model for the retinal vasculature was adapted to study the implications of diameter variations on retinal perfusion. Measured and simulated perfusion was compared to draw conclusions on the diameter variations in different layers of the vascular tree.RESULTS. The measured mean baseline flow was 36.4 6 6.5 ll/min while the mean flow during flicker stimulation was 53.4% 6 8.3 ll/min. The individual increase in TRBF during flicker stimulation ranged between 34% and 66%. The average increase in TRBF over all measured subjects was 47.6% 6 12.6%.CONCLUSIONS. Dual-beam bidirectional Doppler FD-OCT allowed quantifying NC in the human retina in vivo and may be a promising method for monitoring alterations in NC caused by various pathologies. The comparison of the measured data with the results obtained in the simulated vasculature indicates that the vasodilation induced by NC is more pronounced in smaller vessels.