Optic nerve head and retinal blood flow regulation during isometric exercise as assessed with laser speckle flowgraphy.

Katarzyna J Witkowska,Alina Popa-Cherecheanu,Klemens Fondi,Doreen Schmidl,Gerhard Garhöfer,Leopold Schmetterer,Ahmed M Bata,Giacomo Calzetti,Nikolaus Luft,René M Werkmeister,Matthias Bolz,Piotr A Wozniak

doi:10.1371/journal.pone.0184772

Abstract

The aim of the present study was to investigate regulation of blood flow (BF) in the optic nerve head (ONH) and a peripapillary region (PPR) during an isometric exercise-induced increase in ocular perfusion pressure (OPP) using laser speckle flowgraphy (LSFG) in healthy subjects. For this purpose, a total of 27 subjects was included in this study. Mean blur rate in tissue (MT) was measured in the ONH and in a PPR as well as relative flow volume (RFV) in retinal arteries (ART) and veins (VEIN) using LSFG. All participants performed isometric exercise for 6 minutes during which MT and mean arterial pressure were measured every minute. From these data OPP and pressure/flow curves were calculated. Isometric exercise increased OPP, MTONH and MTPRR. The relative increase in OPP (78.5 ± 19.8%) was more pronounced than the increase in BF parameters (MTONH: 18.1 ± 7.7%, MTPRR: 21.1 ± 8.3%, RFVART: 16.5 ±12.0%, RFVVEIN: 17.7 ± 12.4%) indicating for an autoregulatory response of the vasculature. The pressure/flow curves show that MTONH, MTPRR, RFVART, RFVVEIN started to increase at OPP levels of 51.2 ± 2.0%, 58.1 ± 2.4%, 45.6 ± 1.9% and 45.6 ± 1.9% above baseline. These data indicate that ONHBF starts to increase at levels of approx. 50% increase in OPP: This is slightly lower than the values we previously reported from LDF data. Signals from the PPR may have input from both, the retina and the choroid, but the relative contribution is unknown. In addition, retinal BF appears to increase at slightly lower OPP values of approximately 45%. LSFG may be used to study ONH autoregulation in diseases such as glaucoma.Trial Registration: ClinicalTrials.gov NCT02102880

Highlights

The human optic nerve is a structure with vascular supply from different sources.[1, 2] The nerve fiber layer is nourished by vessels that get their supply from the central retinal artery
The % change in MTONH, and MTPPR was, small as compared to the % change in ocular perfusion pressure (OPP), which is indicative for blood flow autoregulation
No gender differences were observed in the time course of ocular hemodynamic parameters during isometric exercise (MTONH: p = 0.542, MTPPR,: p = 0.617, RFVART: p = 0.788, RFVVEIN, p = 0.424)

Summary

Introduction

The human optic nerve is a structure with vascular supply from different sources.[1, 2] The nerve fiber layer is nourished by vessels that get their supply from the central retinal artery. The pre-laminar region gets its vascular input from the peripapillary choroid. Alterations in optic nerve head (ONH) blood flow have been implicated in the pathogenesis of glaucoma. ONH ischemia and altered ONH blood flow autoregulation may play a role in the processes that lead to axon damage and subsequent loss of retinal ganglion cells.[2,3,4,5] data from a variety of studies have provided evidence for altered autoregulation in glaucoma.[6, 7]

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Conclusion