A parametric evaluation of retinal vascular perfusion pressure and visual neural function in man

doi:10.1016/0013-4694(90)90172-G

Electroencephalography and Clinical Neurophysiology

Volume 75, Issue 3, March 1990, Pages 185-199

https://doi.org/10.1016/0013-4694(90)90172-G Get rights and content

Abstract

Body inversion and opthalmodynamometry were used to alter the intraocular pressure/retina vascular perfusion pressure (IOP/RVPP) relationship in 10 normotensive adults. Using scotopic and photopic flash electroretinograms (fERGs), a heightened susceptibility of the rod system relative to the cone system was identified for transient alterations of the RVPP. The scotopic fERG b-wave decreased by about 40% and the photopic fERG was relatively unchanged when the RVPP was reduced by 51%. When the RVPP was increased by some 90%, the scotopic b-wave decreased by about 11%, and the photopic fERG by 8%. The greater vulnerability of the rod system than the cone system to decreased RVPP was tentatively attributed to structural differences between the photoreceptor types, their retinal distribution, and the effectiveness of vascular autoregulatory mechanisms.

The neural generators of the pattern evoked retinal potential (pERG) showeda large impairment in function with both an increase and a decrease in the RVPP. In contrast, pattern evoked cortical potentials (pVEPs) showed a significant reduction in amplitude only when the RVPP was increased. These latter results suggest that the generators of pERGs are dependent on some ideal and narrow range of RVPP for normal activity whereas the generators of pVEPs are more vulnerable to the direct pressure effects of vascular engorgement within the eye and intracranial structures.

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In particular, the ocular perfusion pressure (OPP = Mean arterial blood pressure minus IOP) may decrease in head-down and increase in head-up posture. Changes in OPP may be associated to changes in PERG amplitude (Kothe and Lovasik, 1990; Siliprandi et al., 1988). OPP is also expected to decrease with age-related spontaneous IOP elevation, and to increase with pharmacological IOP-lowering treatment.
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Vascular abnormality and altered hemodynamics play important roles in many ophthalmic pathologies. Much of our knowledge of ocular hemodynamics was gained from invasive animal research, although a number of noninvasive methods suitable for in vivo use in humans have been developed. Data from these methods now produce a significant literature of their own. Understanding the origins of the data and appreciating their limitations can be difficult. Modern hemodynamic assessment techniques each examine a unique facet of the ocular circulation. No single facet provides a complete description of the hemodynamic state of the eye. These methods have contributed a great deal to our understanding of normal hemodynamics. More importantly, they continue to add to our understanding of altered hemodynamics found in disease. Some have found their way into limited clinical practice. The predominant ocular hemodynamic assessment techniques are reviewed with the aims of introducing the fundamental principles behind each, highlighting their inherent advantages and limitations, highlighting their contributions to understanding ocular physiology, and considering their potential to provide signs for diagnosis. (Surv Ophthalmol 42:509–533, 1998.
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Vision loss in glaucoma may be due to the compressive effects of the intraocular pressure (IOP) on the ganglion cell axons, impaired blood flow to the optic nerve, or some combination of these two factors. While reducing the IOP may preserve vision in patients with elevated IOP, not all patients experience longterm benefits from this therapeutic approach. The survival of ganglion cells may be more dependent upon the degree of vascular perfusion of the optic nerve head (ONH). In this report we present some preliminary data on a new noninvasive videographic technique for elaborating the capacity of the ONH vasculature to maintain perfusion constancy in the presence of transient elevations of the IOP and reductions of the ocular perfusion pressure (OPP). Shortterm, stepwise reductions of the OPP in the test eye of visually normal subjects (n = 5) systematically altered both the chromaticity (hue, saturation, brightness) of the ONH and the pulsatile ocular blood flow (POBF) in the choroid. Similar transient reductions in the OPP were seen to impair normal retinal physiology, as indicated by a significant attenuation of the bilateral pattern-reversal electroretinograms (pERGs) in visually normal subjects (n = 7). This technique was also used to reveal spontaneous rhythmical variations in the ONH chromaticity which were linked to the cardiac pulse rate. This so-called “chromatic pulse” of the ONH offers potential as a useful clinical index for evaluating the vascular perfusion of the ONH. The diagnostic and prognostic potential of dynamic digital imaging for the detection of abnormal hemodynamics in the ONH is discussed.
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^☆: Natural Sciences and Engineering Research Council of Canada.

^☆☆: This study was supported by an operating grant (No. A0057) from the Natural Sciences and Engineering Council of Canada to J.V.L. A.C.K. was supported by a post-graduate scholarship from the Natural Sciences and Engineering Research Council of Canada throughout the course of this study.

^∗: We gratefully acknowledge the cooperation of all our subjects, consultation by Dr. A.J. Palmer, the technical/technological support of J. Cassidy, D. Grisebach, R. Jones, and M. Rieck, and expert statistical analyses of data by E. Harvey of the University of Waterloo, Statistics Consulting Department.

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Main articleA parametric evaluation of retinal vascular perfusion pressure and visual neural function in man☆,☆☆

Abstract

Exp. Eye Res.

Ophthalmology

Am. J. Ophthalmol.

Vision Res.

Am. J. Ophthalmol.

Effect of hypoxia on the maintained firing rate of retinal ganglion cells

Invest. Ophthalmol. Vis. Sci.

Das Elektroretinogramm und das evozierte Sehrindenpotential bei normalen und an Glaukom erkrankten Augen.

Alb. v. Graefes Arch. Klin. Exp. Ophthalmol.

Die Änderung der elektrophysiologischen Antwort am mensclichen Auge bei kurzzeitiger Erhöhung des intraokularen Druckes

Alb. v. Graefes Arch. Klin. Exp. Ophthalmol.

The pattern electroretinogram

Eye

The blood supply of the eye and its regulation

The importance of stimulus selection in VEP practice: the clinical relevance of visual physiology

Clinical electroretinography. Part 1: Foundations

Can. J. Ophthalmol.

Clinical electroretinography. Part 2: Applications

Can. J. Ophthalmol.

Rod-cone differences in response to retina ischemia in rabbit

Docum. Ophthalmol.

Effects of aging on visual evoked responses

Arch. Neurol.

Computer assisted quantitative electroretinography. I. A standardized method

Am. J. EEG Technol.

Computer assisted quantitative electroretinography. II. Separation of rod and cone components of the electroretinogram in congenital achromatopsia and congential nyctalopia

Am. J. EEG Technol.

Improved electrode for electroretinography

Invest. Ophthalmol. Vis. Sci.

The effect of hyperbaric oxygenation on retinal ischemia

Invest. Ophthalmol.

Optic nerve dysfunction during gravity inversion. Pattern reversal visual evoked potentials

Arch. Ophthalmol.

Ocular manifestations of gravity inversion

JAMA

Postural changes in the circulation

Visual adaptation: its mechanism

Science

Function of retinal nerve fibers depends on perfusion pressure: neurophysiologic investigations during acute intraocular pressure elevation

Invest. Ophthalmol. Vis. Sci.

Retinal circulation during a spontaneous rise of intraocular pressure

Br. J. Ophthalmol.

Responses of retinal ganglion cells to eyeball deformation. A neurophysiological basis for pressure phosphenes

Main article
A parametric evaluation of retinal vascular perfusion pressure and visual neural function in man☆,☆☆