Study of Choroidal Blood Flow by Comparison of SLO Fluorescein Angiography and Microspheres

doi:10.1006/exer.1996.0163

Experimental Eye Research

Volume 63, Issue 6, December 1996, Pages 693-704

https://doi.org/10.1006/exer.1996.0163 Get rights and content

Abstract

Choroidal hemodynamics estimated with parameters describing the dye build-up curves obtained with video fluorescein angiography, were compared with a classical regional blood flow measurement: radioactively labelled microspheres.

Video fluorescein angiograms (Rodenstock's SLO 101) and microspheres blood flow measurements were made in 13 anaesthetized pigmented rabbits. Ocular perfusion pressures were varied from 60 to 15 mmHg by changing the intraocular pressure. The angiographically derived dye build-up curves were described by means of an exponential model. One of the model parameters is the time constant τ theoretically reflecting local blood refreshment time. Labelled microspheres act as a non-recirculating blood flow indicator, enabling the estimation of regional blood flows. The relation between choroidal blood flow and perfusion pressure is nearly linear, suggesting the passive nature of choroidal vasculature. There is a significant correlation between τand microspheres flow (R=0.67,P<0.01). According to the rheological model the product of blood flow and τcorresponds to the relevant blood volume. Hence, a function for the volume of the choriocapillaris as a function of perfusion pressure was established.

The model parameter τcan be interpreted as the local blood refreshment time. Since the parameter τ, unlike microspheres, can be used clinically, τmay be used to retrieve information on choroidal hemodynamics in clinical practice. Information on the spatial distribution of choroidal hemodynamics is also obtained.

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Cited by (22)

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Since it is difficult to measure the in-vivo pressure in the choriocapillaris, several other methods have been explored. It is possible to assess it from volume data in a fluorescein and microsphere model (Duijm et al., 1996). It is also possible to measure the relative difference in the flow in several conditions with laser doppler flowmetry (Riva et al., 1994), pulsatile choroidal blood flow (Polak et al., 2003) and high-speed indocyanine green angiography (ICG) with precise dye bolus (Flower, 1993).
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The retina blood vessels extend medial and lateral to the optic disc. Most of the retina is avascular and the blood supply is derived from the choriocapillaris (De Schaepdrijver et al., 1989; Duijm et al., 1996). A key advantage of this newly-developed rabbit PRNV model is the persistence of leakage which enables it to be used to examine the efficacy of new drugs for sustained therapeutic effect.
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Here, we described the development of a novel rabbit model of persistent retinal neovascularization (PRNV). Retinal Müller glial are essential for maintaining the integrity of the blood-retinal barrier. Intravitreal injection of DL-alpha-aminoadipic acid (DL-AAA), a selective retinal glial (Müller) cell toxin, results in persistent vascular leakage for up to 48 weeks. We demonstrated that VEGF concentrations were significantly increased in vitreous suggesting VEGF plays a significant role in mediating the leakage observed. Intravitreal administration of anti-VEGF drugs (e.g. bevacizumab, ranibizumab and aflibercept) suppresses vascular leakage for 8–10 weeks, before recurrence of leakage to pre-treatment levels. All three anti-VEGF drugs are very effective in re-ducing angiographic leakage in PRNV model, and aflibercept demonstrated a longer duration of action compared with the others, reminiscent of what is observed with these drugs in human in the clinical setting. Therefore, this model provides a unique tool to evaluate novel anti-VEGF formulations and therapies with respect to their duration of action in comparison to the currently used drugs.
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2015, Experimental Eye Research
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The iris is the anterior portion of the uvea. Iris blood flow has been measured by radioactive labelled microspheres (Alm and Bill, 1972, 1973; Duijm et al., 1996) and laser Doppler flowmetry (Chamot et al., 2000). Iris blood flow can be modulated by ocular perfusion pressure and drugs (Cole and Rumble, 1970; Kogure, 1982; Nagasubramanian, 1975).
The roles of the iris microvasculature have been increasingly recognised in the pathogenesis of glaucoma and cataract; however limited information exists regarding the iris microvasculature and its endothelium. This study quantitatively assessed the iris microvascular network and its endothelium using intra-luminal micro-perfusion, fixation, and staining of the porcine iris. The temporal long posterior ciliary artery of 11 isolated porcine eyes was cannulated, perfusion-fixed and labelled using silver nitrate. The iris microvasculature was studied for its distribution, orders and endothelial morphometrics. The density of three layers of microvasculature was measured. Endothelial cell length and width were measured for each vessel order. The iris has an unusual vascular distribution which consisted of abundant large vessels in the middle of the iris stroma, branching over a relatively short distance to the microvasculature located in the superficial and deep stroma as well as the pupil edge. The average vascular density of the middle, superficial, and deep layers were 38.9 ± 1.93%, 10.9 ± 1.61% and 8.0 ± 0.79% respectively. Multiple orders of iris vessels (capillary, 6 orders of arteries, and 4 orders of veins) with relatively large capillary and input arteries (319.5 ± 25.6 μm) were found. Significant heterogeneity of vascular diameter and shape of the endothelia was revealed in different orders of the iris vasculature. Detailed information of topography and endothelium of the iris microvasculature combined with unique structural features of the iris may help us to further understand the physiological and pathogenic roles of the iris in relevant ocular diseases.
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2000, Japanese Journal of Ophthalmology
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The relationship between blood flow and ocular perfusion pressure in the iris vascular bed of the human eye has not been established yet. Consequently, it is not known whether the iris circulation has some autoregulatory capacity. The aim of the present study was to investigate this relationship in the particular case where the perfusion pressure was decreased by increasing the intraocular pressure.
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2000, Microvascular Research
The purpose of this study was to develop an in vivo, noninvasive method to assess the velocities of normal and sickle red blood cells (RBCs) in the retinal and choroidal vasculatures of rats. Human and rat RBCs were isolated from whole blood, labeled with fluorescein isothiocyanate (FITC), and administered intravenously to anesthetized rats. A Rodenstock scanning laser ophthalmoscope (SLO) was used to image the FITC-labeled RBCs as an NTSC video signal. Video sequences of RBC transit in the retinal (pigmented rats) and choroidal (albino rats) vessels were captured directly to digital format. Following in vivo angiography, the animals were sacrificed, the eyes enucleated, and retinas prepared by our adenosine diphosphatase vascular labeling technique for viewing by conventional optical microscopy. Although rat and normal human RBCs differ slightly in size, their velocities were similar in the retinal arteries and capillaries (within 4%). Velocities of RBCs from sickle cell patients (sRBCs) were slower by 12 and 9% in arteries and by 38 and 25% in capillaries, compared to rat and normal human RBCs, respectively. Compared to velocities in retinal capillaries, the velocities in choroidal capillaries were much slower for rat RBCs (77%), normal human RBCs (79%), and sRBCs (67%). In contrast to normal human RBCs, sRBCs were often retained transiently in retinal capillaries at preferred sites, but in choroidal capillaries large numbers of cells were retained for extended periods. SLO imaging of FITC-labeled RBCs in rat retina and choroid provided a reliable method for evaluating normal and abnormal hemodynamics.

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Regular articleStudy of Choroidal Blood Flow by Comparison of SLO Fluorescein Angiography and Microspheres

Abstract

Regular article
Study of Choroidal Blood Flow by Comparison of SLO Fluorescein Angiography and Microspheres