Retinal Capillary Bed Research Articles

Modeling Hemodynamics in Three-Dimensional, Biomimetic, Branched, Microfluidic, Vascular Networks.

Neovascularization has been extensively studied because of its significant role in both physiological processes and diseases. The significance of vascular microfluidic platforms lies in its essential role in recreating an in vitro environment capable of supporting cellular and tissue systems through the process of neovascularization. Biomechanical properties in a tissue engineered system use fluid flow and transport properties to recapitulate physiological systems. This enables mimicry of organ systems which can further personalized and regenerative medicine. Thus, fluid hemodynamics can be used to study these flow patterns and create a system that mimics real physiological pathways and processes. The establishment of stable flow pathways encourages endothelial cells (ECs) ECs to undergo neovascularization. Specifically, the shear stress applied in capillary beds generates the increased proliferation and differentiation of ECs to build larger microcirculatory beds. Here, we describe a mathematical model that uses branching patterns and vessel morphology to predict hemodynamic parameters in capillary beds. A retinal capillary bed is used as one-use case of our model to show how the mathematical framework can be used to determine hemodynamic parameters for any microfluidic system. In doing so, this tool can be altered to be used to supplement emerging research areas in neovascularization.

Optical coherence tomography angiography in patients with bipolar disorder and major depressive disorder

BackgroundCerebral microvascular dysfunction is a promising area for research into the pathogenesis of major depressive disorder (MDD) and bipolar disorder (BD). Despite the scientific and clinical potential of studying microvascular dysfunction, progress in this area has long been hampered by the lack of methods to study microvessels intravitally. AimsThe aim of the present study was to search for potential optical coherence tomography (OCT) and OCT-angiography (OCTA) biomarkers of BD and MDD. MethodsOne hundred and five consecutive patients with a current depressive episode were enrolled in the study (39 – BD and 66 – MDD). In addition, forty-one generally healthy subjects were enrolled as a control group. Only the right eye was examined in all subjects. Structural OCT and OCTA scans with signal strength ≥7 were included. ResultsStructural OCT measurements showed no significant differences between the groups. OCTA measurements of foveal avascular zone (FAZ), area and skeleton density showed a decrease in the retinal capillary bed in BD patients, whereas OCTA values in MDD patients did not differ from the control group. Several significant differences were found between the BD and control groups. In the BD group, the FAZ of the deep capillary plexus was increased, reflecting a reduction in capillary perfusion in the central subfield of this plexus. ConclusionsOCTA measurements of FAZ, area and skeleton density showed a decrease in the retinal capillary bed in BD patients, whereas OCTA values in MDD patients did not differ from the control group.

Retinal capillary oximetry with visible light optical coherence tomography

Assessing oxygen saturation (sO2) remains challenging but is nonetheless necessary for understanding retinal metabolism. We and others previously achieved oximetry on major retinal vessels and measured the total retinal oxygen metabolic rate in rats using visible-light optical coherence tomography. Here we extend oximetry measurements to capillaries and investigate all three retinal vascular plexuses by amplifying and extracting the spectroscopic signal from each capillary segment under the guidance of optical coherence tomography (OCT) angiography. Using this approach, we measured capillary sO2 in the retinal circulation in rats, demonstrated reproducibility of the results, validated the measurements in superficial capillaries with known perfusion pathways, and determined sO2 responses to hypoxia and hyperoxia in the different retinal capillary beds. OCT capillary oximetry has the potential to provide new insights into the retinal circulation in the normal eye as well as in retinal vascular diseases.

Monitoring retinal responses to acute intraocular pressure elevation in rats with visible light optical coherence tomography.

Elevated intraocular pressure (IOP) is an important risk factor for glaucoma. However, the role of IOP in glaucoma progression, as well as retinal physiology in general, remains incompletely understood. We demonstrate the use of visible light optical coherence tomography to measure retinal responses to acute IOP elevation in Brown Norway rats. We monitored retinal responses in reflectivity, angiography, blood flow, oxygen saturation ( ), and oxygen metabolism over a range of IOP from 10 to 100mmHg. As IOP was elevated, nerve fiber layer reflectivity was found to decrease. Vascular perfusion in the three retinal capillary plexuses remained steady until IOP exceeded 70mmHg and arterial flow was noted to reverse periodically at high IOPs. However, a significant drop in total retinal blood flow was observed first at 40mmHg. As IOP increased, the venous demonstrated a gradual decrease despite steady arterial , which is consistent with increased arterial-venous oxygen extraction across the retinal capillary beds. Calculated total retinal oxygen metabolism was steady, reflecting balanced responses of blood flow and oxygen extraction, until IOP exceeded 40mmHg, and fell to 0 at 70 and 80mmHg. Above this, measurements were unattainable. All measurements reverted to baseline when the IOP was returned to 10mmHg, indicating good recovery following acute pressure challenge. These results demonstrate the ability of this system to monitor retinal oxygen metabolism noninvasively and how it can help us understand retinal responses to elevated IOP.

Fluorescein angiography of retinal vascular involution after intravitreal injection of ranibizumab for retinopathy of prematurity.

To describe the involution patterns of vessel growth of retina through fluorescein angiography (FA) of children, who had been under treatment up to 1y previously intravitreal ranibizumab (IVR) as monotherapy for retinopathy of prematurity (ROP). This is a retrospective study. The medical information and FA of 17 children (34 eyes) whose area of avascular retina from the ora serrata was more than two disc diameters (DD) were analyzed. Among 34 eyes, all were the presence of finger-shaped vessels and arteriolar-venular shunts (100%, 34/34 eyes). Popcorn abnormalities were found in most of the eyes (94.1%, 32/34 eyes). Furthermore, in many cases (23.5%, 8/34 eyes), there were leakage persisting in the region of the junction between avascular and vascular retina. In contrast, just 2 eyes (5.9%) showed damage of retinal capillary bed and 3 eyes (8.8%) showed large area of retinal pigment epithelium (RPE) atrophy. Although IVR can be very effective in ROP, we should remain cautious as infants may remain avascular peripheral retinas and abnormal vessel. FA allows accurate visualization of vessel abnormalities in eyes with ROP, which will be helpful to affect assessment of disease activity and therapeutic effect.

Experience of Various Types of Keratoplasty in Children

The purpose: to determine the features of different stages of active retinopathy prematurely according to fluorescent angiography data.Patients and methods. In 2011–2017, 271 angiographic studies were performed in 207 premature infants born at 25–33 weeks of gestation with 710–1980 grams weight at birth, with different stages of active ROP in age of live 3–12 weeks (30-39 weeks of post-conceptual age). A voluntary informed consent to perform the examination was received from the legal representatives of all patients. FAG was performed using retinal pediatric digital video system “RetCam-3” with built-in angiographic unit under mask anesthesia, in the presence of anesthesiologist-resuscitator, under the monitor control of the respiratory and cardiovascular systems of the child.Results. Unfavorable types of active ROP are characterized by the specific manifestations that are not defined by the standard ophthalmologic methods: early flat neovascularization, the presence of small tortuous peripheral vessels with signs of leakage, reperfusion areas with an apparent lack of capillaries and shunts. This opens up the opportunities for early detection of stages of the disease requiring therapeutic measures. The aggressive posterior ROP is distinguished by a variety of angiographic patterns, the most important feature is the massive loss of the retinal capillary bed in the vascularized retina. FAG data about latent neovascularization and ischemic zones of the retina represent the particular value in the prediction of active ROP course.Conclusion. The obtained results could allow to make the most differentiated approach to the management of children with active ROP, timely and effectively predict the course of the disease and to performed adequate treatment based on objective indications.

Fluorescence Angiography to Determine the Features of Active Retinopathy of Prematurity Course

The purposeis to determine the features of different stages of active retinopathy prematurely according to fluorescent angiography data.Patients and methods. In 2011–2017, 271 angiographic studies were performed in 207 premature infants born at 25– 33 weeks of gestation with 710–1980 grams weight at birth, with different stages of active ROP in age of live 3–12 weeks (30– 39 weeks of post-conceptual age). A voluntary informed consent to perform the examination was received from the legal representatives of all patients. FAG was performed using retinal pediatric digital video system «RetCam-3» with built-in angiographic unit under mask anesthesia, in the presence of anesthesiologist-resuscitator, under the monitor control of the respiratory and cardiovascular systems of the child.Results. Unfavorable types of active ROP are characterized by the specific manifestations that are not defined by the standard ophthalmologic methods: early flat neovascularization, the presence of small tortuous peripheral vessels with signs of leakage, reperfusion areas with an apparent lack of capillaries and shunts. This opens up the opportunities for early detection of stages of the disease requiring therapeutic measures. The aggressive posterior ROP is distinguished by a variety of angiographic patterns, the most important feature is the massive loss of the retinal capillary bed in the vascularized retina. FAG data about latent neovascularization and ischemic zones of the retina represent the particular value in the prediction of active ROP course.Conclusion. The obtained results could allow to make the most differentiated approach to the management of children with active ROP, timely and effectively predict the course of the disease and to performed adequate treatment based on objective indications.

Optical Coherence Tomography Angiography in Healthy Subjects.

Fluorescein angiography and indocyanine green angiography provide information about normal retinal and choroidal anatomy that is nearly comparable to histological findings. These results are absolutely fundamental for the evaluation of retinal and choroidal vascular diseases and allow the clinician to define and diagnose several pathological conditions. Fluorescein angiography has become the 'gold standard' in retinal imaging due to its capacity to allow visualization of the retinal capillary bed and its changes, particularly in the macular area. Although the fluorescence of the injected dye enables improved visualization of retinal capillaries, not all of the different layers of the retinal capillary network can be visualized using this bi-dimensional examination technique, possibly because of a light scattering phenomenon. Optical coherence tomography angiography allows depth-resolved visualization of the retinal and choroidal microvasculature by calculating the difference between static and nonstatic tissue. Given that the main moving elements in the eye fundus are contained within vessels, determining a vascular decorrelation signal enables three-dimensional visualization of the retinal and choroidal vascular network without the administration of intravenous dye and therefore reduces the risk of potential adverse events.

Evaluation of the effect of elevated intraocular pressure and reduced ocular perfusion pressure on retinal capillary bed filling and total retinal blood flow in rats by OMAG/OCT

PurposeTo determine if retinal capillary filling is preserved in the face of acutely elevated intraocular pressure (IOP) in anesthetized rats, despite a reduction in total retinal blood flow (RBF), using optical microangiography/optical coherence tomography (OMAG/OCT). MethodsOMAG provided the capability of depth-resolved imaging of the retinal microvasculature down to the capillary level. Doppler OCT was applied to measure the total RBF using an enface integration approach. The microvascular pattern, capillary density, and total RBF were monitored in vivo as the IOP was increased from 10 to 100mmHg in 10mmHg intervals and returned back to 10mmHg. ResultsIn animals with mean arterial pressure (MAP) of 102±4mmHg (n=10), when IOP was increased from 0 to 100mmHg, the capillary density remained at or above 80% of baseline for the IOP up to 60mmHg [or ocular perfusion pressure (OPP) at 40mmHg]. This was then decreased, achieving 60% of baseline at IOP 70mmHg and OPP of 30mmHg. Total RBF was unaffected by moderate increases in IOP up to 30mmHg, beyond which total RBF decreased linearly, reaching 50% of baseline at IOP 60mmHg and OPP 40mmHg. Both capillary density and total RBF were totally extinguished at 100mmHg, but fully recovered when IOP returned to baseline. By comparison, a separate group of animals with lower MAP (mean=75±6mmHg, n=7) demonstrated comparable decreases in both capillary filling and total RBF at IOPs that were 20mmHg lower than in the initial group. Both were totally extinguished at 80mmHg, but fully recovered when IOP returned to baseline. Relationships of both parameters to OPP were unchanged. ConclusionRetinal capillary filling and total RBF responses to IOP elevation can be monitored non-invasively by OMAG/OCT and both are influenced by OPP. Retinal capillary filling was relatively preserved down to a perfusion pressure of 40mmHg, despite a linear reduction in total RBF.

Effects of acute bouts of endurance exercise on retinal vessel diameters are age and intensity dependent

Alterations of retinal vessel diameters are associated with increased cardiovascular risk. We aimed to investigate changes in retinal vessel diameters in response to acute dynamic exercise of different intensities and whether these changes are age dependent. Seventeen healthy seniors (median (IQR) age 68 (65, 69) years) and 15 healthy young adults (median (IQR) age 26 (25, 28) years) first performed a maximal treadmill test (MTT) followed by a submaximal treadmill test (SMTT) and a resting control condition in randomised order. Central retinal arteriolar (CRAE) and central retinal venular (CRVE) diameter equivalents were measured before as well as 5 (t5) and 40 (t40) minutes after exercise cessation using a static retinal vessel analyser. Both exercise intensities induced a significant dilatation in CRAE and CRVE at t5 compared to the control condition (P < 0.001). At t40, the mean increase in CRAE and CRVE was greater for MTT compared to that for SMTT (CRAE 1.7 μm (95 % confidence interval (CI) −0.1, 3.6; P = 0.061); CRVE 2.2 μm (95 % CI 0.4, 4.1; P = 0.019)). However, the estimated difference at t5 between seniors and young adults in their response to MTT compared to SMTT was 5.3 μm (95 % CI 2.0, 8.5; P = 0.002) for CRAE and 4.1 μm (95 % CI −0.4, 8.6; P = 0.076) for CRVE. Wider arteries and veins after maximal versus submaximal exercise for seniors compared to young adults suggest that myogenic vasoconstriction in response to exhaustive exercise may be reduced in seniors. Age-related loss of vascular reactivity has clinical implications since the arteriolar vasoconstriction protects the retinal capillary bed from intraluminal pressure peaks.Electronic supplementary materialThe online version of this article (doi:10.1007/s11357-014-9650-3) contains supplementary material, which is available to authorized users.

In vivo imaging of human retinal microvasculature using adaptive optics scanning light ophthalmoscope fluorescein angiography

The adaptive optics scanning light ophthalmoscope (AOSLO) allows visualization of microscopic structures of the human retina in vivo. In this work, we demonstrate its application in combination with oral and intravenous (IV) fluorescein angiography (FA) to the in vivo visualization of the human retinal microvasculature. Ten healthy subjects ages 20 to 38 years were imaged using oral (7 and/or 20 mg/kg) and/or IV (500 mg) fluorescein. In agreement with current literature, there were no adverse effects among the patients receiving oral fluorescein while one patient receiving IV fluorescein experienced some nausea and heaving. We determined that all retinal capillary beds can be imaged using clinically accepted fluorescein dosages and safe light levels according to the ANSI Z136.1-2000 maximum permissible exposure. As expected, the 20 mg/kg oral dose showed higher image intensity for a longer period of time than did the 7 mg/kg oral and the 500 mg IV doses. The increased resolution of AOSLO FA, compared to conventional FA, offers great opportunity for studying physiological and pathological vascular processes.

Automated non-rigid registration and mosaicing for robust imaging of distinct retinal capillary beds using speckle variance optical coherence tomography

Variance processing methods in Fourier domain optical coherence tomography (FD-OCT) have enabled depth-resolved visualization of the capillary beds in the retina due to the development of imaging systems capable of acquiring A-scan data in the 100 kHz regime. However, acquisition of volumetric variance data sets still requires several seconds of acquisition time, even with high speed systems. Movement of the subject during this time span is sufficient to corrupt visualization of the vasculature. We demonstrate a method to eliminate motion artifacts in speckle variance FD-OCT images of the retinal vasculature by creating a composite image from multiple volumes of data acquired sequentially. Slight changes in the orientation of the subject’s eye relative to the optical system between acquired volumes may result in non-rigid warping of the image. Thus, we use a B-spline based free form deformation method to automatically register variance images from multiple volumes to obtain a motion-free composite image of the retinal vessels. We extend this technique to automatically mosaic individual vascular images into a widefield image of the retinal vasculature.

Proliferative Diabetic Retinopathy

A 23-year-old man with a long-standing history of insulin-dependent diabetes mellitus presented for ophthalmic examination. Ophthalmic history was remarkable for total retinal detachment of his right eye and laser photocoagulation of his left eye due to diabetic retinopathy and diabetic macular edema. On examination, the patient's best-corrected visual acuity was light perception in the right eye and 20/20 in the left eye. Pupillary examination revealed a relative afferent pupillary defect in the right eye. Dilated fundus examination of the right eye showed end-stage proliferative diabetic retinopathy with tractional retinal detachment (not shown). The left eye had extensive neovascularization (Figures, top and middle, arrows) and fibrovascular proliferation (Figures, top and middle, arrowheads) of the retina secondary to advanced proliferative diabetic retinopathy. These abnormal new vessels showed extensive leakage during fluorescein angiography (Figure, bottom, arrows and arrowheads). In proliferative diabetic retinopathy, ischemia of the inner retinal layers secondary to closure of parts of the retinal capillary bed leads to new vessel formation in the retina.1 The ischemic retina is postulated to produce a new vessel-stimulating factor, eg, vascular endothelial growth factor, capable of acting locally and diffusing through the vitreous to other areas of the retina, to the optic disc, and into the anterior chamber.2 Although new vessels may arise anywhere in the retina, they are most frequently seen posteriorly, within about 45° of the optic disc. In early evolution, new vessels appear bare; later, adjacent delicate white fibrous tissue usually becomes visible. Treatment involves thermal laser photocoagulation of the ischemic retina to decrease the production of vasoproliferative factors.3,4

Macular blood flow measured by blue‐field entoptoscopy and Heidelberg retinal flowmetry: comparison of two techniques in type 1 diabetes women during pregnancy

This study compared macular capillary leucocyte velocity values measured with a psychophysical blue-field entoptic simulation (BFS) technique and confocal scanning laser Doppler flowmetry. A cross-sectional study was performed where macular capillary leucocyte velocity was measured by BFS using an Oculix BFS-2000 V2.1 psychophysical system and by confocal scanning laser Doppler flowmetry using Heidelberg retinal flowmetry (HRF) in 35 type 1 diabetes women during the second trimester. The macular leucocyte velocities measured with BFS correlated significantly with the 50th percentile (r = 0.345, p = 0.042, n = 35, Spearman's non-parametric correlation), the 75th percentile (r = 0.432, p = 0.009) and the 90th percentile (r = 0.373, p = 0.027) of HRF flow values during the second trimester. However, there was no correlation between BFS velocity and the 25th percentile of HRF measurements. Blue-field simulation is known to be an experimental technique that provides a quantitative measure of flow in the perifoveal capillary network. By contrast, HRF imaging reflects quantitative, multispectral, objective and non-invasive measurements in a two-dimensional projection of a three-dimensional retinal capillary bed. Our study showed that BFS velocity was correlated with HRF values in a group of women with diabetes during pregnancy. The positive correlation between BFS and HRF values suggests that the psychophysical BFS and scanning laser-based HRF measure similar functions in the retina.

Central Retinal Vein Occlusion Associated With Cilioretinal Artery Occlusion

To describe the clinical characteristics and pathogenesis of central retinal vein occlusion (CRVO) associated with cilioretinal artery occlusion (CLRAO). The study included 38 patients (38 eyes) who had CRVO associated with CLRAO and were seen in our clinic from 1974 to 1999. At their first visit to our clinic, all patients provided a detailed ophthalmic and medical history and underwent comprehensive ophthalmic evaluation, color fundus photography, and fluorescein fundus angiography. At each follow-up visit, the same ophthalmic evaluations were performed, except for fluorescein fundus angiography. Of 38 eyes, 30 had nonischemic CRVO, 5 had ischemic CRVO, and 3 had nonischemic hemi-CRVO. Patients with nonischemic CRVO were significantly younger (mean age +/- SD: 45.3 +/- 16.0 years) than those with ischemic CRVO (72.3 +/- 9.2 years; P = 0.001) and those with nonischemic hemi-CRVO (64.7 +/- 7.5 years; P = 0.018). At least one third of the patients gave a definite history of episode(s) of transient visual blurring before the onset of constant blurred vision. Initially, the ophthalmoscopic and fluorescein angiographic findings were similar to those seen in CRVO and hemi-CRVO, except that all these eyes had retinal infarct in the distribution of the cilioretinal artery; its size and site varied widely. Fluorescein angiography typically showed only transient hemodynamic block and not the typical CLRAO. During follow-up, visual acuity improved markedly in nonischemic CRVO (P < 0.001) and nonischemic hemi-CRVO but deteriorated in ischemic CRVO. Retinopathy resolved spontaneously in 22 eyes with nonischemic CRVO (mean duration +/- SD: 42.0 +/- 101.0 months), in 2 eyes with ischemic CRVO (15.4 +/- 4.5 months), and in 1 eye with nonischemic hemi-CRVO. Retinociliary collaterals developed in 30% of eyes with nonischemic CRVO, in 40% of eyes with ischemic CRVO, and in 66% of eyes with nonischemic hemi-CRVO. CRVO associated with CLRAO constitutes a distinct clinical entity. The pathogenesis of CLRAO in CRVO is due to transient hemodynamic blockage of the cilioretinal artery caused by a sudden sharp rise in intraluminal pressure in the retinal capillary bed (due to CRVO) above the level of that in the cilioretinal artery.

Increased clonogenic potential of circulating endothelial progenitor cells in patients with type 1 diabetes and proliferative retinopathy

To the Editor: The identification of endothelial progenitor cells (EPCs) along with the description of their essential role in postnatal neovascularisation has been a major achievement for stem cell biology [1]. In particular the finding that the clonogenic potential of EPCs is reduced in patients with high cardiovascular risk [2] represents the first step towards the recognition of the therapeutic effect of EPC transplantation in cardiac and limbic ischaemia [3, 4]. However, two harmful side effects are expected to be associated with EPC transplantation as a consequence of their physiological function: malignant tumour neovascularisation and the induction of proliferative diabetic retinopathy [1]. The contribution of EPCs to tumour neovascularisation has been clearly demonstrated in animal models and confirmed, although to a lesser extent, also in humans [5]. Concerning diabetic retinopathy, recent reports have demonstrated that EPCs play a major role in the retinal neovascularisation of a mouse model of proliferative retinopathy [6], and that the concentration of stromalcell-derived factor 1, the most important chemokine mobilising EPCs, increases with the severity of diabetic retinopathy in vitreous samples of patients affected by type 2 diabetes [7]. These studies are in some way in contrast to two independent reports performed in non-complicated patients showing that type 1 diabetes per se is associated with a reduced number and function of EPCs [8], and that EPCs in type 2 diabetes are impaired in adhesion, proliferation and tubulisation [9]. Finally, a recent study has demonstrated an increased number of CD34+ mononuclear cells in patients affected by type 2 diabetes with both non-proliferative and proliferative retinopathy [10]. Although of interest, these results cannot be easily compared with the ones described above as EPCs represent only one of the different classes of circulating cells staining positively for CD34+ [1]. Taken together, and from a largely speculative point of view, these apparently discrepant results can be explained by a unifying hypothesis. Taking into account the fact that EPCs have a physiological role in the rescue and maintenance of the existing retinal capillary bed [11], it is possible to hypothesise that the reduced number and clonogenic potential of EPCs found in non-complicated diabetic patients [8, 9] might predispose these patients to the later development of diabetic retinopathy. Once the damage is widespread and specific chemokines are produced by the suffering retina, the bone marrow would respond by increasing the production of EPCs, which at this stage, possibly because of the high ambient glucose and/or the badly damaged retina, would give rise to an incompetent neoangiogenesis. To test this hypothesis and verify the possible association between the clonogenic potential of circulating EPCs and proliferative diabetic retinopathy, we isolated EPCs from whole blood obtained from 11 patients with type 1 diabetes and untreated proliferative retinopathy, from 12 patients without retinopathy despite similar age, gender distribution and duration of type 1 diabetes, and from 11 ageand sex-matched non-diabetic controls. Patients affected by type 1 diabetes took no medication other than insulin. Clinical characteristics of subjects included in the study are described in Table 1. Patients were classified with respect to the status of diabetic retinopathy by means of stereoscopic fundus examination and fluorescent angiography. Patients considered for this study either had no signs of diabetic V. Asnaghi . G. Mazzolari . M. R. Pastore . A. Maestroni . D. Ruggieri . L. Luzi . G. Zerbini (*) Renal Pathophysiology of Diabetes Unit, Division of Nutrition–Metabolism, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan, Italy e-mail: g.zerbini@hsr.it

Thrombin Inhibitor Reduces Leukocyte–Endothelial Cell Interactions and Vascular Leakage after Scatter Laser Photocoagulation

Macular edema is one of the most serious adverse effects after retinal scatter laser photocoagulation. It has been suggested that the inflammatory reaction after photocoagulation may be involved in the pathogenesis of macular edema. This study was designed to evaluate quantitatively the inhibitory effects of argatroban, a direct thrombin inhibitor, on leukocyte-endothelial cell interactions and vascular permeability after scatter laser photocoagulation. Argon laser photocoagulation was performed in one half of the retina in pigmented male rats (n = 114). Argatroban was administered just before scatter laser photocoagulation. In the other half of the retina, AO leukocyte fluorography was used to evaluate in vivo leukocyte rolling along the retinal vein and accumulation in the retinal capillary bed. The expressions of P-selectin and intercellular adhesion molecule (ICAM)-1 were evaluated by reverse transcription-polymerase chain reaction. Retinal vessel permeability was quantified by using fluorescein isothiocyanate (FITC)-conjugated dextran. Scatter laser photocoagulation caused significant inflammatory leukocyte-endothelial cell interactions in the nonphotocoagulated half of the retina. Treatment with argatroban suppressed leukocyte-endothelial cell interactions. The maximum number of rolling and accumulating leukocytes was reduced by 46.6% (P < 0.01) and 51.4% (P < 0.01), respectively. The expression of P-selectin and ICAM-1 mRNA was suppressed significantly in the argatroban-treated retinas (P < 0.05). Retinal vascular permeability was also suppressed significantly (P < 0.05). Argatroban suppressed leukocyte-endothelial cell interactions and blood-retinal barrier breakdown after scatter laser photocoagulation, suggesting that argatroban prevents postlaser macular edema.

Confocal laser Doppler flowmeter measurements in a controlled flow environment in an isolated perfused eye

The aim of this study was to improve our ability to interpret and validate Heidelberg Retina Flowmeter (HRF) flow images by recording flow measurements from specific regions of the retinal vasculature by taking advantage of the ability to precisely regulate perfusion flow in an isolated eye preparation. The retinal vasculature in 16 isolated perfused pig eyes was perfused with a 50%/50% Krebs/RBC solution at known flow rates ranging from 0 to 300 μl min −1. At each flow rate, HRF images were obtained at a location approximately two disc diameters from the disc. After HRF image acquisition, the retinal vasculature was perfused with fluorescein isothiocyanate for fluorescence microscopy. Using the standard HRF software and a 10×10 pixel measurement window, flow rates were measured from a retinal artery, vein, arteriole, venule, and the retinal capillary bed and a capillary-free-zone. The relationship between HRF measured flow and perfusion flow in the different measurement locations was determined. At zero perfusion flow the measured HRF flow was consistently greater than zero (∼170 arbitrary units (AU)), and not significantly different at each measurement location except for the retinal vein, which had a significantly higher HRF flow value (∼230 AU). At higher perfusion flow rates the flow signal from the larger vascular elements (arteries and veins) increased rapidly thereafter to reach several thousand AU at a total perfusate flow of 50 μl min −1 and increased less rapidly at higher flow rates. In arterioles, the HRF flow was more linear over a broader range of perfusate flow rates but the peak flow signal was an order of magnitude smaller than that from the retinal artery. Both the linearity and magnitude of the flow signal in venules was less than that in arterioles. In capillary areas and in the capillary free zone, the HRF flow showed only a very weak relationship to perfusion flow when compared to the background noise. The choice of location for HRF flow analysis greatly influences the ability of the technique to measure changes in retinal blood flow. The major arteries and veins provide the strongest signal and greatest signal to noise ratio. However, the retinal arterioles produce an HRF signal that is more linear over a wider range of perfusate flow rates.

The effect of valsartan on the endothelial function of the retinal capillary bed in elderly hypertensive subjects

P-82 Key Words: Retinal Perfusion, Valsartan, LDL

Change in endothelial cell shape in response to ischaemia in the cardiac and retinal capillary beds

The change in shape of cardiac capillary endothelial cells in response to ischaemia and ischaemia followed by reperfusion is well established. We investigated the possibility that this process is an active rather than a passive process and that the change might be prevented or attenuated in order to minimise reperfusion injury and ‘no‐reflow’. We have also compared the change in shape of cardiac capillaries with those of the retina. We used an isolated heart preparation in which global ischaemia was induced by cessation of flow. Retinal capillaries were made ischaemic by one of 2 methods, using firstly superfusion with an oxygen depleted medium, and secondly by occlusion of upstream vessels with starch spheres. Ultrastructural and morphometric analysis of cardiac and retinal capillaries demonstrated that the change in shape seen in cardiac capillaries in response to ischaemia does not occur in retinal capillaries reflecting the different metabolic activities of the 2 tissues. Immunocytochemical localisation of _‐actin showed no apparent difference in the retinal capillaries between control and ischaemic capillaries. Cardiac capillaries, however, showed an irregular redistribution of _‐actin in ischaemic vessels which could be attenuated by exposure to phalloidin. Resin casts of ischaemic capillaries showed focal narrowings which were not present in controls. From these results we conclude that the change in endothelial cell shape in response to ischaemia is not a passive process and can be modulated by agents which target the microfilament system.