Gabriele Fuchsjäger-Mayrl

Medical University of Vienna, Wien, Vienna, Austria

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Publications (46)132 Total impact

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    ABSTRACT: Pentoxifylline, a nonselective phosphodiesterase inhibitor, shows vasodilator effects in certain vascular beds and reduces blood viscosity. We have previously shown that under states of vasoconstriction an interaction between circulating erythrocytes and leukocytes may play a role in the control of blood flow. The reason for this observation is not entirely clear but may be related to a mechanical interaction between red and white blood cells. In the present study we hypothesized that pentoxifylline may alter this interaction during oxygen-induced vasoconstriction. 24 healthy male subjects participated in this double masked, randomized, placebo-controlled 2 way cross over trail. In order to increase white blood cell count (WBC) count, 300μg of G-CSF were administered intravenously. Vasoconstriction of retinal vessels was induced by oxygen inhalation. 400mg of pentoxifylline or placebo were infused at two different study days. White blood cell flux was assessed with the blue-field entoptic technique. Vessel calibers were measured with a Dynamic Vessel Analyzer (DVA) and red blood cell velocity (RBCV) was determined with Laser Doppler Velocimetry (LDV). Retinal blood flow was calculated based on retinal vessel diameters and RBCV. Administration of G-CSF induced a significant increase in WBC, both in the placebo and the pentoxifylline group (p<0.01 for both groups). Retinal vessel diameter, RBCV, calculated retinal blood flow and white blood cell flow were not altered by administration of pentoxifylline. Hyperoxia induced a pronounced decrease in retinal blood flow parameters. No difference was observed between groups during oxygen breathing in vessel diameters (p=0.54), RBCV (p=0.34), calculated retinal blood flow (p=0.3) and white blood cell flow (p=0.26). Our data indicate that short time administration of pentoxifylline does not alter the oxygen-induced effect on ocular blood flow parameters during leukocytosis. Whether long-term treatment could improve retinal blood flow under states of vasoconstriction remains to be investigated.
    Microvascular Research 01/2014; · 2.93 Impact Factor
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    ABSTRACT: AIMS: There is evidence that altered retinal blood flow and altered retinal blood flow regulation play a role in the development and progression of diabetic retinopathy. We compared the association between systemic blood pressure and retinal white blood cell flux in patients with type 1 diabetes and healthy control subjects. METHODS: The study was performed in 100 patients with type 1 diabetes with no or minimal diabetic retinopathy and a group of 313 age-matched healthy controls. Inclusion criteria were systolic blood pressure ≤160 mmHg and diastolic blood pressure ≤95 mmHg. None of the subjects took vasoactive medication except insulin. The blue field entoptic technique was used to assess retinal white blood cell flux, velocity and density in the perimacular region. Pressure-flow relationships were calculated for both groups to assess differences in blood flow regulation. RESULTS: Retinal white blood cell flux was comparable between the two study groups. Both type 1 diabetic patients and healthy subjects showed a significant positive correlation between retinal white blood cell flux and mean arterial pressure (diabetic patients: r = 0.48; p < 0.05, healthy subjects r = 0.28). The correlation coefficients between mean arterial pressure and white blood cell flux were significantly higher in patients with diabetes than in the healthy control group (p = 0.0459). CONCLUSION: Retinal white blood cell flux, as assessed with the blue-field entoptic technique, is not significantly different between type 1 diabetic patients with no or minimal retinopathy and healthy control subjects. Type 1 diabetic subjects do, however, show an abnormal association between systemic blood pressure and retinal white blood cell flux. This indicates altered autoregulation in early diabetic retinopathy.
    Albrecht von Graæes Archiv für Ophthalmologie 11/2012; · 1.93 Impact Factor
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    ABSTRACT: It is known that administration of granulocyte-colony stimulating factor is followed by an increase of white blood cell count. There is evidence from other vascular beds that an increase in white blood cell count impairs blood flow regulation especially in the microcirculation. Whether this also holds true for the ocular circulation is unknown. In the following study we investigated whether an increase in white blood cell count alters the endothelin-1 induced vasoconstriction in humans. Neither granulocyte-colony stimulating factor nor endothelin-1 had any consistent effect on blood pressure, pulse rate or intraocular pressure. Administration of granulocyte-colony stimulating factor induced a pronounced increase in retinal white blood cell density (p < 0.01). Administration of endothelin-1 decreased choroidal (p < 0.01) and retinal blood flow (p < 0.01). The change in choroidal blood flow in response to endothelin-1 was not altered by pre-treatment with granulocyte-colony stimulating factor. By contrast, the decrease in retinal blood flow was more pronounced during an increase in white blood cell count (p = 0.02) when compared to placebo. Our data indicates that during pronounced vasoconstriction, as induced by administration of endothelin-1, vascular regulation can be altered by the number of circulating white blood cells. Whether this effect is caused by an interaction of red and white blood cells in the microcirculation or a yet unknown mechanism needs further investigation.
    Experimental Eye Research 01/2012; 97(1):49-54. · 3.03 Impact Factor
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    ABSTRACT: Little information is available about the relationship between glaucomatous visual field defects, morphological changes of the optic disc and ocular blood flow. In this study, ocular blood flow parameters were correlated with parameters of optic nerve head (ONH) morphology and visual field performance in a cross-sectional study. A total of 103 patients with primary open angle glaucoma were included. Choroidal and ONH blood flow was assessed using laser Doppler flowmetry. Retinal blood velocities and retinal vessel diameters were measured with laser Doppler velocimetry and a Retinal Vessel Analyzer, respectively. To evaluate the ONH morphology, fundus photographs were taken and confocal laser scanning tomography was performed. Among all measured ocular hemodynamic parameters, the ONH blood flow was most strongly correlated to structural parameters of ONH damage and visual field loss. Reduced retinal vessel diameters were only slightly correlated with the degree of glaucomatous damage. Reduced blood flow in the ONH was associated with increasing amount of visual field defect and morphological changes of the ONH. Retinal vessel diameters were only marginally associated with glaucomatous optic nerve damage. Based on retinal vessel diameter determination alone, it is not possible to assess whether reduced retinal blood flow is causative or secondary in glaucoma.
    Acta ophthalmologica 05/2011; 89(7):e544-9. · 2.44 Impact Factor
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    ABSTRACT: The present study tested the hypothesis that human choroidal blood flow (ChBF) regulation in the face of changes in ocular perfusion pressure (OPP) may be modified by a drug-induced decrease in intraocular pressure (IOP). This hypothesis was tested in a double-masked, randomized, placebo-controlled, parallel-group trial in 24 healthy volunteers. OPP was manipulated by 6 minutes of squatting and a subsequent period of artificial increase in IOP induced with a suction cup. These interventions were repeated after 14 days of treatment with either latanoprost or placebo. ChBF was measured continuously with a portable laser Doppler flowmeter. As expected, latanoprost significantly reduced IOP compared with placebo (P = 0.008). The relative increases in OPP during squatting (P = 0.97) and an artificial IOP increase (P = 0.75), however, were comparable after placebo and latanoprost. The response of ChBF was, in contrast, different between the two treatment groups. During the squatting-induced elevation of OPP, ChBF increased less after latanoprost than after placebo treatment (P = 0.049). During the suction cup-induced increase in IOP, the decrease in ChBF was less pronounced after latanoprost than after placebo (P = 0.026). Latanoprost, however, did not modify baseline ChBF at rest (P = 0.30). The data indicate that latanoprost improves ChBF regulation during both an increase and a decrease in OPP. Since latanoprost did not affect baseline ChBF, the authors assume that this effect is related to the decrease in IOP. This finding has important implications for understanding the relation between IOP and vascular factors in glaucoma, because it indicates that a reduction in IOP itself improves ChBF regulation.
    Investigative ophthalmology & visual science 01/2011; 52(7):4410-5. · 3.43 Impact Factor
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    ABSTRACT: A number of previous studies have shown that blood velocities in retrobulbar arteries, as assessed with color Doppler imaging (CDI), are reduced in primary open angle glaucoma (POAG) patients, indicative of reduced blood flow to the eye. In the present study, the authors hypothesized that patients with POAG show an abnormal association between retrobulbar blood flow velocities as assessed with CDI and blood pressure, indicative of vascular dysregulation. A total of 252 POAG patients and 198 healthy age-matched control subjects were included. Mean flow velocity (MFV) in the ophthalmic artery (OA), posterior ciliary artery (PCA), and central retinal artery (CRA) were measured with CDI. Mean arterial blood pressure was measured noninvasively using automated oscillometry, and intraocular pressure was measured using Goldmann applanation tonometry. Intraocular pressure was increased in POAG patients compared with healthy controls (P < 0.01). Mean arterial blood pressure was not different between groups. All blood flow velocities were significantly reduced in POAG patients compared with healthy control subjects (P < 0.01 each). The correlation between MFV and mean arterial blood pressure in the CRA was stronger in POAG subjects than in healthy control subjects. These data indicate that blood flow velocities in retrobulbar vessels are reduced in POAG patients compared with healthy control subjects. In addition, an abnormal correlation between blood velocities and mean arterial blood pressure was found in POAG. This suggests vascular dysregulation and supports the concept that reduced ocular blood flow in glaucoma is not solely a consequence of the disease.
    Investigative ophthalmology & visual science 12/2010; 51(12):6652-7. · 3.43 Impact Factor
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    ABSTRACT: The authors have reported previously that a study population, consisting of patients with glaucoma and ocular hypertension, is characterized by an impaired association between ocular blood flow parameters and systemic blood pressure, indicative of abnormal autoregulation. Here they report on the effects of dorzolamide and timolol on ocular pressure/flow relationships to test the hypothesis that these drugs improve autoregulation. One hundred forty patients with primary open-angle glaucoma or ocular hypertension were included in a clinical trial in a controlled, randomized double-masked study in two parallel groups. Seventy patients were randomly assigned to receive timolol, and 70 patients were randomly assigned to receive dorzolamide for a 6-month period. Scanning laser Doppler flowmetry was used to measure blood flow in the temporal neuroretinal rim and the cup of the optic nerve head. Pulsatile choroidal blood flow was assessed using laser interferometric measurement of fundus pulsation amplitude. The association between blood flow parameters and systemic blood pressure was compared before and after the 6-month treatment period. Before treatment a significant association was observed between ocular blood flow parameters and systemic blood pressure in both parallel groups (r = 0.23-0.42). All regression lines between ocular hemodynamic parameters and systemic blood pressure were less steep after treatment with either dorzolamide or timolol (r = 0.03-0.24). The present study indicates that intraocular pressure reduction with timolol or dorzolamide is associated with normalization of the ocular pressure/flow relationship. Whether this is related to the beneficial effects of IOP-lowering therapy in glaucoma remains to be established. (ClinicalTrials.gov number, NCT00991822.).
    Investigative ophthalmology & visual science 10/2009; 51(3):1289-96. · 3.43 Impact Factor
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    ABSTRACT: Purpose Blood flow regulation in the human choroid appears to be complex. We have recently shown that choroidal blood flow is better regulated during exercise-induced changes in choroidal blood flow than during a suction-cup-induced increase in intraocular pressure (IOP). In the present study we hypothesized that choroidal blood flow regulation may be altered during a latanoprost-induced decrease in IOP.Methods In this prospective, balanced, placebo-controlled parallel group study, 18 healthy male volunteers were included. Choroidal blood flow regulation was assessed using laser Doppler flowmetry during an artificial increase in intraocular pressure using a suction cup and during a 6 minutes squatting period. Results were compared before drug administration and after 14 days of topical instillation of either latanoprost or placebo.Results Neither systemic blood pressure nor choroidal blood flow at baseline was altered by latanoprost. As expected, latanoprost did, however, reduce IOP. The regulation of choroidal blood flow was altered by latanoprost with a wider range of regulation compared to placebo treatment (p < 0.05).Conclusion The present data indicate that administration of latanoprost improves choroidal blood flow regulation. Since latanoprost did not alter baseline choroidal blood flow this effect may be related to the reduction in IOP.
    Acta ophthalmologica 01/2009; 87:0-0. · 2.44 Impact Factor
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    ABSTRACT: Purpose It has been implicated that vascular dysregulation plays a role in the pathogenesis of primary open angle glaucoma (POAG). In the present study the association between optic nerve head blood flow as measured with laser Doppler flowmetry and ocular perfusion pressure in patients with treated and untreated POAG, patients with ocular hypertension and healthy control subjects was compared.Methods 136 patients with treated POAG, 116 patients with untreated POAG, 138 patients with ocular hypertension and 160 control subjects were included in the study. Optic nerve head blood flow was assessed using laser Doppler flowmetry. Ocular perfusion pressure was calculated based on measurement of IOP and systemic hemodynamics.Results Optic nerve head blood flow was significantly reduced in patients with glaucoma compared to patients with ocular hypertension and healthy subjects (p<0.01). However, no difference in optic nerve head blood flow between treated and untreated glaucoma patients was detected. The highest association between ocular perfusion pressure and optic nerve head blood flow was found in untreated glaucoma patients followed by ocular hypertensives and treated glaucoma patients.Conclusion The present study confirms evidence that optic nerve head blood flow is reduced in patients with POAG and patients with ocular hypertension. Correlation coefficients in the glaucoma groups and in the ocular hypertensives indicate a vascular dysregulation in these patients compared to healthy control subjects.
    Acta ophthalmologica 01/2009; 87:0-0. · 2.44 Impact Factor
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    ABSTRACT: The study was conducted to investigate whether the L-arginine/nitric oxide system plays a role in choroidal blood flow (ChBF) regulation during a decrease in ocular perfusion pressure (OPP). Experiments were performed on 3 days in a randomized double-masked, placebo-controlled, three-way crossover design. On different study days, subjects received intravenous infusions of N(G)-monomethyl-L-arginine (L-NMMA), phenylephrine, or placebo. Intraocular pressure was raised in stepwise increments using the suction cup Choroidal blood flow (ChBF, laser Doppler flowmetry), mean arterial blood pressure (MAP), and IOP were assessed. Ocular perfusion pressure was calculated as OPP = 23(MAP - IOP). For correlation analysis all OPP/ChBF data pairs from all subjects were pooled independent of time point of measurement. Then, the pooled data were sorted according to OPP, and correlation analyses were performed. L-NMMA and phenylephrine increased resting OPP by +17% +/- 18% and +14% +/- 21%, respectively (P < 0.05). L-NMMA reduced resting ChBF by -21% +/- 17% (P < 0.05). The relative decrease in OPP during suction cup application was comparable with all drugs administered. The decrease in OPP was paralleled by a significant decrease in ChBF (maximum between -39% and -47%), which was less pronounced, however, than the decrease in OPP (maximum between -69% and -74%). Neither placebo nor L-NMMA, nor phenylephrine, influenced the OPP/ChBF relationship. The data confirm previously published observations that the choroid shows some regulatory capacity during reduced OPP. The L-arginine/nitric oxide-system plays a role in the maintenance of basal vascular tone but seems not to be involved in the choroidal vasodilator response when IOP is increased.
    Investigative ophthalmology & visual science 01/2009; 50(1):372-7. · 3.43 Impact Factor
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    ABSTRACT: To investigate the fluctuations of ocular blood flow parameters over 13 h in patients with primary open-angle glaucoma (POAG) and in healthy eyes, and to relate these fluctuations with variations in intraocular pressure (IOP) and mean ocular perfusion pressure (OPP). 15 patients with POAG and 15 control subjects were included. Measurements of systemic blood pressure (SBP), fundus pulsation amplitude (FPA), choroidal blood flow (CHBF), optic nerve head blood flow (ONHBF) and IOP were performed at 08:00, 12:00, 17:00 and 21:00. OPP was calculated from IOP and SBP. The coefficient of variation (CV) was calculated for all individual parameters to assess their variability. The time response of the ocular haemodynamic variables was not different between the groups. Most of the outcome variables showed significantly larger fluctuations in patients with POAG compared with healthy controls (CV: FPA: 0.085 (SD 0.033) vs 0.054 (0.029), p = 0.012; CHBF: 0.082 (0.030) vs 0.052 (0.023), p = 0.005; ONHBF: 0.086 (0.044) vs 0.059 (0.032), p = 0.063). These changes were not associated with OPP or IOP. Changes over time correlated among the different ocular haemodynamic outcome measures in patients with POAG (r = 0.678, r = 0.557, r = 0.545; p<0.04) but not in the control subjects (r = 0.336, r = -0.227, r = -0.130; p>0.22). Patients with POAG show a larger diurnal fluctuation of ocular blood flow parameters. These fluctuations appear not to be related to a higher statistical error of the applied measurement techniques in POAG patients. These data support the hypothesis that POAG is associated with vascular dysregulation.
    The British journal of ophthalmology 12/2008; 93(4):486-91. · 2.92 Impact Factor
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    ABSTRACT: The aim of the present study was to investigate the reproducibility and potential diurnal variation of optic nerve head and retinal blood flow parameters in healthy individuals over a period of 12 hr. We measured optic nerve head and retinal blood flow parameters in 16 healthy male non-smoking individuals at five time-points during the day (08:00, 11:00, 14:00, 17:00 and 20:00 hr). Outcome parameters were perimacular white blood cell flux (as assessed with the blue field entoptic technique), blood velocities in retinal veins (as assessed with bi-directional laser Doppler velocimetry), retinal arterial and venous diameters (as assessed with the retinal vessel analyser), optic nerve head blood flow, volume and velocity (as assessed with single point and scanning laser Doppler flowmetry) and blood velocities in the central retinal artery (as assessed with colour Doppler imaging). The coefficient of variation and the maximum change from baseline in an individual were calculated for each outcome parameter. No diurnal variation in optic nerve head or retinal blood flow was observed with any of the techniques employed. Coefficients of variation were between 1.6% and 18.5% for all outcome parameters. The maximum change from baseline in an individual was much higher, ranging from 3.7% to 78.2%. Our data indicate that in healthy individuals the selected techniques provide adequate reproducibility to be used in clinical studies. However, in patients with eye diseases and reduced vision the reproducibility may be considerably worse.
    Acta ophthalmologica 11/2008; 87(8):875-80. · 2.44 Impact Factor
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    ABSTRACT: Glaucoma is a group of ocular diseases characterized by optic neuropathy associated with loss of the retinal nerve fibre layer and re-modelling of the optic nerve head, and a subsequent particular pattern of visual field loss. Increased intraocular pressure is the most important risk factor for the disease, but the pathogenesis of glaucoma is not monofactorial. Among other factors, ischaemia and vascular dysregulation have been implicated in the mechanisms underlying glaucoma. The vascular endothelium plays an important role in the regulation of ocular blood flow and pathological alterations of vascular endothelial cells may induce ischaemia and dysregulation. The present review summarizes our current evidence of endothelial dysfunction in glaucoma. This is of interest because endothelial dysfunction is a good prognostic factor for progression in several diseases. Although such data are lacking for glaucoma, endothelial dysfunction may provide an attractive target for therapeutic intervention in open-angle glaucoma and other vascular disorders of the eye.
    Acta ophthalmologica 06/2008; 87(1):4-12. · 2.44 Impact Factor
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    ABSTRACT: There is evidence from theoretical models and animal studies that the biomechanical properties of the optic nerve head and the sclera play a role in the pathophysiology of glaucoma. There are, however, only a few data available that demonstrate such biomechanical alterations in vivo. In this study, the hypothesis was that patients with primary open-angle glaucoma (POAG) have an abnormal ocular structural stiffness based on measurements of intraocular pressure amplitude and ocular fundus pulsation amplitude (FPA). Seventy patients with POAG and 70 healthy control subjects matched for age, sex, intraocular pressure and systemic blood pressure were included. The ocular PA and pulsatile ocular blood flow were assessed with pneumotonometry. The FPA was measured by using laser interferometry. Based on the Friedenwald equation, a coefficient of ocular rigidity (E1) was calculated relating PA to FPA. There was no difference in systemic blood pressure, intraocular pressure, and ocular perfusion pressure (OPP) between the patients with glaucoma and the healthy control subjects. Both, FPA and PA were lower in the patients with glaucoma than in the control subjects. The calculated factor E1 was significantly higher in the patients with POAG (0.0454 +/- 0.0085 AU) than in the control subjects (0.0427 +/- 0.0058 AU, P = 0.03). Multiple regression analysis revealed that E1 was independent of age and sex, and correlated only slightly with OPP. The present study indicates increased ocular rigidity in patients with POAG. This is compatible with a number of previous animal experiments and supports the concepts that the biomechanical properties of ocular tissues play a role in the diseases process.
    Investigative ophthalmology & visual science 06/2008; 49(9):4046-50. · 3.43 Impact Factor
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    ABSTRACT: Administration of low doses of Escherichia coli endotoxin (LPS) to humans enables the study of inflammatory mechanisms. The purpose of the present study was to investigate the retinal vascular reactivity after LPS infusion. In a randomized placebo-controlled cross-over study, 18 healthy male volunteers received 20 IU/kg LPS or placebo as an intravenous bolus infusion. Outcome parameters were measured at baseline and 4h after LPS/placebo administration. At baseline and at 4h after administration a short period of 100% oxygen inhalation was used to assess retinal vasoreactivity to this stimulus. Perimacular white blood cell velocity, density and flux were assessed with the blue-field entoptic technique, retinal branch arterial and venous diameters were measured with a retinal vessel analyzer and red blood cell velocity in retinal branch veins was measured with laser Doppler velocimetry. LPS is associated with peripheral blood leukocytosis and increased white blood cell density in ocular microvessels (p<0.001). In addition, retinal arterial (p=0.02) and venous (p<0.01) diameters were increased. All retinal hemodynamic parameters showed a decrease during 100% oxygen breathing. This decrease was significantly blunted by LPS for all retinal outcome parameters except venous diameter (p=0.04 for white blood cell velocity, p=0.0002 for white blood cell density, p<0.0001 for white blood cell flux, p=0.01 for arterial diameter, p=0.02 for red blood cell velocity and p=0.006 for red blood cell flux). These data indicate that LPS-induced inflammation induces vascular dysregulation in the retina. This may provide a link between inflammation and vascular dysregulation. Further studies are warranted to investigate whether this model may be suitable to study inflammation induced vascular dysregulation in the eye.
    Experimental Eye Research 05/2008; 87(2):131-6. · 3.03 Impact Factor
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    ABSTRACT: Purpose We set out to investigate whether the AREDS medication is capable of normalizing retinal blood flow reactivity to systemic hyperoxia in a human lipopolysaccharide (LPS) model.Methods The present study was a randomized double masked placebo-controlled parallel group study in 21 healthy volunteers. The infusion of LPS was used as a standardized experimental model of systemic inflammation associated with enhanced oxidative stress and widespread endothelial dysfunction in humans. Ocular hemodynamic measurements were performed before endotoxemia and 4 hours after the subjects had received an LPS bolus. At each of these time points the retinal vascular reactivity to hyperoxia was studied. After the first trial day the subjects had to take either the AREDS medication (n=14) or a placebo (n=7) for 14 days. Thereafter a second trial day was performed on which the time schedule exactly followed the first day as described above.Results As expected LPS induced retinal vasodilatation (p < 0.01) together with an increase in retinal leukocyte density, which occurred because to systemic leukocytosis. The oxygen induced decrease in retinal blood flow was reduced after infusion of LPS (p < 0.01). This effect was partially restored after intake of the AREDS medication, but not after intake of placebo (p = 0.04) between groups.Conclusion Our findings support previous data showing that LPS induces impaired endothelial function. This effect was significantly reduced by the AREDS medication. Our model may be used to study the effects of various antioxidants and the components of the AREDS medication on oxidative stress-induced vascular dysregulation in the human retina.
    Acta ophthalmologica 01/2008; 86:0-0. · 2.44 Impact Factor
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    Konstantin Gugleta, Gabriele Fuchsjäger-Mayrl, Selim Orgül
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    ABSTRACT: Rapid development of functional neuroimaging techniques have brought about a growing interest for neurovascular coupling in neuroresearch, which, in turn, has prompted similar research in ophthalmology. There are now hints that neurovascular coupling is disturbed in glaucoma. The contact of the nerve terminals to the cortical blood vessels is mostly realized through astrocytes. A major defining property of glaucoma, cupping of the optic disk, implies tissue remodeling of the optic nerve head and involves an astrocytic responses. A malfunction of the astrocytes in glaucoma may lead not only to the hallmark of glaucoma-cupping and death of retinal ganglion cells-but also to an accompanying or even preceding disturbance in ocular neurovascular coupling. This article is a short overview of research published in this field so far.
    Survey of Ophthalmology 12/2007; 52 Suppl 2:S139-43. · 2.86 Impact Factor
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    ABSTRACT: Clonidine and brimonidine, two alpha-2 agonists, have been shown to reduce intraocular pressure (IOP) in patients with glaucoma. Little is known, however, about the exact role of alpha receptors in the control of ocular blood flow in the posterior pole of the eye. Hence, the study was conducted to investigate the effects of topical clonidine versus topical brimonidine on choroidal blood flow and intraocular pressure during squatting. This was a randomized, double-masked, controlled, two-way crossover study. Twelve healthy male nonsmoking volunteers, aged between 19 and 35 years were included in the study. Two drops of clonidine or brimonidine were administered in the subjects' study eyes. Continuous measurement using the compact laser Doppler flowmeter was performed during a 6-minute squatting period, to assess choroidal blood flow regulation during an increase in ocular perfusion pressure. Both substances induced a pronounced but comparable (P = 0.8) decrease in IOP. Squatting increased mean arterial pressure (MAP) and ocular perfusion pressure (P < 0.01). This increase was comparable between the clonidine and the brimonidine study day (P = 0.88). Squatting induced an increase in choroidal blood flow that was less pronounced than the increase in ocular perfusion pressure. Compared with baseline the alpha-2 agonists decreased choroidal blood flow during squatting (P = 0.0026) to a comparable degree (P = 0.86). Vascular resistance increased at baseline and during squatting after administration of the alpha-2 agonists (P < 0.01) in both groups to a comparable degree (P = 0.56). Topical alpha-2 agonists may induce changes in choroidal blood flow, even after a single administration. Long-term studies are needed to study potential effects of brimonidine and clonidine in the clinical setting.
    Investigative Ophthalmology &amp Visual Science 09/2007; 48(9):4220-5. · 3.44 Impact Factor
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    ABSTRACT: Several studies have recently shown that a transition from light to dark is associated with a reduction in choroidal blood flow. The mechanism underlying this effect is unclear but may be related to changes in neural input. In the present study, the authors hypothesized that either the alpha-receptor agonist phenylephrine or the nitric oxide synthase (NOS) inhibitor L-NMMA may alter the choroidal blood flow response during a transition from light to dark. In 15 healthy male nonsmoking subjects, the response of choroidal perfusion was studied in a randomized placebo-controlled three-way crossover study. Phenylephrine, L-NMMA or placebo was administered on different study days, and the effect of a light/dark transition on choroidal perfusion parameters was studied. Subfoveal choroidal blood flow and fundus pulsation amplitude were assessed with laser Doppler flowmetry and laser interferometry, respectively. Before drug administration, a transition from light to dark reduced both choroidal hemodynamic parameters by 11% to 20%. Neither phenylephrine nor placebo altered basal choroidal blood flow or choroidal blood flow responses to the light/dark transitions. By contrast, the NOS inhibitor L-NMMA significantly reduced basal choroidal blood flow by 20.5% +/- 5.9% (P < 0.001) and basal fundus pulsation amplitude by 21.5% +/- 4.8% (P < 0.001). In addition, the response of subfoveal choroidal blood flow (-6.2% +/- 3.2%; P = 0.008) and fundus pulsation amplitude (-4.2% +/- 2.4%; P < 0.001) to the light/dark transition was significantly diminished. The present study indicates that NO plays a role in the choroidal blood flow decrease during a transition from light to dark. Given that L-NMMA is a nonspecific inhibitor of NOS, the present study does not clarify whether this NO is from endothelial or neural sources.
    Investigative Ophthalmology &amp Visual Science 09/2007; 48(9):4215-9. · 3.44 Impact Factor
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    ABSTRACT: To investigate the ocular blood flow response to systemic nitric oxide synthase inhibition in patients with primary open-angle glaucoma. In 12 patients with glaucoma and 12 age-matched control subjects, subfoveal choroidal blood flow, optic nerve head blood flow, ocular fundus pulsation amplitude, intraocular pressure, and systemic hemodynamic parameters were measured at baseline and after inhibition of nitric oxide synthase by intravenous administration of NG-monomethyl-L-arginine. The increase in blood pressure in response to NG-monomethyl-L-arginine was comparable between the 2 study cohorts. In patients with glaucoma, the decrease of optic nerve head blood flow (P = .03) and fundus pulsation amplitude (P<.001) during nitric oxide synthase inhibition was significantly less pronounced than in healthy control subjects. A tendency toward a reduced response in choroidal blood flow was seen (P = .051 between groups) in patients with glaucoma. This is the first in vivo study providing evidence for an altered ocular L-arginine/nitric oxide system in patients with glaucoma. Normalization of the ocular nitric oxide production may be beneficial in terms of normalization of ocular blood flow and neuroprotection of retinal ganglion cells.
    Archives of Ophthalmology 05/2007; 125(4):494-8. · 3.83 Impact Factor

Publication Stats

609 Citations
132.00 Total Impact Points

Institutions

  • 2005–2014
    • Medical University of Vienna
      • Department of Clinical Pharmacology
      Wien, Vienna, Austria
  • 2002–2003
    • University of Vienna
      • Department of Internal Medicine III
      Wien, Vienna, Austria
  • 2001
    • Vienna General Hospital
      Wien, Vienna, Austria