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At least 667 records · Page 37Linked to original sources
PubMed2002

Effect of noradrenaline on retinal blood flow in healthy subjects.

PURPOSE: To gain insight into the role of circulating catecholamines on retinal blood flow in vivo. DESIGN: Nonrandomized, open, crossover design. PARTICIPANTS: In 10 healthy male subjects, tyramine and noradrenaline were administered in stepwise increasing doses. These doses were selected to induce comparable changes in systemic blood pressure. METHODS: During each infusion step, retinal vessel diameter and retinal venous blood speed were measured with the Zeiss retinal vessel analyzer (Zeiss, Jena, Germany) and laser Doppler velocimetry, respectively. MAIN OUTCOME MEASURES: Retinal blood flow through a major temporal vein was calculated. RESULTS: As expected, tyramine and noradrenaline induced a systemic hypertensive response. Tyramine caused a moderate increase in noradrenaline plasma levels, whereas exogenous noradrenaline increased noradrenaline plasma levels more than 10-fold. Nevertheless, neither tyramine nor noradrenaline induced any effect on retinal hemodynamic parameters. CONCLUSIONS: These data indicate that even high levels of circulating noradrenaline have little impact on retinal vascular tone and retinal blood flow. Hence, the adrenergic system appears not to play a major role in retinal blood flow regulation.

Adrenergic Uptake Inhibitors↗
PubMed2002

Localization of VEGF receptor-2 (KDR/Flk-1) and effects of blocking it in oxygen-induced retinopathy.

PURPOSE: Vascular endothelial cell growth factor (VEGF) has been implicated in vascular development and in proliferative retinopathies. The goal of this study was to examine the immunohistochemical localization and relative levels of VEGF receptor-2 (KDR) in canine retina during postnatal vasculogenesis and during angiogenesis in oxygen-induced retinopathy (OIR) and to investigate the effects of neutralizing KDR on these processes. METHODS: Eyes from normal dogs ranging from 1 to 22 days of age and age-matched oxygen-treated animals were snap frozen for immunohistochemical analysis with antibodies against human KDR. To examine the effects of blocking KDR, 6-day-old air-reared control and oxygen-treated animals were surgically implanted with slow release polymer pellets containing control IgG or anti-KDR. Material eluted from pellets was assessed using a binding assay (measures binding to soluble KDR) to determine the kinetics of anti-KDR release and endothelial cell proliferation to measure bioactivity. Animals were killed at 22 days of age and tissues examined with adenosine diphosphatase (ADPase) histochemical staining of blood vessels. RESULTS: KDR immunoreactivity was only weakly associated with developing retinal vessels and was not observed in angioblasts throughout normal postnatal development. Immunoreactivity was very strong in reforming retinal vessels and intravitreal neovascularization in oxygen-treated animals. Anti-KDR had no effect on vessel morphology or growth in air-reared control animals. In oxygen-treated animals, anti-KDR significantly inhibited revascularization of the retina (P = 0.005) and formation of intravitreal neovascularization compared with control IgG pellet eyes (P < 0.04). CONCLUSIONS: KDR/Flk-1 was only weakly associated with normal developing primary retinal vessels but was strongly expressed by proliferating endothelial cells in reforming retinal vessels and intravitreal neovascularization after hyperoxic insult. Anti-KDR antibody delivered by slow-release pellets had no effect on normal vasculogenesis, but it inhibited the formation of intravitreal neovascularization and retinal vessel development in OIR. The study suggests that blocking KDR may be beneficial for treating pathologic angiogenesis in adult tissue.

Animals↗
PubMedDate not supplied

Response of retinal blood flow to CO2-breathing in humans.

PURPOSE: To investigate the effect of systemic hypercapnia on retinal hemodynamics in humans. METHODS: We studied the effect of breathing a mixture of normal air with 5% CO2 for 13 minutes in ten healthy young male volunteers, using the Zeiss retinal vessel analyzer for continuous measurement of retinal vessel diameter and the blue-field entoptic technique to quantify retinal white blood cell flux. In eight other subjects the effect of hypercapnia was measured with the Zeiss retinal vessel analyzer and by laser Doppler velocimetry to establish retinal blood flow velocity. RESULTS: Retinal arterial and venous vessel diameters increased by a maximum of 4.2% and 3.2%, respectively. Peak effect was observed after 3 minutes of breathing the mixture of normal air with 5% CO2. During hypercapnia red blood cell velocity increased 11.7% and, accordingly, retinal blood flow increased 19.1%. White blood cell density and velocity rose significantly during hypercapnia, resulting in an increase in white blood cell flux (19.2%). CONCLUSIONS: Our data indicate that CO2 induces vasodilation in retinal arteries and retinal veins. Retinal blood flow and perimacular white blood cell flux increased to the same extent in subjects breathing a mixture of normal air with 5% CO2.

Adult↗
PubMed2004

Response of choroidal blood flow to carbogen breathing in smokers and non-smokers.

AIM: To investigate a potential difference in ocular vascular reactivity during carbogen breathing in optic nerve head, choroid, and retina between healthy smokers and non-smokers. METHODS: 25 (13 smokers and 12 non-smokers) healthy male volunteers participated in this observer masked, two cohort study. During inhalation of carbogen (5% CO(2) and 95% O(2)) over 10 minutes measurements were taken using laser Doppler flowmetry to assess submacular choroidal and optic nerve head blood flow, laser interferometry to assess fundus pulsation amplitudes, and retinal vessel analyser (RVA) to assess retinal vessel diameters. RESULTS: At baseline choroidal blood flow was higher (p = 0.018, ANOVA) in smokers than in non-smokers. During administration of carbogen the response in choroidal blood flow was significantly different between the two groups: there was an increase in non-smokers after carbogen breathing (p = 0.048) compared with relatively stable blood flow in smokers (p = 0.049 between groups, ANOVA). A similar response pattern was seen for fundus pulsation amplitude, which increased notably after carbogen breathing in non-smokers but not in smokers (p<0.001 between groups, ANOVA). Optic nerve head blood flow and retinal vessel diameters were reduced in both groups to a comparable degree during carbogen breathing. CONCLUSION: The study indicated abnormal choroidal vascular reactivity in chronic smokers. These early haemodynamic changes may be related to the increased risk to smokers of developing ocular vascular diseases. The specific mechanisms underlying abnormal choroidal vascular reactivity in chronic smokers remain to be characterised.

Adult↗
PubMed2006

Potential role of microglia in retinal blood vessel formation.

PURPOSE: The role of microglia, present in the retina early in development before vascularization, remains ill defined. The authors investigated whether microglia are implicated in retinal blood vessel formation. METHODS: The microglia and vasculature of developing human fetal and rodent retinas were examined by labeling the endothelial cells with lectin and the microglia with CD18 antibody or green fluorescent protein driven by the promoter of the chemokine receptor CX(3)CR1. Rodent ischemic proliferative retinopathy induced by hyperoxia or hypercapnia, which model retinopathy of prematurity, and ex vivo retinal explants were used to assess microglial involvement in vascular pathology. Microglial participation in developmental retinal vessel formation was further studied in neonatal rats after pharmacologic macrophage depletion with the use of clodronate liposomes and subsequent intravitreal injection of microglia. RESULTS: Microglia intimately appose developing vessels of human and murine retinas. Ischemic retinopathy models exhibit decreased microglia concomitant with the characteristic reductions in vasculature observed in these retinopathies. Retinal explants exposed to conditions resulting in ischemic retinopathies (in vivo) reveal that antioxidants protect against microglial loss. Depletion of resident retinal microglia, but not systemic macrophages, reduced developmental vessel growth and density, which were restored by intravitreal microglial injection. CONCLUSIONS: These observations suggest that proper retinal blood vessel formation requires an adequate resident microglial population because diminished microglia are associated with decreased vascularity in models of ischemic retinopathy and retinal vascular development. In light of these findings, the traditional definition of microglia as merely immunocompetent cells should be reconsidered to encompass this new function related to blood vessel formation.

Animals↗
PubMed1985

Morphometric analysis of retinal blood vessels in retinopathia diabetica.

A quantitative investigation of the retinal blood vessels was carried out in 80 diabetics and 20 metabolically healthy controls of the same age and sex distribution. The blood vessels were isolated by trypsinization, stained with PAS, and analyzed by light microscopy. After 1-5 years' duration of diabetes mellitus, capillary lesions in the ocular fundus can be seen microscopically in the slides, but not with a stereomicroscope. In the retinae of persons with normal carbohydrate metabolism, capillary defects were found to a far lesser extent; they were also always localized in the periphery of the retina, whereas the diabetic lesions were localized in the retinal center. In the diabetics, both capillary lesions (e.g., loss of pericytes) and damage of the retinal neurons occurred nearly simultaneously and with the same retinal localization. This suggests that the capillary lesions are not the cause of neuronal degeneration but that both events are caused by the same mechanisms of pathogenesis.

Adult↗
PubMed1986

Neovascularization in urethane rat retinopathy demonstrated by thymidine labelling.

Rat urethane retinopathy produces sequential and progressive loss of the photoreceptor cells, proceeding from the posterior to the peripheral retina. The inner retina, the retinal pigment epithelium and the choriocapillaris are spared. After loss of the photoreceptor cells, a vasculopathy develops which includes progressive retinal capillary loss and formation of coil-like tufts of retinal vessels which are embedded in the retinal pigment epithelium. Some of the retinal vessels within the retinal pigment epithelium have changed their phenotype from continuous to fenestrated endothelial cells. To elucidate whether DNA synthesis was necessary for formation of the coil-like vessel tuft formation, an autoradiographic study was performed. At 12, 14, 16 and 20 weeks of age, times during which the vasculopathy is known to be forming, urethane and control rats were injected with 3 successive doses of methyl-3H-thymidine. Autoradiography of trypsin-digested retinal vessel preparations was compared with histological sections of the paired eye. The frequency of tritium labelled endothelial cells was much higher in the urethane rats than control animals, and were predominantly in the posterior pole, rather than the periphery. Labelled endothelial cells tended to be associated with, or near, the coil-like vessel tufts. Capillary dropout was observed in urethane, but not control animals. Frequently, adjacent endothelial cells were labelled, suggestive of mitosis. The occurrence of thymidine uptake and a change in phenotype of the endothelial cells leads us to suggest that new cell synthesis, or neovascularization, has occurred in these vessels. Since the retina is less than half the normal thickness and the choriocapillaris is intact, it appears unlikely that ischemia is responsible for inducing these pathological responses. We suggest that the retinal pigment epithelial cell is responsible for the increase in DNA synthesis and change in phenotype of the retinal endothelial cell.

Animals↗
PubMed2001

[A research on the quantification of retinal blood vessels in cases of arteriovenous crossing pressure syndrome caused by hypertension].

The method for quantification of retinal blood vessels in cases of arteriovenous crossing pressure syndrome caused by hypertension was studied. The matched filtering pre-processing of image enhancement for local retinal blood vessels and closing of mathematical morphology for image smoothing, and the method of scale-up lineation for contour determination of retinal blood vessels and optimal seeking algorithm with reversible quantification were used to measure the pathological deformation of vessel, thus providing a computer method for auxiliary diagnosis of relative diseases.

Algorithms↗
PubMed2002

Effect of inhalation of different mixtures of O(2) and CO(2) on retinal blood flow.

AIM: To determine the effects of various mixtures of O(2) and CO(2) on retinal blood flow in healthy subjects. METHODS: A randomised, double masked, four way crossover trial was carried out in 12 healthy male non-smoking subjects. Gas mixtures (100% O(2), 97.5% O(2) + 2.5% CO(2), 95% O(2) + 5% CO(2), and 92% O(2) + 8% CO(2)) were administered for 10 minutes each. Two non-invasive methods were used: laser Doppler velocimetry (LDV) for measurement of retinal blood velocity and fundus imaging with the Zeiss retinal vessel analyser (RVA) for the assessment of retinal vessel diameters. Arterial pH, pCO(2), and pO(2) were determined with an automatic blood gas analysis system. Retinal blood flow through a major temporal vein was calculated. RESULTS: Retinal blood velocity, retinal vessel diameter, and retinal blood flow decreased during all breathing periods (p <0.001 each). Administration of 92% O(2) + 8% CO(2) significantly increased SBP, MAP, and PR (p <0.001 each, versus baseline), whereas the other gas mixtures had little effect on systemic haemodynamics. Addition of 2.5%, 5%, and 8% CO(2) to oxygen caused a marked decrease in pH and an increase in pCO(2) (p <0.001 versus pure oxygen). CONCLUSIONS: Breathing of pure oxygen and oxygen in combination with carbon dioxide significantly decreases retinal blood flow. Based on these data the authors speculate that hyperoxia induced vasoconstriction is not due to changes in intravascular pH and cannot be counteracted by an intravascular increase in pCO(2).

Adult↗
PubMed1992

[Retinopathy score: assessment of fluorescein angiography findings in diabetic retinopathy].

Scoring of the pathological changes shown by fluorescein angiography in patients with diabetic retinopathy was performed to assess the severity of retinopathy and the effectiveness of treatment. A total of 480 fluorescein angiography sessions were performed in 142 eyes of 71 patients. Eleven items of 7 signs were assessed (microaneurysms, extent of non-perfused area (NP), intraretinal microvascular abnormalities, neovascularization from the optic disc or from retinal vessels, leakage from retinal vessels and macular edema). First, the gradings for the 11 items were analysed by the quantification analysis method III and classified into 6 clusters. These 6 clusters corresponded to the grades of retinopathy. The relative severity of each grade of retinopathy was calculated by this analysis. Second, in order to determine the relative contribution of each item to the grading of retinopathy, the quantification analysis method I was used with the above 6 grades of retinopathy, which were adopted as outside criteria. The regression coefficient of the extent of NP was found to be greatest. Scores were defined as the summation of the category numbers (weights) of the main 7 items.

Diabetic Retinopathy↗
PubMed2005

Retinal vascular diameter in young subjects with a vasospastic propensity.

PURPOSE: Retinal vascular diameters have recently been shown not to be related to an increased risk of open-angle glaucoma. Because vasospastic propensity has been suggested to represent a risk factor for various ocular diseases, especially glaucoma, the steady-state retinal vascular diameter in subjects with a propensity for systemic vascular dysregulation was compared with a group of age-matched gender-matched controls. METHODS: Thirty healthy non-smoking individuals [female/male 26/4; mean +/- SD age 22.8+/-3.4 (range 18-31) years] were enrolled into the study. Subjects were classified as having vasospasm (15 subjects) if they related a clear history of frequently cold hands and as healthy subjects (15 subjects) if they denied such a history. Vasospastic propensity or the absence of it had to be confirmed by nail-fold capillaroscopy. Vascular diameter of retinal vessels was measured repeatedly on two days with the retinal vessel analyser and corrected for perfusion pressure, age, and refraction. RESULTS: Neither retinal arteriole diameter (P=0.30) or retinal venule diameter (P=0.49), nor retinal arteriole-to-venule ratio (P=0.96), differed between the two experimental groups. CONCLUSIONS: Although vasospastic propensity has been suggested to represent a risk factor in various ocular diseases, the steady-state retinal vessel diameters are not altered in healthy vasospastic subjects. It is probable that the steady-state retinal vessel diameters are no adequate risk indicators for the haemodynamic risk in diseases such as glaucoma.

Adolescent↗
PubMed1988

Measurement of retinal blood vessel width using computerized image analysis.

We report a new method for quantitating retinal blood vessel width from fluorescein angiogram negatives using a computerized image analyser. Interuser and intrauser variability were 3 to 4 times lower than reported with older methods. In addition, model blood vessels were used to test the accuracy of our method under four clinically relevant conditions: variations in vessel width, fluorescein concentration, flash intensity and background fluorescence. Although computed measurements were affected by vessel width, fluorescein concentration and flash intensity, the linearity of the actual versus computed width was maintained during wide variations in all four conditions (r = 0.95, P less than 0.0001). Accuracy was best achieved at a flash intensity of 150 W/sec and a fluorescein concentration of 45 micrograms/ml. The results of this study provide a better understanding of factors affecting the apparent width of retinal blood vessels in fluorescein angiograms. This technique should be useful in rapidly obtaining accurate measurements of blood vessel width from fluorescein angiograms.

Animals↗
PubMed2005

Short-term increase of intraocular pressure does not alter the response of retinal and optic nerve head blood flow to flicker stimulation.

PURPOSE: It has been shown that stimulation with diffuse luminance flicker induces vasodilatation in the human retina and increases optic nerve head (ONH) blood flow. The present study was designed to investigate the influence of a short-term increase in intraocular pressure on flicker-induced changes in ONH blood flow and retinal vessel diameters. METHODS: In a group of 15 healthy volunteers, IOP was increased by the episcleral suction cup technique. ONH blood flow was assessed with a laser Doppler flowmeter, and retinal vessel diameters were measured with the retinal vessel analyzer. Flicker responses of retinal vessel diameters and ONH blood flow were determined at baseline conditions and during suction of 70 and 140 mm Hg. Flicker light consisted of 8-Hz square-wave flashes at a wavelength below 550 nm and produced a retinal irradiance of 140 muW/cm(2). RESULTS: Suction increased IOP from 12 +/- 2 to 27 +/- 4 mm Hg and 43 +/- 4 mm Hg. Stimulation with diffuse luminance flicker induced an increase in ONH blood flow of +24.0% +/- 20.7%. Increased IOP did not significantly change the flicker response in the ONH (+19.3% +/- 26.6% and +22.1% +/- 25.1%). In retinal veins, flicker induced an increase in vessel diameter of +3.0% +/- 2.0%. Flicker responses in retinal veins were not significantly altered after the IOP was increased, compared with those recorded at baseline IOP (+2.8% +/- 2.5% and +3.2% +/- 2.2%). The flicker response in retinal arteries at baseline IOP was +3.5% +/- 2.0%. Again, the increase in IOP did not significantly alter this flicker response (+2.8% +/- 1.6% and +3.1% +/- 2.4%). CONCLUSIONS: A short-term increase in IOP does not alter the response of retinal vessel diameters and ONH blood flow to diffuse luminance flicker, which indicates that increased IOP does not alter retinal or ONH regulation during neuronal stimulation.

Blood Flow Velocity↗
PubMed1992

Ocular microangiopathy in familial amyloidotic polyneuropathy, type I.

To obtain precise information on ophthalmological manifestations in patients with familial amyloidotic polyneuropathy (FAP), we performed ophthalmological and histopathological studies on 18 FAP patients and 6 asymptomatic individuals with a mutant transthyretin (TTR) gene. The incidence of vascular abnormalities of the conjunctiva and retina was surprisingly high in FAP patients. Abnormal conjunctival vessels were found mainly in the limbal area of FAP patients, but not in asymptomatic individuals with a mutant TTR gene. Conjunctival biopsy of 5 FAP patients and autopsy of another 2 FAP patients revealed that a significant amyloid deposit could be recognized in the superficial substantia propria of the conjunctiva and wall and perivascular area of the conjunctival vessels in all cases, a finding that is of diagnostic value. As for the retinal vessels, an abnormal arteriovenous ratio (A/V ratio), tortuous retinal vessels, cotton wool exudates and retinal hemorrhages were found in FAP patients. However, histopathological analysis of the retina in two autopsied cases revealed only a trace amount of amyloid deposit around the retinal vessels. Ophthalmological examination of three patients with pandysautonomia revealed that the appearance of both the conjunctival and retinal vessels of these patients was similar to that in FAP patients. These results indicate that in FAP patients ocular microangiopathy may be related to autonomic dysfunction as well as amyloid deposit.

Adolescent↗
PubMed1985

[Retinal vascular occlusion in antithrombin III deficiency].

Deficiency of Antithrombin III (AT III), which is one of the main inhibitors of blood coagulation, may lead to severe thrombosis and embolism. The authors detected AT III deficiency in two patients with retinal vessel occlusion. Both patients were otherwise healthy. One had recurrent retinal vein thrombosis, the other cilioretinal occlusion. To the authors' knowledge, only one case of retinal vessel occlusion with AT III deficiency has been reported in literature. Furthermore, in the patients reported here retinal vessel occlusion may have been caused by AT III deficiency, which has considerable therapeutic and prophylactic consequences for patients with this disorder. AT III should therefore be determined in retinal vessel occlusion of unknown cause.

Aged↗
PubMed1999

Digital red-free photography for the evaluation of retinal blood vessel displacement in epiretinal membrane.

OBJECTIVE: To evaluate the displacement of retinal blood vessels during the natural course of epiretinal membrane (ERM) formation. DESIGN: Consecutive observational case series. PARTICIPANTS: Thirteen patients (13 eyes) diagnosed with unilateral idiopathic ERM and 10 normal fellow eyes of the same patients served as a control group and constituted the study group. TESTING: All eyes underwent digital red-free filter photography of the fundus using the Topcon Imagenet-1024 System. Photographs were taken on entry to the study and again after 8 to 13 months. Distances were measured between the major and minor blood vessel junctions at the upper and lower temporal arcades and between the disc margin and vessel junctions temporal to the macula on follow-up examinations. To clearly visualize vessel shift, both photographs of each patient were overlaid using the peripheral landmarks of major blood vessel crossings as reference points. MAIN OUTCOME MEASURES: The parameters measured were shifting of blood vessels caused by the ERM formation. The distances were measured in micrometers using the measurement feature of the Topcon Imagenet System. RESULTS: Blood vessel shift (range, 30 microm-434 microm) was noted in all 13 eyes, but in 15 measurements the shift was less than 30 microm and was considered as no shift. In four eyes (31%), the distances decreased in all directions, indicating contraction of the ERM. In four eyes (31%), the distances increased in all directions, indicating release of the ERMs. A mixed pattern of release and contraction of the ERM in the same eye was noted in five eyes (38%). No shift of blood vessels was noted in the control eyes. Findings on image overlay corresponded with the objective measurements. CONCLUSIONS: Noninvasive digital red-free photography is an informative tool for the objective measurement of the vessel displacement during ERM formation. Contraction and release of the ERM were noted.

Aged↗
PubMed1987

Retinal blood vessel test in young-onset diabetic patients.

136 patients with insulin-dependent diabetes mellitus (IDDM) were shown the entoptic blood vessel figure. All patients were examined independently by retinal fluorescein angiography and ophthalmoscopy. 34 patients had no retinopathy, none of them believed to see alterations. 102 patients had different phases of diabetic retinopathy. If there were 1-5 microaneurysms within the 15 degrees meridian surrounding the central fovea, 55% of the patients were able to detect their alterations. If there were 6-20 microaneurysms, 77% of the patients were able to diagnose them. 90% of the patients with an even more severe retinopathy could see their abnormalities. Obviously there are no incorrectly positive results. For intelligent and well-observing patients with IDDM the retinal blood vessel test is a useful method for early detection and self control of diabetic retinopathy. Nevertheless, control of the fundus by an ophthalmologist is still necessary.

Adolescent↗