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Biomedical subjects

O Arend

Publications and source records attributed to O Arend.

At least 73 records · Page 4Linked to original sources
PubMed1995

In vivo fluorescence of the ocular fundus exhibits retinal pigment epithelium lipofuscin characteristics.

PURPOSE: To characterize the intrinsic fluorescence (autofluorescence) of the human ocular fundus with regard to its excitation and emission spectra, age relationship, retinal location, and topography, and to identify the dominant fluorophore among the fundus layers. METHODS: Using a novel fundus spectrophotometer, fluorescence measurements were made at 7 degrees temporal to the fovea and at the fovea in 30 normal subjects and in 3 selected patients. Topographic measurements were made in 3 subjects. Ex vivo measurements of fluorescence of human retinal pigment epithelium (RPE) were obtained and compared to in vivo data. RESULTS: Fundus fluorescence reveals a broad band of emission between 500 and 750 nm, a maximum of approximately 630 nm, and optimal excitation of approximately 510 nm. Exhibiting a significant increase with age, this fluorescence is highest at 7 degrees to 15 degrees from the fovea, shows a well-defined foveal minimum, and decreases toward the periphery. In vivo fluorescence spectra are consistent with those obtained ex vivo on human RPE. Measurements with short wavelength excitation are strongly influenced by ocular media absorption and reveal an additional minor fluorophore in the fovea. CONCLUSIONS: Spectral characteristics, correlation with age, topographic distribution, and retinal location between the choriocapillaris and the photoreceptors suggest that the dominant fundus fluorophore is RPE lipofuscin. The minor fluorophore is probably in the neurosensory retina but has not been identified.

Adult↗
PubMed1995

[In vivo fundus fluorescence measurements in patients with age related macular degeneration].

UNLABELLED: This study was performed to measure and characterize the intrinsic fluorescence of the ocular fundus in patients with age-related macular degeneration (AMD). METHOD: Fluorescence spectral measurements from discrete retinal locations were made using the fundus spectrophotometer with excitations at 470 and 510 nm. Two normal subjects and seven patients with different stages of AMD were investigated. RESULTS: The spectral characteristics of fundus fluorescence are consistent with those of lipofuscin in the retinal pigment epithelium (RPE). The fluorescence spectrum is broad, with a maximum at about 620 nm. The shape and intensity of the fluorescence spectra are affected by age, site of measurement, pathology, ocular media absorption, and excitation wavelength. Spectra from areas with drusen reveal an additional fluorophore, with maximum around 560 nm, probably emanating from drusen and Bruch's membrane. Measurements in atrophic reveal a decrease of lipofuscin fluorescence and/or a contribution likely due to choroidal and sclera collagen fluorescence. Fluorescence from lipofuscin is more efficiently excited at 510 nm, whereas that of drusen and subretinal structures is relatively more efficient with 470 nm excitation, allowing for discrimination of various fluorophores. CONCLUSION: The spectral characteristics of RPE lipofuscin could be identified and quantified in AMD patients. In addition, the spectra are affected by other fluorophores such as drusen and choroid contributions in atrophy. Fluorescence spectra measurements in AMD patients allow for discrimination of lipofuscin fluorescence, drusen fluorescence, and choroidal or scleral fluorescence. The non-invasive measurement of lipofuscin and drusen fluorescence in AMD may be helpful in monitoring the disease, understanding its evolution, and testing therapeutic concepts.

Aged↗
PubMed1995

Protein C, protein S, and antithrombin III in acute ocular occlusive diseases.

Hereditary and acquired deficiencies of protein C, protein S, and antithrombin III are important risk factors of thrombosis, especially in peripheral veins. In a prospective study, concentrations of these factors were measured to determine the prevalence of deficiencies of these proteins in ocular vascular occlusive disease. A total of 167 patients with acute retinal arterial (28%) or venous occlusion (55%) or ischemic optic neuropathy (17%) were included. Exclusion criteria were anticoagulant therapy, renal insufficiency, and hepatic disease. The mean values obtained for all patients were in normal range (protein C, 102 +/- 25%; protein S, 109 +/- 22%; antithrombin III, 23.6 +/- 3.1 IU/ml). Antithrombin III was pathologically reduced in one patient with branch venous occlusion. Proteins C and S were severely altered in two patients with central venous occlusion, in one individual with ischemic optic neuropathy, and in one patient with branch arterial occlusion. Subnormal values were found in 21 patients for antithrombin III (16.1-19.9 IU/ml), in 7 patients for protein C (55-65%). Two of these five patients with pathologic findings showed severe vascular manifestations in the form of current deep-vein thrombosis and multiple retinal occlusions. Their age was 30 and 53 years, respectively, and differed considerably from the mean age of the entire group (65 +/- 12 years). This study suggests that these proteins were important factors for the development of ocular vascular occlusive diseases in single patients. Although the prevalence is low, measurement of these parameters in young patients may be useful in preventing other vascular complications.

Acute Disease↗
PubMed1994

Hemodilution therapy in central retinal vein occlusion. One-year results of a prospective randomized study.

Systemic hemorheologic abnormalities may play a part in the pathogenesis of central retinal vein occlusions. A statistically significant elevation of plasma viscosity was found in patients with acute central retinal vein occlusion compared with control patients. Local retinal blood flow parameters including arteriovenous passage time and mean arterial dye bolus velocity were significantly altered in the central retinal vein occlusion patients compared with age-matched controls at baseline examination. We performed a randomized, prospective, single-blind clinical investigation to determine the effect of hemorheological manipulation on the clinical course and retinal blood flow of eyes with central vein occlusion. Hemodilution included plasma expansion with hydroxyethyl-starch, withdrawal of whole blood if the hematocrit was above 42%, and rheologic manipulation with parenteral pentoxifylline. We found a statistically significant improvement in visual acuity at 1 year post-treatment for the treated group compared with the control group (increase of visual acuity of 1.5 lines vs decrease of 1.5 lines). The retinal blood flow parameters were markedly improved soon after the institution of therapy, and this may have contributed to the improvement in visual acuity in the treated group. There was no statistically significant difference between the two groups in the progression to ischemic central vein occlusion.

Aged↗
PubMed1994

Perifoveal microcirculation with non-insulin-dependent diabetes mellitus.

Fluorescein angiograms were performed to evaluate perifoveal capillary blood velocities (v), capillary density (perifoveal intercapillary areas: PIA) and the foveal avascular zone (FAZ) by means of the scanning laser technique (SLO-101 Rodenstock). The angiograms were digitally stored and the data quantified off-line with an image analyzing system (IBAS). In the present study 46 patients with non-insulin-dependent diabetes mellitus (NIDDM) were examined and their data compared with that of 31 healthy volunteers. The perifoveal capillary flow velocity of the NIDDM subjects (v = 2.33 +/- 0.36 mm/s) was significantly (P < 0.01) decreased as compared to healthy subjects (v = 2.86 +/- 0.41 mm/s). The perifoveal intercapillary areas in the foveal avascular zone were significantly increased in patients with NIDDM (PIA = 10029 +/- 3402 microns2; FAZ = 0.415 +/- 0.272 mm2) as compared with healthy subjects (PIA = 3965 +/- 467 microns2; FAZ = 0.221 +/- 0.071 mm2). These data suggest the possibility that a decrease in perifoveal capillary blood velocities in combination with decreased capillary density (enlarged PIA) and an enlargement of the foveal avascular zone may occur in patients with NIDDM. The determination of these parameters could help in monitoring the progress of diabetic retinopathy and diabetic maculopathy.

Adult↗
PubMed1994

Physiological perturbation of ocular and cerebral blood flow as measured by scanning laser ophthalmoscopy and color Doppler imaging.

Retinal blood flow regulation in health remains poorly described. We hypothesized that retinal perfusion is controlled to provide constant O2 delivery to that tissue, and that changes in retinal blood flow in response to chemical stimuli parallel changes in carotid and retrobulbar perfusion. Accordingly, in 11 young adults with normal eye examinations, we measured retinal blood flow indices (via scanning laser ophthalmoscopy [SLO] during fluorescein angiography) and carotid, ophthalmic, and central retinal arterial blood flow indices (via Doppler imaging [CDI]) under control, hypoxic (alveolar PO2 = 55 +/- 3 mmHg) and hyperoxic (alveolar PO2 = 655 +/- 18 mmHg) conditions. The three conditions were counterbalanced in order and isocapnia was maintained in each. Retinal arterial mean dye velocity and arteriovenous passage time, as measured by SLO, were slowed by hyperoxia and accelerated by hypoxia, in rough proportion to the changes in arterial O2 content (+/- 10%; p < 0.05). In the seven subjects in which relative measurements of retinal arterial diameters were obtained, neither hypoxia nor hyperoxia significantly altered vessel diameter. At the same time, mean retinal capillary transit velocity was independent of PO2, suggesting that, in health, retinal capillaries may be recruited as PO2 falls. O2-induced changes in carotid, ophthalmic, or central retinal arterial blood flow velocities (via CDI) were not found, though a wide coefficient of variation (30% for CDI vs. 14% for SLO) may have contributed to this failure. We conclude that, under isocapnic conditions, retinal perfusion may be regulated to provide constant O2 delivery.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Measurement of retinal hemodynamics with scanning laser ophthalmoscopy: reference values and variation.

High resolution video fluorescein angiography using scanning laser ophthalmoscopy allows the assessment of retinal macro- and microcirculation. Data on the retinal macrocirculation were obtained from 221 healthy subjects. The data were derived from estimations of the arm-retina time, the arteriovenous passage time and mean arterial dye velocity, characterizing the passage of fluorescein to the eye, the mean arterial plasma velocity, and the arteriovenous passage through the entire vascular bed of one segment. Additionally, the transit of hypofluorescent segments in the capillary macular network were measured in 90 healthy subjects. These parameters provide a wide range of information for understanding the physiology of healthy and diseased eyes. Fundamental for all interpretations is the knowledge of the physiological variations. In the present study the inter- and intraindividual variability of retinal hemodynamics in healthy volunteers were assessed. The interindividual variation was 23.8% for the arm-retina time, 20.7% for the arteriovenous passage time, 23.7% for the mean arterial dye velocity, and 14.2% for the capillary flow velocity; the coefficient for variation, characterizing the intraindividual variation, was 26.6%, 15.6%, 16.7%, and 7.9%, respectively. The knowledge of the inter- and intraindividual variation of retinal blood flow indices allows for a priori power estimations for pathophysiologic and pharmacological studies.

Adult↗
PubMed1994

Retinal blood velocities during carbogen breathing using scanning laser ophthalmoscopy.

Hyperoxic-hypercapnic gas mixture ('carbogen': 6% CO2-94% O2) is widely used clinically. Its influence on retinal perfusion remains unclear, since past work suggests that high O2 may reduce and high CO2 may increase retinal blood flow. To examine the changes in retinal blood velocity during 'hyperoxic-hypercapnic' gax mixture breathing, we quantified retinal blood velocity indices. Twenty-eight healthy subjects were studied using scanning laser video fluorescein angiograms at baseline and after gas inhalation. Retinal arteriovenous passage time and mean arterial dye velocity were measured by means of a digital image processing system. Arterial diameter measurements showed no change (4%) during carbogen breathing. Increased arterial Pco2 and Po2 resulted in small but statistically significant increases in systolic and diastolic blood pressure and heart rate (each c. 8%, p < 0.05), and a dramatic increase in mean dye velocity (27%, p < 0.01), with parallel reduction in arteriovenous passage time (40%, p < 0.01). The substantial acceleration of retinal dye velocity and transit under combined hyperoxia and hypercapnia strongly suggests that this clinically standard gas mixture may indeed improve oxygenation without reducing retinal perfusion.

Adult↗
PubMed1994

Quantification of retinal capillary density and flow velocity in patients with essential hypertension.

Arterial hypertension is known to be an important risk factor for cerebral and cardiovascular disease. Previous studies in rats have demonstrated that changes in both capillary density and vessel diameter may contribute to increased vascular resistance in hypertension. In vivo studies of human subjects with essential hypertension revealed a reduction in the number of arterioles in the skin and conjunctiva; no other in vivo data are available from other tissues. By means of a new imaging technique, capillary density and capillary blood flow velocity can now be assessed in the human retina. We undertook the present investigation to determine whether patients with essential hypertension and only minor clinical retinal vascular alterations have decreased retinal capillary density and altered capillary flow velocity. Seventeen hypertensive patients with only minor retinal vascular alterations and 17 healthy volunteers matched for age were selected. All study participants underwent ophthalmologic examination and fluorescein angiographic studies by means of scanning laser ophthalmoscopy. Capillary density and capillary blood flow velocity in the perifoveal network were evaluated from the angiograms. The retinal microcirculation in the perifoveal capillary network of hypertensive patients showed significant alterations. Both the capillary density and capillary flow velocities were significantly reduced compared with the control group. For the first time alterations of capillary blood flow and capillary density in a vascular network very similar to that of the brain have been demonstrated in hypertensive patients in vivo. Further studies with this technique may help identify patients at high risk for cerebrovascular diseases.

Adult↗
PubMed1994

[Effect of hemodilution on retinal hemodynamics in retinal branch vein occlusion].

The aim of hemodilution therapy in branch retinal vein occlusion is to lower the hematocrit (HCT) and plasma viscosity and thus to ameliorate perfusion of the affected areas. In this study we compared the influence of hemodilution therapy on the retinal hemodynamics of affected areas with unaffected areas. Thirty patients with branch vein occlusion (duration of symptoms less than 14 days) aged 40-84 years (mean 63 +/- 11 years) were examined. All patients received iso- (HCT > or = 42%) or hypervolemic (HCT < 42%) hemodilution with hydroxyethyl-starch (MW 200,000/0.5 10%, HAES-steril) for 10 days. Retinal hemodynamics were quantified by means of video fluorescein angiography assessing arteriovenous passage time (AVP) of the affected and unaffected branches. Hemodilution resulted in a significant decrease in hematocrit, plasma viscosity and erythrocyte aggregation. The arteriovenous passage time of the affected area improved significantly (before therapy 4.91 +/- 2.2 s, after therapy 3.9 +/- 1.6 s). The unaffected branch showed no significant change in the arteriovenous passage time (1.85 +/- 0.7 s before and 1.79 +/- 0.7 s after therapy). The decrease in AVP in the affected branch indicates ameliorated perfusion in the affected branch area without changing the retinal hemodynamics in unaffected areas.

Adult↗
PubMed1994

Indocyanine green video angiography in patients with age-related maculopathy-related retinal pigment epithelial detachments.

Previous studies have stressed the benefit of laser photocoagulation for patients with age-related macular degeneration (AMD) and well-defined subretinal neovascularization (SRN). However, such lesions account for only 30% of cases with exudative age-related maculopathy. Especially in patients with retinal pigment epithelial detachment (PED), SRN is usually occult. This study was performed to reveal the role of digital indocyanine green (ICG) video angiography in the diagnosis of SRN in patients with PED. A total of 34 patients with AMD-associated retinal PED participated in the current study and underwent fluorescein and ICG angiography using scanning laser ophthalmoscopy. In these patients fluorescein angiography revealed no distinct SRN, whereas in 21 eyes (62%) ICG angiography showed well-demarcated choroidal neovascularization. The present study demonstrates that SRN can be detected in more than 50% of patients with PED by means of ICG video angiography. Therefore, ICG video angiography improves the detection of SRN in patients with AMD-associated PED.

Aged↗
PubMed1994

[Follow-up of arteriosclerosis-induced anterior ischemic optic neuropathy].

In 22 patients with acute arteriosclerotic anterior ischemic optic neuropathy (AION), examinations were conducted before the start of therapy and between 1 and 3 years later. In the acute stage of the disease the patients were treated with hemodilution for 10 days. The visual acuity improved from 0.2 to 0.4 (median). Compared with the visual acuity before therapy, at the follow-up 1-3 years later visual acuity had improved by 3 lines or more in 11 patients, remained stationary in 9 patients (+/- 1 line), and worsened in 2 patients by 3 lines or more. The visual fields (Goldmann) improved in 8 patients, did not change in 10 patients and worsened in 4 patients. After 1-3 years, 14 patients (64%) showed a sectorial pallor and 8 patients (36%) a diffuse pallor of the optic disc. Videofluorescein angiography revealed hypofluorescent discs in all patients. No difference in arm-retina time (ART) was found between the acute phase (13.0 +/- 3.3 s) and the examination 1-3 years later (13.1 +/- 2.2 s). ART was within normal limits in all patients. The arteriovenous passage time (AVP) dropped significantly, from 2.36 (+/- 0.81) s in the acute phase to 1.91 (+/- 0.56) s 1-3 years later. However, the AVP still did not fall to normal levels (1.45 +/- 0.40 s). Slowed retinal hemodynamics (AVP) with normal ART at the same time suggests a disturbance in microcirculation still present 1-3 years after the acute phase of AION. The rheological parameters (hematocrit, plasma viscosity, erythrocyte aggregation index) did not show any change between examinations.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

Retinal hemodynamics after pars plana vitrectomy with silicone oil tamponade.

Pars plana vitrectomy with silicone-oil tamponade is frequently performed in cases of complicated retinal detachment. Because of the lower specific gravity and the lower surface tension of silicone oil in comparison with the aqueous phase of the vitreous, an influence on the blood flow in the retinal vessels would be expected. However, not only the silicone oil but also the operative trauma and a buckling procedure may have an influence on the retinal blood flow. To examine this question we measured the arteriovenous passage time in the silicone-oil-filled eye and in the contralateral eye in 14 cases using a laser scan ophthalmoscope at 3-5 days after surgery. The arteriovenous passage time is a parameter for the retinal microicirculation. In all cases we found a prolonged arteriovenous passage time in the silicone-oil-filled eye in comparison with the contralateral eye (mean value +/- SD, 2.5 +/- 0.8 vs 1.25 +/- 0.25 s; P < 0.01). The prolongation of arteriovenous passage times observed in silicone-oil-filled eyes indicates that the microcirculation is worsened at least during the early postoperative period.

Adult↗
PubMed1993

Retinal hemodynamics using scanning laser ophthalmoscopy and hemorheology in chronic open-angle glaucoma.

PURPOSE: Recent studies suggest that elevated intraocular pressure is not the only causative factor for the development of visual field loss and optic nerve damage in glaucomatous eyes. The authors determine whether retinal hemodynamics or blood fluidity are alternated in eyes of patients with open-angle glaucoma compared with those of age- and sex-matched healthy subjects. METHOD: High-quality video fluorescein angiograms were obtained from single eyes of 51 patients with chronic open-angle glaucoma. From these angiograms, the arm-retina time, mean dye velocity, and arteriovenous passage time were quantified. The data from patients were compared with those of an age- and sex-matched group of healthy subjects. RESULTS: In patients with chronic open-angle glaucoma, an 11% reduction of the mean dye velocity (P < 0.05) and a 41% prolongation of the arteriovenous passage time (P < 0.01) was observed relative to the values obtained among the control subjects. Among hematocrit values, plasma viscosity, and erythrocyte aggregation, only plasma viscosity showed a significant increase (4%; P < 0.01) in patients with chronic open-angle glaucoma. CONCLUSION: These results indicate that a pronounced circulatory deficit exists within the retinal vasculature of glaucomatous eyes, which may coexist with, but cannot be fully attributed to, an increase in plasma viscosity.

Adult↗
PubMed1993

[Hemodilution therapy in patients with acute anterior ischemic optic neuropathy].

A prospective study was performed in 22 patients with an anterior ischaemic optic neuropathy (AION). All patients underwent iso- (Hct > or = 42%) or hypervolemic (Hct < 42%) haemodilution for 10 days with daily infusion of 250 ml hydroxyethyl starch (MW 200,000/0.5, 10% HAES-sterile) in combination with pentoxifylline (p.o.: 1200 mg/day; i.v.: 300 mg/day; Trental). Only patients with recent AION (less than 2 weeks' duration of symptoms) were considered for the prospective trial. Clinical, haemodynamic (arterio-venous passage time) and rheological (haematocrit, plasma viscosity, erythrocyte aggregation) data of all patients were recorded before therapy and after 10 days. An improvement of central vision by 2 or more lines was seen in 7 patients after 10 days. Initially the arterio-venous passage time was significantly prolonged in patients (2.42 +/- 0.7 s) with AION compared with healthy volunteers (1.45 +/- 0.4 s). After the 10-day trial arterio-venous passage time was significantly shorter than baseline values. In addition, the initially elevated plasma viscosity (1.33 +/- 0.1 mPa) was significantly lowered by haemodilution therapy.

Aged↗