Biomedical subjects

W Vilser

Publications and source records attributed to W Vilser.

At least 19 recordsLinked to original sources

PubMed2006

[Variance of retinal vessel diameter response to flicker light. A methodical clinical study].

AIM: The study investigated the variance of the retinal vessel response to flicker light between the right and left eyes and after a short and a medium-length time interval. METHODS: The prospective study included 28 volunteers. In the first exam both eyes were examined. One eye selected randomly was measured again after 1 h and after 1 month. The diameter response of an arterial and venous vessel segment was measured continuously by a Dynamic Vessel Analyzer (DVA, IMEDOS, Jena). Each examination consisted of 50 s baseline measurement and three periods of 20-s flicker light provocation followed by 80 s observation. The mean of three provocational cycles was calculated as dynamic vessel response. RESULTS: A significant correlation of the flicker response parameters between the right and left eyes was found. Arterial and venous baseline diameter, flicker light dilation, AVDQ, and BP did not change significantly between the first and follow-up examinations. There was no correlation between changes of BP and changes of vessel diameter parameters in the follow-up exams. CONCLUSION: Flicker-evoked dilation of retinal arterioles measured by the DVA is characterized under similar conditions by small variance after short and medium-length time periods. Therefore, this parameter is suitable as a functional parameter of the regulation ability of retinal arteries.

Anatomy, Cross-Sectional↗

PubMed2005

[Comparison of diameter response of retinal arteries and veins to flickering light. A clinical study with healthy people].

PURPOSE: The aim of this study was to compare the diameter response of retinal arteries and veins after provocation with flickering light regarding the amplitude and temporal course. METHODS: The study included 26 healthy volunteers. The vessel diameter was automatically and continuously measured by the retinal vessel analyzer. The examination consisted of a baseline measurement (100 s) followed by five periods of 20-s flicker light provocation and 80-s follow-up observation. RESULTS: A diameter dilation was observed immediately after the end of the flicker period in arteries (6.9+/-2.8%) and veins (6.5+/-2.8%, difference n.s.). The quotient of arterial and venous dilation (AVDQ) was 1.25+/-0.69 (range: 0.2-2.8). A significant correlation of age and arterial or venous dilation or the AVDQ was not observed. The arterial diameter reduced faster than the venous and reached a minimum of -2.7+/-1.4% at 25.9+/-10.8 s after the end of the flicker phase. The veins were dilated by 0.5+/-1.3% at the time of the maximal individual arterial constriction (p<0.0001). CONCLUSIONS: Flicker-evoked response of retinal arteries and veins did not differ in the dilative amplitude but in the temporal course of the abatement of the dilation.

Adult↗

PubMed2005

[Haemodynamics and diabetic retinopathy].

Diabetic retinopathy is the most common cause of blindness in adults in all industrialised countries. A much better pathophysiological understanding of the disease has been achieved during the last years. There is evidence that a functional deficit in haemodynamics proceeds the morphological changes of the retina. Modern technologies for measuring haemodynamic parameters and their correlation to pathophysiology in diabetic retinopathy are discussed. In the near future it will be possible to use these parameters as an early sign of worsening before morphological changes occur. Measurement of the therapeutic success, e. g., in laser coagulation would seem to be possible.

Blood Flow Velocity↗

PubMed2004

Flicker observation light induces diameter response in retinal arterioles: a clinical methodological study.

AIM: To investigate diameter changes in retinal arterioles in response to flicker variations of the examination light. METHODS: One randomised eye of five healthy subjects (mean age 33.8 (SD 1.6) years) was examined. The arterial diameter response to flicker light (12.5 Hz, 530-600 nm, duration 20 seconds) was automatically and continuously measured online three times by retinal vessel analyser (RVA) and once offline from flash images using the VesselMap program. RESULTS: An arterial diameter response to flicker light was found both by RVA and by analysis of flash images (p<0.001). The maximum induced dilation reached at the end of the flicker period was +7.4% (SD 2.4%) in the RVA measurements and +3.5% (0.8%) in the photographs (p = 0.01). In both techniques the vascular diameter overshot the baseline approximately 10 seconds. In the RVA measurements a minimum of -4.6% (1.9%) (p = 0.01) was measured 22 (4.7) seconds after the end of flicker exposure. CONCLUSION: Flicker evoked response for retinal arterioles was found both by RVA and by analysis of flash images. The authors believe that the method is suitable for the quantitative investigation of retinal vasosclerosis, especially in association with arteriosclerotic and hypertensive systemic disease.

Adult↗

PubMed2002

Functional analysis of retinal vessel diameter reaction to artificially raised intraocular pressure in glaucoma patients with and without dorzolamide therapy.

BACKGROUND: Examination of the influence of dorzolamide on the autoregulation of retinal vessel diameter in glaucoma patients. PATIENTS AND METHODS: Eleven patients with primary open angle glaucoma (age 60 +/- 11) without medication and four weeks after starting therapy with dorzolamid eye drops three times daily were examined in the study. Short-time rise of intraocular pressure (IOP) was obtained via suction-cup. Functional reaction of the diameter of a segment of a retinal artery and corresponding vein were assessed by retinal vessel analyzer. RESULTS: Dorzolamid lowered the IOP from 23.3 +/- 1.3 to 17.6 +/- 2.2 mmHg (p = 0.004). Therapy did not influence the absolute diameter of retinal vessels regarding maximal dilatation caused by the pressure rising provocation. In eyes with treatment the diameter decreased faster to baseline values (arteries 100 sec, veins 220 sec) compared to those without treatment (arteries 350 sec, veins 480 sec). CONCLUSION: Dorzolamid might possibly be able to accelerate autoregulation of retinal vessels in response to short term artificial IOP increase.

Adult↗

PubMed2002

Retinal Vessel Analyzer (RVA)--design and function.

The Retinal Vessel Analyzer (RVA) is a measuring device for online measurement of the diameter of retinal vessels in relation to time and locations along the vessel. It is furthermore provided with several tools for analyzing the measured data. The fundamental components consist of a fundus camera with CCD measuring camera attached and an advanced image-processing unit. The measurement range is from 90 microns, temporal resolution is 40 ms and measurement resolution is less than 1 micron. Systematic error of non-linearity is S < or = 1.6%, reproducibility is given by variation coefficient: short term vcs = 1.5%, long term vcl = 2.8%.

Artifacts↗

PubMed2002

Retinal Vessel Analysis--new possibilities.

Retinal Vessel Analysis is a new technique to assess behavior of large retinal vessels based on diameter measurements. The Retinal Vessel Analyzer (RVA) measures continuously on-line obtaining data in relation to time and local position. Possible analysis tools include (a) Time Course Analysis of physiological, pathological, or therapy induced changes; (b) Local Course Analysis to recognize local narrow or wide vessel segments along the vessel; (c) Vasomotoric Analysis to determine vasomotions and blood pressure related diameter changes; (d) Functional Analysis to examine dynamic behavior e.g. the ability to autoregulate and (e) Functional Imaging to visualize functional parameters of vessels in single vessel segments. RVA is thus able to recognize and study different autoregulation mechanisms.

Fluorescein Angiography↗

PubMed2001

[Measurement of the diameter of segments of retinal branch vessels in digital fundus images - An experimental study of the method and reproducibility].

PURPOSE: The aim of this study was the evaluation of new algorithms to measure diameter of segments of retinal branch vessels offline in local dependence and independent by observer. Methods 360 flashed fundus images (camera FF 450 ZEISS Germany, Visualis IMEDOS GmbH Weimar/Germany) of 12 eyes of healthy volunteers (10 independent sessions containing 3 images for every eye) were analysed. Algorithms detect the vessel diameter along the vessel course automatically. Corresponding segments of a retinal artery and vein were examined (mean length of the segment 2.5 mm) in every image of one eye. Results The marked arterial segment was detected automatically in 359 pictures and the venous segment in all pictures. The mean vessel diameter was detected in single pictures with a mean coefficient of variation (CV) for arteries of 3.4 % and for veins of 2.7 %. The differences of arterial and venous diameter between images were not significant. Analyzing sessions the CV of the mean vessel diameter were reduced for arteries to 2.7 % and for veins to 2.5 %. The standard deviation of the mean vessel diameter was independent of the vessel diameter (branch vessels with diameter of 120 to 200 micrometer). The mean CV of the vessel diameter at single locations were 5.7 % for arteries and 3.8 % for veins. Conclusions The new algorithms are useful for retinal vessel analysis, if there are no questions concerning the dynamic of vessel behaviour.

Adult↗

PubMed2000

[Dilatation of large retinal vessels after increased intraocular pressure].

PURPOSE: To measure dilation of large retinal branch vessels. METHODS: Diameters of a vessel section of a branch artery and vein were examined by the retinal vessel analyzer. Intraocular pressure (IOP) was increased briefly by an oculo-oscillo-dynamograph. The examination was repeated after 2 weeks. RESULTS: A vessel reaction was found in all volunteers. The mean venous diameter decreased 9.9 +/- 9.4% during the suprasystolic phase of intraocular pressure. A maximal dilation was found in arteries (7.0 +/- 6.2%) and veins (9.3 +/- 5.2%) 1 min after lowering of IOP. The results were reproduced in the second examination for veins in all phases of the examination and for arteries in the middle phase after lowering IOP (4 min). Various changes in mean systolic blood pressure did not significantly affect reproducibility of the vessel reaction. CONCLUSION: The vessel reaction caused by rise in IOP can be measured for single vessel sections. The venous reaction is well reproducible in healthy volunteers. Further research should examine the benefit of this method in the diagnosis and follow-up of glaucoma.

Adult↗

PubMed2000

[Retinal vessel reaction to 100% O2-breathing--functional imaging using the retinal vessel analyzer with 10 volunteers].

BACKGROUND: Retinal vessel diameter assessment is complicated by various components among them dynamic changes due to vasomotoric effects. Measurement of these diameters was usually obtained from fundus photographs. Functional diameter changes induced by external stimuli were difficult to evaluate because of their dynamic nature. The Retinal Vessel Analyzer (RVA) allows continuous on-line measurement of those dynamic changes. Whether functional changes due to 100% O2 breathing can be assessed by RVA is investigated in this study. MATERIALS AND METHODS: Continuous on-line registration of retinal arterial and venous branch vessels was obtained in 10 healthy volunteers. A baseline was taken during the first minute. Then for 5 minutes 100% O2 was delivered by mask. Further recording ensued for 4 minutes, while breathing room air. Vessel diameter change in percent to baseline was calculated for each individual and for a mean of the group. RESULTS: Each individual demonstrated vasoconstriction. The mean diameter reduction for the group was 6.5% for arteries and 15% for veins. CONCLUSIONS: RVA allows assessment of functional retinal branch vessel reactions. Retinal branch vessels diameters are denominators for capillary perfusion. RVA might be able to demonstrate an individual vessel's regulation potential by purposeful stimulation to constrict and dilate. This property could be helpful in understanding pathophysiologic processes as well as improving diagnosis and therapeutic effects in diseases influencing ocular perfusion such as diabetes, retinal vessel occlusion or even glaucoma. Further evaluation of effects of systemic diseases might be an additional application of functional retinal vessel diameter assessment by RVA.

Adult↗

PubMed1999

Noninvasive measurement of the Bayliss effect in retinal autoregulation.

PURPOSE: The Bayliss effect describes the reaction of smooth muscle cells in the arterial wall to changes in blood pressure. A rise in mean arterial blood pressure (MAP) causes an autoregulatory myogenic vessel constriction by smooth muscle cells in the arterial wall. The responsiveness of retinal vessels to changes in MAP were analyzed using the Retinal Vessel Analyzer (RVA). METHODS: Continuous measurement of retinal arterial vessels was performed in 40 healthy volunteers (age 18-56 years.) over a 9-min period. After a 3-min baseline measurement (phase I), isometric exercise caused a rise in MAP over the next 3 min (phase II). During the last 3 min (phase III) recovery was observed. Blood pressure and ECG were documented simultaneously throughout the experiment. RESULTS: Exercise caused a significant rise of 22.8 (+/-6.0) mm Hg in MAP (phase II vs. phase I: P<0.001). Retinal arterioles showed 5.5% (+/-2.8%) vasoconstriction (P<0.001). During phase III vessel diameters returned to normal, with no difference from phase I (P = 0.179). CONCLUSION: Noninvasive measurement and quantitative analysis of the Bayliss effect in human retinal vessels by means of the RVA is possible. Analysis of retinal arterial autoregulation may provide valuable insight into pathologic conditions such as diabetic or hypertensive retinopathy.

Adolescent↗

PubMed1997

[Online measurement of retinal artery branches in type II diabetic patients. Initial clinical trials before and after laser coagulation].

UNLABELLED: By the use of a new online measuring system the effect of argon-laser coagulation in diabetics on the diameters of retinal arteries was measured. METHOD: The vessel diameter of retinal branch arteries were measured in patients with type-II diabetes before and after (0.5 h) argon-laser coagulation. Ten patients without previous laser treatment were included in this study. Measurements were taken in all four quadrants by the use of a new automatic online measuring system. RESULTS: The new technique allowed measurements to be made within an acceptable period of time and with little strain on patients. After argon-laser coagulation 56.7% of retinal arteries showed a significant vasodilation. No significant changes in vessel diameter were found in 18.9% of these arteries, whereas 24.3% showed significant vasoconstriction. CONCLUSION: The new online measuring system is able to measure the effects of photocoagulation on an individual basis with a noninvasive technique. The first findings presented here confirm previous studies of larger groups, with a considerable reduction in efforts required.

Aged↗

PubMed1995

[Adaptive algorithm for automatic measurement of retinal vascular diameter].

A new adaptive computer-aided method for the measurement of blood vessel diameters has been developed. Within areas of interest in the image, the algorithm detects, line-wise, the edges of the vessels, which are then used for image-wise approximation and noise filtration. A high level of adaptivity with respect to numerous measuring parameters ensures its use in a wide range of applications. Thus, it has been shown to significantly improve clinically relevant reproducibility in the area of follow-up observations. The standard deviation for vessel diameter was (2.2 +/- 0.7)% in the case of arteries and (1.8 +/- 0.5)% in the case of veins. Testing the algorithm in images of poor quality revealed its high level of reliability and sensitivity.

Algorithms↗

PubMed1995

A new approach for detecting the position of retinal vessels and calculating their diameter on the basis of dynamic spectral analysis.

Fast adaptive algorithms were used for the detection of retinal vessels and for pre-processing the signals. By using different methods of dynamic spectral analysis, the local frequency of the vessels was determined. On this basis a method of calculating the diameters of the vessels was constructed; it is robust in relation to disturbances in the domain of the edges.

Algorithms↗

PubMed1995

[Adaptive procedures for measuring arterial blood flow velocity in retinal vessels using indicator technique].

There are highly significant differences in the measuring results of arterial blood velocity between the indicator and laser-Doppler techniques (up to 800%). A new measuring procedure for the analysis of indicator dilution curves was developed based on indicator model and experimental results. The use of this new measuring procedure results in reduced mean systematic error between the indicator and laser-Doppler techniques to values around 10%. With the introduction of adaptive measuring arrays for the creation of indicator dilution curves and the application of adaptive algorithms for centering and spectral normalizing of the dilution curves, improved reproducibility can be expected.

Blood Flow Velocity↗

PubMed1992

[Measuring retinal vascular diameter using the scanning laser ophthalmoscope and computer. Initial results].

The diameter of the large retinal vessels is an important factor in retinal microcirculation. A system configuration was developed that uses SLO images to measure the diameter of retinal branch vessels off-line. The place for measurement is defined in the image by the investigator, and the diameter is measured automatically. The mean standard deviation of the diameter of arterial vessels was 2.37% and for veins 3.43% by repeat measurement in sequential pictures by optimal scanner settings. The reproduction of vessel diameters was unsatisfactorily for repeat examinations. The course of these results may be changes in the fundus image connected with changes in the position of the scanner-bulbus (e.g., new examination, poor fixation). The scanner-bulbus position is not yet precisely defined and not reproducible enough.

Adult↗

PubMed1992

[Does timolol modify retinal hemodynamics in patients with normal pressure glaucoma?].

In 31 patients with normal-pressure glaucoma, retinal blood flow, diameter of the retinal vessels and velocity were measured with 2-point fluorometry and automatic measurement of the diameters before and after administration of 0.5% timolol over 2 weeks. After timolol therapy the tension was significantly decreased (before therapy: 18.26 +/- 2.50; after therapy: 15.61 +/- 2.56 mm Hg, P < or = 0.01). The arterial and venous diameters and blood flow were nearly unchanged, but a slight increase in the arterial and venous velocity was noted. We conclude that timolol does not significantly influence the retinal hemodynamics in patients with normal-pressure glaucoma.

Adult↗

PubMed1991

[Automated measurement of retinal vascular diameter].

We describe a new unit of the Jena retinal camera for automatic measurement of retinal vessel diameter. The brightness profile perpendicular to the vessel is registered by CCD line sensor and the signal is transmitted to the computer. An adaptive computer program recognizes the edges of vessels and estimates the vessel diameters automatically. Applying several measurements per vessel, the intraindividual standard deviation may be smaller than 3%. By using the same objective measuring edge criterion, the measuring results are comparable between different observers and methods. Error sources are discussed. Measured vessel reactions to oxygen breathing and reduced perfusion pressure are presented to demonstrate the efficiency of this new method.

Adult↗