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Results for “RETINAL VESSELS”

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At least 541 records · Page 30Linked to original sources
PubMed1977

Reticulum fibres in relation to retinal vessels.

Argyrophilic perivascular and intervascular fibres in the mammalian retina are shown by specific antireticulin immunofluorescence to consist of reticulin. The possible significance of these findings is briefly discussed.

Animals↗
PubMed1996

HTLV-I associated uveitis revisited: characteristic grey-white, granular deposits on retinal vessels.

AIMS: To elucidate whether there exists any clinical sign characteristic of HTLV-I associated uveitis. METHODS: Fifty five patients with HTLV-I associated uveitis were reviewed. These cases had serum antibodies to HTLV-I, and any other uveitis entities were carefully excluded by means of clinical and laboratory studies. RESULTS: Eight cases (14.5%) developed vascular lesions in the retina, characterised by grey-white, granular deposits scattered on the retinal veins and/or arteries in the posterior pole. The vascular changes did not accompany any haemorrhage, sheathing, or leakage of fluorescent dye on angiograms, and the retina was otherwise unremarkable. A single or clustered form of similar materials was also found to deposit on the vitreo-retinal interface of the foveolar area. These deposits resolved in a few weeks spontaneously or in response to corticosteroids together with anterior uveal inflammation. CONCLUSION: The vascular lesions described here suggest a characteristic sign for HTLV-I associated uveitis, and it may provide, if recognised, an additional clinical marker to establish diagnosis.

Adult↗
PubMed1995

Response of parapapillary retinal vessels to exercise.

PURPOSE: Using blue field entoptoscopy, we have recently shown that blood flow in the paramacular capillaries remained constant after moderate exercise. In the present study, our objective was to identify a mechanism by which perfusion of an area populated by capillaries of invariable diameter can be maintained constant during exercise, which changes blood flow throughout the body. METHODS: Twelve healthy volunteers between 20 and 30 years of age participated in the present study. Color fundus slides centered on vessels within 1 disc diameter of the optic nerve head and synchronized with systole or diastole were taken while subjects rested, and after 20 min of stationary bicycling. High resolution measurements of vessel diameter were based on density plot profiles generated from magnified and digitized images of neighboring arteries and veins. RESULTS: Our results showed that the group-averaged diameter of arteries measured either in systole or diastole decreased after exercise, but the group-averaged diameter of veins did not differ from baseline. CONCLUSIONS: We interpret the constriction of parent arteries as an effective mechanism for gating the flow of blood to downstream vessels such as those perfusing the macular area.

Adult↗
PubMed1994

Quantitative circulatory measurements in branch retinal vessel occlusion.

We used the laser Doppler technique to quantify retinal circulatory abnormalities in three patients with branch retinal artery occlusion and in two patients with branch retinal vein occlusion, each of whom had shown delayed filling on fluorescein angiography. Blood flow in occluded arteries was 40-50% lower than in non-occluded arteries of the same branching order. In the patients with branch retinal vein occlusion blood flow in arteries supplying the affected regions was 80-90% lower than in arteries supplying the unaffected regions. One vein occlusion patient was measured serially over 18 months. Blood flow increased from 4 to 12 microliters/min in the artery supplying the affected region in this patient. The results demonstrate that retinal circulatory abnormalities can be evaluated quantitatively during the course of retinal vascular occlusive disease, and suggest that the efficacy of therapy can be monitored using our techniques.

Aged↗
PubMed2006

Retinal vessel segmentation using the 2-D Gabor wavelet and supervised classification.

We present a method for automated segmentation of the vasculature in retinal images. The method produces segmentations by classifying each image pixel as vessel or nonvessel, based on the pixel's feature vector. Feature vectors are composed of the pixel's intensity and two-dimensional Gabor wavelet transform responses taken at multiple scales. The Gabor wavelet is capable of tuning to specific frequencies, thus allowing noise filtering and vessel enhancement in a single step. We use a Bayesian classifier with class-conditional probability density functions (likelihoods) described as Gaussian mixtures, yielding a fast classification, while being able to model complex decision surfaces. The probability distributions are estimated based on a training set of labeled pixels obtained from manual segmentations. The method's performance is evaluated on publicly available DRIVE (Staal et al., 2004) and STARE (Hoover et al., 2000) databases of manually labeled images. On the DRIVE database, it achieves an area under the receiver operating characteristic curve of 0.9614, being slightly superior than that presented by state-of-the-art approaches. We are making our implementation available as open source MATLAB scripts for researchers interested in implementation details, evaluation, or development of methods.

Algorithms↗
PubMed1996

New concepts of regulation of retinal vessel tone.

OBJECTIVE: To review the mechanisms of local regulation of the vascular tone of the retinal and choroidal circulations. DESIGN: Literature review. RESULTS: The vascular endothelial cell may produce nitric oxide, endothelins, prostaglandins, and renin-angiotension products in response to chemical stimuli such as acetylcholine and bradykinin, to changes in blood pressure and vessel wall stress, to changes in local oxygen levels, and to other local stimuli. These substances are among the most potent vasoconstrictors and vasodilators known. Preliminary investigations suggest a potential role for these substances in endothelial autoregulation of the retinal and choroidal vasculatures. CONCLUSION: Hormonal products of the vascular endothelium may provide the final common pathway for vessel autoregulation in response to varying physiologic stress in many vascular beds, including the retina and choroid. Pharmacologic modulation of this process may provide treatment modalities for diseases such as hypertensive and diabetic retinopathies.

Animals↗
PubMed1987

Preparation of retinal vessels for scanning electron microscopic examination using microdissection by ultrasonication.

A method of microdissection by ultrasonication was used to prepare blood vessels of the retina for scanning electron microscopic examination. Eye cups were treated with 2% OsO4 that contained 2% CHAPS or 1% saponin (16 hrs.), dehydrated to 100% acetone, sonicated at 80 kHz (40 min.), and further processed by conventional means. This treatment resulted in the separation of the outer and inner retina at the level of blood vessels in the outer plexiform layer. The overall pattern of the blood vessels was maintained. Venules were distinguished from capillaries. This technique may provide information that is not possible to obtain with corrosion casts or trypsin digests.

Animals↗
PubMed1980

Degenerative changes in retinal vessels. Photodocumentation with monochromatic filters.

The appearance of certain ocular structure changes due to changes in absorption, reflection, and optical transmission depends on the wavelength of light. By means of this physical quality of the light, it is possible to demonstrate certain parts of the fundus better than others. Several examples described in this article demonstrate how degenerative vascular alterations can be judged much better and more safely by use of monochromatic light and light of varying wavelengths. Alterations of blood vessel caliber show the most contrast in yellow-green light where there is maximum absorption by the blood. Alterations in blood vessel wall reflection that are invisible in white light can be demonstrated in short-wave light and also partially in red light. Ophthalmoscopy in connection with the xenon arc lamp as a method of examination is suprior to photography alone.

Color↗
PubMed2002

Detection and measurement of retinal vessels in fundus images using amplitude modified second-order Gaussian filter.

In this paper, the fitness of estimating vessel profiles with Gaussian function is evaluated and an amplitude-modified second-order Gaussian filter is proposed for the detection and measurement of vessels. Mathematical analysis is given and supported by a simulation and experiments to demonstrate that the vessel width can be measured in linear relationship with the "spreading factor" of the matched filter when the magnitude coefficient of the filter is suitably assigned. The absolute value of vessel diameter can be determined simply by using a precalibrated line, which is typically required since images are always system dependent. The experiment shows that the inclusion of the width measurement in the detection process can improve the performance of matched filter and result in a significant increase in success rate of detection.

Computer Simulation↗
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↗