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PubMed2004

Retinal vessel reaction in response to chromatic flickering light.

BACKGROUND: Flickering light stimulation of the retina is known to increase retinal vessel diameter in animals and humans. The aim of the study was to quantify the response of retinal vessel diameter to red-green and blue-green flickering light. METHODS: In 11 normal healthy volunteers (mean age: 25.2+/-6.8 years) retinal arterial and venous diameters were examined by Retinal Vessel Analyzer (IMEDOS Ltd., Weimar, Germany) before, during and after red-green and blue-green flicker stimulation with a frequency of 12 Hz and duration of 10 and 30 s. RESULTS: For red-green flicker at 10 s there was a 2.4+/-1.4% arterial diameter increase at 9.1+/-3.3 s with a return to baseline after 30 s and a 2.4+/-1.1% venous diameter increase at 12.1+/-2.6 s with a return to baseline after 30 s. For red-green flicker at 30 s there was a 3.2+/-1.5% arterial diameter increase at 26.9+/-12.6 s with a return to baseline after 40 s and a 4.9+/-1.8% venous diameter increase at 31.4+/-7.6 s with a return to baseline after 40 s. For blue-green flicker at 10 s there was a 2.0+/-0.7% arterial diameter increase at 10.6+/-5.3 s with a return to baseline after 30 s and a 2.3+/-1.1% venous diameter increase at 12.0+/-5.5 s with a return to baseline after 30 s. For blue-green flicker at 30 s there was a 2.6+/-1.3% arterial diameter increase at 20.7+/-8.0 s with a return to baseline after 40 s and a 3.4+/-2.2% venous diameter increase at 28.8+/-10.5 s with a return to baseline after 40 s. CONCLUSIONS: Retinal vessel diameter dilation is a reproducible response to the applied flicker stimuli. This finding supports the existence of neurovascular coupling in the human retina. Flicker stimulation in either red-green or blue-green might be a useful stimulus for examination of retinal vessel behavior to regulatory demands.

Adolescent↗
PubMed1987

In vivo cannulation of retinal vessels.

In vivo cannulation of retinal blood vessels has not been reported but would be useful in exploring local vascular parameters and new treatment modalities. We developed a microsurgical technique for cannulating rabbit and cat retinal vessels, using glass micropipettes with curved shanks made from standard capillary tubing. The micropipette was held by a micromanipulator, which was fitted with a fiberoptic sleeve for intraocular illumination and for micropipette tip protection during insertion through the sclera. Direct aspiration from and injection into retinal blood vessels were possible.

Animals↗
PubMed1988

Evaluation of micrometric and microdensitometric methods for measuring the width of retinal vessel images on fundus photographs.

The width of retinal vessel images on fundus photographs was determined by projection micrometry and microdensitometry. These methods were evaluated on 12 retinal vessels using the negatives of 570-nm monochromatic fundus photographs. For projection micrometry, the intraobserver reproducibility of vessel width measurements was 1.6%-2.9%, depending upon the experience of the observer. Significant interobserver differences in the measured widths were demonstrated. For microdensitometry, three distinct measurement criteria were used. Significant differences in width as measured by the three criteria were found, but there were no interoperator differences for each criterion. The intraoperator reproducibility of vessel width measurements by microdensitometry was 2.1%-2.5%. Significant differences were found in the vessel widths determined by the micrometry and densitometry methods, and results obtained by micrometry are discussed in terms of edge-detection phenomena.

Adult↗
PubMed2004

Variation associated with measurement of retinal vessel diameters at different points in the pulse cycle.

BACKGROUND/AIMS: To assess the variability in retinal vessel measurements at different points in the pulse cycle. METHODS: A healthy white male aged 19 years had 30 digitised images taken at three distinct points in the pulse cycle over a one hour period. A pulse synchronised ear clip trigger device was used to capture images at the desired point in the pulse cycle. Two trained graders measured the retinal vessel diameter of one large arteriole, one large venule, one small arteriole, and one small venule 10 times in each of these 30 images. RESULTS: Within an image, variability was similar between graders, pulse point, and vessel type. Across images taken at the same point in the pulse period, the change from the minimum to maximum measurement was between 6% and 17% for arterioles and between 2% and 11% for venules. In addition, measurements of small vessels had greater changes than large vessels and no point in the pulse period was more variable than another. Ignoring pulse cycle increased variability across images in the large venule, but not in the other vessel types. Mixed effect models were fit for each of the vessel types to determine the greatest source of variability. Controlling for pulse point and grader, the largest source of variability for all four vessels measured was across images, accounting for more than 50% of the total variability. CONCLUSION: Measurements of large retinal venules is generally less variable than measurements of other retinal vessels. After controlling for pulse point and grader, the largest source of variation is across images. Understanding the components of variability in measuring retinal vessels is important as these techniques are applied in epidemiological studies.

Adult↗
PubMed1990

Microperfusion studies on the permeability of retinal vessels. A new model demonstrating organic anion transport and a reabsorptive fluid flux.

We developed an experimental model to study the permeability of individual retinal vessels in vitro using microperfusion techniques adapted from kidney tubule studies. The retinal vessels were isolated by freehand dissection and mounted on a microperfusion apparatus. When inulin was perfused luminally, it was diluted to 80.2 +/- 2.3% of its initial concentration. However, no radioactive leak into the bath side was observed, suggesting that the dilution was due to fluid flux from bath to lumen. The dilution of fluorescein (81.9 +/- 3.8%) was in the same range as that of inulin, the reference marker. The extremely low lumen-to-bath fluorescein flux, 0.5 +/- 0.9 X 10(-12) mol/min/mm, increased by 68% when probenecid was added to the perfusate and by 210% when probenecid was placed in the bath. The effect was concentration-dependent. When placed in the bath, fluorescein moved rapidly across the retinal vessel walls, accumulating in the lumen to concentrations 40 times higher than in the bath. This movement from bath to lumen, which was much higher (13.6 +/- 0.3 X 10(-12) mol/min/mm) than the lumen-to-bath fluorescein flux for the same fluorescein concentration, decreased by adding probenecid to the bath. The kinetics of this unidirectional movement of fluorescein were consistent with a saturable active transport process. The fluid flux from bath to lumen across the retinal vessels, which was 6.3 +/- 1.0 nl/min/mm for perfusion rates of 6.6 +/- 0.2 nl/min, was temperature-dependent and was coupled to the fluorescein transport. Fluorescein stimulated the fluid flux by 17% when added to the perfusate and by 60% when added to the bath, and this effect could be reversed by probenecid. Our results showed an active transport of fluorescein in the rabbit retinal vessels coupled with net fluid flux from outside the vessels into the lumen.

Animals↗
PubMed1977

[Changes in the retinal vessels in mandibular nerve anesthesia. A potential for complications].

Examinations of the eyegrounds were made on thirty subjects after conduction anesthesia with xylocitin of the inferior alveolar nerve as well as on nine subjects after sodium chloride injections in order to determine the effect of mandibular conduction anesthesia on retinal vessels. Retinal vascular widths were measured and arteriovenous indices determined. The subjects were divided into groups according to preexisting general diseases, age, sex, and smoking habits. Retinal vascular changes were determined in dependence on age and smoking habits after injections made into the mandibular foramen, and the manner of origin and the results are discussed with particular reference to data reported in the literature.

Anesthesia, Conduction↗
PubMed1995

Increase of retinal vessel width in ocular hypertensives with timolol therapy.

PURPOSE: The purpose of this study was to determine whether timolol drops compared to placebo drops had a significant effect on retinal vessel width in ocular hypertensives. METHODS: Thirty-seven ocular hypertensives were randomly assigned to receive placebo or 0.5% timolol drops to both eyes for 18 to 24 months in a double masked clinical trial. Measurements of ocular pressure and retinal vessel width by computerized image analysis from fundus photographs were made at about 3 month intervals for 18 to 24 months of follow-up. RESULTS: None of the subjects developed visual field loss when tested with the Goldmann perimeter by kinetic and static means at six month intervals. Subjects treated with the placebo showed no change in ocular pressure and a significant decrease in retinal vessel width over time especially in the right eye. Subjects treated with timolol had an increase in retinal vessel width compared to the placebo group significant especially for the superior temporal vein. Multivariate analyses indicated that the increase of retinal vessel width was not associated mainly with the ocular pressure on treatment or decrease in ocular pressure on treatment. CONCLUSION: Timolol treatment was associated with an increase of retinal vessel width. The effect of timolol appears to be related primarily to mechanisms other than the decrease in ocular pressure.

Double-Blind Method↗
PubMed1994

A case of 11q-syndrome associated with abnormalities of the retinal vessels.

A case of 11q- syndrome associated with abnormalities of the retinal vessels similar to those of familial exudative vitreoretinopathy was followed from 6 months to 3 years of age. The patient was a female infant born at 39 weeks of gestation and weighing 2,360 g without oxygen therapy. A chromosomal analysis showed a 46,XX,del(11)(q23.3). An ocular examination revealed exotropia and a positive kappa angle of the left eye with psychomotor retardation. An abnormal pattern of the retinal vessels and an avascular retina was observed in the periphery of both eyes. Therefore we concluded that the abnormalities of the retinal vessels may be related to the deletion of the long arm of chromosome 11.

Chromosome Aberrations↗
PubMed1986

The relationship between retinal vessel tortuosity, diameter, and transmural pressure.

Increases in retinal vein tortuosity are thought to be caused by increases in vascular transmural pressure. We have attempted to determine the relationship between retinal vessel tortuosity, diameter, and transmural pressure by examining the effects of changes in transmural pressure on latex tubes with fixed ends. As the transmural pressure is raised, tube diameter increases, but tortuosity does not begin increasing until a critical pressure is reached. Above the critical pressure, tortuosity increases more rapidly than diameter. Our results support the above hypothesis and also suggest that at high transmural pressures, retinal vessel tortuosity is a more sensitive indicator than is the diameter of changes in retinal venous transmural pressure, but diameter is more sensitive than tortuosity at lower pressures.

Humans↗
PubMed1996

The accurate assessment of changes in retinal vessel diameter using multiple frame electrocardiograph synchronised fundus photography.

PURPOSE: Detection and precise quantification of changes in retinal vessel diameter by image analysis techniques is important in a number of fields of research. The retinal vessels have been shown to exhibit pulse related changes in diameter. These may need to be taken into account when studying diameter changes due to other causes. This study examined the effect of using multiple fundus photographs with and without electrocardiographic synchronisation on the size and statistical significance of changes in mean retinal vessel diameter. METHODS: Twelve fundus photographs spaced throughout the cardiac cycle by electrocardiographic synchronisation were taken in 10 normal volunteers: (a) at rest, (b) during isometric exercise, and (c) during oxygen inhalation. Vessel diameters were measured using a computer assisted image analysis system. Subsequently smaller sample sizes, with and without electrocardiograph synchronisation were modeled from the available data. RESULTS: With a group of ten subjects six or more electrocardiograph synchronised photographs enable reliable detection of small diameter changes (1.4%) induced by isometric exercises while other methods either failed to detect change or were unreliable at doing so. With six subjects twelve synchronised photographs were required to reliably detect a change of the same magnitude. Larger diameter changes (5.4%) were detected by any method including a single unsynchronised photograph. CONCLUSIONS: Multiple frame electrocardiograph synchronized fundus photography permits more accurate detection of small changes in retinal vessel diameter.

Adult↗
PubMed1977

Vitreoretinal juncture over retinal vessels.

Previous studies have attributed changes in the retinal surface over or adjacent to large superficial retinal vessels to a variety of conditions, the most common being 'anomalous vitreoretinal attachments.' The fundamental nature of the lesions and their pathogenesis, however, has remained controversial. The present study was undertaken to categorize the ultrastructural alterations of the vitreoretinal juncture over retinal vessels in the posterior fundus of man, and to clarify the relationship of these fundamental changes to clinically significant lesions in this region. Results show no difference in vitreoretinal, or more specifically vitreolaminar attachments over vessels when compared with adjacent regions. The cause of the more significant anomalies, notably surface breaks and their sequelae, is apparently multifactorial and related to a sequence of events. Initially three events predispose to or cause small surface breaks: developmental thinning of the inner limiting lamina; subsurface retinal degeneration; and transmigrating macrophages. These small surface breaks, when complicated by vitreous incarceration or by simple epiretinal membrane formation, can during posterior vitreous detachment cause peeling of the retinal surface, and the resulting large surface breaks may in turn provoke more complex proliferative lesions of the vitreoretinal juncture.

Adult↗
PubMed1994

Shape of the neuroretinal rim and position of the central retinal vessels in glaucoma.

Glaucomatous neuroretinal rim loss can occur in a sequence of sectors with the temporal inferior disc sector as the first and the nasal superior disc sector as the last to be affected. This study evaluated whether the position of the central retinal vessel trunk is correlated with this pattern of glaucomatous rim loss. Morphometrically stereo colour optic disc photographs of 157 glaucomatous eyes and 67 normal eyes were checked. In the normal and glaucomatous eyes, the central retinal vessel trunk was located eccentrically in the upper nasal quadrant of the optic disc. Taking into account the vertically oval disc shape, the distance to the central vessel trunk was largest for the temporal inferior disc region and shortest for the nasal superior disc area. An abnormal form of the glaucomatous neuroretinal rim was found in eyes with an atypical location of the retinal vessel trunk. Also in these glaucomatous eyes, the rim loss was usually most and least marked in that sector with the longest and shortest distance, respectively, to the central retinal vessel trunk. One could infer that the sequence of rim loss in glaucoma is dependent upon the distance of the region to the central retinal vessel trunk; the further away the region from the retinal vessel trunk, the more likely it is to be affected by rim loss. This suggest that the distance from the central retinal vessels is one factor among others that is correlated with the regional vulnerability of the neuroretinal rim to the glaucomatous process.

Adult↗
PubMed2002

Effects of dopamine on human retinal vessel diameter and its modulation during flicker stimulation.

We performed a randomized, subject-blinded, placebo and time-controlled, two-way crossover study in 12 healthy male subjects. Placebo or dopamine was administered on two separate study days. After saline infusion, dopamine hydrochloride was infused in three consecutive doses (5, 10, and 15 microg x kg(-1) x min(-1)). Plasma levels of dopamine were determined at each perfusion step. Arterial and venous retinal vessel diameters were measured with the use of a Zeiss retinal vessel analyzer. Diffuse luminance flicker stimuli of 8 Hz were applied for 60 s. Blood pressure and pulse rate were monitored continuously. Flicker stimulation (8 Hz) increased retinal vessel diameters under basal conditions. The response to 8-Hz flicker light was significantly reduced by dopamine administration. In addition, dopamine slightly but significantly increased retinal vessel diameters. Dopamine hydrochloride significantly increased systolic but not diastolic or mean arterial pressure. The present study indicates that dopamine has a distinct effect on retinal vessel diameters also attenuating the flicker-induced response reactivity of retinal vessels. This implies a role of dopamine in retinal blood flow hemodynamics.

Adult↗
PubMed1991

Parapapillary atrophy and retinal vessel diameter in nonglaucomatous optic nerve damage.

Parapapillary chorioretinal atrophy and decreased retinal vessel diameter occur in glaucomatous eyes. To evaluate the frequency and degree of these signs in nonglaucomatous optic neuropathy, the authors evaluated morphometrically and compared 47 patients with nonglaucomatous optic nerve atrophy from extraocular causes with 292 patients with primary open-angle glaucoma and 179 normal subjects. Eyes with anterior ischemic optic neuropathy were excluded. The parapapillary atrophy was differentiated into a central zone (beta) with sclera and large choroidal vessels visible by ophthalmoscopy and a peripheral zone (alpha) with irregular pigmentation. Both zones did not differ significantly in the eyes with nonglaucomatous optic neuropathy and the normal eyes. In the glaucomatous eyes, they were significantly larger and occurred more frequently. The retinal vessel diameter was significantly smaller in both groups with optic nerve atrophy than in the normal group. It was concluded that decreased retinal vessel diameters unspecifically suggest optic nerve atrophy. Evaluation of parapapillary chorioretinal atrophy can be helpful in differentiating nonglaucomatous from glaucomatous optic neuropathy.

Adolescent↗
PubMed2006

Retinal vessel centerline extraction using multiscale matched filters, confidence and edge measures.

Motivated by the goals of improving detection of low-contrast and narrow vessels and eliminating false detections at nonvascular structures, a new technique is presented for extracting vessels in retinal images. The core of the technique is a new likelihood ratio test that combines matched-filter responses, confidence measures and vessel boundary measures. Matched filter responses are derived in scale-space to extract vessels of widely varying widths. A vessel confidence measure is defined as a projection of a vector formed from a normalized pixel neighborhood onto a normalized ideal vessel profile. Vessel boundary measures and associated confidences are computed at potential vessel boundaries. Combined, these responses form a six-dimensional measurement vector at each pixel. A training technique is used to develop a mapping of this vector to a likelihood ratio that measures the "vesselness" at each pixel. Results comparing this vesselness measure to matched filters alone and to measures based on the Hessian of intensities show substantial improvements, both qualitatively and quantitatively. The Hessian can be used in place of the matched filter to obtain similar but less-substantial improvements or to steer the matched filter by preselecting kernel orientations. Finally, the new vesselness likelihood ratio is embedded into a vessel tracing framework, resulting in an efficient and effective vessel centerline extraction algorithm.

Algorithms↗
PubMedDate not supplied

Retinal vessel responses to systemic autonomic stimulation in fellow eyes of patients with retinal vein occlusion.

The retinal vessel calibre responses to systemic autonomic stimulation were studied in fellow eyes of 11 patients with central retinal vein occlusion (CRVO) and 10 patients with branch retinal vein occlusion (BRVO), using sustained isometric muscle contraction as the stimulus. These vessel responses were compared to those of a control group of 11 subjects of similar ages. The changes in retinal vessel calibre were measured using the Quantimet Image Analyser. There was no significant difference in mean arteriolar constriction during isometric muscle contraction (mean +/- SEM) between the CRVO group (6.0 +/- 1.34%) and the BRVO group (5.4 +/- 0.31%), (p greater than 0.05), and between either of these groups compared with the control group (7.4 +/- 1.20%), (p greater than 0.50). Similarly there was no significant difference in mean venule responses between the groups (CRVO 4.9 +/- 0.48%; BRVO 4.6 +/- 0.63%; control subjects 3.8 +/- 0.90%; p greater than 0.05). The diastolic blood pressure responses were similarly not significantly different between the 3 groups (CRVO 22.3 +/- 1.27, range + 17 to 29 mmHg; BRVO 25.8 +/- 2.9 mmHg, range 18 to 45 mmHg; control subjects 21.3 +/- 1.7 mmHg, range 16 to 35 mmHg), (p greater than 0.10). The implications of the results are discussed.

Adult↗
PubMed1980

Retinal vessel abnormalities of phototoxic retinopathy in rats.

Phototoxic retinopathy in rats is characterized by a progressive loss of the outer retinal layers. During the neural degenerative phases, a sequence of vascular change occurs. Whole mounts of ink-injected retinal vessels and flat mounts of trypsin-digested retinal vessels show areas of capillary nonperfusion and acellularity and enlargement of retinal capillaries in the deep bed. When the photoreceptor and outer nuclear layers have disappeared, portions of the remaining deep capillary bed become surrounded by cells of the retinal pigment epithelium (RPE). Thin sections show fenestrae in some vessel walls within the retinal pigment epithelial layer. Since serial sections show continuity between those fenestrated vessels and the deep retinal vessels and no evidence of vessels breeching Bruch's membrane, this morphologic phenomenon is considered to be an in situ alteration of retinal vessels. We conclude that a factor(s) within the retinal pigment epithelial layer determines the morphology of vessels within that environment.

Animals↗
PubMed1994

Organic anion transport and reabsorptive fluid flux in diabetic retinal vessels: a microperfusion study.

Microperfusion techniques were used to characterize in vitro the fluorescein transport and fluid movement across isolated diabetic rabbit retinal vessels. Unbranched segments of arterioles of alloxan-induced diabetic rabbits were isolated and cannulated on a microperfusion apparatus. Movement of 3H-inulin, the reference tracer, and 14C-fluorescein, the test tracer, across the vascular walls was studied using microperfusion techniques adapted by us to study vascular permeability. The diabetic retinal vessels showed a fluid flux from bath to lumen of 3.6 +/- 0.6 nl min-1 mm-1 with perfusion rates of 7.1 +/- 0.3 nl min-1. This value was 43% (P < or = 0.05) lower when compared with normal values obtained in previous work. Bath to lumen fluorescein fluxes were 2.1 +/- 0.5 and 7.6 +/- 1.6 x 10(-12) mol min-1 mm-1, for fluorescein concentrations of 0.87 x 10(-4) and 1.5 x 10(-4) M, respectively. These values are 23% (P < or = 0.05) and 38.7% (P < or = 0.05), respectively, lower when compared to values obtained from normal retinal vessels. Probenecid, a competitive inhibitor of organic anion transport, added to the bath, had no effect. Increasing bath concentrations of fluorescein caused increasing fluid flux from bath to lumen, and again, probenecid added to the bath has no effect. These results show a significant decrease of fluorescein transport and of net fluid flux across diabetic retinal vessel walls from outside into the lumen, suggesting that in experimental alloxan-induced diabetes there is an early, probably functional, involvement of the retinal vessels in the initial alteration of the blood-retinal barrier (BRB).

Absorption↗