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The retinal vessel is the only microvascular network that can be directly and non‐invasively observed in humans. Cardiovascular and cerebrovascular diseases, such as diabetes, hypertension, can lead to structural changes of the retinal microvascular network. Therefore, it is of great significance to study effective retinal vessel segmentation methods and assist doctors in early diagnoses with quantitative results for vascular networks. In this study, we propose a novel convolutional neural network named feature pyramid U‐Net (FPU‐Net) that extracts multiscale representations by constructing two feature pyramids both on the encoder and the decoder of U‐Net. In this representation, objects features with different size like micro‐vessels and pathology will be fused for better vessel segmentation. The experimental results show that compared with state‐of‐the‐art methods, FPU‐Net is superior in terms of accuracy, sensitivity, F1‐score, and area under the curve and capable of stronger domain generalisation across different datasets.

Retinal blood vessel segmentation and analysis is critical for the computer‐aided diagnosis of different diseases such as diabetic retinopathy. This study presents an automated unsupervised method for segmenting the retinal vasculature based on hybrid methods. The algorithm initially applies a preprocessing step using morphological operators to enhance the vessel tree structure against a non‐uniform image background. The main processing applies the Radon transform to overlapping windows, followed by vessel validation, vessel refinement and vessel reconstruction to achieve the final segmentation. The method was tested on three publicly available datasets and a local database comprising a total of 188 images. Segmentation performance was evaluated using three measures: accuracy, receiver operating characteristic (ROC) analysis, and the structural similarity index. ROC analysis resulted in area under curve values of 97.39%, 97.01%, and 97.12%, for the DRIVE, STARE, and CHASE‐DB1, respectively. Also, the results of accuracy were 0.9688, 0.9646, and 0.9475 for the same datasets. Finally, the average values of structural similarity index were computed for all four datasets, with average values of 0.9650 (DRIVE), 0.9641 (STARE), and 0.9625 (CHASE‐DB1). These results compare with the best published results to date, exceeding their performance for several of the datasets; similar performance is found using accuracy.

PURPOSE: This cross-sectional study investigates the association between retinal vessel complexity and age and studies the effects of cardiovascular health determinants. METHODS: Retinal vessel complexity was assessed by calculating the box-counting fractal dimension (Df ) from digital fundus photographs of 850 subjects (3-97 years). All photographs were labelled as 'non-pathological' by the treating ophthalmologist. RESULTS: Statistical models showed a significantly decreasing relationship between age and Df (linear: R-squared = 0.1897, p

PURPOSE To assess changes of retinal vessel oxygen saturation and vessel diameter in healthy individuals during high-altitude exposure. METHODS Retinal oxygen saturation and vessel diameter were obtained at sea level (SL, 40 m) and high altitude (HA, 3681 m) on 17 healthy individuals from Beijing (six males, 28.06 ± 8.06 years) using Oxymap T1 and then compared with 21 residents from Yushu (10 males, 28.63 ± 6.00 years). Systemic and ocular parameters were also measured before and after high-altitude exposure. Data were presented as mean ± SD and analysed using paired and independent Student t-test with significance accepted at p

Purpose This study aimed to elucidate the relationship between visual field defects in the upper and lower hemifields and the corresponding oxygen saturation of the retinal vessels in patients with glaucoma. Methods Patients with glaucoma (n = 44) exhibiting more than a 10 dB difference between the upper and lower total deviation (TD) were enrolled in the study. After measuring the retinal vessel oxygen saturation by a non-invasive spectrophotometric retinal oximeter, the hemifields in one eye of each patient were divided into worse (worse TD) and better (better TD) hemifield areas. We additionally evaluated a separate group of 40 patients with glaucoma who exhibited less than a 5 dB difference between the upper and lower TD. Statistical analysis was performed using a Student's t-test. Results A higher mean venous saturation of oxygen (SaO2) was observed in the worse (59.0 ± 8.0%) hemifield compared to the better (55.4 ± 7.2%) hemifield (p

Purpose To analyse a prognostic value of initial retinal vessel flicker response for the 3-year development of functional (visual field) and morphological (nerve fibre layer thickness) damage progression in primary open-angle glaucoma patients. Patients and methods Initially, 70 patients were recruited, and flicker response was measured by standardized procedure with the retinal vessel analyser (RVA). Ocular coherence tomography of retinal nerve fibre layer (OCT RNFL) and a visual field testing were performed at beginning and every 6 months for 3 years; 56 patients completed the study. Results No correlation was found between the progression of visual field (VF) mean defect and retinal nerve fibre layer (RNFL) thinning over 3 years on one and the maximal flicker reaction in arteries and veins on the other side (all p > 0.1). However, the calculated difference of examined parameters in the superior versus inferior retinal halves correlated significantly between the RNFL thinning and the initial maximal flicker response for arteries (p = 0.01) and veins (p = 0.003). Conclusion This longitudinal study did not find a general correlation between initial retinal vessel response to flicker light and the glaucoma damage progression measured by OCT and VF, hence limiting the relevance of the RVA device as a predictor of future glaucomatous damage.

Purpose To examine the effect of caffeine on retinal vessel diameters in the Inter99 Study. Methods The Inter99 Study comprised a population‐based age‐and sex‐stratified sample of 13,016 residents of a suburban section of Greater Copenhagen, Denmark. From 6784 participants aged ...

Purpose Evaluation of retinal vessels in cardiovascular disease traditionally relies upon funduscopy, but more recently digital photo analysis has expanded the spectrum. As spectral domain optical coherence tomography (OCT) allows an in-vivo assessment of retinal tissue and its vessels on a histological scale, our study aimed at using this tool for the analysis of the retinal vasculature. Methods Circumferential peripapillary OCT scans (3DOCT-2000; Topcon Inc., Tokyo, Japan), with centration on the optic nerve head, were taken from 20 eyes (20 participants) with normal blood pressure and 20 eyes (20 participants) with arterial hypertension above 120 mmHg (mean blood pressure). The diameter of all vessels intersecting the scan line was measured in the OCT and used to calculate central vessel equivalents, and the A/V ratios were calculated. Bland-Altman analysis was performed to evaluate reliability. Correlation coefficients were determined for reliability of the method as well as with the individual mean arterial blood pressures. Results Forty eyes (40 participants) were included in the study. Mean arterial blood pressure was 96 ± 4 mmHg in the control group and 132 ± 7 mmHg in the hypertonic group. Mean A/V ratio as determined from OCT scans was 0.82 ± 0.13 (normotonic) versus 0.62 ± 0.11 (hypertonic). A Pearson's correlation coefficient of 0.67 (p

Retinal Vessel Analyser (RVA) is a validated instrument to measure retinal vessel diameter in humans. The purpose of this study was to assess the reproducibility (inter-observer reliability) and the repeatability (test-retest reliability) of RVA with a microscope-mounted fundus camera to determine retinal vessel diameter in minipigs.Ocular fundus image from five anaesthetized minipigs was recorded in a digital videotape for approximately 5 min, under stable systemic arterial pressure and gas conditions. To evaluate the reproducibility, each one of two investigators used RVA to measure the diameter of the superior temporal retinal artery on five separate 30-second video sequences from each minipig, which were the same video sequences for both investigators. To evaluate the repeatability, one investigator performed five measurements on a single, randomly selected, 30-second video sequence from each minipig. The reproducibility was determined using the intra-class correlation coefficient (ICC), and the repeatability was assessed using the coefficient of variation (COV). Bland-Altman plots were also used to assess agreement between the two investigators.Retinal arteriolar diameter measurements with RVA in minipigs were highly reproducible. Differences between the two investigators were lower than 0.7%. The ICC was 1.00, indicating perfect reproducibility, and the mean COV was 0.18%, reflecting excellent repeatability of the measurements with RVA.Retinal vessel diameter can reliably be determined not only in humans, but also in minipigs, using the commercially available RVA apparatus and a microscope-mounted fundus camera.

Objectives This study aims to compare retinal vessel anatomy of normal rhesus monkeys and humans and to provide a basis from a structural perspective for the use of rhesus monkey as an experimental model in future studies of retinal vessels. Methods The retinas of six normal rhesus monkey eyes and eight human eyecups following corneal transplantation were obtained and stained using adenosine diphosphatase methods. The distributions, orders, layers of the retinal vessels and the perifoveal vascular ring were compared. Results With adenosine diphosphatase staining, distinct retinal vessels were fully discernable from the first order surrounding the optic disc to the fifth order. There were no statistically significant differences between rhesus monkeys and humans in the percentages of vessels surrounding the optic disc at the equator and the peripheral region. Vascular networks in both species were arranged in several layers around the optic disc, two anastomotic layers at the equator and one sparse layer peripherally. Capillaries at the macular area were quite dense and an intact perifoveal vascular ring was observed. No differences were observed between rhesus monkeys and humans in the percentage area of the vessels and the area, perimeter and diameter of the perifoveal vascular ring. Conclusions The distributions, orders, layers and the perifoveal vascular ring of the retinal vessels of rhesus monkey are quite similar to those of humans. The data suggest that from an anatomical perspective, the rhesus monkey is a good animal model for the study of human retinal vessels, particularly the macular capillaries.

Retinal vessel responses to flickering light are different in various systemic and ocular diseases and can be improved after successful therapy. We investigated retinal vessel response to flickering light in age-related macular degeneration (AMD) patients before and after treatment with a single intravitreal bevacizumab (Avastin(®) ) injection.In 10 patients with exudative AMD [age: median (1.quartile; 3.quartile) 76.0 (73.5; 80.0) years], retinal vessel reactions were examined by Dynamic Vessel Analyser (DVA) before and 3 months after a single intravitreal application of bevacizumab (1.25 mg). A baseline measurement was followed by three consecutive monochromatic flicker stimulations (530-600 nm, 12.5 Hz, 20 seconds). Temporal retinal vessel reaction was analysed and compared with the reaction in healthy controls.Mean arterial dilation at the end of flicker was not different in all groups. For veins this parameter amounted to: pre-treatment, 2.6 (1.7; 3.9)%; post-treatment, 2.9 (2.4; 4.0)%; control, 4.3 (3.2; 5.7)%; significant: pre-treatment - control (Dunnett's procedure, p0.05). Maximal dilation occurred in arteries at: pre-treatment, 17.5 (14.8; 32.5) seconds; post-treatment, 18.0 (16.6; 30.6) seconds; control, 14.5 (10.8; 17.3) seconds. Both AMD groups were slower (p0.05): in veins at 17.0 (14.5; 20.0) seconds, 12.8 (8.6; 14.8) seconds and 18.5 (17.1; 19.9) seconds, respectively; significant post-treatment - control (p0.05). In the post-treatment AMD group arterial constriction after stimulation occurred more slowly compared with the control group (p0.05).Dynamic retinal arterial and venous reactions to flickering light are altered in AMD compared with controls. Three months after a single injection of a vascular endothelial growth factor inhibitor, the investigated retinal dynamic vascular parameters were not altered in our study.

Objective Quantification of retinal vessel morphology has emerged as a marker of cardiovascular health. We examined retinal microvascular diameters in RA, particularly in regard with systemic inflammation, subclinical atherosclerosis and cardiovascular risk. Methods Retinal images from RA patients and controls were processed using computerized software, to obtain central retinal arteriolar (CRAE) and venular (CRVE) equivalent and arteriovenous ratio (AVR). Subclinical atherosclerosis was assessed with carotid intima-media thickness (cIMT), and 10-year risk of general cardiovascular disease was calculated. Results Both CRAE (78.8±8.9 vs 90.2±9.9 μm, p

The purpose of this paper was to develop a technique using computerized image analysis to measure the width of retinal arteries and veins on color fundus photographs. The width of the retinal vessel was determined from digitized fundus photographs by programs based on edge detection and boundary tracing. The average vessel width was determined at different distances or eccentricities from the center of the optic disc and using various lengths of vessel segment. Measurements of superior and inferior temporal vessel width for 20 eyes by 2 operators showed that about 75% of the measurements could be obtained without the use of plan points. The average percent coefficient of variation of the measurements was 2.17% for 3 measurements of each vessel. This technique provides a reproducible and objective method for obtaining the following parameters: the edges of the vessel, the length of the vessel segment to be measured, location of the measurement along the vessel and subsequent retinal vessel width. This technique is readily suitable for application to clinical studies particularly clinical trials.

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.

Changes in the caliber of retinal vessels may be of haemodynamic and morphological significance in various local and systemic vascular diseases. In this paper we present a theoretical study on the effects of structural density changes of the vessel wall on the ‘true’ width of the streaming column of erythrocytes. By use of simplified models of an eye and a retinal vessel, we perform numerical experiments using a computer. The results show that variations in the index of refraction and in the thickness of the vessel wall have negligible influence on the apparent width of the blood column. The image of the vessel can safely be measured as a ‘true’ caliber of the retinal blood column. This might implicate that an early differentiation between vessel constriction caused by increased tonus of systemic-hypertension versus irreversible arteriosclerosis is probably not within physical and optical reach, using ophthalmoscopy.

The placoid lesions of acute posterior multifocal placoid pigment epitheliopathy consist of two distinct areas: a light yellow area surrounding a dark yellow center. On two occasions, the authors compared indocyanine green video angiographic with fluorescein angiographic findings in a typical case of acute posterior multifocal placoid pigment epitheliopathy. In the acute stage, the multiple placoid lesions observed in the early phase of indocyanine green video-angiography showed hypofluorescent lesions corresponding to those seen with fluorescein angiography which blocked choroidal vessels. Some fluorescent intermediate sized choroidal vessels, which traversed the hypofluorescent areas, were dark due to a slight degree of blocked fluorescence. On both indocyanine green video and fluorescein angiography, hypofluorescent lesions were almost the same size as the light yellow area and the dark yellow center of a placoid lesion. A hypofluorescent lesion, seen on fluorescein angiography, obscured a retinal vessel. When the placoid lesions had disappeared, fewer hypofluorescent lesions, corresponding to some of the hypofluorescent lesions originally observed, were seen in the early phase of indocyanine green video angiography. They were also smaller in size. These hypofluorescent lesions decreased in size and some had completely disappeared in the late phase. No hypofluorescent lesions were seen in the early phase of fluorescein angiography. Findings in the acute stage suggest that the hypofluorescence observed in the early phase of indocyanine green video and fluorescein angiography is mainly blockage due to a light yellow area of placoid. When the placoid lesion disappeared, filling delays, which were detectable on only indocyanine green video angiography, persisted in the choriocapillaris.

Purpose To evaluate retinal vessel oxygen saturation and its relationship with ocular volume and axial length. Methods We included 65 healthy individuals (age range: 19–51 years) of varying axial lengths (20.74–28.24 mm). All subjects underwent full ocular examination including intra-ocular pressure measurements and systemic blood pressure measurements which was followed by auto-refraction, axial length, anterior chamber, corneal radii and retinal oxygen saturation assessments. In addition, all subjects underwent routine retinal photography which was used to determine their retinal arterial and venular calibres. Results Retinal vessel calibres, both arteries and venules were significantly decreasing with increasing axial length (arteries: β = −0.37; p

This study assessed the correlation between computer-assisted retinal vessel measurements of right and left eyes, from subjects in a defined, community-based older population. Retinal photographs from participants in the Blue Mountains Eye Study were digitized. All retinal arterioles and venules located 0.5-1.0 disc diameters from the optic disc margin were identified and a computer program measured their diameters. Pearson correlation (R2) statistic was used to assess the correlation in a random subsample of 1546 images. Substantial correlation between right and left eye measurements was found for summary indices of retinal arterioles (R2 = 0.70) and venules (R2 = 0.77). Higher correlation was found for intragrader (R2 0.75-079) than for intergrader assessment (R2 0.67-0.72). Moderate correlation was found in arteriole-to-venule ratio assessed by the same (R2 = 0.57) or different (R2 = 0.52) graders. Measurements from one eye can thus adequately represent the retinal vessel diameters of a person.

The purpose of the study was to assess the intergrader and intragrader reliability of computer-assisted retinal vessel dia-meter measurement in a defined, community-based population. Retinal photographs from participants in the Blue Mountains Eye Study were digitized using standard techniques. A grader identified all retinal vessels located 0.5-1.0 disc diameter from the optic disc margin,and a computer program measured the width of these vessels. Intergrader and intragrader reliability was assessed on a random sub-sample of 184 and 97 images, respectively, using quadratic weighted kappa(kappa) and correlation analysis (R2). Intergrader reliability was high for summary indices of retinal arteriolar (kappa = 0.85, R2 = 0.88)and venular (kappa = 0.90, R2 = 0.90)diameters, and their ratio, the arteriole-to-venule ratio (kappa = 0.75, R2 = 0.79).Intragrader reliability was also high, with kappa values ranging from 0.80 to 0.93 and from 0.80 to 0.92 for graders 1 and 2, respectively. It is concluded that the retinal vessel diameters could be reliably measured using computer-assisted software and may be used for population-based research.

Dual wavelength retinal oximetry has proven to be a useful tool for detecting abnormal retinal vessel oxygen saturation in various diseases. Oximetry images are acquired in a similar fashion as regular fundus images. Oximetry calculations use light intensity measured from oximetry images. A ratio is taken of light intensity at and beside the retinal vessels. This means that the overall illumination of the image has less effect on the result. Despite the ratiometric approach, it is clear from experience and studies on cataract patients that image quality does influence oxygen saturation calculations. The challenge is to estimate or quantify image quality in a reliable manner and to control for image quality in all comparisons between healthy groups and patient groups. Commercial interest

Purpose Studies of diameter regulation in retinal arterioles in vitro have mostly been performed on larger vessels, but evidence suggests that perturbations in the retinal microcirculation may also play a role in the development of vision threatening retinal diseases. Therefore, the purpose of the present study was to develop an in vitro technique for studying diameter regulation in both larger and smaller vessels. Methods A special tissue chamber was developed for mounting, cannulating and perfusing porcine hemiretinas while controlling temperature, pH and oxygen saturation. The chamber was mounted in a flourescens microscope, and the effect on the diameter of larger arterioles, pre-capillary arterioles and capillaries was studied after intravascular and extravascular addition of the thromboxane analogue U46619 and lactate (n=6 for each variable) and NMDA (preliminary). Results In all vessel calibers the thromboxane analogue U46619 induced a significant contraction after extraluminal application (p 0.13). Lactate had no effect on the diameter of non-precontracted vessels (p>0.21), but in pre-contracted vessels lactate relaxed the vessel diameter. Conclusion The response to vasoactive compounds is different after intraluminal and extraluminal application, and the diameter response of vasoactive compounds is different in larger and smaller retinal vessels. The dilating effect of lactate depends on the state of contraction of the retinal vessel.

Purpose To explore the association of renal function and retinal vessel oxygen saturation in patients suffering from diabetes and cardiovascular disease. Methods We examined three groups of patients (1: Diabetics, 2: Diabetics with cardiovascular disease and 3: patients suffering from cardiovascular disease without diabetes). All patients Intraocular Pressure, Systemic Blood Pressure and Dual Wavelength Retinal Vessel Oxygen Saturation (arterial and venous vessel saturation and a-v saturation difference) and Retinal Vessel Calibers were measured following phlebotomy to determine their HbA1c levels. Markers of renal function (ceratinine, eGfr and uACR) were measured in all patients. Results All three groups were age matched (1: 63 (10)yrs; 2: 64 (9)yrs and 3:65 (10)yrs). Unsurprisingly HbA1c was significantly different between groups (p

Purpose To determine the different clinical findings between good and poor prognosis group which is diagnosed with branch retinal artery obstruction(BRAO) and treated with conservative care. We evaluate the average macular thickness, foveal thickness, outer nuclear layer(ONL) on optical coherence tomography(OCT) and retinal artery diameter in both groups. Methods 9 eyes(9 patients) in patients with non-complicated BRAO with good prognosis and a poor prognosis control group with non-complicated BRAO of 11 eyes(11 patients) were used in this study. The average macular thickness, foveal thickness and ONL thickness at the center of fovea on OCT were measured. And branch retinal artery widths were measured by a semi-automated retinal vessel width measurement system retrospectively. Results The average age of the patients was 67.3 ± 11.5 years. The average ONL thickness at the central fovea of the good prognosis group was significantly thicker than that of the control group (p = 0.016). There were no statistically significant result at average macular thickness and foveal thickness. In good prognosis group, Ischemic retinal artery diameter and Central retinal artery equivalent(CRAE) were wider than those of poor prognosis group and they were statistically significant (p = 0.028, p = 0.01). Conclusion In the patients diagnosed with BRAO and treated with conservative care, foveal thickness, ischemic retinal artery diameter and CRAE were statistically significant between good and poor prognosis groups. In the patients diagnosed with BRAO, foveal thickness and retinal artery diameter could be prognostic factors that predict visual prognosis.

Purpose To characterize the optic disc and retinal vessels in healthy children and adolescents. Methods Fundus photographs were evaluated by digital image analysis in one hundred healthy Swedish children and adolescents (3-19 years). Results Median optic disc area was 2.67 mm2 (range, 1.93 to 4.39), median cup area was 0.41 mm2 (range, 0 to 1.45) and median neuroretinal rim area was 2.24 mm2 (range, 1.60 to 3.05). The size of the cup and neuroretinal rim increased with increasing size of the optic disc. There were no correlations between the measured variables and age, sex or refraction. Conclusion The measurements of optic disc size in healthy children, between 3 and 19 years of age, are in accordance with optic disc values found in most studies on adults. The resulting reference intervals may be helpful in clinical pediatric ophthalmology, to facilitate identification of children with abnormal optic disc and retinal vessel morphology.

Purpose An analysis was performed with a view of determining potential associations between typical patterns seen on autofluorescence (AF) imaging in patients with Macular Telangiectesia (MacTel) type 2 and distance visual acuity at presentation as well as visual change over a 2-year follow-up period, thus ascribing predictive value to AF patterns in MacTel. Methods A subgroup of 135 patients (229 eyes) enrolled in the MacTel study underwent AF imaging. Images were graded at the Moorfields Eye Hospital Reading Centre. Recorded AF patterns at baseline and at two years included the typical pattern of increased central AF due to loss of foveal masking, localized decreased AF at the end of a retinal vessel and a large area of decreased AF. Best-corrected visual acuity (BCVA) was measured by means of the Early Treatment for Diabetic Retinopathy Study charts at baseline and after two years. Statistical associations were derived by means of a generalized linear model. Results Presence of increased macular AF (p=0.004), a large area of decreased AF (p

Disturbances in retinal oxygenation are believed to play an important role in several eye diseases, such as retinal vessel occlusions, diabetic retinopathy and retinopathy of prematurity. Non-invasive measurements of retinal oxygenation are important for better understanding of disease mechanisms and the technology will hopefully, in the near future, aid in management of the diseases. The technology for retinal oximetry has been developed in the past years and decades and the current oximeters are sensitive to changes in oxygen saturation and give repeatable results. Studies have confirmed differences in retinal vessel oxygen saturation in various eye diseases. Further studies of retinal oxygenation will benefit from development of the methodology. This includes hardware and software development but also standardisation of measurement techniques with the current instruments and better understanding of confounding factors. Commercial interest

Association FA b MD b FA b MD b FA b MD b FA b MD b ATR -0.26 0.55 -0.21 0.47 -0.07 0.29 -0.05 0.24 IFO -0.35 0.49 -0.33 0.47 -0.16 0.28 -0.12 0.25 ILF -0.27 0.54 -0.25 0.52 -0.16 0.40 -0.11 0.36 PTR -0.32 0.49 -0.31 0.47 -0.18 0.37 -0.15 0.32 SLF -0.18 0.28 -0.19 0.29 -0.10 0.18 -0.11 0.19 UNC -0.30 0.42 -0.25 0.40 -0.25 0.34 -0.19 0.31 Commissural FMA -0.36 0.41 -0.31 0.36 -0.29 0.36 -0.22 0.30 FMI -0.39 0.40 -0.30 0.34 -0.36 0.35 -0.24 0.25 Limbic CGC -0.22 0.24 -0.23 0.24 -0.22 0.23 -0.23 0.23 CGH -0.29 0.36 -0.29 0.35 -0.29 0.36 -0.29 0.35 Sensorimotor CST -0.01 0.09 -0.03 0.12 0.02 0.08 0.00 0.10 MCP 0.05 0.15 -0.01 0.09 0.06 0.16 0.00 0.09 ML 0.01 0.09 0.01 0.11 0.01 0.09 0.01 0.11 STR -0.03 0.02 -0.04 0.02 0.00 0.02 -0.01 0.02

Purpose Measurements of retinal blood flow in the rodent is a major challenge because of the small size and the poor optical quality of the eye. We present a technique based on the measurement of retinal vessel diameters using a fundus camera specifically designed for the rodent eye. This is combined with a Doppler OCT technique for measuring retinal blood velocities. Methods In the rat retinal vessel diameters and retinal blood velocities were measured during several stimuli. These included systemic hyperoxia by breathing 100% oxygen, systemic hypercapnia by breathing increasing concentrations of CO2 and by stimulation with diffuse flicker light. Results Retinal blood flow was quantified in larger retinal venules in our studies. As expected systemic hyperoxia induced a pronounced decrease in retinal vessel diameter, retinal blood velocity, and retinal blood flow (p < 0.01 each). Breathing increasing concentrations of CO2 on the other hand induced a dose-dependent increase in retinal vessel diameter, retinal blood velocity and retinal blood flow (p < 0.01 each). Finally, stimulation with flicker-light also increased retinal vessel diameter, retinal blood velocity and retinal blood flow (p < 0.01 each). Conclusion Our data indicate that changes in retinal blood flow in the rodent can be adequately measured using combined fundus photography and Doppler OCT. This technique can also be used to study neurovascular coupling. Our results are important, because the mechanisms of retinal blood flow regulation remain largely obscure.

Purpose One of the clinical signs observed at the funduscopic examination of the eye of the intracranial hypertension patients, apart from the papillary edema is the reduction, even the disappearance of the spontaneous pulsatility of the retinal vessels..A new device, Retinal Vessel Analyzer (Imedos) now makes it possible to measure negligible variations of the vascular diameter (arteriolar and venular) . We thus measured the retinal vascular pulsatility found among patients having a benign intracranial hypertension (BIH) which we compared with a control population. Methods We included 6 patients presenting a benign intracranial hypertension. For each participant, an examination with RVA was carried out right before the lumbar puncture (J0) then at 1 month (M1) and 3 months intervals (3M). We compared these results with a control population (n=76). Results The mean venous pulsatility found at the 76 controls was 5,07m ± 1,57. Our 6 patients presenting a BIH, had a venous pulsatility that was lower than 0,5m at D0 (p < 0,05), lower than 0,8m± 0,52 at M1 (p < 0,05) and between 0,5 and 3m at m3. All the 6 patients had an abnormal measurement of the intracranial pressure . It was not found a correlation between the value of pulsatility and the value of the intracranial pressure Conclusion The variation of the vascular diameter, measured by RVA, is an indirect reflection of the vascular transmural pressure.Our results show that even in the case of a moderate BIH it exist an early, identifiable repercussion at the level of the retinal vascular network quantifiable by RVA.This reduction in the venous pulsatility can be explained by an increase in the intravascular pressure and/or by a parietal remodeling, especially at the later stage.