Retinal Vessel Measurements Research Articles

Measurement of Retinal Vessels as a Biomarker of Cerebrovascular Aging in Older HIV-Positive Men Compared With Controls.

To compare retinal vascular measurements, biomarkers of cerebral small vessel disease, in HIV-positive men aged 50 years and older with similarly aged HIV-negative men and younger HIV-positive men. We recruited white, nondiabetic men into a cross-sectional substudy of a larger cohort including 3 demographically matched groups. Optic disc-centered 45-degree color fundus photographs were used to calculate central retinal arterial and venous caliber and the arterial-venous ratio (AVR). We used univariate and multivariable linear regression to compare retinal vessel measurements in the 3 groups and to identify factors associated with AVR. All HIV-positive men were virologically suppressed. In a multivariable model, study group was not associated with AVR [adjusted β 0.010 for HIV-positive men <50 (n = 39) compared with HIV-positive men aged ≥50 years (n = 120), 95% confidence interval [CI] -0.018 to 0.038, P = 0.47; adjusted β 0.00002 for HIV-negative men ≥50 years (n = 52), 95% CI -0.022 to 0.022, P = 0.99]. Factors associated with lower AVR were systolic blood pressure (adjusted β -0.009 per +10 mm Hg, 95% CI -0.015 to -0.003, P = 0.002), history of stroke or transient ischemic attack (adjusted β -0.070, 95% CI -0.12 to -0.015, P = 0.01), and recent recreational drug use (adjusted β -0.037, 95% CI -0.057 to -0.018, P = 0.0002). There were no differences in retinal vascular indices between HIV-positive men aged ≥50 years and HIV-negative men aged ≥50 years or HIV-positive men aged <50 years, suggesting that HIV is not associated with an increased burden of cerebral small vessel disease.

A spectrum of retinal vasculature measures and coronary artery disease

Background and aimsWe aimed to comprehensively describe a spectrum of retinal vessel measures including fractal dimension (Df) and their associations with indices of coronary artery disease (CAD) extent and severity, as well as hypertension and diabetes. MethodsThe Australian Heart Eye Study (AHES) is an observational study that surveyed 1680 participants presenting to a tertiary referral hospital for the evaluation of potential CAD by coronary angiography. A range of newer retinal vessel geometric measures (Df, curvature tortuosity, and branching angle) were quantified from retinal photographs using semi-automated software, the Singapore ‘I’ Vessel Assessment (SIVA) tool. A combined retinal score was constructed, aiming to assess the joint effect of multiple retinal vessel parameters on CAD, comprising of those variables that were most strongly significant in multivariate analysis - Df, arteriolar curvature tortuosity, and retinal arteriolar calibre. CAD was objectively quantified using a range of measures obtained from coronary angiography. ResultsA total of 1187 participants had complete data on retinal vessel measurements and coronary vessel evaluation. Retinal vascular Df and curvature tortuosity decreased with increasing age; women had significantly lower Df than men (p<0.003). Straighter retinal vessels were associated with CAD extent and Gensini scores in multivariable analysis (p<0.02). Accounting for media opacity by sub-group analysis in pseudophakic patients, the combined retinal score was associated with stenosis greater than 50% in any coronary artery segment (vessel score) and obstructive coronary stenosis in all three main coronary arteries (segment score) (p = 0.01). Lower Df and narrower arteriolar branching angle were associated with CAD vessel score (p<0.03). In sex-stratified multivariate analyses, straighter arterioles were associated with greater odds of CAD in men, and narrower venular branching angle was associated with CAD in women. ConclusionsA range of retinal vessel measures were associated with CAD extent and severity. A sparser retinal microvascular network (smaller Df) was associated with older age and female gender. After accounting for the impact of media opacity, retinal vessel measures were associated with more diffuse and severe CAD.

Study of Enhanced Depth Imaging Optical Coherence Tomography in Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy.

Background:Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a hereditary small artery disease caused by NOTCH3 gene mutation. We performed enhanced depth imaging optical coherence tomography (EDI-OCT) to evaluate the retinal vessel changes in CADASIL patients and assessed their consonance with brain magnetic resonance imaging (MRI) findings.Methods:Of 27 genetically confirmed patients and an equal number of controls were recruited at the Peking University First Hospital from January 2015 to August 2016. All patients underwent 7T-MRI of the brain. Fazekas score, number of small infarcts and microbleeds were evaluated. All patients and controls underwent EDI-OCT to measure subfoveal choroidal thickness (SFCT), inner and outer diameters as well as arterial and venous wall thickness, and arterial venous ratio of the inner (AVRin) and outer diameters (AVRout). The relation between retinal vessel changes and Fazekas scores, numbers of small infarcts, or microbleeds was analyzed. Paired t-test was used to compare the SFCT and retinal vessel measurement data between patients and controls. Spearman's correlation was used to investigate the correlation between retinal vessel changes and MRI lesions.Results:In CADASIL patients, mean SFCT (268.37 ± 46.50 μm) and mean arterial inner diameter (93.46 ± 9.70 μm) were significantly lower than that in controls (P < 0.001, P = 0.048, respectively). Mean arterial outer diameter (131.74 ± 10.87 μm), venous inner (128.99 ± 13.62 μm) and outer diameter (164.82 ± 14.77 μm), and mean arterial (19.13 ± 1.85 μm) and venous (17.91 ± 2.76 μm) wall thickness were significantly higher than that in controls (P = 0.023, P = 0.004, P < 0.001, P < 0.001, respectively). Arterial inner diameter (rs= −0.39, P = 0.044), AVRin (rs= −0.65, P < 0.001), and AVRout (rs= −0.56, P = 0.002) showed a negative correlation with the number of small infarcts. Venous inner diameter (rs = 0.46, P = 0.016) showed a positive correlation with the number of small infarcts. Venous inner diameter (rs = 0.59, P = 0.002), outer diameter (rs = 0.47, P = 0.017), showed a positive correlation with the number of cerebral microbleeds (CMBs). AVRin (rs= −0.52, P = 0.007) and AVRout (rs= −0.40, P = 0.048) showed a negative correlation with the number of CMBs.Conclusions:Measurement of retinal vessels using EDI-OCT correlates moderately well with MRI parameters. EDI-OCT might be a useful evaluation tool for CADASIL patients.

Effect of Axial Eye Length on Retinal Vessel Parameters in 6 to 12-Year-Old Malay Girls.

PurposeRetinal vessel analysis is affected by both systemic and ocular factors. Malays are the major ethnicity in South East Asia. Data on the retinal microvasculature in Malays is limited, especially among children. We aim to evaluate the influence of ocular biometry on retinal vessel parameters in young Malay girls.MethodsThis was a cross-sectional, hospital-based study involving 86 Malay girls aged 6 to 12 years old in Hospital Universiti Sains Malaysia from 2015–2016. Ocular examination, refraction, biometry, retinal photography, and anthropometric measurements were performed. The central retinal arteriolar equivalent (CRAE), central retinal venular equivalent (CRVE) and overall fractal dimension (Df) were measured using validated computer-based methods (Singapore I vessel analyzer, SIVA version 3.0, Singapore). The associations of ocular biometry and CRAE, CRVE and Df were analyzed using multivariable analysis.ResultsThe mean CRAE, CRVE and Df in Malay girls were 171.40 (14.40) um, 248.02 (16.95) um and 1.42 (0.05) respectively. Each 1 mm increase in axial length was associated with a reduction of 4.25 um in the CRAE (p = 0.03) and a reduction of 0.02 in the Df (p = 0.02), after adjustment for age, blood pressure and body mass index. No association was observed between axial length and CRVE. Anterior chamber depth and corneal curvature had no association with CRAE, CRVE or Df.ConclusionAxial length affects retinal vessel measurements. Narrower retinal arterioles and reduced retinal fractal dimension were observed in Malay girls with longer axial lengths.

Preliminary investigation of multispectral retinal tissue oximetry mapping using a hyperspectral retinal camera

Oximetry measurement of principal retinal vessels represents a first step towards understanding retinal metabolism, but the technique could be significantly enhanced by spectral imaging of the fundus outside of main vessels. In this study, a recently developed Hyperspectral Retinal Camera was used to measure relative oximetric (SatO2) and total hemoglobin (HbT) maps of the retina, outside of large vessels, in healthy volunteers at baseline (N = 7) and during systemic hypoxia (N = 11), as well as in patients with glaucoma (N = 2). Images of the retina, on a field of view of ∼30°, were acquired between 500 and 600 nm with 2 and 5 nm steps, in under 3 s. The reflectance spectrum from each pixel was fitted to a model having oxy- and deoxyhemoglobin as the main absorbers and scattering modeled by a power law, yielding estimates of relative SatO2 and HbT over the fundus. Average optic nerve head (ONH) saturation over 8 eyes was 68 ± 5%. During systemic hypoxia, mean ONH saturation decreased by 12.5% on average. Upon further development and validation, the relative SatO2 and HbT maps of microvasculature obtained with this imaging system could ultimately contribute to the diagnostic and management of diseases affecting the ONH and retina.

Comparison of retinal vessel measurements using adaptive optics scanning laser ophthalmoscopy and optical coherence tomography.

We compared adaptive optics scanning laser ophthalmoscopy (AOSLO) and optical coherence tomography (OCT) vessel caliber measurements. AOSLO videos were acquired from 28 volunteers with healthy eyes. Artery measurements were made 0.5-1 disc diameters away from the optic disc margin. Individual segmented retinal arterial caliber was measured in synchronization with cardiac pulsation and averaged to obtain final horizontal retinal arterial caliber (ACH) and horizontal retinal arterial lumen (ALH). All OCT images were obtained with the Spectralis OCT, a spectral-domain OCT system. Vertical retinal arterial caliber (ACV) and vertical retinal arterial lumen (ALV) were measured on the same artery measured with AOSLO. Measurements made with the two imaging systems were compared. Average ACH, measured with AOSLO, was 123.4±11.2 and average ALH was 101.8±10.2µm. Average ACV, measured with OCT, was 125.5±11.4 and average ALV was 99.1±10.6µm. Both arterial caliber (r=0.767, p<0.0001) and arterial lumen (r=0.81, p<0.0001) measurements were significantly correlated between imaging modalities. Additionally, ACH and ACV were not significantly different (p=0.16). However, ALH measurements were significantly higher than ALV measurements (p=0.03). Vessel measurements made with AOSLO and OCT were well correlated. Moreover, plasma is visible and distinguishable from the retinal vessel wall in AOSLO images but not in OCT images. Therefore, AOSLO may measure vessel width more precisely than OCT.

The effect of oxygen saturation targeting on retinal blood vessel growth using retinal image data from the BOOST-II UK Trial.

PurposeRetinopathy of prematurity (ROP) is a disorder of developing retinal blood vessels in preterm infants. The purpose of this nested study was to investigate the effects of higher (91–95%) and lower (85–89%) oxygen saturation (SpO2) targeting on retinal blood vessel growth in preterm infants.MethodsRetinal blood vessel growth in the higher (91–95%) and lower (85–89%) oxygen saturation (SpO2) targeting groups was compared. Suitable RetCam (Clarity, Pleasanton, CA, USA) images collected in the BOOST-II UK trial were used. The distances between the centre of the optic disc and the ROP ridge in the temporal and nasal retina were measured in pixel units.ResultsImages from 38 infants were studied, 20 from the higher SpO2 target group and 18 from the lower SpO2 target group. On average, temporal blood vessels extended further from the optic disc than nasal blood vessels, mean (standard deviation (SD)) 463.39 (55.05) pixels compared with 360.13 (44.47) pixels, respectively, P<0.0001. Temporal blood vessels extended less far from the optic disc in the higher SpO2 target group than in the lower SpO2 target group: mean (SD) 449.83 (56.16) pixels compared with 480.02 (49.94), respectively, P=0.055. Nasal retinal blood vessel measurements were broadly similar in the higher and lower SpO2 target groups; mean (SD) 353.96 (41.95) compared with 370.00 (48.82) pixels, respectively, P=0.38.ConclusionsRelatively high oxygen saturation targeting (91–95%) was associated with a trend (P=0.055) towards reduced retinal blood vessel growth in this study of preterm infants.

Correlation between Retinal Vessel Calibre and Neurodegeneration in Patients with Type 2 Diabetes Mellitus in the European Consortium for the Early Treatment of Diabetic Retinopathy (EUROCONDOR)

Purpose: To investigate the correlation between retinal vessel calibre and measurements of neurodegeneration in patients with type 2 diabetes (T2D) and no or early diabetic retinopathy (DR). Methods: Baseline data on 440 patients with T2D from the EUROCONDOR clinical trial were used. DR was graded according to the Early Treatment of Diabetic Retinopathy Study (ETDRS) scale, and patients with ETDRS levels 10-35 were included. Retinal vessel diameters were measured by semi-automatic software. Calibres were summarized into central retinal artery and vein equivalents (CRAE and CRVE). Results: Median age and diabetes duration were 64.0 and 10.3 years, respectively. ETDRS levels were 10 (42.3%), 20 (27.5%) and 35 (30.2%). The median CRAE and CRVE were 146.7 and 215.3 µm, respectively. CRAE did not differ according to ETRDS level (p = 0.12), but wider CRVE were found in patients with higher ETDRS levels (p = 0.04). In a multivariable linear regression model, CRAE was associated with macular ganglion cell layer thickness (coefficient 0.27 per micrometre, p < 0.01), and CRVE was correlated with macular retinal thickness (coefficient -0.07 per micrometre, p = 0.04) and retinal nerve fibre layer thickness at the optic disc (coefficient 0.32 per micrometre, p < 0.01). Conclusion: Retinal vessel calibre was independently associated with structural changes of the neuroretina in patients with no or early DR.

Altered retinal flicker response indicates microvascular dysfunction in women with preeclampsia.

Flicker-induced dilatation is reduced in patients with cardiovascular risk, and the following arteriolar constriction is reduced with aging, leading to a reduced arteriolar amplitude and, thereby, indicating microvascular endothelial dysfunction. As endothelial dysfunction is associated with preeclampsia, we assessed retinal flicker response during pregnancy and postpartum. Between 2006 and 2013, women were recruited from University Hospital Jena and Prenatal Diagnostic Center Erfurt, Germany, of which 34 women with preeclampsia, 45 women with normal pregnancy, and 22 nonpregnant controls were included in the study. Women with normal pregnancy were matched for age, nulliparity, smoking, previous gestational hypertensive disorders, and family history of cardiovascular disease. Nonpregnant women were age-matched, nulliparous, nonsmoking, without family history of cardiovascular disease. Retinal vessel measurement using Dynamic Vessel Analyzer consisted of 50-seconds baseline acquisition, followed by three 20-second flicker and 80-second relaxation periods. Arteriolar constriction and arteriolar amplitude were reduced during pregnancy (P=0.001 and P=0.008) and postpartum (P=0.018 and P=0.034) in women with preeclampsia, adjusted for age, body mass index, mean arterial pressure, baseline diameter, and family history of cardiovascular disease. Flicker-induced dilatation was unchanged within the groups and throughout the study period. The unchanged flicker-induced dilatation may support a preserved autoregulatory competence of the microvasculature, and the diminished arteriolar amplitude, mainly because of the absence of the arteriolar constriction, indicates a commenced retinal microvascular dysfunction in women with preeclampsia during pregnancy and postpartum. Mechanisms responsible for altered retinal flicker response in preeclampsia need to be clarified in further studies.

Automated retinal vessel recognition and measurements on large datasets.

The characteristics of the retinal vascular network have been prospectively associated with many systemic and vascular diseases. QUARTZ is a fully automated software that has been developed to localize and quantify the morphological characteristics of blood vessels in retinal images for use in epidemiological studies. This software was used to analyse a dataset containing 16,000 retinal images from the EPIC-Norfolk cohort study. The objective of this paper is to both assess the suitability of this dataset for computational analysis and to further evaluate the QUARTZ software.

Correlation of Retinal Vessel Analysis and Nerve Fiber Layer Thickness in Normal Tension Glaucoma

Background: To investigate the retinal vessel diameter and its possible relationship with the retinal nerve fiber layer (RNFL) thickness in normal tension glaucoma (NTG). Methods: 86 NTG patients with detailed eye examination including retinal vessel analysis (DVA) and measurement of the RNFL thickness with scanning laser polarimetry (SLP; GDxVCC) were included in this retrospective study. The temporal retinal arteriolar diameters, temporal retinal venular diameters, vascular flicker response were compared with RNFL thickness and NFI (nerve fiber index). Results: The flicker response of DVA was significantly reduced as compared to normal eyes. The diameters of the temporal retinal arteriolar vessels were significantly correlated with RNFL thickness (P=0.0204) and NFI of GDxVCC (P=0.0021). The diameters of the temporal retinal venular were significantly correlated with the NFI (P=0.0298). Conclusion: Our results show that narrower arteriolar vessels are found in advanced NTG patients. These findings may be due to the decreased demand for retinal blood flow in damaged retina, but also may be one reason for the damage. Vessel analysis can contribute to the available tools predicting glaucomatous damage before visual field loss becomes manifest.

Optical coherence tomography-based retinal vessel analysis for the evaluation of hypertensive vasculopathy.

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. 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. 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<0.001) was determined between A/V ratio and blood pressure. Our results highlight the feasibility of retinal vessel measurements in spectral domain OCT. A relation between mean arterial blood pressure and OCT-based A/V ratio was established. Further research will elucidate influencing factors and provide a broader basis for therapeutic approaches.

Retinal Vessel Detection and Measurement for Computer-aided Medical Diagnosis

Since blood vessel detection and characteristic measurement for ocular retinal images is a fundamental problem in computer-aided medical diagnosis, automated algorithms/systems for vessel detection and measurement are always demanded. To support computer-aided diagnosis, an integrated approach/solution for vessel detection and diameter measurement is presented and validated. In the proposed approach, a Dempster-Shafer (D-S)-based edge detector is developed to obtain initial vessel edge information and an accurate vascular map for a retinal image. Then, the appropriate path and the centerline of a vessel of interest are identified automatically through graph search. Once the vessel path has been identified, the diameter of the vessel will be measured accordingly by the algorithm in real time. To achieve more accurate edge detection and diameter measurement, mixed Gaussian-matched filters are designed to refine the initial detection and measures. Other important medical indices of retinal vessels can also be calculated accordingly based on detection and measurement results. The efficiency of the proposed algorithm was validated by the retinal images obtained from different public databases. Experimental results show that the vessel detection rate of the algorithm is 100% for large vessels and 89.9% for small vessels, and the error rate on vessel diameter measurement is less than 5%, which are all well within the acceptable range of deviation among the human graders.

A Posteriori–Derived Dietary Patterns and Retinal Vessel Caliber in an Elderly Population

To examine the association between a posteriori-derived dietary patterns (DP) and retinal vessel caliber in an elderly population. This was a cross-sectional study of 288 elderly adults (>65 years) who participated in the European Eye study (EUREYE) Northern Irish cohort. DP were extracted using principal component analysis from completed food frequency questionnaires. Semi-automated computer grading was used to determine the mean retinal vessel diameters (central retinal arteriole equivalent [CRAE] and central retinal venule equivalent [CRVE]) from digitized visual field one images using a standard measurement protocol. THREE MAJOR DP WERE IDENTIFIED IN THIS POPULATION, WHICH ACCOUNTED FOR 21% OF THE TOTAL VARIANCE: a "healthy" pattern with high factor loadings for oily fish, fruits and vegetables, and olive oil; an "unhealthy" pattern with high factor loadings for red and processed meat, refined grains, eggs, butter, sugar and sweets; and a "snack and beverage" pattern with high factor loading for pizza, nuts, and coffee. Multivariable linear regression analysis indicated no significant association between major identified DP and mean CRAE or CRVE in all models. This is the first study to investigate associations between a posteriori-derived DP and retinal vessel caliber. There was no evidence of a relationship between extracted DP and retinal vessel measurements in this population. However, it is possible that potentially important relationships exist between single nutrients or foods and vessel diameters that cannot be identified using a DP approach. Further studies to examine the role of dietary factors in the microcirculation are required.

Fast Retinal Vessel Detection and Measurement Using Wavelets and Edge Location Refinement

The relationship between changes in retinal vessel morphology and the onset and progression of diseases such as diabetes, hypertension and retinopathy of prematurity (ROP) has been the subject of several large scale clinical studies. However, the difficulty of quantifying changes in retinal vessels in a sufficiently fast, accurate and repeatable manner has restricted the application of the insights gleaned from these studies to clinical practice. This paper presents a novel algorithm for the efficient detection and measurement of retinal vessels, which is general enough that it can be applied to both low and high resolution fundus photographs and fluorescein angiograms upon the adjustment of only a few intuitive parameters. Firstly, we describe the simple vessel segmentation strategy, formulated in the language of wavelets, that is used for fast vessel detection. When validated using a publicly available database of retinal images, this segmentation achieves a true positive rate of 70.27%, false positive rate of 2.83%, and accuracy score of 0.9371. Vessel edges are then more precisely localised using image profiles computed perpendicularly across a spline fit of each detected vessel centreline, so that both local and global changes in vessel diameter can be readily quantified. Using a second image database, we show that the diameters output by our algorithm display good agreement with the manual measurements made by three independent observers. We conclude that the improved speed and generality offered by our algorithm are achieved without sacrificing accuracy. The algorithm is implemented in MATLAB along with a graphical user interface, and we have made the source code freely available.

Computer-assisted image analysis of temporal retinal vessel width and tortuosity in retinopathy of prematurity for the assessment of disease severity and treatment outcome

To quantify the severity of retinopathy of prematurity (ROP) through temporal retinal vessel diameter and tortuosity by the use semiautomated analysis and to evaluate the effects of laser treatment on retinal vessel measurements. A total of 176 RetCam digital fundus images from 63 infants diagnosed with ROP between January 2005 and December 2008 were retrospectively analyzed with Retinal Vessel Measurement V5.8 software. Patients were classified into 1 of 3 groups: stage 1 and 2 (Group 1), stage 3 not requiring treatment (Group 2), and stage 3 requiring treatment (Group 3). Diameter and tortuosity of the 4 major temporal retinal arteries and veins close to the optic disk were quantified. Tortuosity was measured as central (within 2 disk diameters from the center of the optic disk) and paracentral (from 2 to 4 disk diameters). For Group 3, measurements of vessels immediately before treatment and all follow-up post-treatment measurements of vessels were analyzed. Differences in central and paracentral arteriolar tortuosity were pronounced. The average central arteriolar tortuosities were 1.12 ± 0.018 for Group 1, 1.13 ± 0.018 for Group 2, and 1.32 ± for Group 3; the paracentral arteriolar tortuosities were 1.11 ± 0.019 for Group 1, 1.12 ± 0.019 for Group 2, and 1.31 ± 0.02 for Group 3. In the post-treatment analysis of Group 3 patients, significant reductions in all vascular measurements were observed compared to pre-treatment, except for central and paracentral vein tortuosity. Computerized systems can be used to objectively assess differences in vascular parameters between ROP stages.

Stability of 35-mm Scanners as Used in Ophthalmologic Research

To assess the consistency of digitization of 35-mm slides as practiced in ophthalmologic research and estimate the impact of variation on semi-automated retinal vessel width measurements. A single retina slide was repeatedly digitized under various conditions on three scanner models. Average color levels were extracted from the resulting images, from which vessel widths were graded. The color channel level variations and possible correlation with width were analyzed. The Nikon 5000 scanner (Nikon Corp., Tokyo, Japan) had average coefficients of variation of 0.4, 2.3, and 0.5 for the red, green, and blue channel levels across all runs. The P values of the correlation between the red, green, and blue color channel levels and the width of the large retinal arteriole were .89, .27, and .58, respectively. The results suggest that the tested scanners digitize the 35-mm slides in a reliable manner without biasing the retinal vessel measurements.

Grading techniques for the assessment of retinal

AbstractHistorical perspective Brief history of vascular measurement ‐Leishman ‐Kagan ‐Parr ‐Wisconsin (WESDR, ARIC, CHS) ‐CERA, Melbourne Retinal vessel measurement ‐Validation as epidemiological tool ‐Brief history of technology ‐Retinal arteriolar signs predict various vascular diseases Application of retinal vessel measurement to retinal diseases ‐Diabetic retinopathy, retinal vascular occlusive disorders, uveitis, age‐related macular degeneration, glaucoma ‐Response to treatment (laser, VEGF inhibitors) Exploration of vessel measurement as a vascular test ‐Retinal microvascular evaluation to predict systemic disease Challenges regarding vessel measurement Conclusion

Advances in the detection of the retinal vasculature

Abstract Purpose: The detection and measurement of retinal vessels is discussed. Methods: A model based on fitting “ribbon of twin” active contour models, that sandwich the vessel edges between contours pulled together by forces, is used. The use of these twins, with a constraining force maintaining approximate vessel width, serves to avoid errors instituted by a variety of noise sources. Results: The method detects vessel segments with high reliability, and is able to measure the vessel width to within sub‐pixel accuracy. We present results comparing the performance with reference standard measurements constructed by a number of human assessors. Conclusions: Retinal vascular measurements are potentially extremely useful in the diagnosis of a number of disease.

Association of Retinal Vessel Caliber to Optic Disc and Cup Diameters

To investigate whether optic disc size is related to retinal venule and arteriole diameters. The population of Beaver Dam, Wisconsin, aged 43 to 86 years were invited to participate in a baseline examination from 1988 to 1990. During this examination, photographs, centered on the optic discs, were taken after pupil dilation. Optic discs and cups were measured from stereoscopic photographs, whereas retinal vessel measurements were taken from a single digitized photograph. Central retinal vein and central retinal arterial equivalents were subsequently calculated. Data for 3887 right eyes are included in the analyses. Narrower retinal venules and arterioles were found in the smaller optic discs controlling for optic cup diameter as well as age, systolic and diastolic blood pressure, refraction, and sex. Central retinal artery equivalents ranged from 156.04 +/- 16.82 microm in the smallest optic disc category to 165.93 +/- 15.17 microm in the larger disc category (P < 0.001). Central retinal vein equivalents ranged from 228.93 +/- 21.26 microm in the smallest to 243.18 +/- 22.32 microm in the larger disc categories (P < 0.001). The significant reduction in retinal vessel diameters was only apparent for the smallest optic disc sizes. A reduction in retinal vessel diameters was less consistent and not significant for small optic cup sizes. Smallest optic discs were associated with smaller central retinal artery and central retinal vein diameters. This anatomic relationship may be useful as an additional associated indicator for nonarteritic anterior ischemic optic neuropathy as well as for retinal vascular events.