Search

Purpose : To assess the agreement between Line 3-5 raster scan mode and circular scan mode for measuring retinal vessel diameter, and to analyze the influence of scanning distance on retinal vessel diameter and agreement. Methods : 79 healthy participants (79 eyes) were scanned with two modes. The scanning distance was defined as the distance from the center of the optic disc to the intersection of the blood vessel and the scan line on the raster image. The large superior temporal vessel was measured, with the distance between vascular wall hyperreflectivities measured to obtain vessel diameters. The degree of agreement between the line 3-5 raster scan and circular scan modes, and the effect of scanning distance on agreement and vascular diameter were assessed. Results : There was good agreement between line 3 subgroup and the circular scan for measuring venous and arterial diameter (venous: intraclass correlation coefficients (ICCs) = 0.87, p < .001; arterial: ICCs = 0.84, p < .001). Unexpectedly, diameters from the fourth raster scan were only comparable to the circular scan in measuring venous diameter (ICCs = 0.86, p < .001), despite the same scanning distance between the fourth raster line and circular scan. Vessels with a scanning distance between 1400 μm - 1799 μm showed good agreement with the circular scan (venous and arterial: all ICCs ≥ 0.84, p < .001). In addition, venous diameter and arterial diameter decreased with increasing distance from the optic disc center, with venous and arterial diameter decreasing by 0.02 μm/μm ( p < .001) and 0.007 μm/μm ( p = .02), respectively. Conclusion : Arterial and venous diameter measured by the circular mode was comparable to only one scan line and two scan lines of the raster scan mode, respectively. Our study identified a difference between the two scan modes, with the difference not fully attributable to differences in scanning distance. Prospective studies reporting vascular diameter as a primary outcome should report the scan mode used.

Purpose: Little data exist detailing the normal cup-to-disc (CD) ratios and arteriole-to-venule (A/V) ratios of school age children. In addition, controversy exists in the literature regarding associations between CD and A/V ratios and visual and biometric parameters. The present study investigates the success rates of obtaining useable optic disc images from the portable Nidek Handheld Non-Mydriatic Fundus Camera (NM-200D) from school-age children and describes the distribution of CD ratios and A/V ratios in children aged 6-7 years of age and 12-13 years of age. In addition, the present study explores associations between CD and A/V ratios and a range of visual function and biometric parameters in children., Methods: Fundus images were obtained from 195 6-7 year old children and 227 12-13 year old children participating in a wider study of visual function in childhood (Northern Ireland Childhood Errors of Refraction Study or NICER). ImageJ software was used to obtain CD and A/V ratios from the digital images. Visual function measures and biometric parameters were also available for all participants including; cycloplegic refractive error, vision, corneal curvature, axial length, height and weight., Results: One hundred and eighty fundus images (92.3%) from the 6-7 year olds and 194 images (85.5%) from the 12-13 year olds children were considered useable. Analysis (one way anova) demonstrated statistically significant differences between CD ratios and A/V ratios between the age groups. Participants aged 12-13 years had larger CD ratios and smaller A/V ratios (mean CD ratio 0.37 ± 0.09, mean A/V ratio 0.75 ± 0.10) than 6-7 year old participants (mean CD ratio 0.30 ± 0.09, mean A/V ratio 0.78 ± 0.12). No significant associations were noted between CD ratios and A/V ratio and any visual, ocular or biometric parameters., Conclusions: The present study provides novel normative data on CD and A/V ratios in UK school age children for clinicians in practice., (Ophthalmic & Physiological Optics © 2011 The College of Optometrists.)

A decreased ratio of the width of retinal arteries to veins [arteriolar-to-venular diameter ratio (AVR)], is well established as predictive of cerebral atrophy, stroke and other cardiovascular events in adults. Tortuous and dilated arteries and veins, as well as decreased AVR are also markers for plus disease in retinopathy of prematurity. This work presents an automated method to estimate the AVR in retinal color images by detecting the location of the optic disc, determining an appropriate region of interest (ROI), classifying vessels as arteries or veins, estimating vessel widths, and calculating the AVR. After vessel segmentation and vessel width determination, the optic disc is located and the system eliminates all vessels outside the AVR measurement ROI. A skeletonization operation is applied to the remaining vessels after which vessel crossings and bifurcation points are removed, leaving a set of vessel segments consisting of only vessel centerline pixels. Features are extracted from each centerline pixel in order to assign these a soft label indicating the likelihood that the pixel is part of a vein. As all centerline pixels in a connected vessel segment should be the same type, the median soft label is assigned to each centerline pixel in the segment. Next, artery vein pairs are matched using an iterative algorithm, and the widths of the vessels are used to calculate the AVR. We trained and tested the algorithm on a set of 65 high resolution digital color fundus photographs using a reference standard that indicates for each major vessel in the image whether it is an artery or vein. We compared the AVR values produced by our system with those determined by a semi-automated reference system. We obtained a mean unsigned error of 0.06 (SD 0.04) in 40 images with a mean AVR of 0.67. A second observer using the semi-automated system obtained the same mean unsigned error of 0.06 (SD 0.05) on the set of images with a mean AVR of 0.66. The testing data and reference standard used in this study has been made publicly available.

Purpose: To evaluate the reproducibility of ImageJ software in analyzing the color of the optic disc., Methods: One hundred twelve normal participants (56 males and 56 females) were enrolled in this study. The image of the optic disc was taken using Kowa digital disc photo-graphy, and the gray scales of the nasal rim (NR), brightest cupping center (BCC) and largest inferior retinal vein (IRV) were calculated using histogram in ImageJ. Three different observers calculated the gray scales three separate times. Reproducibility was assessed using the interclass correlation coefficient (ICC)., Results: The mean age of the participants was 50.6 years old (range, 11 to 82 years). The mean gray scales of the nasal rim were 91.81, 94.91, and 93.24; those of the brightest cupping center were 174.84, 179.94, and 177.76; and those of the largest inferior retinal vein were 61.85, 53.48, and 56.73 for observers 1, 2, and 3, respectively. Inter-observer reproducibility for NR, BCC and IRV was considered good based upon ICC values of 0.944, 0.860, and 0.789 for observers 1, 2, and 3, respectively. Significant age-related differences between the values of the brightest cupping center were noted, and the gray scale score was decreased in the older participants (p < 0.001)., Conclusions: The gray scale of the brightest cupping center diminished with age. ImageJ can be a useful objective tool with high reproducibility in the analysis of optic disc color.

Purpose: To determine if adjusting for blood vessel (BV) location can decrease the intersubject variability of retinal nerve fiber layer (RNFL) thickness measured with optical coherence tomography (OCT)., Subjects and Methods: One eye of 50 individuals with normal vision was tested with OCT and scanning laser polarimetry (SLP). The SLP and OCT RNFL thickness profiles were determined for a peripapillary circle 3.4 mm in diameter. The midpoints between the superior temporal vein and artery (STva) and the inferior temporal vein and artery (ITva) were determined at the location where the vessels cross the 3.4 mm circle. The average OCT and SLP RNFL thicknesses for quadrants and arcuate sectors of the lower and upper optic disc were obtained before and after adjusting for BV location. This adjustment was carried out by shifting the RNFL profiles based upon the locations of the STva and ITva relative to the mean locations of all 50 individuals., Results: Blood vessel locations ranged over 39 (STva) and 33 degrees (ITva) for the 50 eyes. The location of the leading edge of the OCT and SLP profiles was correlated with the location of the BVs for both the superior [r=0.72 (OCT) and 0.72 (SLP)] and inferior [r=0.34 and 0.43] temporal vessels. However, the variability in the OCT and SLP thickness measurements showed little change due to shifting. After shifting, the difference in the coefficient of variation ranged from -2.1% (shifted less variable) to +1.7% (unshifted less variable)., Conclusions: The shape of the OCT and SLP RNFL profiles varied systematically with the location of the superior and inferior superior veins and arteries. However, adjusting for the location of these major temporal BVs did not decrease the variability for measures of OCT or SLP RNFL thickness.

Purpose: To describe the normal physiological relationship between retinal arteriolar and venular caliber and retinal nerve fiber layer (RNFL), macular, and optic nerve head parameters., Methods: The Sydney Childhood Eye Study assessed 2038 adolescents aged 12 years. Retinal vessel calibers were measured from digital fundus photographs using standardized protocols. Optical coherence tomography measurements of RNFL, macular, and optic nerve head parameters were obtained with the Fast-scan protocol of the Stratus OCT (Carl Zeiss Meditec, Inc., Dublin, CA). Mixed model analyses were performed., Results: After adjustment for covariates, each micrometer increase in RNFL thickness was associated with a 0.22-microm (0.15%, P < 0.0001) and 0.49-microm (0.23%, P < 0.0001) increase in mean arteriolar and venular caliber, respectively. This positive association existed across all RNFL quadrants (0.07%-0.24%, P

The mammalian eye is a remarkable optical device, but its design is not perfect. The blood vessels that supply the inner retina are located in front of the photoreceptor layer, blocking access to light. Their shadows create a pattern of blindness in the field of vision that corresponds precisely to the location of the largest vessels in the eye. We show here that in squirrel monkeys, focal deprivation by blood vessels leads to rewiring of the eye's geniculocortical projections, imprinting an image of the retinal vascular tree onto the primary visual cortex. This process illustrates vividly that local imbalances in neuronal activity can influence column formation during normal development.

The subject of the blood supply of the optic nerve head (ONH) is reviewed briefly. The circulation of the posterior ciliary artery is the main source of blood supply to the ONH, except for the surface nerve fiber layer which is supplied by the retinal circulation. The blood supply in the ONH is sectoral in nature, which is the reason why there is the sectoral involvement of the ONH in its ischemic disorders. It is essential to understand that the pattern of blood supply in the ONH shows marked interindividual variation, and so consequently does the pattern of visual loss in its ischemic disorders. The venous drainage from the ONH is by the central retinal vein. Reasons for various controversies on the subject are discussed.

The exact anatomy of the central retinal vein as it exits the eye is unknown. In this study serial sections of the central retinal vein and artery in the anterior optic nerve from six globes (five from cornea donors and one exenteration specimen) were examined by image analysis and three-dimensional reconstruction to determine their luminal characteristics. The retinal artery was found to have a uniform perimetric length and cross-sectional area. The vein, however, had a reduction in these measurements at the level of the lamina cribrosa, signifying a constriction of the vessel at this site. In addition, the cross section of the vein usually formed a "D" or crescentic shape adjacent to the circular artery. We propose that the constriction of the vein acts as a "throttle" mechanism on venous blood flow. Thus, a relatively high venous blood pressure is maintained within the high-pressure intraocular environment, thereby maintaining the patency of the retinal venules and capillaries.

Morphologic findings on scanning electron microscopy of vascular cast of the posterior pole in primates are presented. The prelaminar region of the optic disc received the majority of its blood supply from the short posterior ciliary arteries, mainly from direct branches arising from peripapillary arterioles surrounding the optic nerve but also from indirect branches from the peripapillary choroid. The capillaries from this prelaminar region drained directly into the central retinal vein. The peripapillary choriocapillaris was a single layer of anastomosing capillaries supplied by precapillary choroidal arterioles. The peripapillary choriocapillaris was not seen to contribute to the vascular supply of the optic disc. Our results are in general agreement with those of previous scanning electron microscopy studies of the vascular supply of the distal part of the optic nerve.