Comparison of Two Spectral-domain Optical Coherence Tomography Scan Modes for Measuring Retinal Vessel Diameter.

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.

The entry point of the central retinal artery into the outer meningeal sheath of the optic nerve.

INTRODUCTION: The entry point of the central retinal artery (CRA) into the outer meningeal sheath of the optic nerve posterior to the globe has been studied and debated for more than one hundred years. The authors have supervised an orbital anatomy course for more than two decades. This article summarizes previous studies of the CRA and presents the results of dissections of 67 orbits. MATERIALS AND METHODS: Heads were hemisected prior to dissection at the Vagelos College of Physicians and Surgeons of Columbia University. The authors measured the entry point of the CRA with a caliper and noted the meridional orientation of the CRA. RESULTS: The mean entry point was 10.65 mm posterior to the globe, with a range of 5 to 18 mm. Most commonly, the CRA entered the sheath in the inferior meridian, but some entered slightly inferomedially or inferolaterally. CONCLUSIONS: The entry point of the CRA into the sheath of the optic nerve is variable, and without detailed angiography the clinician cannot know the course of the CRA prior to performing invasive intraorbital procedures. Knowledge of common variations in CRA entry into the outer meningeal sheath of the optic nerve should help to minimize injury during surgery.

Retinal vessel diameter changes after 6 months of treatment in the Idiopathic Intracranial Hypertension Treatment Trial.

BACKGROUND/AIMS: Prior studies support an association between increased retinal venule diameter and elevated intracranial pressure (ICP). The purpose of this study was to test the hypothesis that retinal venule diameters decrease in association with long-term therapy for high ICP in subjects with idiopathic intracranial hypertension (IIH). METHODS: This is a retrospective analysis of multicentre randomised controlled trial data. Standardised procedures were used to measure area of optic nerve head elevation (ONHA) and diameters of 4 arterioles and 4 venules 2.7 mm from the optic disc centre on fundus photos collected at baseline and after 6 months of randomised treatment with placebo+diet or acetazolamide+diet in subjects participating in the IIH Treatment Trial (IIHTT) (n=115). Change in arteriole (Da) and venule (Dv) diameters from baseline to 6 months was studied as a function of IIH, haemodynamic and demographic variables. RESULTS: Dv decreased following 6 months of therapy (8.1 µm, 5.9%, p<0.0005) but Da did not change. Dv change was associated with ONHA change (p<0.0005, r=0.47) and this association persisted in multiple variable models. CONCLUSIONS: Retinal venule diameter decreased, and arteriole diameter did not change in association with treatment for elevated ICP with a weight loss intervention and placebo or acetazolamide in IIHTT participants. Further study is needed to determine how retinal vessel measurements can be combined with other clinical observations to inform disease management.

Microsurgical Anatomy of the Central Retinal Artery.

BACKGROUND: The central retinal artery (CRA) has been described as one of the first branches of the ophthalmic artery.It arises medial to the ciliary ganglion and after a sinuous path within the orbital cavity it penetrates the lower surface of the dura mater that covers the optic nerve, approximately 1 cm behind the eyeball. However, the numerous anatomic descriptions that were made of the CRA have been insufficient or unclear in relation to certain characteristics that are analyzed in the present study. METHODS: An electronic literature search was made in the PubMed database and a cadaver dissection was performed on 11 orbits fixed in formaldehyde. RESULTS: Results were obtained regarding the source, collateral branches, curves, direction, length of the optic nerve, dural perforation site, distance, path and relations, diameter, and area of the central artery of the retina. CONCLUSIONS: Our anatomic study innovates in 2 aspects of the CRA: area and curves. Not only was there a simple count of the number of curves, but it also analyzed the angle presented by each of the curves based on photos obtained in high definition, with a digital program to reduce the margin of error. These curvatures of the CRA were classified according to their spatial disposition within the orbital cavity based on a pattern that was easy to understand. Data were obtained from the area of the CRA on the penetration of the CRA into the dural sheath of the optic nerve.

Differentiating Veins From Arteries on Optical Coherence Tomography Angiography by Identifying Deep Capillary Plexus Vortices.

PURPOSE: To introduce a simple method for differentiating retinal veins from arteries on optical coherence tomography angiography (OCTA). DESIGN: Cross-sectional pilot study. METHODS: Four default en face slabs including color depth encoded, grayscale full-thickness retina, superficial plexus, and deep capillary plexus (DCP) from nine 3×3-mm and nine 6×6-mm OCTA scans were exported and aligned. Nine ophthalmologists with minimum OCTA experience from 2 eye institutions were instructed to classify labeled vessels as arteries or veins in 3 stages. Classification was performed based on graders' own assessment at stage 1. Graders were taught that a capillary-free zone was an anatomic feature of arteries at stage 2 and were trained to identify veins originating from vortices within the DCP at stage 3. Grading accuracy was analyzed and correlated with grading time and graders' years in practice. RESULTS: Overall grading accuracy in stages 1, 2, and 3 was (50.4% ± 17.0%), (75.4% ± 6.0%), and (94.7% ± 2.6%), respectively. Grading accuracy for 3×3-mm scans in stages 1, 2, and 3 was (49.9% ± 16.3%), (79.2% ± 9.6%), and (96.9% ± 3.1%), respectively. Accuracy for 6×6-mm scans in stages 1, 2, and 3 was (51.4% ± 20.8%), (72.3% ± 7.9%), and (93.2% ± 3.3%), respectively. Grading performance improved significantly at each stage (all P < .001). No significant correlation was found between accuracy and time spent grading or between accuracy and years in practice (r = -0.164 to 0.617, all P ≥ .077). CONCLUSIONS: We describe a simple method for accurately distinguishing retinal arteries from veins on OCTA, which incorporates the use of vortices in the DCP to identify venous origin.

Comparisons Between Histology and Optical Coherence Tomography Angiography of the Periarterial Capillary-Free Zone.

PURPOSE: To use the capillary-free zone along retinal arteries, a physiologic area of superficial avascularization, as an anatomic paradigm to investigate the reliability of optical coherence tomography angiography (OCTA) for visualizing the deep retinal circulation. DESIGN: Validity analysis and laboratory investigation. METHODS: Five normal human donor eyes (mean age 69.8 years) were perfusion-labeled with endothelial antibodies and the capillary networks of the perifovea were visualized using confocal scanning laser microscopy. Regions of the capillary-free zone along the retinal artery were imaged using OCTA in 16 normal subjects (age range 24-51 years). Then, 3 × 3-mm scans were acquired using the RTVue XR Avanti (ver. 2016.1.0.26; Optovue, Inc, Fremont, California, USA), PLEX Elite 9000 (ver. 1.5.0.15909; Zeiss Meditec, Inc, Dublin, California, USA), Heidelberg Spectralis OCT2 (Family acquisition module 6.7.21.0; Heidelberg Engineering, Heidelberg, Germany), and DRI-OCT Triton (Ver. 1.1.1; Topcon Corp, Tokyo, Japan). Images of the superficial plexus, deep vascular plexus, and a slab containing all vascular plexuses were generated using manufacturer-recommended default settings. Comparisons between histology and OCTA were performed. RESULTS: Histologic analysis revealed that the capillary-free zone along the retinal artery was confined to the plane of the superficial capillary plexus and did not include the intermediate and deep capillary plexuses. Images derived from OCTA instruments demonstrated a prominent capillary-free zone along the retinal artery in slabs of the superficial plexus, deep plexus, and all capillary plexuses. The number of deep retinal capillaries seen in the capillary-free zone was significantly greater on histology than on OCTA (P < .001). CONCLUSION: Using the capillary-free zone as an anatomic paradigm, we show that the deep vascular beds of the retina are not completely visualized using OCTA. This may be a limitation of current OCTA techniques.

Carotid stiffness is significantly correlated with wall-to-lumen ratio of retinal arterioles.

BACKGROUD AND PURPOSE: Wall-to-lumen ratio of retinal arterioles (W/L ratio) might serve as an in-vivo parameter of microvascular damage. No study has investigated the relationship between carotid stiffness and W/L ratio of retinal arteries. Therefore, the aim of the current study was to assess the correlation between local carotid stiffness, as assessed by echotracking technique, and W/L ratio of retinal arterioles, as assessed by noninvasive flowmetry in normotensive patients and in patients with primary hypertension. METHODS: Two hundred and twenty-seven patients underwent renal arteries W/L ratio and local carotid-pulse wave velocity (carotid PWV) measurement. One hundred and fifteen patients had a diagnosis of primary hypertension, whereas 112 were normotensive patients. RESULTS: W/L ratio and carotid PWV were both related with clinic SBP (r = 0.17, P < 0.05; r = 0.50, P < 0.001), clinic pulse pressure (r = 0.22, P < 0.001; r = 0.55, P < 0.001), carotid SBP (r = 0.18, P < 0.05; r = 0.51, P < 0.001) and carotid pulse pressure (r = 0.24, P < 0.001; r = 0.56, P < 0.001). W/L ratio was correlated with carotid PWV (r = 0.18, P < 0.005). At multivariate analysis, carotid PWV remained independently associated with W/L ratio. CONCLUSION: In hypertensive and normotensive patients, carotid stiffness is significantly correlated with W/L ratio of retinal arteries, independently of possible confounders.

Ametropia, retinal anatomy, and OCT abnormality patterns in glaucoma. 1. Impacts of refractive error and interartery angle.

Retinal nerve fiber layer thickness (RNFLT) measured by optical coherence tomography (OCT) is widely used in clinical practice to support glaucoma diagnosis. Clinicians frequently interpret peripapillary RNFLT areas marked as abnormal by OCT machines. However, presently, clinical OCT machines do not take individual retinal anatomy variation into account, and according diagnostic biases have been shown particularly for patients with ametropia. The angle between the two major temporal retinal arteries (interartery angle, IAA) is considered a fundamental retinal ametropia marker. Here, we analyze peripapillary spectral domain OCT RNFLT scans of 691 glaucoma patients and apply multivariate logistic regression to quantitatively compare the diagnostic bias of spherical equivalent (SE) of refractive error and IAA and to identify the precise retinal locations of false-positive/negative abnormality marks. Independent of glaucoma severity (visual field mean deviation), IAA/SE variations biased abnormality marks on OCT RNFLT printouts at 36.7%/22.9% of the peripapillary area, respectively. 17.2% of the biases due to SE are not explained by IAA variation, particularly in inferonasal areas. To conclude, the inclusion of SE and IAA in OCT RNFLT norms would help to increase diagnostic accuracy. Our detailed location maps may help clinicians to reduce diagnostic bias while interpreting retinal OCT scans.

Shiftwork and the Retinal Vasculature Diameters Among Police Officers.

OBJECTIVE: To investigate associations of central retinal arteriolar equivalent (CRAE), a measure of retinal arteriolar width, and central retinal venular equivalents (CRVE), a measure of retinal venular width, with shiftwork in 199 police officers (72.9% men). METHODS: Shiftwork (day, afternoon, night) was assessed using electronic payroll records. Four digital retinal images per officer were taken. Mean diameters of the retinal vasculature were compared across shifts using analysis of variance (ANOVA)/analysis of covariance (ANCOVA). RESULTS: Among all officers (mean age = 46.6 ±â€Š6.8 years), shiftwork was not significantly associated with CRAE or CRVE. However, among current and former smokers, night-shift officers had a wider mean (±standard error [SE]) CRVE (230.0 ±â€Š4.5 µm) compared with day shift officers (215.1 ±â€Š3.5 µm); adjusted P = 0.014. CONCLUSIONS: Night shift schedule in current and former smokers is associated with wider retinal venules. Reasons for this association are not known. Longitudinal studies are warranted.

Inter-Relationship of Arterial Supply to Human Retina, Choroid, and Optic Nerve Head Using Micro Perfusion and Labeling.

Purpose: The prevailing view is that the human retina is supplied by the central retinal artery (CRA), the short posterior ciliary arteries (SPCAs) support the choroid, and both the CRA and the SPCAs are so-called "end artery" systems. In this study, we investigate whether vascular connections among the retina, choroid, and the optic nerve head (ONH) exist, using selective cannulation and microperfusion-labeling techniques. Methods: The CRA and/or one or more of the SPCAs were selected for cannulation in 18 human donor eyes. Fluorescent probes with different excitation wavelengths were perfused through different arteries on the same eye to distinguish the supply sources of different vascular beds. After labeling and fixation, the ONH region was dissected either longitudinally or transversely as thick sections for confocal microscopy. Retina, choroid, and ONH were imaged from whole-mount specimens. Results: Probes perfused through the CRA or the SPCA alone labeled the microvessels in the retina, choroid, and ONH regions, as well as the optic nerve trunk. The vessels of the lamina cribrosa and the optic nerve trunk were labeled when probes were perfused through the SPCA. Perfusion through both the CRA and SPCA produced double labeling of vessels in the retina, the choroid, and the ONH. Conclusions: The results indicate an inter-relationship of arterial supply to the retina, choroid, and ONH in the human eye. This has important implications in understanding clinical observations and disease mechanisms such as that of glaucoma and ischemic optic nerve disease.

Retinal Vascular Branching in Healthy and Diabetic Subjects.

Purpose: To measure the effect of nonproliferative diabetic retinopathy (NPDR) on retinal branching. To compare vascular branching in healthy and diabetic subjects with established biophysical models. Methods: Vascular bifurcations in arteries and veins were imaged in 17 NPDR and 26 healthy subjects with the Indiana adaptive optics scanning laser ophthalmoscope (AOSLO). Vessel measurements were grouped according to parent vessel diameters into large (≤50 ∼ <100 µm) and small (≤20 ∼ <50 µm) sizes. Vessel diameters and bifurcation angles were measured manually. Vascular diameters were compared with predictions of Murray's law using curve fitting. For analysis of bifurcation angles, two models from Zamir were compared: one based on the power required for blood pumping, the other based on drag force between blood and vascular wall. Results: For normal larger vessels, the exponent relating the parent and daughter branching diameters was significantly less than the value of 3 predicted by Murray's law (arteries: 2.59; veins: 1.95). In NPDR, the best-fit exponent was close to 3 for arteries but close to 2 in healthy subjects in veins, (arteries: 3.09; veins: 2.16). For both small arteries and veins, diabetics' exponent differed from healthy subjects (P < 0.01). Bifurcation angles in the healthy subjects (78° ± with a standard error (SE) of 0.9°) were not much different than in NPDR (79° ± SE 1.3°). The model based on minimizing pumping power predicted the measurements better than the one minimizing the vascular drag and lumen surface area. Conclusions: The relation between parent and daughter branch diameters changes in diabetes, but the branching angles do not.

Live imaging of primary ocular vasculature formation in zebrafish.

Ocular vasculature consists of the central retinal and ciliary vascular systems, which are essential to maintaining visual function. Many researchers have attempted to determine their origins and development; however, the detailed, stepwise process of ocular vasculature formation has not been established. In zebrafish, two angioblast clusters, the rostral and midbrain organizing centers, form almost all of the cranial vasculature, including the ocular vasculature, and these are from where the cerebral arterial and venous angioblast clusters, respectively, differentiate. In this study, we first determined the anatomical architecture of the primary ocular vasculature and then followed its path from the two cerebral angioblast clusters using a time-lapse analysis of living Tg(flk1:EGFP)k7 zebrafish embryos, in which the endothelial cells specifically expressed enhanced green fluorescent protein. We succeeded in capturing images of the primary ocular vasculature formation and were able to determine the origin of each ocular vessel. In zebrafish, the hyaloid and ciliary arterial systems first organized independently, and then anastomosed via the inner optic circle on the surface of the lens by the lateral transfer of the optic vein. Finally, the choroidal vascular plexus formed around the eyeball to complete the primary ocular vasculature formation. To our knowledge, this study is the first to report successful capture of circular integration of the optic artery and vein, lateral transfer of the optic vein to integrate the hyaloidal and superficial ocular vasculatures, and formation of the choroidal vascular plexus. Furthermore, this new morphological information enables us to assess the entire process of the primary ocular vasculature formation, which will be useful for its precise understanding.

Pattern of omega-3 polyunsaturated fatty acid intake and fish consumption and retinal vascular caliber in children and adolescents: A cohort study.

We aimed to investigate whether fish and long chain omega-3 polyunsaturated fatty acid (LCn-3 PUFA) consumption changed appreciably during adolescence. We also assessed whether these dietary variables are associated with retinal microvascular signs (possible markers of future cardiovascular disease risk). 633 children had dietary data at ages 12 and 17. Fish and LCn-3 PUFA [eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA)] intake was assessed by a food frequency questionnaire. Retinal vessel caliber was quantified from digital photographs using computer software. Mean energy-adjusted intakes (mg/day) of total LCn-3 PUFA, EPA, and DHA at age 12 were 297.1±261.1; 102.5±106.9; and 129.7±137.7, respectively; and this increased significantly at age 17 to: 347.0±324.0 (p<0.0001); 122.5±132.7 (p = 0.0001); and 160.3±171.4 (p <0.0001), respectively. Increasing quartiles of LCn-3PUFA intake were associated with widening of mean retinal arteriolar caliber among 17-year old girls ~3.9 µm (multivariable-adjusted P-trend = 0.001). Girls who consumed ≥2 serves of fish/week versus those who did not had ~2.1 µm wider retinal arterioles (p = 0.03). No associations were observed among boys or with retinal venules. Mean dietary intakes of LCn-3 PUFA increased during adolescence, but are still below recommended levels of consumption. These results suggest that LCn-3 PUFA and fish intake might have a beneficial influence.

Correlations Between Retinal Nerve Fiber Layer Thickness and Axial Length, Peripapillary Retinal Tilt, Optic Disc Size, and Retinal Artery Position in Healthy Eyes.

PURPOSE: To determine the correlations between the retinal nerve fiber layer thickness (RNFLT) and the axial length, peripapillary retinal tilt (PRT), and optic disc size, and retinal artery position. METHODS: A prospective, observational cross-sectional study of 119 healthy right eyes of 119 volunteers. All participants underwent comprehensive ophthalmologic examinations including peripapillary RNFLT imaging and measurements of the axial length. The RNFLT was determined by the TOPCON 3D OCT-1000, MARK II. The RNFLT in a 3.4 mm circular scan was divided into 12 clock-hour sectors and 4 quadrant sectors around the optic disc. The PRT was assessed using the RNFLT B-scan images. The angle between the supra-temporal and infra-temporal retinal arteries was determined in the color fundus photographs. The correlations between the sectorial RNFLTs and the axial length, PRT, optic disc size, and artery angles were determined by simple and multiple regression analyses. RESULTS: Multiple regression analyses showed that the nasal and inferior quadrants and the whole RNFLT were significantly and negatively correlated with the axial length (standardized coefficient (SC)=-0.39 to -0.30, P<0.05). The PRT was significantly and positively associated with all of the quadrants and the whole RNFLT (SC=0.22 to 0.45, P<0.05). The retinal artery angle was significantly and negatively associated with the temporal RNFLT and positively associated with inferior RNFLT (SC=-0.49 to 0.31, P<0.05). The optic disc size was significantly and positively associated with the superior and nasal quadrants, and the whole RNFLT (SC=0.20 to 0.27, P<0.05). CONCLUSIONS: The axial length, PRT, optic disc size, retinal artery angle can affect the peripapillary RNFLT. These variables should be considered when assessing the peripapillary RNFLT.

An Anatomical Analysis of the Supratrochlear Artery: Considerations in Facial Filler Injections and Preventing Vision Loss.

BACKGROUND: Embolia cutis medicamentosa (ECM) is a rare phenomenon attributed to intra-arterial drug injection. Glabellar filler injections can result in potentially devastating visual loss from inadvertent retrograde arteriolar embolization due to the extensive vasculature within the upper face. The minimum amount of filler necessary to potentiate this complication has not yet been reported. OBJECTIVES: We aim to determine the volume of filler necessary to occupy the supratrochlear artery from the glabella to the bifurcation of the ophthalmic and central retinal arteries. We specifically examine the volume of the supratrochlear artery from the glabella to orbital apex. METHODS: The study was approved by Duke University Institutional Review Board and involved surgical dissection of six fresh tissue cadaver heads (12 hemifaces). The arterial system in each cadaver head was injected with latex for visualization. The supratrochlear arteries were isolated anteriorly from the glabella to the orbital apex posteriorly. Intra-orbital vessel radius and length were measured. The vessel volume was calculated by water displacement of the intra-arterial latex. RESULTS: The vessel volumes ranged from 0.04 to 0.12 mL. The average vessel volume was calculated as 0.085 mL, the average length as 51.75 mm, and the average radius as 0.72 mm. CONCLUSIONS: Vascular occlusion from filler injections can lead to devastating visual consequences due to inadvertent retrograde intra-arterial embolization. Our findings indicate that the average entire volume of the supratrochlear artery from the glabella to the orbital apex is 0.085 mL. Injectors should be aware that a bolus of this critical volume may lead to a significant adverse outcome.

Human Vision-Motivated Algorithm Allows Consistent Retinal Vessel Classification Based on Local Color Contrast for Advancing General Diagnostic Exams.

PURPOSE: Abnormalities of blood vessel anatomy, morphology, and ratio can serve as important diagnostic markers for retinal diseases such as AMD or diabetic retinopathy. Large cohort studies demand automated and quantitative image analysis of vascular abnormalities. Therefore, we developed an analytical software tool to enable automated standardized classification of blood vessels supporting clinical reading. METHODS: A dataset of 61 images was collected from a total of 33 women and 8 men with a median age of 38 years. The pupils were not dilated, and images were taken after dark adaption. In contrast to current methods in which classification is based on vessel profile intensity averages, and similar to human vision, local color contrast was chosen as a discriminator to allow artery vein discrimination and arterial-venous ratio (AVR) calculation without vessel tracking. RESULTS: With 83% ± 1 standard error of the mean for our dataset, we achieved best classification for weighted lightness information from a combination of the red, green, and blue channels. Tested on an independent dataset, our method reached 89% correct classification, which, when benchmarked against conventional ophthalmologic classification, shows significantly improved classification scores. CONCLUSIONS: Our study demonstrates that vessel classification based on local color contrast can cope with inter- or intraimage lightness variability and allows consistent AVR calculation. We offer an open-source implementation of this method upon request, which can be integrated into existing tool sets and applied to general diagnostic exams.

Reliability of retinal vessel calibre measurements using a retinal oximeter.

BACKGROUND: Summarised retinal vessel diameters are linked to systemic vascular pathology. Monochromatic images provide best contrast to measure vessel calibres. However, when obtaining images with a dual wavelength oximeter the red-free image can be extracted as the green channel information only which in turn will reduce the number of photographs taken at a given time. This will reduce patient exposure to the camera flash and could provide sufficient quality images to reliably measure vessel calibres. METHODS: We obtained retinal images of one eye of 45 healthy participants. Central retinal arteriolar and central retinal venular equivalents (CRAE and CRVE, respectively) were measured using semi-automated software from two monochromatic images: one taken with a red-free filter and one extracted from the green channel of a dual wavelength oximetry image. RESULTS: Participants were aged between 21 and 62 years, all were normotensive (SBP: 115 (12) mmHg; DBP: 72 (10) mmHg) and had normal intra-ocular pressures (12 (3) mmHg). Bland-Altman analysis revealed good agreement of CRAE and CRVE as obtained from both images (mean bias CRAE = 0.88; CRVE = 2.82). CONCLUSIONS: Summarised retinal vessel calibre measurements obtained from oximetry images are in good agreement to those obtained using red-free photographs.

NEW INSIGHT INTO THE MACULAR DEEP VASCULAR PLEXUS IMAGED BY OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY.

PURPOSE: To describe the macular deep capillary plexus (DCP) in normal eyes using optical coherence tomography angiography. METHODS: Retrospective study including 41 consecutive normal eyes imaged using optical coherence tomography angiography (RTVue XR Avanti; Optovue Inc). Default autosegmentation of the superficial capillary plexus (SCP) and DCP, and manual adjustments of "deep settings" were used to analyze the organization of the normal macular microvascularization and to investigate in vivo the connection between these capillary networks. RESULTS: Mean age was 31 years (range, 22-55 years). The SCP and DCP had 2 different organizations, but the plexus autosegmentation was imperfect: In 68% of cases, the image of the SCP variably superimposed on the DCP, interfering with its analysis. The SCP was composed on average of 7 pairs of arterioles and venules obvious on each 3-mm × 3-mm optical coherence tomography angiography scanning area. The DCP was composed of a capillary vortex arrangement, whose centers were aligned along the course of the macular superficial venules. CONCLUSION: The SCP and DCP had two different topographic organizations. The pattern of the capillary units converging into capillary vortexes highly suggests that they drain into the superficial venules. The different structural properties of the SCP and DCP could explain the differences in flow resistance and perfusion.

Comparison of Two Formulas Used to Calculate Summarized Retinal Vessel Calibers.

PURPOSE: To compare the Parr-Hubbard and Knudtson formulas to calculate retinal vessel calibers and to examine the effect of omitting vessels on the overall result. METHODS: We calculated the central retinal arterial equivalent (CRAE) and central retinal venular equivalent (CRVE) according to the formulas described by Parr-Hubbard and Knudtson including the six largest retinal arterioles and venules crossing through a concentric ring segment (measurement zone) around the optic nerve head. Once calculated, we removed one arbitrarily selected artery and one arbitrarily selected vein and recalculated all outcome parameters again for (1) omitting one artery only, (2) omitting one vein only, and (3) omitting one artery and one vein. All parameters were compared against each other. RESULTS: Both methods showed good correlation (r 2for CRAE = 0.58; r2 for CRVE = 0.84), but absolute values for CRAE and CRVE were significantly different from each other when comparing both methods (p < 0.000001): CRAE had higher values for the Parr-Hubbard (165 [± 16] µm) method compared with the Knudtson method (148 [± 15] µm). In addition, CRAE and CRVE values dropped for both methods when omitting one arbitrarily selected vessel each (all p < 0.000001). Arteriovenous ratio (AVR) calculations showed a similar change for both methods when omitting one vessel each: AVR decreased when omitting one arteriole whereas it increased when omitting one venule. No change, however, was observed for AVR calculated with six or five vessel pairs each. CONCLUSIONS: Although the absolute value for CRAE and CRVE is changing significantly depending on the number of vessels included, AVR appears to be comparable as long as the same number of arterioles and venules is included.

Retinal Artery-Vein Classification via Topology Estimation.

We propose a novel, graph-theoretic framework for distinguishing arteries from veins in a fundus image. We make use of the underlying vessel topology to better classify small and midsized vessels. We extend our previously proposed tree topology estimation framework by incorporating expert, domain-specific features to construct a simple, yet powerful global likelihood model. We efficiently maximize this model by iteratively exploring the space of possible solutions consistent with the projected vessels. We tested our method on four retinal datasets and achieved classification accuracies of 91.0%, 93.5%, 91.7%, and 90.9%, outperforming existing methods. Our results show the effectiveness of our approach, which is capable of analyzing the entire vasculature, including peripheral vessels, in wide field-of-view fundus photographs. This topology-based method is a potentially important tool for diagnosing diseases with retinal vascular manifestation.