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.

Characterization of microvascular tortuosity in retinal vein occlusion utilizing optical coherence tomography angiography.

We investigated the characteristics of microvessel tortuosity in branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO) and their associations with visual outcomes using optical coherence tomography angiography (OCTA). Thirty-four BRVO and 21 CRVO patients and 31 healthy subjects were included. From OCTA, the branch number (BN), mean branch length (BL), mean Euclidean length (EL), vessel density (VD) and vessel tortuosity (VT) were quantified. In BRVO eyes, compared with that in the controls, the affected area of the deep capillary plexus (DCP) showed a decreased BN and VD, an increased BL, and unchanged VT. The nonaffected area of the DCP showed decreases in BN, VD and VT. The affected area of the superficial capillary plexus (SCP) showed higher VT. In CRVO eyes, the DCP showed a lower BN, VD and VT, while the SCP showed a lower BN and greater BL and EL. Improved visual acuity (VA) after 1 year in BRVO eyes was associated with decreases in BN, BL, VD and VT in the affected area in the DCP and lower VT in the nonaffected area of the SCP; in CRVO eyes, improved VA was associated with a higher BL and EL in the DCP. VT, BL, and EL may be new microvascular markers associated with changes in VA in BRVO and CRVO.

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.

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.

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.

Medición semiautomática de la relación arteriovenosa retiniana como posible marcador de riesgo de infarto cerebral silente en pacientes hipertensos / Semi-automatic measuring of arteriovenous relation as a possible silent brain infarction risk index in hypertensive patients

PROPÓSITO: Evaluar la utilidad de un sistema semiautomático de medición de relación arteriovenosa (RAV) retiniana sobre imágenes retinográficas de pacientes hipertensos en la valoración del riesgo cardiovascular y la detección de isquemia cerebral silente (ICS). MÉTODO: Un total de 976 pacientes de la cohorte Investigating Silent Strokes in Hypertensives: a magnetic resonance imaging study (ISSYS) estudiados mediante resonancia magnética craneal para valorar la presencia o no de ICS fueron invitados a realizar una retinografía para un examen convencional de fondo de ojo y una medición semitautomática del promedio de los calibres vasculares para el cálculo de la relación arteriovenosa (RAV). RESULTADOS: Se analizaron las retinografías de 768 pacientes. Entre las lesiones observadas, solamente se encontró una asociación con la detección de ICS en aquellos pacientes con microaneurismas (OR: 2,50; IC 95%: 1,05-5,98) o una RAV alterada (<0,666) (OR: 4,22; IC 95%: 2,56-6,96). En el análisis de regresión logística multivariante ajustado por edad y sexo, solamente la RAV alterada continuó manifestándose como un factor de riesgo (OR: 3,70; IC 95%: 2,21-6,18). CONCLUSIONES: Los resultados muestran que el análisis semiautomático de la vasculatura retiniana a partir de retinografías tiene el potencial de ser considerado como un factor de riesgo vascular importante en la población hipertensa

OBJECTIVE: To evaluate the usefulness of a semiautomatic measuring system of arteriovenous relation (RAV) from retinographic images of hypertensive patients in assessing their cardiovascular risk and silent brain ischemia (ICS) detection. METHODS: Semi-automatic measurement of arterial and venous width were performed with the aid of Imedos software and conventional fundus examination from the analysis of retinal images belonging to the 976 patients integrated in the cohort Investigating Silent Strokes in Hypertensives: a magnetic resonance imaging study (ISSYS), group of hypertensive patients. All patients have been subjected to a cranial magnetic resonance imaging (RMN) to assess the presence or absence of brain silent infarct. RESULTS: Retinal images of 768 patients were studied. Among the clinical findings observed, association with ICS was only detected in patients with microaneurysms (OR 2.50; 95% CI: 1.05-5.98) or altered RAV (<0.666) (OR: 4.22; 95% CI: 2.56-6.96). In multivariate logistic regression analysis adjusted by age and sex, only altered RAV continued demonstrating as a risk factor (OR: 3.70; 95% CI: 2.21-6.18). CONCLUSIONS: The results show that the semiautomatic analysis of the retinal vasculature from retinal images has the potential to be considered as an important vascular risk factor in hypertensive population

Phase and amplitude of spontaneous retinal vein pulsations: An extended constant inflow and variable outflow model.

The constant inflow and variable outflow (CIVO) theory correctly predicts that spontaneous pulsation of the retinal veins will be visible close to the point where the vein exits the eye at the lamina cribrosa but will decrease rapidly in amplitude and become too small to see only a short distance upstream. However, the phase of vein oscillation relative to the oscillation of the intraocular pressure (IOP) predicted by CIVO has been unclear and controversial. We show that the CIVO model is indeterminate in predicting such phase relations. We propose a simple extension of the CIVO model that retains its basic equations but applies them to a larger domain that includes not only the intraocular (pre-laminar) portion of the vein but also the retrobulbar (post-laminar) portion of the vein behind the eye. We show that this extended CIVO model makes definite predictions about the phase of vein oscillation relative to the oscillation of IOP. This phase relationship is determined by the relative amplitude and phase of pulsations of the IOP and of the cerebrospinal fluid pressure (CSFP). If IOP and CSFP oscillate in phase, then the pre-laminar vein oscillates in phase with IOP when the amplitude of CSFP exceeds the amplitude of IOP but oscillates in counter phase with IOP when the amplitude of IOP exceeds that of CSFP. These relationships are modified when there is a phase difference between the oscillations of IOP and CSFP. When CSFP leads IOP, the phase of vein oscillation is advanced if the amplitude of CSFP exceeds that of IOP and is delayed if the amplitude of IOP exceeds that of CSFP. The result in each case is that maximum vein size occurs during the rising phase of IOP (ocular systole). We conclude that the driving force of vein oscillation is the difference between the oscillations of IOP and CSFP. The phase of this difference determines the phase relationships above. We show that additional delays in the phase of venous pulsation relative to that of IOP are induced by constriction of the vein within the lamina cribrosa and by recording the vein pulsations upstream from the lamina cribrosa. The amplitude of vein oscillation is proportional to the amplitude of the driving force and to the venous capacitance. Loss of spontaneous retinal vein pulsation with increase in mean CSFP is determined primarily by reduced venous capacitance. Increased amplitude of pulsation may occur when IOP is increased. It is the result of increased venous capacitance and possibly increased driving force of the pulsation. However, in chronic glaucoma the increase in capacitance may be counteracted by venous outflow obstruction, and the increase in driving force may be counteracted by reduced ocular blood flow. As a result retinal vein oscillation may be reduced in amplitude.

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.

Anteroposterior Tortuosity of the Retinal Vein at Arteriovenous Crossings in Healthy Subjects.

PURPOSE: The purpose of this study was to investigate the effects of aging on anteroposterior tortuosity of the retinal vein at the arteriovenous (AV) crossing in healthy subjects. METHODS: We examined 48 eyes of 24 healthy older Japanese subjects (>60 years), and, as controls, 42 eyes of 21 healthy younger Japanese subjects (<30 years). Retinal vein images at the AV crossing were obtained by optical coherence tomography. The depth of the vein was measured vertically from the outer border of the retinal pigment epithelium to the outer vein wall. We defined "m" as the deepest point of the vein at the AV crossing and "M" as the shallowest point. To evaluate the anteroposterior tortuosity of the retinal vein, we calculated the ratio m/M. RESULTS: Mean m, M, and m/M in older subjects were 76.5 ± 13.1 µm, 142.7 ± 21.2 µm, and 0.52 ± 0.09, respectively. In younger control subjects, the values were 64.1 ± 12.6 µm, 139.9 ± 22.4 µm, and 0.46 ± 0.06. The values of "M" were not significantly different between groups, whereas both "m/M" and "m" were significantly (p = 0.021) lower in the older subjects than in the younger subjects. CONCLUSION: Anteroposterior tortuosity of the retinal vein was evaluated based on the maximum and minimum retinal vein depth measurements at the AV crossing using optical coherence tomography. Anteroposterior tortuosity of the retinal vein at the AV crossing is increased with age.

The relationship between changes in body mass index and retinal vascular caliber in children.

OBJECTIVE: To examine the longitudinal relationship between changes in childhood body mass index (BMI) and retinal vascular caliber. STUDY DESIGN: A prospective study of 421 healthy children aged 7-9 years in 2001 who returned for follow-up in 2006. At both visits, retinal photographs and anthropometric measurements were taken following standardized protocols. Retinal arteriolar and venular calibers were measured using a computer-based program and summarized as central retinal artery equivalent (CRAE) and central retinal vein equivalent (CRVE). RESULTS: At follow-up, mean weight, height, and BMI increased significantly (P < .001). Mean CRVE increased by 3.4 µm (P < .001) but mean CRAE did not alter significantly (P = .340). On multivariate analysis, greater BMI was cross-sectionally associated with narrower CRAE (P < .01) and wider CRVE (P < .01). On longitudinal analysis, increasing BMI was associated with increasing CRVE (P = .04) over the 5-year period. Baseline BMI was associated with increased venular caliber and decreased arteriolar caliber at follow-up, and vice versa (P < .05). CONCLUSIONS: Increasing BMI is associated with increasing retinal venular caliber over time in children, and baseline retinal vascular caliber changes increase the risk of higher BMI at follow-up. As both widened retinal venular caliber and greater BMI are associated with risk of cardiovascular events in adults, progressive retinal venular widening could be a manifestation of an adverse microvascular effect of obesity early in life.

Comparison of two non-mydriatic fundus cameras to obtain retinal arterio-venous ratio.

PURPOSE: To analyze device-dependent variability of two non-mydriatic fundus cameras to obtain arterio-venous ratio (AVR), central retinal arteriolar equivalent (CRAE), and central retinal venular equivalent (CRVE) in static vessel analysis (SVA). METHODS: We examined 53 participants (29 men, 24 women; median age 46 years) of the Study of Health in Pomerania (SHIP). We took 45° optic-disc-centered fundus images of the right eye with two different non-mydriatic fundus cameras. The first photograph was obtained from the TRC-NW 200, the second from the OCT 2000 (both Topcon Corporation, Tokyo, Japan). One experienced grader graded image quality from 1 "ideal quality" to 5 "not analyzable" and determined AVR, CRAE, and CRVE with the software Vesselmap3 (Imedos, Jena, Germany). RESULTS: Average image quality was 1.8 for the TRC-NW 200 and 1.6 for the OCT 2000. AVR could not be determined in 5 images of the TRC-NW 200 due to low image quality, while six images of the OCT 2000 were not analyzable. The difference between AVR taken from two different non-mydriatic cameras was 0.01 ± 0.03 in Bland-Altman plots. The difference between CRAE was 0.17 ± 10.15 and between CRVE was -2.32 ± 11.76. CONCLUSIONS: The two different non-mydriatic cameras showed good agreement with respect to image quality. When using the same reading software, AVR, CRAE, and CRVE agreed well. Thus, funduscopy and SVA seem to be robust against inter-device variability. As a result, device dependency can remain unconsidered in follow-up examinations with different technical equipment. However, variability might impact more with devices from different manufacturers.

Update on retinal vessel structure measurement with spectral-domain optical coherence tomography.

This study was conducted to demonstrate a new scan method for retinal vessel structure measurement in a specific region of fundus (zone B) using spectral-domain optical coherence tomography (SD-OCT), and to assess its reliability. One temporal superior retinal vessel pair passing through a concentric ring (zone B), which was defined between half and one disc distance from the optic disc border, was chosen for the measurement using a volume scan in SD-OCT. On the SD-OCT image, retinal arteriolar outer diameter (RAOD), retinal arteriolar lumen diameter (RALD), retinal venular outer diameter (RVOD) and retinal venular lumen diameter (RVLD) were measured. Retinal vessel diameters on color fundus photographs were also analyzed. Fifty-five healthy individuals were recruited to evaluate intraobserver and interobserver reproducibility between the two examiners. The intraobserver intraclass correlation coefficient (ICC) ranged from 0.972 to 0.981, and the interobserver ICC ranged from 0.968 to 0.980. In the Bland-Altman plot, the 95% limits of interobserver agreement for the RAOD, RALD, RVOD and RVLD were -5.60 to 4.84µm, -5.78 to 5.05µm, -7.52 to 5.62µm and -7.10 to 5.63µm, respectively. The retinal arteriolar and venular lumen diameters on the SD-OCT image were close to the mean arteriolar and venular diameters obtained from the color fundus photographs. Volume scan method produced better images of retinal vessels showing the fine structures of the vessel wall, and provided reliable retinal vessel structure measurement in zone B with good repeatability and reproducibility.

Three-dimensional optical coherence tomography evaluation of vascular changes at arteriovenous crossings.

PURPOSE: To study the three-dimensional morphologic features of retinal arteriovenous crossings with optical coherence tomography (OCT) and elucidate the vascular changes associated with crossing phenomena as seen on fundus photographs. METHODS: We examined 150 consecutive eyes with no ocular disease. In each eye, fundus photographs were taken, and one randomly selected arteriovenous crossing was examined by OCT. The OCT analysis was performed by using sequential thin sections along and perpendicular to the retinal vessels. RESULTS: The OCT analysis of these arteriovenous crossings showed that the veins abruptly changed their directions to pass the artery and frequently displayed focal luminal narrowing with no compression or flattening. The OCT measurements revealed that the veins narrowed by 21.0% ± 12.9% at the crossings. The degree of narrowing correlated positively with the diameter of the crossing arteries (r = 0.419, P < 0.001). On fundus photographs, crossing phenomena were observed in 103 of the 150 selected crossings. Venous narrowing measured by OCT was more severe in eyes with crossing phenomena on fundus photographs (P < 0.001). Four types of crossing phenomena were observed: concealment, tapering, deflection, and humping. Venous narrowing rates were similar among all four types. Although the subjects with deflection or humping phenomena were more likely to suffer from hypertension, the mean venous narrowing rate at such crossings was similar to that observed with the other crossing phenomena. CONCLUSIONS: Arteriovenous crossings exhibited focal narrowing of the venous lumen with no compression or flattening. Increased venous narrowing and larger arteries were observed at crossings with crossing phenomena.

Semi-automated retinal vessel analysis in nonmydriatic fundus photography.

PURPOSE: Funduscopic assessment of the retinal vessels may be used to assess the health status of microcirculation and as a component in the evaluation of cardiovascular risk factors. Typically, the evaluation is restricted to morphological appreciation without strict quantification. Our purpose was to develop and validate a software tool for semi-automated quantitative analysis of retinal vasculature in nonmydriatic fundus photography. METHODS: matlab software was used to develop a semi-automated image recognition and analysis tool for the determination of the arterial-venous (A/V) ratio in the central vessel equivalent on 45° digital fundus photographs. Validity and reproducibility of the results were ascertained using nonmydriatic photographs of 50 eyes from 25 subjects recorded from a 3DOCT device (Topcon Corp.). Two hundred and thirty-three eyes of 121 healthy subjects were evaluated to define normative values. RESULTS: A software tool was developed using image thresholds for vessel recognition and vessel width calculation in a semi-automated three-step procedure: vessel recognition on the photograph and artery/vein designation, width measurement and calculation of central retinal vessel equivalents. Mean vessel recognition rate was 78%, vessel class designation rate 75% and reproducibility between 0.78 and 0.91. Mean A/V ratio was 0.84. Application on a healthy norm cohort showed high congruence with prior published manual methods. Processing time per image was one minute. CONCLUSIONS: Quantitative geometrical assessment of the retinal vasculature may be performed in a semi-automated manner using dedicated software tools. Yielding reproducible numerical data within a short time leap, this may contribute additional value to mere morphological estimates in the clinical evaluation of fundus photographs.

Variability of measurement of retinal vessel diameters.

PURPOSE: To examine the effects of various cardiovascular, ocular, and lifestyle factors on retinal vessel diameters over short periods of time. METHODS: Subjects were invited to have photographs of their retina taken at each of three study visits. The same eye was photographed each time. The photographs were digitized and retinal vessel diameters were measured. Measurements from the retinal photographs taken consecutively (at visit 2 and visit 3), and 1, 3, and 4 weeks apart (between visits 1 and 2, 2 and 3, and 1 and 3, respectively) were compared. RESULTS: There were 63 persons who participated in all study visits and had gradable vessel measurements from all five images used in the analysis. Correlations for pairs of study visits were high, and decreased slightly with increasing length of the time interval. For consecutive photographs taken, and 1 week, 3 weeks, and 4 weeks apart, correlations were 0.95, 0.90, 0.91, and 0.86, respectively, for central retinal arteriolar equivalent (CRAE) and 0.95, 0.90, 0.91, and 0.87, respectively, for central retinal venular equivalent (CRVE). We examined the associations of blood pressure levels, smoking habits, time since last eating, exercising, consuming caffeine, and taking anti-hypertensive medication, and image focus with CRAE and CRVE. We found no consistent pattern of association of any of these characteristics with short-term changes in CRAE and CRVE. CONCLUSION: Retinal vessel diameters are stable over short intervals of time and none of the factors studied were consistently associated with change in the diameters of either vessel type.