Moreover, graders evaluated the presence and number of new blood vessels. Statistical analysis was performed using SPSS v. Data were analyzed using Shapiro-Wilk test to evaluate the normality of sample distribution. The Wilcoxon signed rank test was used to compare the mean values between different groups. A P-value less than 0. The agreement of measurements between readers was assessed using interclass correlation coefficient ICC. A total of 43 eyes of 27 patients age, New blood vessels were found in OCTA is a recent imaging technique that allows qualitative and quantitative assessment of retinal and choroidal vessels in a limited area using computer-generated algorithms to determine blood flow [ 4 , 5 ].
One of the main deficiencies of this imaging technique is related to its limited field of view suggesting a primary application to disorders affecting the macular region. However, previous reports have documented the possibility of using additional convex lenses to increase the examination field of view EFI technique [ 8 ].
This is a great advantage since EFI OCTA consists in a single fast acquisition able to obtain more informations of the retina without need for montage techniques that necessarily require extra time to obtain multiple scans, overlapping areas and an extra time to remove inaccuracies due to subtle misalignments. We also performed a qualitative and quantitative analysis regarding the presence and the number of new blood vessels finding no differences comparing several imaging modalities.
In this contest, to evaluate new blood vessels is recommended the use of vitreoretinal interface slab that excludes the retinal vessels and enhances the visualization of new blood vessels protruding in the vitreous cavity as shown in Fig 2. The vitreoretinal interface segmentation D reveals the new blood vessels in the vitreous cavity. In fact, the extension of non-perfusion areas is negatively correlated with VD and FD, suggesting that the increase of non-perfusion areas is associated with a reduction of VD defined as the area occupied by vessels divided by the total area and consequently of FD.
Moreover, VD is positively correlated with FD, suggesting that the increase of VD is associated with the increase of the branching complexity of the capillary network. At the same time, we have to consider that the use of EFI technique can potentially overestimate the non-perfusion areas due to an over-representation of the edges of the images where the curved surface is projected flat. Another factor that should be taken into account is the different resolution of the images obtained.
This different resolution could explain the findings of larger areas of non-perfusion and the lower valued of VD and FD. Other factors that could influence the analysis are blood flow velocity and possible errors in the segmentation boundaries. Interestingly, OCTA images display an interrupted vessel white arrow whereas FA apparently displays a complete filling of the same vascular trunk white arrow. The analysis of FA early phases revealed slow but compete filling suggesting that the velocity of blood flow influences the OCTA signal thus possibly leading to an over estimation of non-perfusion.
Hirano et al.
Optical Coherence Tomography Angiography
However, they did not find significant differences between the two imaging modalities on the extension of non-perfusion areas and number of new blood vessels. In particular, the average extension of EFI SS-OCTA was inferior to our study since they presented cropped rectangular images while in our series we used a prototype lens designed specifically by Zeiss to perform EFI examination and to avoid the positional instability of the lens. Moreover, we also evaluated the branching complexity of the capillary network with the FD that showed significantly correlations between VD and areas of non-perfusion explaining the changes in the perfusion of the retina.
Differently, Kakihara et al. This is related to the respective limitations of the two imaging techniques. OCTA is influenced by the velocity of flow in which a slow flow inside the vessels resulting in black signal misinterpreted as non-perfusion as shown in Fig 3. On the other side, in FA the leakage of the dye from the vessels may mask the capillary non-perfusion resulting in an underestimate evaluation.
Optical Coherence Tomography Angiography | IOVS | ARVO Journals
The present study has several limitations as the small number of included eyes. Moreover, we have to consider that other factors may have influenced the results of our analysis as the poor pupil dilation or media opacities. At least, in our series we included a limited subset of pathologies and with only a retinal involvement. Despite, the determination of retinal ischemia seems to be easier and more accurate using EFI SS-OCTA, FA offers more details of the perfusion status of the retina as it is not influenced by the velocity of the flow.
At this moment, FA should be considered as the gold standard for the evaluation of retinal perfusion. Furthers studies are needed on the comparison between FA and OCTA to clearly assess the condition of diseases affecting the retinal vasculature in more peripheral regions. Browse Subject Areas? Linking retinal microvasculature features with severity of diabetic retinopathy using optical coherence tomography angiography.
Optical coherence tomography angiography of the foveal avascular zone in diabetic retinopathy. Graefes Arch Clin Exp Ophthalmol. Visualization of 3 distinct retinal plexuses by projection-resolved optical coherence tomography angiography in diabetic retinopathy. Chalam KV, Sambhav K. Optical coherence tomography angiography in retinal diseases. J Ophthalmic Vis Res.
A review of optical coherence tomography angiography OCTA. Int J Retina Vitreous. Optical coherence tomography angiography. A major review of optical coherence tomography angiography. Expert Rev Ophthalmol. An overview of the clinical applications of optical coherence tomography angiography. Eye Lond. Optical coherence angiography: a review.
Medicine Baltimore. Capillary plexus anomalies in diabetic retinopathy on optical coherence tomography angiography. Sample sizes of studies on diagnostic accuracy: literature survey. Detection of microvascular changes in eyes of patients with diabetes but not clinical diabetic retinopathy using optical coherence tomography angiography. Optical coherence tomography angiography of asymptomatic neovascularization in intermediate age-related macular degeneration. Download references. Correspondence to Nicolas S. Reprints and Permissions. Advanced search.
Skip to main content. Subjects Diagnosis Outcomes research. Abstract Objective To investigate the diagnostic accuracy of optical coherence tomography angiography OCTA in detecting vascular characteristics of chorio-retinal disease. Methods Evidence acquisition: We searched Web of Science, Scopus, and Medline by the citation of references and complemented these electronic searches by checking the list of references of included and review articles.
Results Evidence synthesis: Systematic review and exploratory meta-analysis. Conclusions The results of highly biased and heterogeneous studies assessing the diagnostic performance of OCTA highlight the need for further analyses of methodologically sound and sufficiently sized clinical evaluations. Rent or Buy article Get time limited or full article access on ReadCube.
References 1. Article Google Scholar 3. The study was approved by the Western Institutional Review Board, and patients signed written informed consent forms. The study was performed at a private practice retinal clinic from March 14, , through June 24, , and included 2 volunteers with no significant medical history and no signs or symptoms of ocular disease. Seven patients had ocular problems that were unilateral or, in 1 patient, not involving the macula. The fluorescein angiograms uniformly were well focused, with adequate exposure and sharpness to visualize the perifoveal capillaries.
Each B-scan contained A-scans. Five consecutive B-scans M-B frames were captured at a fixed position before proceeding to the next sampling location. A total of locations B-scans along the slow transverse direction were sampled to form a 3-dimensional data cube.
With a B-scan frame rate of frames per second, the B-scans in each scan sequence were acquired in approximately 4 seconds. Four volumetric raster scans, including 2 horizontal priority fast transverse x-fast scans and 2 vertical priority fast transverse y-fast scans, were obtained consecutively in 1 session. The best x-fast and y-fast scans were registered using the contained software ReVue, version After the processing of the volume scans, the decorrelation in the images, which is essentially 1 minus the correlation, was calculated.
Stationary tissue shows a high correlation in imaging characteristics from one frame to the next. Blood flowing through vessels causes a changing reflectance over time and localized areas of low correlation between frames or conversely a high decorrelation. This method does not use phase information from the OCT signal. The correlated frames were evaluated and statistical outliers were removed from the averaging process to reduce the possibility of tissue motion being present. The spectrum of the light source was split into 4 component parts to decrease the noise present in the image; each was used to perform the decorrelation step, and the results of all 4 were averaged.
This split-spectrum strategy trades axial resolution for decreased noise. After this step, a block of information exists that contains levels of decorrelation that range from 0 to 1. In any given region of tissue, the maximal projection image can be viewed to obtain an image of the contained blood flow. Because the retina is a laminar structure with a corresponding stratification of the blood supply, segmentation of the retina in specific layers allows simple en-face visualization of the corresponding vascular supply for that layer.
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Three main regions were evaluated for the purposes of this study. The internal limiting membrane was used as a plane of reference, and a slab thickness sufficient to contain the full thickness of the nerve fiber layer in the surrounding retina was selected.
The thickness of the nerve fiber layer becomes thinner with increasing distance, but the software reveals increasing noise with thinner sections. The aggregate images of the radial peripapillary capillary network were merged after elastic warping of the images was performed. The larger vessels were segmented and given a blue color and the radial peripapillary capillaries a red color. For the purposes of this study, the multiple retinal vascular planes as described by Weinhaus et al 11 were simplified into 2 main layers as was done by Snodderly et al.
The inner capillary layers were imaged by starting with the internal limiting membrane in the macular region and selecting sufficient thickness to include the ganglion cell layer. The inner retina at the fovea and its margin were included in this scan. The inner nuclear layer is ordinarily bracketed by a layer of capillaries on either side.
The fluorescein image was selected from the earliest frames that showed venous filling that had the sharpest imaging of the retinal capillaries. Because the OCT angiography encompasses a very limited field of view, the corresponding angiographic image had to be substantially enlarged.
Retinal angiography and optical coherence tomography
The fluorescein angiographic image was placed on the right side, and a stack that contained the inner and outer capillary plexuses was placed on the left. Each grader R. The test images were loaded into Photoshop CS6, and each grader adjusted the slider so that the details in the mixed inner and outer retinal plexus images as visualized by the SSADA scan matched the details seen on the fluorescein angiogram. Each grader performed the assessment independently and was masked to the results of the others. There were 12 eyes, with the patients ranging in age from 24 to 60 years median, 52 years.
In some eyes, radial arranged capillaries, potentially consistent with the radial peripapillary capillary network, could be imaged in the fluorescein angiogram superotemporal or inferotemporal to the disc, but in no eye could the capillaries be clearly identified elsewhere Figure 2. The radial peripapillary capillary network was readily visible around the disc in all eyes in the SSADA scans.
With the use of multiple montaged images, a map of the radial peripapillary network could be achieved Figure 4. It seems axiomatic that fluorescein, an efficient fluorophore injected intravenously and then imaged with a high-resolution fundus camera, should be able to show the vessels embedded in a nearly transparent structure only hundreds of micrometers thick. Early investigators examining the radial peripapillary capillary network used histologic techniques and did not find correlative fluorescein angiographic images.
The actual capillaries could not be seen outside the affected areas. It seems likely that multiple scattering by the adjacent nerve fiber bundles may lead to a diffuse glow of fluorescence instead of a sharply defined capillary image. Using animal models, Weinhaus et al 11 and Snodderly et al 12 found that fluorescein angiography does not image the deeper capillary plexus well in animal models.
They thought that scattering from the deeper layers obliterated the specific image of the capillaries. It is common to see the retinal capillaries in a fluorescein angiogram over a backdrop of low-level, poorly defined fluorescence. The diffuse fluorescence is often ascribed to background choroidal fluorescence, but it may be derived, in part, from the deeper capillary plexus.
Using the SSADA technique, we found the radial peripapillary capillary network and the inner and outer retinal plexuses were readily imaged. The fluorescein image corresponded to the inner retinal vascular plexus in the present series of human eyes, which seems to confirm the histologic findings of experimental animal models. These findings may portend important consequences in our understanding of the associations between retinal vasculature and ocular diseases. The relative importance of the radial peripapillary capillary network in diseases as wide ranging as glaucoma 6 , 25 to diabetic retinopathy 24 has been proposed but has not been studied in detail because of imaging difficulties.
Likewise, the relative importance of the outer retinal plexus in retinal diseases has been difficult to ascertain. It is possible that for many disease states the outer plexus is affected in parallel to the inner plexus and fluorescein angiography is sufficient to grade the amount of vascular compromise.
It is possible that some conditions, particularly those that involve perfusion, could affect one layer differently from the other. Appreciation that the deeper layer may be selectively involved in vein occlusions and other diseases has come to the fore, not because of unequivocal primary evidence supplied by fluorescein angiography but because of the need to explain opacification in middle layers of OCT B-scans of affected patients.
The inherent advantages of OCT angiography appear to be the ability to optically dissect and visualize the flow in various layers of the retina, the high resolution obtainable, and the freedom and safety of not having to use an injected dye. Fluorescein angiography provides flow information in that the speed of filling can be roughly compared in patients, physiologic information concerning the health of vessels can be assessed by looking for leakage, and the field of view is much larger.
In addition, OCT angiography requires that the patient fixate precisely for several seconds, whereas a useful fluorescein angiographic frame can be obtained in a fraction of a second. Fluorescein angiography involves injection of a dye, which has a small probability of serious complications but a common incidence of minor adverse effects, such as nausea and hives. A dedicated adaptive optics instrument is used to acquire a large number of images, and this is followed by image averaging, which in turn is followed by montaging separate images to obtain a field of view large enough to have clinical utility.
Adaptive optics imaging has a limited depth of focus, so each layer of circulation being evaluated has to be specifically targeted at the time of acquisition. With OCT angiography, the layers can be dissected arbitrarily any time after acquisition to obtain flow-based images.
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