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The Cirrus HD-OCT is an image acquisition modality and review application. The Cirrus HD-OCT employs spectral domain optical coherence tomography (OCT) to acquire 2-dimensional and 3-dimensional tomographic and biomicroscopic images of the posterior ocular structures of the eye. The Cirrus HD-OCT software allows to: • Verify communication. Evaluation of Aircraft Contrails using Dynamic Dispersion Model. Contrail cirrus computational model and simulation software, called Contrail Cirrus Prediction Tool (CoCiP). Evaluation of Aircraft Contrails using Dynamic Dispersion Model.
It includes User Acceptance Testing (UAT). It includes the most current commercially released software version of Cirrus Tech WCS. It includes customized integration between any proprietary system and/or Cirrus Tech software. 24/7/365 Customer Service and Support Our WCS solution controls, directs and integrates all facets of an operations warehouse automation systems into a single, efficient transportation system using proven work flow that allows for Just-in-Time Inventory (also called Just-in-Time Business) to become a reality at your distribution center. WANT TO LEARN MORE?
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Results The presence or absence of inner segment/outer segment junction was visible on both spectral-domain optical coherence tomography en face and retinal cross sections. Thirty eyes (40.6%) had no retinal pathology and an average logMAR visual acuity of 0.116.
Twenty-five eyes (33.8%) had intraretinal edema, with visual acuity of 0.494. Nineteen eyes had nonneovascular age-related macular degeneration (dry age-related macular degeneration, 25.6%), with visual acuity of 0.392. In all eyes, central 1-mm and 400-µm en face areas were 58.3 ± 25.0% and 56.4 ± 26.0%, which showed significant correlation with visual acuity (Pearson correlation, r = −0.66 and −0.56, both P. Optical coherence tomography (OCT) was introduced in 1991 as a noninvasive, diagnostic ophthalmic imaging technique and made the routine clinical measurement of retinal thickness possible. Since 2004, higher resolution spectral-domain (SD) OCT has entered clinical practice with reported resolutions of 1 µm to 5 µm and improved visualization of retinal morphology and pathology., One aspect of SD OCT that is greatly improved compared with its predecessor, time-domain OCT, is the ability to clearly differentiate outer retinal layers.
This has led to novel findings, not observable on clinical examination, including the description of several distinct hyperreflective layers in the outer retina corresponding to Verhoeff outer limiting membrane, the photoreceptor inner segment/outer segment (IS/OS) junction, and the inner and outer borders of the retinal pigment epithelium (RPE). – Furthermore, data from several recent OCT studies have indicated that the integrity of the IS/OS is important for visual function and may be a predictor of visual acuity in eyes with many different retinal pathologies including diabetic macular edema (DME), epiretinal membrane, macular holes, and central or branch retinal vein occlusion (RVO). – In this manner, SD OCT technology has provided improved correlation of outer retinal structural imaging and visual function. In a recent study, images acquired with Cirrus SD OCT (Carl Zeiss Meditec, Dublin, CA) were used to correlate quantifiable SD OCT findings, including macular thickness and outer photoreceptor length, to visual acuity in eyes with diabetic DME. The authors reported that there was a significantly greater correlation coefficient for outer photoreceptor length (range of Pearson correlation, r = −0.61 to −0.81) than with macular thickness (r = 0.13–0.22) in the entire 6 × 6-mm macular grid, central 1-mm subfield, and central 330-µm foveal point.
Another intriguing derivation of SD OCT technology is en face visualization (also called a transverse-, coronal-, or C-scan) of specific layers of the retina, including the IS/OS. This allows the clinician or patient to view the whole area, or specific retinal layer length and width, from “a bird’s eye view” rather than the length and depth observed with traditional OCT cross sections. Although this modality is not yet available on all the commercially produced SD OCT systems, one group determined that en face OCT may help provide prognostic indicators for visual acuity based on pre- and postoperative analysis of macular hole area measurement using a specific software program.
Another report, written by a coauthor of this study (D.F.K.), described novel en face outer retinal findings in a patient with acute zonal occult outer retinopathy using the advanced visualization three-dimensional (3D) analysis function of Cirrus SD OCT. In this case, IS/OS obliteration, observed with en face SD OCT scan of the outer retinal layers, precisely correlated with clinical observations, fundus autofluorescence, Goldmann visual field, and the IS/OS junction observable on SD OCT cross-sectional scans.
Interestingly, the central 5° to 10° of macula was spared and the patient’s visual acuity remained 20/20. Based on this background and our clinical experience with en face OCT imaging, we developed the hypothesis that there may be a significant correlation between en face OCT visualization of the outer retina, which includes the IS/OS, and visual acuity in both healthy patients and those with retinal pathology. Therefore, in this study, we sought to further describe en face visualization of the outer retina using Cirrus SD OCT and determine whether there was any correlation between the central 1-mm and 400-µm outer retinal areas and visual acuity. In addition, we explored how these results compared with routine measurements provided by Cirrus SD OCT software including central subfield thickness (CST), macular volume (MV), and average macular thickness (AMT). Methods This study was approved by the Institutional Review Board of The University of Chicago Hospitals Medical Center.
Health Insurance Portability and Accountability Act compliance was maintained. This was a case– control study of patients who received clinical examinations and Cirrus SD OCT macular cube scans (128 B-scans, each consisting of 512 A-scans over a 6 × 6-mm area with a maximal scan velocity of 27,000 axial scans per second) at a satellite university clinic over a 5-month period. All scans were performed by the same experienced, OCT-certified ophthalmic technician. To minimize software-induced miscorrelation, only high-quality scans, defined as those that were centered on the fovea, with a signal strength ≥6 and which displayed correctly aligned automatic software segmentation of the internal limiting membrane and inner RPE boundary were included. Only patients who had vision measurable on a Snellen chart with a range of 20/20–20/400 were included.
Healthy eyes were defined as eyes without a history of eye disease, or clinical and SD OCT findings of retinal pathology. Exclusion criteria included OCT scan acquisition defects on any part of the macular cube, recent intraocular surgery (within 4 weeks), a diagnosis of glaucoma, any media opacity precluding complete macular cube scan or a history of trauma, or any vitreoretinal surgery in the study eye. These criteria were chosen to minimize those eyes that may have had decreased visual acuity because of optic neuropathy or media opacity, rather than outer retinal pathology.
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Cirrus SD OCT en face scans were analyzed using advanced visualization 3D analysis, RPE slice mode. The Cirrus software automatically generated the en face images based on the density of the IS/OS junction signal for each individual scan. The authors did not manually alter the algorithm. All images were rotated in order that the RPE slice was viewed as an en face image, which was aligned equally in the horizontal and vertical planes without adjusting the zoom characteristic. Images were saved and exported as Joint Photographic Experts Group (JPEG) files and then converted into Tagged Image File Format (TIFF) data. These were then analyzed using Metamorph image processing software Version 7.6 (Molecular Devices, Sunnyvale, CA). The TIFF images were imported and converted into 16-bit grayscale images, and then inclusive thresholds were applied to each image.
Determination of image thresholds was based on the reflective signal intensities of the OCT scan, which was automatically applied to the en face images by Cirrus software. A specific software threshold algorithm was developed, to differentiate hyperreflective from hyporeflective OCT signals in an attempt to include intact IS/OS and exclude other areas, and applied to all images.
The threshold value, based on the contrasts between the peaks of the “hottest” signal color (orange-yellow) compared with the “coolest” color (blue-green), was established by applying the Metamorph software’s threshold calculation of each individual scan of healthy controls and then applying this summed average threshold to all other images. Circular regions of 1 mm and 400 µm were centered on the fovea, and the percentage inclusive threshold was determined for both regions in each image using Metamorph region analysis.
Optical coherence tomography measurements including CST, MV, and AMT, which had been automatically determined by the Cirrus OCT software, were recorded. For statistical analysis, best-corrected Snellen visual acuity was converted to a logarithm of the minimum angle of resolution (logMAR) score. The logMAR visual acuity was compared with both en face outer retinal OCT area analyses and with CST, MV, and AMT measurements using Pearson correlation analysis. The 2 en face areas were compared using a paired Student t-test. Any differences with a P value. Results Eighty eyes of 58 patients were analyzed.
Six scans were excluded, because of scanning errors within the 6 × 6-mm scan area because of patient movement or blinking. A total of 74 eyes of 53 patients were included in this study. The average patient age was 63.6 years (±17.6 years), and 29 patients were women (54.7%).
The mean visual acuity for all eyes was 0.315 (Snellen equivalent, 20/40, range 20/20–20/400). Thirty eyes (40.5%, 5 of which were healthy fellow eyes of patients affected in the other eye) had no previous or established retinal pathology on clinical examination, 25 eyes (33.7%) had intraretinal edema on clinical examination because of retinal vein occlusion (n = 6, 8.1%), DME (n = 6, 8.1%), idiopathic epiretinal membrane (n = 4, 5.4%), pseudophakic cystoid macular edema (n = 4, 5.4%), neovascular age-related macular degeneration (wet AMD, n = 3, 4%), or vitreomacular traction (n = 2, 2.7%). Nineteen eyes had intermediate or advanced nonneovascular (dry) AMD (25.6%) on clinical examination, with medium and/or large drusen, pigmentary changes, and/or geographic atrophy of the RPE noted on clinical examination. Results of visual acuity, CST, MV, and average macular thickness by diagnosis are listed in. N, number; VA, visual acuity (logarithm of the minimum angle of resolution); SD, standard deviation; VO, retinal vein occlusion; CME, cystoid macular edema; ERM, idiopathic epiretinal membrane; VMT, vitreomacular traction. Demonstrates SD OCT en face images and corresponding central macular cube horizontal cross sections highlighting the 1-mm and 400-µm zones, which were analyzed in 4 different patients.
When present, the hyperreflective orange signal demonstrated with en face scans corresponded with the hyperreflective orange IS/OS junction visible on cross-sectional scans. In patients with retinal pathology, the less reflective, green-blue colors in en face scans corresponded with irregular or absent IS/OS on cross-sectional images.
En face OCT images of different patients with corresponding (black arrows) cross-sectional OCT scans. Red circles indicate analyzed areas corresponding to red arrows, which point to the inner/outer photoreceptor junction location. Top to bottom (visual acuity): healthy (20/20), dry AMD (20/50), DME (20/400), and pseudophakic macular edema (20/40). Demonstrates examples of the Cirrus SD OCT en face images, images converted into 16-bit grayscale, and images with thresholds and area regions applied, which were then analyzed with Metamorph software.
Inclusion and exclusion thresholds in the analyzed areas and in the entire macular cube scan corresponded with hyperreflective and hyporeflective areas, respectively, on the original en face images. The results of outer retinal en face OCT analyses of the central 1-mm and 400-µm area are listed in. Similar to standard OCT macular thicknesses and volume, en face OCT area measurements varied by diagnosis.
Although there was no statistically significant difference between central 1-mm and 400-µm en area measurements for all eyes as a group ( P = 0.12), healthy eyes showed a higher percentage of outer retinal area in the central 1-mm compared with 400-µm area (78.1 ± 12.1% and 73.3 ± 14.2%, respectively, P = 0.013). N, number; SD, standard deviation; VO, retinal vein occlusion; CME, cystoid macular edema; ERM, idiopathic epiretinal membrane; VMT, vitreomacular traction. In all eyes, mean CST was 298.0 ± 114.6 mm, mean MV was 10.15 ± 1.71 mm 3, and mean AMT was 283.7 ± 45.9 mm. Depending on whether eyes were healthy or affected with retinal pathology, visual acuity and OCT thickness measurements varied considerably.
The results of visual acuity, correlated with en face area, OCT retinal thickness, and volume are listed in and –. En face area measurements demonstrated greater correlation than retinal thickness or volume in the majority of analysis. In all eyes, central 1mm and 400-µm en face areas were 58.3 ± 25.0% and 56.4 ± 26.0%, respectively, which showed significant correlation with visual acuity (Pearson correlation, r = −0.664 and −0.560, respectively, P. Diagnosis n 1-mm Area Pearson P 400-µm Area Pearson P t-Test 400 µm vs. 1 mm CST Pearson P MV Pearson P AMT Pearson P All eyes 74 −0.664.
N, number; VO, retinal vein occlusion; CME, cystoid macular edema; ERM, idiopathic epiretinal membrane; VMT, vitreomacular traction; na, sample size too small to calculate significance. The significance of the correlations varied by diagnosis; en face OCT area correlation was much greater compared with CST, MV, and AMT in all eyes as a group, healthy eyes, and eyes with macular edema ( and ). These differences varied depending on the macular edema etiology, although the few eyes studied precluded statistical significance in many subanalysis groups. However, in eyes with dry AMD, there was poor and nonstatistically significant correlation observed for all measurements. Excluding eyes with dry AMD, all measurements demonstrated statistically significant correlation with visual acuity, but it was highest for the 1-mm (r = −0.812, P.
Discussion Using Cirrus SD OCT and a specific Metamorph computer software algorithm, we have described en face OCT visualization of the outer retina in a variety of patients and attempted to correlate visual acuity with parafoveal areas of intact IS/OS. We report a relatively strong correlation between en face area and visual acuity especially when compared with standard OCT measurements. To our knowledge, this is the first comparative study describing the close association of outer retinal layer en face visualization with the IS/OS seen on crosssectional scan using a commercial SD OCT device for healthy eyes and a variety of pathologies, and the first to correlate en face area with visual acuity for the same. Previous studies attempting to generate en face fundus images have used scanning laser ophthalmoscopy with relatively high transverse resolution and contrast; however, pupil aperture and ocular aberrations limited the axial resolution to a level insufficient to realize fine retinal details such as the IS/OS junction. In contrast to this, large volumes of rapid, high-resolution images can be obtained with SD OCT despite the long depth of focus as occurs during in vivo retinal imaging., Other research has used retinal densitometry to experimentally measure in vivo changes of visual pigment density within rods and cones. Hofer et al also used high-resolution adaptive optics imaging combined with retinal densitometry to differentiate the relative numbers of L, M, and S photoreceptors identified near the central 1° of the macula, essentially describing a “cone mosaic,” which exists within the fovea.
A separate study used SD OCT to view en face retinal topography in patients with macular edema and correlate cross-sectional thickness with Stratus OCT, but did not separately visualize the outer retina or IS/ OS. Another recent article described the creation of high-resolution en face images of the outer retinal layers, built with prototype SD OCT systems, including the central 2° to 4° of the parafoveal IS/OS junction and tips of the outer photoreceptors. The authors described the cellular morphology and photoreceptor density seen in a normal subject, and abnormalities observed in 1 patient with Type 2 macular telangiectasia and another with retinitis pigmentosa.
Although this was a small, qualitative study using experimental technology, the data did reveal disruption of the IS/OS junction in diseased compared with healthy eyes with en face images, which we also observed in our study. However, none of these previous studies attempted to correlate structural findings with visual function. Forooghian et al examined patients with DME and demonstrated a much stronger correlation of photoreceptor outer length to visual acuity than was seen with macular thickness in 3 different zones, including CST and the central 330-µm central fovea point, which is similar to the 2 central areas studied in this report. Although their correlations of outer retinal analysis were slightly lower than ours (r = −0.81, P.