Repeatability and reproducibility of retinal nerve fibre layer thickness measurements with the iVue-100 optical coherence tomographer

Background: Accurate and repeatable measurements of the retinal nerve fibre layer (RNFL) thickness are important in the diagnosis and management of glaucoma and other disorders. Objective: To assess the repeatability and reproducibility of the iVue-100 optical coherence tomographer (OCT).Methods: The thickness of the RNFL was measured for 50 healthy participants using the iVue-100 OCT. Although both eyes per participant were measured, only right eyes were analysed here. Repeatability and reproducibility of the iVue-100 OCT were assessed using the intraclass correlation coefficient (ICC), coefficient of variation (CoV), paired t-tests and Bland-Altman analysis.Results: Good intra-observer repeatability was obtained as indicated by the ICC of observer 1 (range: 0.941 - 0.976) and observer 2 (range: 0.829 – 0.953) as well by the CoV of observer 1 (range: 0.098 – 0.137) and observer 2 (0.091 – 0.132). In terms of inter-observer reproducibility, significant differences (p< 0.05) in mean measurements between the observers were noted for the average RNFL readings and in the superior and inferior quadrants as assessed with paired t-tests. Even though significant inter-session differences were found for the average RNFL thickness and the superior quadrant (p = 0.003 and p = 0.013, respectively), excellent ICCs were obtained for inter-session reproducibility (range: 0.914 – 0.979). Conclusion: The iVue-100 OCT demonstrated good repeatability and reproducibility for RNFL thickness measurements.Keywords: Retinal nerve fibre layer thickness, optical coherence tomography, repeatability, reproducibility, iVue-100 OCT

Automated Retinal Layer Segmentation Using Spectral Domain Optical Coherence Tomography: Evaluation of Inter-Session Repeatability and Agreement between Devices

Retinal and intra-retinal layer thicknesses are routinely generated from optical coherence tomography (OCT) images, but on-board software capabilities and image scaling assumptions are not consistent across devices. This study evaluates the device-independent Iowa Reference Algorithms (Iowa Institute for Biomedical Imaging) for automated intra-retinal layer segmentation and image scaling for three OCT systems. Healthy participants (n = 25) underwent macular volume scans using a Cirrus HD-OCT (Zeiss), 3D-OCT 1000 (Topcon), and a non-commercial long-wavelength (1040nm) OCT on two occasions. Mean thickness of 10 intra-retinal layers was measured in three ETDRS subfields (fovea, inner ring and outer ring) using the Iowa Reference Algorithms. Where available, total retinal thicknesses were measured using on-board software. Measured axial eye length (AEL)-dependent scaling was used throughout, with a comparison made to the system-specific fixed-AEL scaling. Inter-session repeatability and agreement between OCT systems and segmentation methods was assessed. Inter-session coefficient of repeatability (CoR) for the foveal subfield total retinal thickness was 3.43μm, 4.76μm, and 5.98μm for the Zeiss, Topcon, and long-wavelength images respectively. For the commercial software, CoR was 4.63μm (Zeiss) and 7.63μm (Topcon). The Iowa Reference Algorithms demonstrated higher repeatability than the on-board software and, in addition, reliably segmented all 10 intra-retinal layers. With fixed-AEL scaling, the algorithm produced significantly different thickness values for the three OCT devices (P<0.05), with these discrepancies generally characterized by an overall offset (bias) and correlations with axial eye length for the foveal subfield and outer ring (P<0.05). This correlation was reduced to an insignificant level in all cases when AEL-dependent scaling was used. Overall, the Iowa Reference Algorithms are viable for clinical and research use in healthy eyes imaged with these devices, however ocular biometry is required for accurate quantification of OCT images

Optical coherence tomography: evaluation and clinical application

The ability to examine the appearance of the retina is of paramount importance for the diagnosis and monitoring of ophthalmic disease and for the evaluation of treatment outcomes. Direct cross-sectional imaging of retinal structure could be useful for early diagnosis and more sensitive monitoring of a variety of retinal conditions such as macular oedema and glaucoma. The view of the fundus given by ophthalmoscopy provides very limited depth information and clinicians will often have to resort to additional techniques such as flourescein angiography or visual field testing for information on structural abnormalities within the retina. Other currently available imaging techniques do not provide sufficient depth resolution to produce useful cross-sectional images of retinal structure. Optical coherence tomography (OCT) is a new imaging technique which is capable of producing cross-sectional images of the retina with a resolution that surpasses that of conventional imaging techniques. This new technique has axial resolution of around 1 O.tm and can resolve individual retinal layers, thus providing information on retinal structure. In principle, OCT is very similar to ultrasound however it makes use of a light source rather than an acoustic one. The technique is non-contact and non-invasive and is generally well tolerated by patients. This thesis describes the evaluation of this new imaging technique with regards to its potential within routine clinical practice. A number of investigations were performed to fuffil this evaluation. Tests were carried out to experimentally measure the system's resolution and the accuracy and precision of measurements made from the OCT scans. A number of factors that could affect the quality of the scans were identified and their effects were minimised wherever possible. The software provided with the system was rigorously tested and potential sources of error were identified. Various studies were undertaken to quantify the repeatability and reproducibility of measurements made from scans and normative values were established. These results were used to assess the ability of the technique to detect and quantify several retinal disorders. The potential of the technique for corneal imaging was investigated - a scanning protocol was established and customised software for processing cornea! scans was developed. The relationship between OCT bands and retinal morphology was investigated by correlating scans from canine retina with corresponding light microscopy images and by observing the position of retinal abnormalities on scans from patients with a variety of conditions that affected different parts of the retina. Finally the clinical potential of OCT was investigated by carrying out various studies on a number of retinal conditions. Further clinical studies which combine anatomical information from OCT with functional information from electrophysiology are currently underway. Current developments are aimed at improving the imaging processing features and user interface so as to provide a more robust, user-friendly system for routine clinical use

Repeatability of nerve fiber layer thickness measurements in patients with glaucoma and without glaucoma using spectral-domain and time-domain OCT

Background: The aim of this work is to assess the repeatability of spectral-domain-OCT (SD-OCT) retinal nerve fiber layer thickness (RNFL) thickness measurements in a non-glaucoma group and patients with glaucoma and to compare these results to conventional time-domain-OCT (TD-OCT). Methods: In a prospective, comparative, observational case-control study, 50 eyes of 25 non-glaucoma and 22 eyes of 11 patients with primary open angle glaucoma (POAG) were included. SD-OCT and TD-OCT circle scans were centered on the optic disc. In each eye, OCT scans were performed three times by two independent observers. RNFL thickness was measured in four quadrants around the optic disc. In addition, the overall mean RNFL thickness was assessed. Intraclass correlation coefficients (ICC) and coefficients of variation (COV) were calculated. Inter-observer and inter-OCT repeatability was visualized by using Bland-Altman analysis. Results: Intra-observer repeatability for TD- OCT was good with an ICCmean RNFL thickness of 0.939 in non-glaucomas and 0.980 in glaucomatous eyes. For SD-OCT, intra-observer repeatability was higher with an ICC of 0.989 for non-glaucomas and 0.997 for glaucomatous eyes. COVs for TD-OCT ranged from 2.9-7.7% in non-glaucomas and from 6.0-13.3% in glaucoma patients. COVs for SD-OCT ranged from 0.3-1% in non-glaucomas and from 0.9-2.3% in glaucomatous eyes. COVs were influenced by various factors. In the glaucoma group, COVs were significantly higher (p < 0.001) compared to the non-glaucoma group. COVs increased by a mean of 5.1% when TD-OCT was used instead of SD-OCT (p < 0.001). Conclusions: SD-OCT RNFL thickness measurements in healthy volunteers and glaucoma patients showed good intra- and inter-observer repeatability. Especially in glaucomatous eyes, repeatability of SD-OCT was superior to TD-OC

Functional and structural reliability of optic nerve head measurements in healthy eyes by means of optical coherence tomography angiography

Background and Objectives: the aim of the study was to evaluate the repeatability and reproducibility of optical microangiography (OMAG)-based optical coherence tomography angiography (OCTA) in the optic nerve head (ONH) and radial peripapillary capillary (RPC) perfusion assessment of healthy eyes. Materials and Methods: in this observational study, a total of 40 healthy subjects underwent ONH evaluation, using an OMAG-based OCTA system at baseline (T0), after 30 min (T1), and after 7 days (T2). The main outcome measures were the vessel density (VD) and flux index (FI) of the RPCs, as well as peri-papillary retinal nerve fibre layer (pRNFL) thickness. The analysis was performed by two observers independently. The coefficient of repeatability (CR), within the subject coefficient of variation (CVw) and intrasession correlation coefficient (ICC), to evaluate intrasession repeatability of measurements was calculated for each observer. Results: the high intrasession and intersession repeatability and reproducibility were assessed in the two observers for all three outcome measures. Of note, the CRs for the first and the second observer were 0.011 (95% confidence interval (CI) 0.009–0.014) and 0.016 (95% CI 0.013–0.020) for FI, 0.016 (95% CI 0.013–0.021) and 0.017 (95% CI 0.014–0.021) for VD, and 2.400 (95% CI 1.948–3.092) and 3.732 (95% CI 3.064–4.775) for pRNFL thickness, respectively. The agreement between them was excellent for pRNFL assessment and very good for FI and VD. Conclusion: OCTA has a great potential in the accurate assessment of ONH and peri-papillary microcirculation. It allows for repeated and reproducible measurements without multiple scans-related bias, thus guaranteeing an independent operator analysis with good reproducibility and repeatability

Imaging retinal nerve fiber bundles using optical coherence tomography with adaptive optics

AbstractEarly detection of axonal tissue loss in retinal nerve fiber layer (RNFL) is critical for effective treatment and management of diseases such as glaucoma. This study aims to evaluate the capability of ultrahigh-resolution optical coherence tomography with adaptive optics (UHR-AO-OCT) for imaging the RNFL axonal bundles (RNFBs) with 3×3×3μm3 resolution in the eye. We used a research-grade UHR-AO-OCT system to acquire 3°×3° volumes in four normal subjects and one subject with an arcuate retinal nerve fiber layer defect (n=5; 29–62years). Cross section (B-scans) and en face (C-scan) slices extracted from the volumes were used to assess visibility and size distribution of individual RNFBs. In one subject, we reimaged the same RNFBs twice over a 7month interval and compared bundle width and thickness between the two imaging sessions. Lastly we compared images of an arcuate RNFL defect acquired with UHR-AO-OCT and commercial OCT (Heidelberg Spectralis). Individual RNFBs were distinguishable in all subjects at 3° retinal eccentricity in both cross-sectional and en face views (width: 30–50μm, thickness: 10–15μm). At 6° retinal eccentricity, RNFBs were distinguishable in three of the five subjects in both views (width: 30–45μm, thickness: 20–40μm). Width and thickness RNFB measurements taken 7months apart were strongly correlated (p<0.0005). Mean difference and standard deviation of the differences between the two measurement sessions were −0.1±4.0μm (width) and 0.3±1.5μm (thickness). UHR-AO-OCT outperformed commercial OCT in terms of clarity of the microscopic retina. To our knowledge, these are the first measurements of RNFB cross section reported in the living human eye

Reproducibility of corneal, macular and retinal nerve fiber layer thickness measurements using the iVue-100 optical coherence tomography

Purpose: To determine the intra-session and inter-session reproducibility of corneal, macular and retinal nerve fiber layer thickness (RNFL) measurements with the iVue-100 optical coherence tomography in normal eyes.Methods: These parameters were measured in the right eyes of 50 healthy participants with normal vision. Six scans each for corneal thickness, macular and optic nerve head were taken on one day (intra-session), followed by similar repeated measures on five separate days (inter-session). Reproducibility was computed using intra-class correlation coefficient (ICC), coefficient of variation (COV), and test-retest variability (TRV).Results: For intra-session reproducibility, the ICC, COV and TRV values for mean corneal thickness were 0.924, 2.82%, and 3.06 μm respectively. For the mean macular thickness, they were 0.978, 4.64% and 4.51 μm respectively, while for mean RNFL thickness they were 0.946, 3.19%, and 5.66 μm respectively. Inter-session values for mean corneal thickness were 0.926, 2.65% and 3.48 μm, and 0.916, 2.24% and 2.03 μm for mean macular thickness. For mean RNFL thickness, they were 0.962, 2.21%, and 4.72 μm respectively.Conclusion: There was good reproducibility of all measured parameters. However, mean RNFL thickness measurements were the most reproducible, suggesting that this may be the best parameter to use to determine measured changes over time.Keywords: Corneal thickness, macular thickness, retinal nerve fiber layer thickness, iVue-100, reproducibilit

The Reliability of Parafoveal Cone Density Measurements

Background Adaptive optics scanning light ophthalmoscopy (AOSLO) enables direct visualisation of the cone mosaic, with metrics such as cone density and cell spacing used to assess the integrity or health of the mosaic. Here we examined the interobserver and inter-instrument reliability of cone density measurements. Methods For the interobserver reliability study, 30 subjects with no vision-limiting pathology were imaged. Three image sequences were acquired at a single parafoveal location and aligned to ensure that the three images were from the same retinal location. Ten observers used a semiautomated algorithm to identify the cones in each image, and this was repeated three times for each image. To assess inter-instrument reliability, 20 subjects were imaged at eight parafoveal locations on one AOSLO, followed by the same set of locations on the second AOSLO. A single observer manually aligned the pairs of images and used the semiautomated algorithm to identify the cones in each image. Results Based on a factorial study design model and a variance components model, the interobserver study\u27s largest contribution to variability was the subject (95.72%) while the observer\u27s contribution was only 1.03%. For the inter-instrument study, an average cone density intraclass correlation coefficient (ICC) of between 0.931 and 0.975 was calculated. Conclusions With the AOSLOs used here, reliable cone density measurements can be obtained between observers and between instruments. Additional work is needed to determine how these results vary with differences in image quality

Agreement Between Spectral-Domain and Swept-Source Optical Coherence Tomography Retinal Thickness Measurements in Macular and Retinal Disease

INTRODUCTION: To assess inter-device agreement in optical coherence tomography-derived retinal thickness measurements in patients with known macular conditions between spectral-domain and swept-source optical coherence tomography (OCT). METHODS: Two hundred seventy-two subjects were included in the study. They consisted of 91 male (33.5%) and 181 female (66.5%) subjects, and 132 left (48.5%) and 140 right (51.5%) eyes. Each subject underwent spectral-domain OCT (SD-OCT, Spectralis, Heidelberg Engineering; RTVue XR Avanti XR HD, Optovue) and swept-source OCT (SS-OCT; DRI-OCT-1, Atlantis, Topcon) in a single imaging session performed by the same clinical trial-certified technician. The comparison of retinal thickness reproducibility between devices was performed using Bland-Altman analyses and across the entire data set using the intraclass correlation coefficient (ICC). RESULTS: The ICC of the retinal thickness measurements (95% confidence interval) made using all three OCT instruments was 0.81 (0.77-0.84). The mean difference in mean retinal thickness between Spectralis SD-OCT and Topcon SS-OCT was 59.1 μm (95% limit of agreement [LoA] -21.7 to 139.8 μm). The mean difference in mean retinal thickness between Optovue SD-OCT and Topcon SS-OCT was 21.8 μm (95% LoA -34.7  to 78.3 μm). CONCLUSIONS: Retinal layer thickness measurements vary between SS-OCT and SD-OCT devices. We describe inter-device agreement in retinal thickness between SS-OCT and SD-OCT in patients with macular conditions. Clinicians should be aware of the differences in retinal thickness values when imaging patients using different OCT devices and should consider using the same OCT device model in order to monitor clinical change. TRIAL REGISTRATION: ClinicalTrials.gov Identifier (NCT02828215)

Repeatability and reproducibility of retinal nerve fibre layer thickness measurements with the iVue-100 optical coherence tomographer

Background: Accurate and repeatable measurements of the retinal nerve fibre layer (RNFL) thickness are important in the diagnosis and management of glaucoma and other disorders. Objective: To assess the repeatability and reproducibility of the iVue-100 optical coherence tomographer (OCT). Methods: The thickness of the RNFL was measured for 50 healthy participants using the iVue-100 OCT. Although both eyes per participant were measured, only right eyes were analysed here. Repeatability and reproducibility of the iVue-100 OCT were assessed using the intraclass correlation coefficient (ICC), coefficient of variation (CoV), paired t-tests and Bland-Altman analysis. Results: Good intra-observer repeatability was obtained as indicated by the ICC of observer 1 (range: 0.941 - 0.976) and observer 2 (range: 0.829 \u2013 0.953) as well by the CoV of observer 1 (range: 0.098 \u2013 0.137) and observer 2 (0.091 \u2013 0.132). In terms of inter-observer reproducibility, significant differences (p&lt; 0.05) in mean measurements between the observers were noted for the average RNFL readings and in the superior and inferior quadrants as assessed with paired t-tests. Even though significant inter-session differences were found for the average RNFL thickness and the superior quadrant (p = 0.003 and p = 0.013, respectively), excellent ICCs were obtained for inter-session reproducibility (range: 0.914 \u2013 0.979). Conclusion: The iVue-100 OCT demonstrated good repeatability and reproducibility for RNFL thickness measurements