Increasing scans per examination improves the reproducibility on retinal nerve fiber layer measurements by optical coherence tomography.

PURPOSE: To investigate whether increasing the number of scans per examination would improve the reproducibility of retinal nerve fiber layer (RNFL) measurements by optical coherence tomography (OCT) in healthy and glaucomatous eyes. METHODS: A total of 28 eyes of 28 healthy subjects and 20 eyes of 20 patients with primary chronic open-angle glaucoma were recruited. OCT RNFL assessments were obtained in one randomly selected eye. Each subject underwent seven scans on five separate occasions within a 1-month period. RESULTS: In the healthy group, the intervisit mean coefficient of variations (COV's) for the average RNFL thickness (100 sampling points) and the quadrant RNFL measurements (25 sampling points) were similar in a series of three, five, and seven scans per examination (p > 0.05), but COV's for the two clock-hour segment measurements (seven sampling points, superotemporal and inferotemporal) were significantly lower in a series of five and seven scans per examination than that of three scans per examinations (p < 0.01). In the glaucoma groups, COV's for the two quadrant (superior and inferior) and five clock-hour segment RNFL measurements (superior, superotemporal, temporal, inferotemporal, and superonasal) were significantly lower in a series of five and seven scans per examination than that of three scans per examination (p < 0.01). There was no statistical difference in the COV's between a series of five scans and that of seven scans per examination in all OCT RNFL thickness parameters in healthy and glaucomatous eyes (p > 0.05). Similar results were observed with intravisit COV comparisons. CONCLUSION: Increasing the number of scans per examination may improve the reproducibility of quadrant and clock-hour segment OCT RNFL measurements in healthy and glaucomatous eyes. A series of five scans per examination is recommended for OCT RNFL measurements.     

Repeatability and reproducibility of vessel density measurements on optical coherence tomography angiography in diabetic retinopathy

Graefe's Archive for Clinical and Experimental Ophthalmology - Understanding the precision of measurements on and across optical coherence tomography angiography (OCTA) devices is critical for...     

Repeatability and reproducibility of corneal thickness measurements by optical coherence tomography

PURPOSE: To assess the repeatability and interoperator and intersession reproducibility of central corneal thickness (CCT) measurements made by a commercially available optical coherence tomography (OCT) system. METHODS: Intersession and interoperator reproducibility and repeatability were defined according to the guidelines of the British Standards Institution and examined in a control group of 14 normal subjects. An in-house computer program was used to evaluate central corneal thickness from these scans. RESULTS: The coefficient of interoperator reproducibility was 0.18%, whereas that for intersession reproducibility was 1.11%. Wilcoxon analysis (5% level of significance) showed that there was no statistically significant difference between scans acquired during different sessions or by different operators. Coefficients of repeatability were all less than 3%. The average CCT was 526 +/- 28 microm (SD) and the range of normal CCT between 5th and 95th percentiles was 498 to 576 microm. CONCLUSIONS: Although the commercially available OCT scanner was designed for retinal imaging, with a few minor modifications, the system may be used to image the anterior segment. Previous studies have shown that OCT measurements correlate well with those from conventional techniques, and it has the added advantage of being a noncontact technique. This study further demonstrates that the OCT measurements show a high degree of repeatability and reproducibility. Thus, OCT is emerging as a promising tool for evaluation of CCT in the clinical setting.     

Astigmatism and optical coherence tomography measurements

Background  

To evaluate the effect of astigmatism change on measurement of retinal nerve fiber layer (RNFL) and macular thickness by Cirrus HD spectral-domain optical coherence tomography (Cirrus HD OCT; Carl Zeiss Meditec, Dublin, CA, USA).     

OCT的光密度研究在眼科的应用

光密度测量是一种通过结合计算机技术,将待测组织的图像信号转换成数字化格式,分析图像像素及计算后获得待测组织透射/反射光强度,从而达到客观分析组织特性的一种分析技术.光密度可根据测量仪器产生图像的维度而提供二维或三维的信息,立体、全面地体现组织内部微结构的变化,近年来在眼科影像中逐渐引起关注,已有研究表明其在眼科疾病诊断及随访中的应用价值.现结合国内外研究从光密度的定义、光密度在各领域的应用、光密度测量的优缺点、眼科领域中的光密度分析方法、光学相干断层扫描的光密度研究在眼科疾病中的应用5个方面进行综述.     

Symmetry of optical coherence tomography retinal measurements in young children

PURPOSE: To examine symmetry of macular, peripapillary nerve fiber layer (NFL), and optic disk measurements in healthy children. DESIGN: Cross-sectional study. METHODS: We examined a population-based sample of six-year-old children (n = 1,765) in the Sydney Childhood Eye Study. Optical coherence tomography (OCT) scan data for right and left eyes were compared. RESULTS: High interocular correlations (>0.8) were found for foveal minimum thickness and cup-to-disk ratios. Average NFL thickness was moderately correlated (0.7). Other macular, NFL, and optic disk parameters showed negligible or small mean interocular differences. In 95% of children, interocular difference in macular thickness was <22 microm for foveal minimum and <40 microm for other areas, and 16 to 17 microm for average NFL thickness. Cup-to-disk ratio was highly symmetric, varying by <0.25 in 95% of children. CONCLUSIONS: Interocular asymmetry of retinal/optic disk parameters should be interpreted in the context of other clinical measures because of the potential for large degrees of asymmetry among individuals.     

Assessment of accuracy and repeatability of anterior segment optical coherence tomography and reproducibility of measurements using a customised software program

Purpose: The aim was to study the reliability of measurements of the RTVue (Optovue, Fremont, CA, USA) anterior segment optical coherence tomographer (AS‐OCT) and assess how results can be improved by analysing raw optical coherence tomography data with customised image analysis software and applying correction factors. Methods: Five RTVue AS‐OCT instruments (ver. 4.0) were assessed by imaging gauge blocks of three different lengths, single/stepped glass plate (microscope slides) and flat window glass to check for width, depth and linearity of the measurement scans. Five repeats per calibration tool were imaged and averaged. Raw data were exported and loaded into customised image analysis software written in LabWindows/CVI for further analysis. Using two calibration balls with different radii, measurement scans were validated. Repeatability of the optical coherence tomographs and the edge detection procedure were checked and statistical analyses performed. Results: Variations ranging from 0.01 to 1.93 mm in scan width and 0.1 to 0.17 mm in scan depth were found between the five instruments. Slight curvature distortion of 0.06 ± 0.01 mm (mean and standard deviation) was found in the raw images. By isolating the three sources of image distortion and applying individual correction factors, accuracy for corneal curvature measurements could be improved to better than 0.1 mm. Manual edge detection limited the coefficient of repeatability value to 0.06 and 0.08 mm for anterior and posterior radii of curvature, respectively. The coefficient of repeatability of corneal thickness measurements was less than 8 µm. Conclusions: Accuracy of the RTVue AS‐OCT varied between instruments. By applying calibration scale factors calculated by customised software, accuracy of thickness and curvature values of the anterior eye was improved. The achievable precision is sufficient to detect clinically relevant corneal curvature variations.