Features of the normal choriocapillaris with OCT-angiography: Density estimation and textural properties

The main objective of our work is to perform an in depth analysis of the structural features of normal choriocapillaris imaged with OCT Angiography. Specifically, we provide an optimal radius for a circular Region of Interest (ROI) to obtain a stable estimate of the subfoveal choriocapillaris density and characterize its textural properties using Markov Random Fields. On each binarized image of the choriocapillaris OCT Angiography we performed simulated measurements of the subfoveal choriocapillaris densities with circular Regions of Interest (ROIs) of different radii and with small random displacements from the center of the Foveal Avascular Zone (FAZ). We then calculated the variability of the density measure with different ROI radii. We then characterized the textural features of choriocapillaris binary images by estimating the parameters of an Ising model. For each image we calculated the Optimal Radius (OR) as the minimum ROI radius required to obtain a standard deviation in the simulation below 0.01. The density measured with the individual OR was 0.52 ± 0.07 (mean ± STD). Similar density values (0.51 ± 0.07) were obtained using a fixed ROI radius of 450 μm. The Ising model yielded two parameter estimates (β = 0.34 ± 0.03; γ = 0.003 ± 0.012; mean ± STD), characterizing pixel clustering and white pixel density respectively. Using the estimated parameters to synthetize new random textures via simulation we obtained a good reproduction of the original choriocapillaris structural features and density. In conclusion, we developed an extensive characterization of the normal subfoveal choriocapillaris that might be used for flow analysis and applied to the investigation pathological alterations

Optical Coherence Tomography in the UK Biobank Study – Rapid Automated Analysis of Retinal Thickness for Large Population-Based Studies

Purpose: To describe an approach to the use of optical coherence tomography (OCT) imaging in large, population-based studies, including methods for OCT image acquisition, storage, and the remote, rapid, automated analysis of retinal thickness. Methods: In UK Biobank, OCT images were acquired between 2009 and 2010 using a commercially available “spectral domain” OCT device (3D OCT-1000, Topcon). Images were obtained using a raster scan protocol, 6 mm x 6 mm in area, and consisting of 128 B-scans. OCT image sets were stored on UK Biobank servers in a central repository, adjacent to high performance computers. Rapid, automated analysis of retinal thickness was performed using custom image segmentation software developed by the Topcon Advanced Biomedical Imaging Laboratory (TABIL). This software employs dual-scale gradient information to allow for automated segmentation of nine intraretinal boundaries in a rapid fashion. Results: 67,321 participants (134,642 eyes) in UK Biobank underwent OCT imaging of both eyes as part of the ocular module. 134,611 images were successfully processed with 31 images failing segmentation analysis due to corrupted OCT files or withdrawal of subject consent for UKBB study participation. Average time taken to call up an image from the database and complete segmentation analysis was approximately 120 seconds per data set per login, and analysis of the entire dataset was completed in approximately 28 days. Conclusions: We report an approach to the rapid, automated measurement of retinal thickness from nearly 140,000 OCT image sets from the UK Biobank. In the near future, these measurements will be publically available for utilization by researchers around the world, and thus for correlation with the wealth of other data collected in UK Biobank. The automated analysis approaches we describe may be of utility for future large population-based epidemiological studies, clinical trials, and screening programs that employ OCT imaging

The effect of topical anti-muscarinic agents on subfoveal choroidal thickness in healthy adults

PURPOSE: To investigate the effects of tropicamide and cyclopentolate, which are two anti-muscarinic agents commonly used in the ophthalmologic practice, on subfoveal choroidal choroidal thickness (ChT) in healthy adults. METHODS: A total of 74 healthy adult subjects were enrolled in the study. Subjects were randomly divided into two groups: (1) cyclopentolate group (n=37) in which the right eye (study eye) of each subject received topical cyclopentolate 1%, and the fellow eye (control eye) received artificial tears and (2) tropicamide group (n=37) in which the right eye (study eye) of each subject received topical tropicamide 1% and the fellow eye (control eye) received artificial tears. Each topical medication was applied three times with 10-min intervals. ChT measurements were performed at baseline and 40 min after the last drops of the topical medications by enhanced depth imaging (EDI) optical coherence tomography (OCT). RESULTS: In the cyclopentolate group, subfoveal ChT significantly increased in the study eyes (P=0.013), whereas it did not significantly change in the control eyes (P=0.417). On the other hand, in the tropicamide group, no significant subfoveal ChT changes were observed in either the study eyes (P=0.715) or the control eyes (P=0.344). CONCLUSIONS: The current study demonstrated that cyclopentolate caused significant choroidal thickening, whereas tropicamide had no significant effect on ChT in healthy adults. As a result, mydriasis by cyclopentolate may complicate ChT measurements by EDI OCT. Use of tropicamide may provide more reliable results for evaluation of ChT in ocular pathologies

Influence of Hyperopia and Amblyopia on Choroidal Thickness in Children

WOS: 000393691000030PubMed: 26541109Purpose: To compare subfoveal choroidal thicknesses (ChTs) of anisometropic hyperopic amblyopic, hyperopic nonamblyopic, and emmetropic control eyes and to investigate the associations between ChT and ambylopia, spherical equivalent (SE), and axial length in the pediatric population. Methods: Forty-six hyperopic nonamblyopic (hyperopic group), 33 anisometropic hyperopic amblyopic (amblyopic group), and 42 emmetropic (emmetropic group) eyes were enrolled in this cross-sectional comparative study. Enhanced depth imaging spectral-domain optical coherence tomography was used for quantitative analysis of subfoveal ChT. ChT was quantified manually as the distance between the hyperreflective line corresponding to the retinal pigment epithelium and the chorioscleral interface at the subfoveal area. Results: the mean age was 10.6 +/- 3.3 years (range 5-17) in the hyperopic group, 10.7 +/- 3.3 years (range 5-17) in the amblyopic group, and 11.2 +/- 3.3 years (range 5-17 years) in the emmetropic group (p = 0.627). the hyperopic and amblyopic groups had significantly thicker choroid compared to the emmetropic group (p1 = 0.005 and p2 = 0.006, respectively). However, there was no significant difference between the hyperopic and amblyopic groups concerning subfoveal ChT (p = 0.857). in addition, covariance analysis showed that although SE was independently associated with subfoveal ChT (p = 0.014), amblyopia had no significant independent effect on subfoveal ChT (p = 0.671). Further, subfoveal ChT had weak correlations with the axial length (r = -0.297, p = 0.001) and SE (r = 0.274, p = 0.002). Conclusions: Hyperopia was associated with subfoveal ChT, whereas amblyopia had no independent significant effect on subfoveal ChT in our study population