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Timothy Holmes, Sean Larkin, Markie Dowing, Karl G Csaky; Imaging and Analysis of the Inner-Segment Ellipsoid Layer. Invest. Ophthalmol. Vis. Sci. 2014;55(13):278. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
It is generally believed that the integrity of the photoreceptor layer is, in part, reflected by characteristics of the inner segment ellipsoid (ISE) layer as it appears in optical coherence tomography (OCT) B-scans. This idea is supported by the developments presented here. Algorithms and software were developed for the following means of analyzing the ISE layer with OCT: (1), automated ISE layer isolation in the B-scans, (2), production of an en-face view of the ISE reflectance, (3), alignment and overlay of (2) onto reflectance images of the retina, and (4), alignment and overlay of (3) with microperimetry sensor points.
Tests were carried out by comparing outputs of groups of datasets from normal and dry age related macular degeneration (AMD) subjects. Scalar measurements for correlation with disease condition included the mean and standard deviation of the ISE reflectance over the en-face image. Other aspects of the algorithms and software that were prototyped and tested included an automatic marking of geographical atrophy that can be calculated from a distance measurement between the ISE and retinal-pigment epithelium (RPE) layers. The techniques for automatically finding the ISE and RPE layers are novel to prior methods of others and are based upon a calculation of optical flow which, in a sense, tracks the edges of laminated structures across an image.
A very good statistical significance (e.g, P-value = 10-5) was shown in paired T-tests of these measurements with the population pools separated as normal and dry-AMD subjects. A display of en-face ISE layer reflectance shows a clear and recognizable difference between any of the normal and dry-AMD subjects in that they show generally uniform and nonunimorm reflectance, respectively, over the region near the macula. While no statistical tests were carried out with the microperimetry correlations, we could see the obvious point that regions of low sensitivity values also have nonregular and generally lower levels of ISE reflectance nearby.
The findings described above support the speculation that the photoreceptor integrity could be affecting both the ISE reflectance and the sensitivity numbers.
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