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Karl G Csaky, Markie Dowing, Joost Felius, Tim Holmes; The Relationship between 2-Color Microperimetry (2-MP) and the Inner Segment Ellipsoid (IS/E) Integrity in Subjects with Dry Age-Related Macular Degeneration (AMD). Invest. Ophthalmol. Vis. Sci. 2014;55(13):5214. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Scotopic and photopic sensitivities are decreased in AMD but the relationship to anatomic changes within the retina remains unclear. Specifically the IS/E integrity may be an anatomic indicator of photoreceptor function, but the assessment of this layer has been hampered by challenges to segmentation and en-face integrity quantitation. The goals of the present study were 1) to develop and test novel image analysis software capable of isolating and quantifying IS/E integrity and 2) to understand the relationship between the calculated IS/E integrity and altered photoreceptor function as determined by changes in in 2-MP.
One eye from patients with early AMD (n=3), intermediate AMD (n=4) or central geographic atrophy (GA) (n=3) was examined. Following dark adaptation, rod-mediated sensitivities or following light exposure cone-mediated sensitivities were measured at 9-22 locations per eye within the retinal arcades using a modified fundus microperimeter (MP-1S, Nidek Technologies). Test locations were set up on a grid pattern and avoided areas of GA. IS/E integrity was determined using novel software that isolated the IS/E from 46 sequential scans centered on the fovea and spaced 15 μm apart of a spectral domain optical coherence tomography unit (Heidelberg Engineering) utilizing eigenvector calculations to calculate flow vectors that allowed for IS/E anomalies. Integrity values were divided into 5 distinct categories based on numeric scores of IS/E pixel intensities.
There was a statistical decrease in rod sensitivities in the geographic atrophy (GA) group compared with other AMD stages (P=0.025); early AMD (21.4 ± 4.7 dB), intermediate AMD (20.0 ± 5.2 DB) and GA (16.4 ± 8.0) - (mean ± SD). IS/E integrity values were assessed within subjects and demonstrated that both rod- and cone-mediated sensitivity were significantly associated with IS/E integrity category (linear mixed effects model, P=0.0002 and P=0.0037, respectively).
In this preliminary study, changes in both rod and cone sensitivities were statistically associated with IS/E integrity as determined by a novel software algorithm. Thus direct assessment of IS/E integrity may be a useful approach to understanding photoreceptor function in dry AMD.
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