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Marketa Cilkova, Adam M Dubis, Esther Papamichael, Padraig Joseph Mulholland, Andrew Rider, Steven Dakin, Adnan Tufail, Gary S Rubin, Roger S Anderson; Differences in retinal cone morphology between subjects with dry AMD and healthy participants observed with OCT and narrow-angle Heidelberg Retinal Angiograph 2. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4936.
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© ARVO (1962-2015); The Authors (2016-present)
We used a multimodal imaging approach to uncover differences in outer retinal layer and cone mosaic morphology between patients with dry age related macular degeneration (AMD) and age matched normal controls.
Five subjects with early to intermediate dry AMD (69 ± 5 years) and five age matched controls with healthy eyes (66 ± 5 years) underwent Spectralis 30° infrared reflectance imaging, optical coherence tomography (OCT) and cone photoreceptor imaging using a narrow-angle Heidelberg Retinal Angiograph 2 (HRA2). OCT images were analyzed manually using the manufacturer’s software and callipers to measure outer retinal (outer plexiform layer to retinal pigment epithelium) and outer segment (ellipsoid zone to retinal pigment epithelium) thickness. The HRA2 was modified in order to visualise parafoveal cone photoreceptors through a reduction in the scan angle from 30° to 3° and a subsequent increase in the system resolution. The internal fixation target was set at 9°. Images of two pairs of adjacent regions of interest were acquired for each subject and photoreceptor densities were determined with a manual counting algorithm. Photoreceptor densities of adjacent pairs were compared to OCT layer thicknesses at the same locations.
AMD patients had on average fewer visible cones than normal controls (3131 vs. 3994 cones/mm2). In addition to the global reduction of detectable cones, there was also variable loss in photoreceptor density with the adjacent regions of interest varying by 9.0% for the normal controls and 22.2% in the AMD patients (p=0.001). Interestingly, there was no significant difference in outer retinal thickness between normal controls and AMD subjects at the locations of imaging (p=0.23), however, there was a significant reduction in outer segment thickness in the AMD group (p=0.011).
While our data is limited, it suggests that the ‘lost’ photoreceptor cells may still be present in subjects with AMD, however their outer segment morphology may be altered.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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