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Katie M Litts, Xiaolin Wang, Mark E Clark, Christine A Curcio, Yuhua Zhang; Reflectivity of cone photoreceptors in outer retinal tubulation (ORT) in age-related macular degeneration (AMD). Invest. Ophthalmol. Vis. Sci. 2016;57(12):29.
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© ARVO (1962-2015); The Authors (2016-present)
ORT is a gliotic formation of degenerating cone photoreceptors and Müller cells in interconnecting tubes commonly found in advanced AMD . By spectral domain optical coherence tomography (SD-OCT), ORT is a hyperreflective border surrounding a hyporeflective lumen in the outer nuclear layer (ONL) [1,2]. To investigate the microscopic structure of ORT and the capacity of cones as waveguides in ORT in vivo, we studied ORT appearance by multimodal imaging, including adaptive optics scanning laser ophthalmoscopy (AOSLO) and SD-OCT.
Four eyes of 4 subjects with advanced AMD underwent multimodal imaging, which included color fundus photography, infrared imaging, SD-OCT (Heidelberg Spectralis), and AOSLO, using a high-resolution research instrument [3,4]. ORT was identified in high density SD-OCT volume scans. Multimodal images were compared to examine ORT microstructure and reflectivity of cones in ORT.
ORT was identified in SD-OCT, as previously described in B-scans (Figure 1D) [1,2], and compared to AOSLO images (Figure 1). AOSLO of ORT revealed a hyporeflective structure with few waveguiding cone photoreceptors (Figure 1B). In contrast, en face OCT of ORT revealed a hyporeflective structure surrounded by a hyperreflective border (Figure 1C).
Lack of cone reflectivity in ORT by AOSLO suggests that signal generation via waveguiding in this modality requires intact outer segments , which are largely absent from ORT cones. Reflective cones in ORT by SD-OCT in contrast may depend in part on mitochondria as light scatterers within inner segments of these degenerating cells . Multimodal imaging of ORT may provide deep insight into cone degeneration and disease progression. 1. Schaal PMID 25635579. 2. Zweifel PMID 20008714. 3. Zhang PMID 24907433. 4. Zhang PMID 25935100. 5. Jacob PMID 25284764.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Figure 1. ORT (cyan arrowhead) imaged by AOSLO and SD-OCT. 82 year old man with geographic atrophy AMD OD. (A) AOSLO montage in grayscale overlaid on color fundus photograph. (B) AOSLO image of ORT in yellow box in A. (C) En face view of ORT from SD-OCT transverse reconstruction of high density B-scans through center of ORT (D, inset). (D) SD-OCT B-Scan along green line in A, revealing circular cross-section of a closed ORT  with internal hyporeflective lumen bounded by a hyperreflective border, located in the ONL.
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