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Akihito Uji, Tomoaki Murakami, Noriyuki Unoki, Ken Ogino, Shin Yoshitake, Yoko Dodo, Nagahisa Yoshimura; Parallelism for Quantitative Image Analysis of Photoreceptor-Retinal Pigment Epithelium Complex Alteration in Diabetic Macular Edema. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3422.
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© ARVO (1962-2015); The Authors (2016-present)
To propose a new method to evaluate the degree of photoreceptor-retinal pigment epithelium (RPE) complex alteration quantitatively and comprehensively using “Parallelism” in spectral-domain optical coherence tomography (SD-OCT), and to investigate the association between parallelism and visual acuity in eyes with diabetic macular edema (DME).
A consecutive series of 90 eyes of 79 patients with DME and 30 healthy eyes of 30 volunteers were enrolled in this retrospective observational cross-sectional study. SD-OCT images were obtained using a Spectralis OCT system in all subjects. Rectangular areas encompassing the subfoveal photoreceptor layer of OCT images were skeletonized through a filtering process, and the orientation of segmented lines in the image was termed “Parallelism,” which reflected the image complexity. Discontinuity of the external limiting membrane (ELM) and the junction between the inner and outer segments (IS/OS) at the fovea was categorized by the graders into 3 groups as follows: intact (+), discontinuous (±), or absent (-). Moreover, the presence of hyperreflective foci in the outer retinal layers was assessed by the graders. The relationships between parallelism and visual acuity and between parallelism and qualitative assessment of photoreceptor layers by the graders were evaluated.
Parallelism was significantly lower in eyes with DME than in normal eyes (P < 0.0001), and correlated strongly with visual acuity in eyes with DME (R = -0.592; P < 0.0001). There were significant differences between the three ELM or IS/OS groups in parallelism (P < 0.0001) and logMAR VA (P < 0.0001), and the eyes with intact IS/OS or ELM had better visual acuity and higher parallelism than eyes with discontinuous or absent IS/OS or ELM. Parallelism was significantly higher (P < 0.0001) and logMAR VA was significantly better in the group without hyperreflective foci in the outer retinal layers compared with the group with hyperreflective foci in the outer retinal layers.
Parallelism has potential as a robust and easily determined parameter that reflects structural changes of photoreceptor layers including not only discontinuity of IS/OS or ELM lines, but also other changes such as the presence of hyperreflective foci.
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