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Andrew Francis, Justin Wanek, Jennifer Lim, Mahnaz Shahidi, ; Depth Resolved Enface Imaging of Inner Retinal Pathologies and Photoreceptor Integrity in Diabetic Retinopathy. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3637.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies have shown the brightness of the photoreceptor inner/outer segment (ISOS) junction is an indicator of photoreceptor integrity. The purpose of this study is to relate intensity abnormalities in an inner retinal layer to the ISOS intensity and retinal thickness in patients with diabetic retinopathy using spectral domain optical coherence tomography (SD OCT).
Ten subjects (age; 60 ± 6 years) diagnosed with diabetic retinopathy (DR) and 10 healthy control subjects (age; 55 ± 8 years) of similar age participated in the study. High density SD OCT images were obtained using a commercially available instrument (Spectralis; Heidelberg). The volume scans consisted of 145 raster B-scans separated by 31 microns, covering a 4.4 x 4.4 mm area centered on the fovea. Depth-resolved enface images of the ISOS junction and an inner retinal layer (IRL), located at the normal anatomical depth of the inner plexiform layer, were generated. From the IRL enface image, multiple dark regions (100 µm x 100 µm) corresponding to DR pathologies were selected. For each region, an intensity index was calculated as the ratio of the mean intensity to the average intensity of the corresponding region in all control subjects. Retinal thickness indices were calculated in a similar manner.
In normal control subjects, IRL and ISOS enface images displayed relatively uniform intensity and patterns of the retinal vasculature outside of the fovea (Figure 1). In DR subjects, the IRL enface images had patches of dark regions which corresponded to cystoid macular edema on SD OCT B-scans (Figure 2). The ISOS enface images showed intensity variations due to overlying retinal pathologies or scars from previous laser treatments. The intensity indices of the dark regions ranged between 0.09 and 0.96 in the IRL enface image and 0.46 and 1.26 in the ISOS enface image. The ISOS intensity index was significantly correlated with the IRL intensity index (R = 0.6; p = 0.003; N = 27). The retinal thickness indices ranged between 0.79 and 2.18. The retinal thickness index was negatively correlated with the IRL intensity index (R = -0.6; p < 0.001; N = 27).
Intensity abnormalities of the inner retinal enface image are significantly correlated with ISOS integrity and retinal thickness and may have potential diagnostic and therapeutic implications in patients with diabetic retinopathy.
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