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J. van der Schoot, K. A. Vermeer, J. F. de Boer, H. G. Lemij; The Influence of Glaucoma on Retinal Reflectivity in SD-OCT Images. Invest. Ophthalmol. Vis. Sci. 2010;51(13):212.
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Spectral Domain Optical Coherence Tomography (SD-OCT) is increasingly used in glaucoma assessment. The RNFL thins in glaucoma. To determine its thickness, the RNFL needs to be segmented from deeper retinal layers. Segmentation requires a clear contrast between the various layers. Contrast of the layers is determined by differences in reflectivity. We explored the retinal reflectivity in SD-OCT images in healthy and glaucomatous eyes.
The peripapillary areas of 8 healthy and 8 glaucomatous eyes, scanned with the Spectralis OCT (Heidelberg Engineering, Dossenheim, Germany), were analysed in 4 quadrants at fixed locations. The reflectivity (as reported by the device) of each manually segmented retinal layer was determined. We used an analysis of variance to test any differences in retinal layer reflectivity, between healthy and glaucomatous eyes.
The mean reflectivity of the RNFL was significantly lower in glaucomatous eyes than in healthy eyes (0.506 [SE 0.015] vs 0.619 [SE 0.015], p < 0.01). In the Ganglion Cell Complex (GCC) (Ganglion Cell Layer and Inner Plexiform Layer) we found no difference in reflectivity between glaucomatous and healthy eyes (0.383 [SE 0.009] vs 0.387 [SE 0.009], p = 0.75). The contrast between the RNFL and the GCC was significantly lower in glaucomatous eyes than in healthy eyes (0.123 [SE 0.011] vs 0.232 [SE 0.011], p < 0.01).
The reflectivity of the RNFL was lower in glaucomatous eyes than in healthy eyes. Because the reflectivity of the GCC in both glaucomatous and healthy eyes was similar, the difference in reflectivity of the RNFL could not be due to media opacities. As a result, the contrast between the RNFL and the GCC was markedly lower in glaucomatous eyes. This may impair segmentation algorithms in glaucomatous eyes and therefore limit the use of SD-OCT in the management of glaucoma.
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