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B. Kiss, H. Resch, C. H. Resch, B. Brela, R. Schubert, C. Vass; Segmental Macular Retinal Layer Measurements With HR-OCT in Healthy Subjects of Different Refractive Status. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1011.
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Fast scanning high resolution optical coherence tomography (HR-OCT) enables quantitative analysis of histological retinal layers. Aim of the study was to measure overall macular thickness of retinal ganglion cell plus inner plexiform layers (RGIPL) and mean maximum thickness after segmental analysis measured by HR-OCT in healthy subjects in order to assess characteristics to their refractive status.
Macular HR-OCT scans (Cirrus, Carl Zeiss Meditec) were obtained in 62 healthy subjects (refraction between -5.5 sph and +6.0 sph) using raster scanning of a 20x20 field at a resolution of 512x128x1024 voxels. The scans were analysed using a software algorithm for automated segmentation and quantification in retinal layers. The macular area scans were dissected into one central area and 4 concentric rings with an incremental radius of 500 µm and further subdivided into 16 sectors each. For each of the 16 axis orientations in respect to the fovea the concentric ring segment with the maximum thickness has been determined and these segments have been averaged as the mean maximum thickness of the retinal layers. This was performed separately for the retinal nerve fiber layer (RNFL), the RGIPL and the total retinal thickness (RT). The impact of refractive error on mean maximum thickness of retinal nerve fibre layer (RNFL), RGIPL and total retinal thickness (RT) as well as on mean macular thickness of those layers within the central 8 deg radius has been analysed using ANOVA.
Mean 8deg RT and RGIPL was thicker in hyperopes than in myopes (p=0.02, p<0.01) and mean 8deg RNFL was thinner in hyperopes than in emmetropes and myopes (p=0.01, p=0.04). Mean maximum RT and RGIPL did not show any significant difference, while mean maximum RNFL was thinner in hyperopes than in emmetropes (p=0.04).
Differences in mean 8deg RT, RGIPL between the refractive groups could not be confirmed when comparing the mean maximum thicknesses of the retinal layers around the fovea. These findings might be explained by a refraction dependent magnification of the macular OCT scans. The effective scan areas of hyperopes are smaller compared to myopes thus fractions of thicker RGIPL take up a larger proportion of the image. Our findings indicate that maximum RGIPL within the macula might be a representative parameter for patients with different refractive errors in glaucoma diagnosis.
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