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Andrew Hong Nguyen, Sharon Henry, Joseph Caprioli, Kouros Nouri-Mahdavi; The Fovea-Disc Axis Angle and Macular Thickness Vertical Asymmetry across The Temporal Raphe. Invest. Ophthalmol. Vis. Sci. 2017;58(8):694.
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© ARVO (1962-2015); The Authors (2016-present)
Vertical thickness asymmetry in retinal ganglion cell layer (GCL) or GCIPL (combined thickness of GCL with inner plexiform layer) across horizontal raphe is a strong biomarker for early glaucoma. We tested the hypothesis that the fovea-disc axis angle (FoDi angle) affects vertical asymmetry in GCIPL thickness across temporal raphe in normal subjects as measured with spectral domain optical coherence tomography (SD-OCT).
131 eyes (68 normal subjects) with macular and RNFL SD-OCT images were enrolled. FoDi angle was estimated by the RNFL imaging algorithm of Spectralis SD-OCT. Macular images acquired with Posterior Pole Algorithm were segmented. GC/IPL thickness was calculated on a horizontal 8x8 array of 3-degree superpixels (Fig.1). Vertical asymmetry was defined as the difference in average thickness of the 3 most temporal superpixels above and below horizontal meridian (Fig.1). Association of FoDi angle and other predictors with vertical GCIPL asymmetry was explored on bivariate plots and correlation and multivariate regression analyses correcting for contribution of two eyes of same subjects.
Median (IQR) age of study sample was 54.5 (49.5-61.8) years. The median (IQR) FoDi angle was –6.7 (–9.5 to –4.8) degrees. A more negative (inferiorly tilted) FoDi angle was associated with thinner inferior compared to superior GCIPL thickness on superpixels adjacent to the temporal raphe (superpixels 5.1-5.3 vs. 4.1-4.3, r=0.334; p<0.001; Fig. 2) whereas the second row of temporal superpixels farther from raphe did not show this tendency (r=0.025, p=0.788). FoDi angle was not associated with central GCIPL asymmetry (i.e. asymmetry between superpixels 3.4-3.6 vs. 6.4-6.6 on Fig.1, r=0.121; p=0.194). No other clinical factor including age or axial length correlated with vertical asymmetry (p>0.312). Correlation analyses of absolute GCIPL thickness along raphe with FoDi angle demonstrated that progressively thicker superior GCIPL along raphe with more negative FoDi angle was the likely cause of the changing asymmetry.
GCIPL vertical thickness asymmetry adjacent to the temporal raphe varies as a function of the FoDi angle whereas temporal superpixels farther from the raphe do not demonstrate this tendency. This finding has important clinical implications as new SD-OCT algorithms are developed for incorporating vertical GCIPL asymmetry as a biomarker for early detection of glaucoma.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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