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W. S. Queiroz, D. R. Lucena, M. L. V. Rodrigues, J. S. Paula; Optic Cup Size/ Retrobulbar Optic Nerve Thickness Proportion Assessed by Echography Correlated With Optic Cup/ Disc Ratio in Glaucomatous Eyes. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5806.
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To determine whether 20 MHz B-scan ultrasonography assessment of the proportion between optic cup size and retrobulbar optic nerve width (C/RON) is significantly correlated with optic cup/ disc ratio (C/D) obtained with Optical Coherence Tomography (OCT) and fundus biomicroscopy (FB).
Fifteen (30 eyes) open angle glaucoma patients underwent echographic measurements of vertical optic cup size and maximal vertical interpial diameter of the retrobulbar optic nerve. All measures were taken by one experienced ultrasonographer, using a 20 MHz B-scan probe placed in the temporal limbus (transverse plane), after topical anesthesia. Vertical C/D ratio was estimated by another author in a masked fashion, through a direct view of optic disc at FB and the fast optic disc protocol of OCT. Linear regression analysis and correlation tests were performed to verify the correlation between C/RON and FB or OCT. Bland-Altmann plot was used to analyze the agreement between C/RON and FB or OCT measurements.
Mean C/Ds were 0.72±0.15 and 0.70±0.17, obtained with OCT and FB, respectively. Mean C/RON assessed was 0.49±0.15. Spearman correlation tests showed better correlation between C/RON and FB (r= 0.782, P<0.0001) than between C/RON and OCT (r=0.664, P=0.0002). Bland-Altmann plot revealed good agreement between C/RON and FB (95% confidence interval: 0.16 to 0.25).
Echographic assessment of C/RON proportion may be correlated with C/D in glaucomatous eyes and could be considered as a ratio of optic excavation, within a different decimal scale. Thus, C/RON proportion could be used to assess optic nerve damage due to glaucoma in cases of no visualization of the optic disc.
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