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Rafael L Furlanetto, Sergio H Teixeira, Tiago S Prata, Norma Allemann, Augusto Paranhos; Cup-To-Disc Ratio Measured By 20MHz B-Scan Ultrasound In The Analysis Of The Optic Nerve Head In Glaucoma. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4738. doi: https://doi.org/.
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To evaluate the performance of the 20 MHz ultrasonography (US) in assessing the cup-to-disc ratio (CDR) of the optic nerve head in comparison with currently available structural tests for glaucoma.
This was a cross-sectional study including healthy volunteers and primary open angle glaucoma patients with wide range of visual field (VF) damage. All participants were submitted to high-resolution US with 20Mhz probe (VuMax II, Sonomed, Inc.), optic disc stereophotograph (SPH), spectral-domain optical coherence tomography (OCT; Cirrus HD-OCT) confocal scanning laser ophthalmoscopy (HRT) and VF testing. High-resolution US images were obtained using a para-axial orientation with closed eyelids, whereas the fellow eye was kept in primary gaze. The optic disc size was considered as the largest diameter of the scleral canal, whereas the cup size was considered as the largest diameter of the hypo-reflective area within the optic nerve head parallel to the scleral canal opening. Optic disc and cup measurements were obtained vertically and horizontally by an experienced examiner masked to clinical data, and CDR calculated. Statistical analysis included Bland-Altman plots and area under receiving operator characteristics curve (AUC).
We included 53 subjects (106 eyes; and 41 glaucoma patients and 12 normals), of which 56.86% were women. Mean age was 62.87±0.71 years in glaucoma and 62.3±6.17 years in control groups (p=0,898). Mean Mean Deviation (MD) was -15.39±9.9 dB in glaucoma group. When glaucoma diagnosis was determined by VF damage according to the Hodapp-Parrish-Anderson criteria, the AUC for US vertical CDR was 0.846 (95% confidence interval [CI], 0.761 - 0.931), whereas for SPH, HRT and OCT were 0.992 (95% CI, 0.979 - 1.0), 0.946 (95% CI, 0.905 - 0.988) and 0.988 (95% CI, 0.972 - 1.0), respectively (Graphic 1). The mean difference of CDR between SPH and US was 0.48 (95% CI, 0.19 - 0.76), as US tended to underestimate CDR measurements (Graphic 2).
Our findings suggest that 20 MHz US may provide a useful quantitative assessment of the optic nerve head and CDR in glaucoma. This may be advantageous mainly in eyes with media opacity, in which clear optic media-based exams, such as OCT, HRT and SPH, are unviable or do not provide reliable information. However, we observed that US tended to underestimate CDR results in comparison with other structural tests.
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