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E. Sharifi, J. B. Biebesheimer, H. Ishikawa, S. Lin; Ultrasound Biomicroscopy: Effect of Upright versus Supine Positioning on Anterior Chamber Width Using a New Probe. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1209. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Ultrasound biomicroscopy (UBM) is a promising technology for quantitative assessment of the anterior chamber angle width. Concerns over UBM in the past have arisen since measurements are not made in the physiologic upright position. Recent advances in UBM allow assessment of patients in the upright position and also have the added advantage of ease of use. This study specifically assesses the differences in the quantitative measurement between the standard supine position and the newer upright position.
Twelve eyes of 12 consecutive patients with clinically known narrow angles were examined with ultrasound biomicroscopy (VuMax II, Sonomed, Lake Success, NY). Patients were placed in a dark room with candela measurements that were nearly undetectable. All patients were examined in the temporal quadrant of the right eye, in the upright and supine position. Supine scans were performed with an eyecup and water bath system; upright scans were performed with step-off and membrane on the probe to obviate the water bath. Raw images were processed to make them compatible with UBM Pro 2000 software, which was then used to calculate the Angle Recess Area (ARA), defined as the triangular area demarcated by the anterior surface of the iris, the corneal endothelium, and a line perpendicular from the corneal endothelium drawn 750 microns anterior to the scleral spur. The ARA in the supine and upright position was compared using a two-tailed paired t-test.
The mean ARA in the supine position was 0.090 mm2. The mean ARA in the upright position was 0.080 mm2. This represents an 11.5% decrease in ARA in the upright compared with the supine position, although this was not statistically significant (p=0.08).
Quantitative UBM reveals no statistically significant difference in anterior chamber angle width when comparing Angle Recess Areas in the supine and upright positions. A trend toward slightly narrower angles in the upright position is consistent with a more anterior position of the lens-iris diaphragm when the effect of gravity is neutralized. Upright UBM may allow more physiologic evaluation of the anterior chamber angle.
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