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H. Wong, M.J. Sinai, D. Garway-Heath; Circle Versus Ellipse: A Comparison of GDx Measurements Obtained by Using Two Different Optic Disc Marking Methods . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3377.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare the utility of employing a peripapillary circle of fixed diameter against the standard operator-marked ellipse, when analysing scanning laser polarimeter images. Methods: Fifty-six normal eyes and 55 glaucomatous eyes were imaged using the GDx with a Variable Corneal Compensator. Retinal nerve fibre layer (RNFL) thickness was measured with the ellipse and with a circle of fixed diameter (85 pixels) centred around the disc. Receiver operating characteristic (ROC) curves were generated for all parameters. Results: For both populations, the circle method resulted in lower average thickness values (paired sample t-test; p<0.001). This method also produced less inter-individual variability for RNFL thickness and most of the summary output measures in normal eyes. The area under the ROC curve for the most discriminating parameters was larger for the fixed circle. Conclusions: The fixed circle method may have better discriminating capability than the ellipse for GDx measurements, and its relative simplicity may reduce inter-operator variability.
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