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D. Piñero Llorens, J. Moreno–Montañes, M. Diez–Cuenca, P. Fernandez, R. Rodriguez–Conde, M.J. Maldonado; Validation of the anterior chamber angle measurements with the Orbscan II system using two extrapolation methods . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5555.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare the iridocorneal angle measurement with conventional Gonioscopy (CG), using the Shaffer classification system, with the Orbscan system (OS), and to evaluate the validity of the OS for measuring the anterior chamber angle (ACA) width. Methods: ACA width evaluation was performed in 83 eyes of 49 subjects ranging in age from 31 to 90 years by an experienced examiner using two devices: the Zeiss four–mirror gonioscopy lens and the OS. With the OS the angles were determined using two extrapolation methods of the iris surface: plane and 2D polynomial. Results: Using CG we obtained 9 eyes with angle opened grade I, 16 eyes with grade II, 18 with grade III and 40 with grade IV. With the OS mean gonioscopic values obtained with the "plane" mode were larger than those measured with the "polynomial" mode (p<0.001). This device was unable to measure 6 of the 9 grade I angles. Among the 4 angle groups, there were statistically significant differences in Orbscan measurements (one–way ANOVA, p<0.001) for each extrapolation mode. Except for the comparison between grade II and III groups with the "polynomial" method, all results within angle groups were significantly different (p<0.01). Mean difference between the angle values obtained using the "plane" and "polynomial" methods was 4.12 ± 8.17 degrees and the range of agreement was 32.02 degrees. Conclusions: The "plane" extrapolation method of the OS is capable of detecting significant differences in the numeric gonioscopic measurements according to Shaffer classification criteria. The "polynomial" extrapolation method of the OS cannot differentiate between angles grade II and III. Both extrapolation methods are unable to quantify some occludable angles and cannot be used interchangeably.
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