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H.T. Nguyen, K.P. Pikey, S.K. Gardiner, G.A. Cioffi, S.L. Mansberger; Variability of HRT Parameters in Contour Line Placement, With and Without the Aid of Stereographic Photographs . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3369.
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© ARVO (1962-2015); The Authors (2016-present)
The use of optic disc photos in placing contour lines for images taken by the Heidelberg Retina Tomograph (HRT) has been advocated by many, but may not be necessary. The purpose of this study is to assess variability of repeated contour line placement on images taken by the HRT with and without the use of optic disc photos.
Patients and Methods: :
We randomly chose one eye of 71 patients who were imaged with HRT within a community screening in the developing world. Using the same image and in a random order, a single observer drew contour lines three separate times, twice with photos (C1 and C2) and once without photos (S). With variability defined as the absolute differences of the topographic parameters between two images drawn, we compared the variability of parameters when contour lines were placed using stereo photos |C1–C2| versus when not using photos |S–C1| or |S–C2|. Statistical analysis was performed using the nonparametric Mann–Whitney test for paired data.
There was no statistical difference between the groups in any of the 20 global topographic parameters (p > 0.1 in all cases). In fact, for seven of the parameters, the mean absolute difference (variability) between the two groups using photos |C1–C2| was greater than between one group without photos and one with photos |S–C1|. The parameters with greatest variability caused by differences in the contour line included maximum contour elevation, vertical cup/disc ratio, and rim volume; whereas the parameters with the least variability included maximum cup depth, rim/disc area ratio, and mean cup depth. However, none of these were statistically significant.
Optic disc photos did not decrease the intra–individual variability of contour line placement on any of the topographic parameters obtained with the HRT.
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