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Seng Chee Loon, Wan Ling Wong, Victor Koh, Paul R. Healey; Optic Nerve Head Tilt: Correlation Of Different Methods Of Objective Measurement. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3003.
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To examine the correlation of different objective methods of optic disc tilt measurement - index of ovality and 2 HRT-based optic disc tilt measurements.
This is a prospective study involving 20 patients (40 eyes), with significant optic disc tilt detected clinically, recruited from the general ophthalmology clinic. HRT images (SD < 50) were procured for all 40 eyes. The optic disc contours were defined as the inner edge of Elschnig’s ring. The first method (A), index of ovality, is the ratio of minimum over maximum optic disc diameter. The second method (B) was an observer-dependent disc tilt measurement on Heidelberg Retinal Tomography (HRT) 3-D topographic images. The third method (C) was an automated HRT-derived parameter, horizontal disc tilt (tilt angle of the reference plane relative to a plane perpendicular to the optical axis). Analysis was done using t-test, intra-class correlation (ICC) and Bland-Altman (BA) graphs.
A total of 40 eyes were included (mean age 54.6 ± 16.1, 75.0% male, mean spherical equivalent -0.76 ± 0.69 dioptres). The mean tilt and standard deviation (SD) from the axis perpendicular to the visual axis of methods A, B and C were 0.85 degrees (SD 0.09,) 6.80 degrees, (SD 3.82 and 4.11 degrees (SD 3.59) respectively. There was a statistically significant difference between the three mean tilt measurements (P <0.001). The ICC values between A and B, A and C, B and C were -0.015, -0.13 and 0.43 respectively. The BA graphs suggested little agreement with the ovality method. But we found that the agreement between the manual and HRT methods to be much better.
The ovality method shows low correlation with the other methods of optic disc tilt measurements but there was agreement between the manual and automated HRT methods . The HRT automated method can be a possible way for diagnosing for optic disc tilt determination.
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