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Editors Selection IGR 19-2
Structural Examination Methods: Agreement among three OD measurement methods
Comment by Murray Fingeret on:
27017 Agreement among 3 methods of optic disc diameter measurement., Rao HL; Puttaiah NK; Babu JG et al., Journal of Glaucoma, 2010; 19: 650-654
Measuring the optic disc for its size is one of the steps performed as it is evaluated for signs of glaucomatous damage. There are different ways the disc size may be evaluated with the authors of this study comparing several of them. Rao et al. (1692) compare disc photography, clinical exam and Heidelberg Retinal Tomography in this prospective, observational study. The clinical method consisted of using the vertical or horizontal slit width, adjusted to match the disc diameter with the use of a correction factor. The HRT provides the disc dimensions once the contour line is drawn. For optic disc photographs, the horizontal and vertical disc diameters were obtained using calipers. The results, using intraclass correlation coefficient and Bland and Altman plots, showed that the optic disc photographs and clinical exam agreed closely, with both measurements differing from the HRT measurements. This is not surprising, as clinicians who use the HRT have found its measurements do not always match clinical appearance.
HRT measurements do not always match clinical appearance
Measurements obtained with one instrument often do not agree with a different one, which is in large part what the authors found. The limitation for the study is that disc size was manually determined by locating specific markers on the optic disc. Thus a person's ability to determine these landmarks may vary leading to differing results. The authors did not evaluate the new spectral OCTs that detect
Measurements obtained with one device may not be similar when a different one is used
the tips of the retinal pigment epithelium and determine optic disc size automatically. Perhaps this innovation, taking the need to manually determine the contour line or disc margin out of the clinician's hand will lead to better accuracy and improve agreement between instruments. Until this is investigated, the clinician needs to remember that measurements obtained with one device may not be similar when a different one is used.
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