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Editors Selection IGR 9-2
Examination methods: Laser scanning: MRA and GPS
Comment by Stefano Miglior on:
18170 The effect of disc size and severity of disease on the diagnostic accuracy of the Heidelberg Retina Tomograph Glaucoma Probability Score, Zangwill LM; Jain S; Racette L et al., Investigative Ophthalmology and Visual Science, 2007; 48: 2653-2660
The cross-sectional study by Zangwill et al. (583)about the effect of disc size and severity of disease on the diagnostic accuracy of HRT Glaucoma Probability Score and Moorfields Regression Analysis is based on the analysis of 99 glaucomatous and 62 normal eyes, examined by means of both MRA and GPS. The 99 glaucoma eyes have been classified on the basis of the AGIS visual field score and disc size was used as covariate in the analysis. The study is characterized by a sophisticated statistical analysis which allowed to take into account the severity of glaucoma and disc size when calculating the standard parameters of diagnostic accuracy (sensitivity, specificity and AUROC) as well as the Likelihood Ratios, which have a practical impact in everyday clinical practice.
HRT3 may be helpful both in confirming a normal disc, by means of GPS, and in confirming a suspicion of glaucoma, by means of MRA
The results of the study show that both MRA and GPS have a good diagnostic accuracy, confirming the observations of several previous investigations, and that diagnostic accuracy was significantly affected by severity of glaucoma and by disc size, although the latter at a lesser extent. The MRA likelihood ratios of an Outside Normal Limits result were all six, indicating a moderate to large effect on the posttest probability of glaucoma. The GPS Outside Normal Limits value had a moderate effect on posttest probabilities of glaucoma, with values ranging from 4.04 to 10.02. The likelihood ratios for a Within Normal Limits result were smaller for GPS than for MRA, with most GPS likelihood ratios having a moderate to large effect on posttest probabilities (range, 0.014 - 0.18), whereas MRA likelihood ratios had an insignificant effect (range, 0.20 - 0.59). Borderline values had an insignificant or weak effect on posttest probabilities, with likelihood ratios for MRA ranging from 1.06 to 3.54 and for GPS ranging from 0.66 to 1.19. In terms of clinical practice these results are relevant, as they indicate that HRT3 may be helpful both in confirming a normal disc, by means of GPS, and in confirming a suspicion of glaucoma, by means of MRA.
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