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Editors Selection IGR 20-2

Diagnostic Methods: Disparities among diagnostic technologies

Comment by Linda Zangwill on:

50629 Understanding disparities among diagnostic technologies in glaucoma, De Moraes CG; Liebmann JM; Ritch R et al., Archives of Ophthalmology, 2012; 130: 833-840

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There have been numerous studies highlighting the relatively modest agreement between structural and functional tests for glaucoma detection. However, few studies have focused on exploring the reasons for the discrepancies among diagnostic tests. In this study by De Moraes and colleagues, 138 eyes of 69 patients with glaucomatous optic neuropathy were tested using three different diagnostic tests, standard automated perimetry (SAP), the multifocal visual evoked potential (mfVEP), and Straus time-domain optical coherence tomography (OCT) to determine reasons for differences in the test results. The authors assumed that if two of the three tests agree regarding the presence and topographic location of an abnormality (as defined using instrument specific comparison to internal normative databases), it is likely that there is true glaucoma damage. For the 94 hemifields with abnormalities, the three tests were consistent in showing the same hemifield abnormality in 50 hemifields (53%). At least two tests were abnormal in 65 of the 94 hemifields (69%); the authors then investigated why the third test did not also indicate glaucomatous damage. In each of these 94 hemifields, the authors identified a clear reason for the discrepancy related to known limitations of each technique and inter-individual variability. Often there was some evidence of glaucomatous damage, but the expected test locations did not each statistical significance or the specific criteria used to define the abnormality were not met. The authors conclude that agreement among diagnostic tests may be better than summary statistics suggest and that disagreements among tests do not necessarily indicate discordance in the structure-function relationship.

Understanding the limitations of each test, and how to identify goodquality information is essential for appropriate clinical decision-making

Moreover, the authors highlight the importance of understanding the strengths and limitations of each test so that clinicians can appropriately integrate the often conflicting test results in their management of glaucoma patients. Another reason that test results may not agree is that the quality of each test may not be optimal. Understanding the limitations of each test, and how to identify good-quality information is essential for appropriate clinical decision making.

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