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Editors Selection IGR 16-3
Clinical Examination Methods: Ruling out glaucoma based on VF indices
Comment by Nomdo Jansonius on:
59182 Role of Visual Field Reliability Indices in Ruling Out Glaucoma, Rao HL; Yadav RK; Begum VU et al., JAMA ophthalmology, 2015; 133: 40-44
Rao et al. studied the influence of the visual field reliability indices (fixation loss [FL] and false-positive [FP] and false-negative [FN] response rates) on the ability of standard automated perimetry (SAP) to rule out glaucoma in glaucoma suspect patients. In this study, glaucoma suspect patients were patients referred by general ophthalmologists because of a suspected optic disc ‒ that was in the end deemed normal by glaucoma specialists. Suspects with a high FN response rate were found to have more often an abnormal SAP (Humphrey field analyzer SITA standard 24-2) test result, based on the glaucoma hemifield test and the pattern standard deviation (PSD). FL and FP response rate were not associated with the SAP classification.
At first sight, these results are surprising. As the authors mention, FN response rate is supposed to be related to the presence and severity of glaucoma and to have little influence on the test result. FP response rate, on the other hand, is considered to be the most important indicator of visual field reliability. This was recently confirmed in a longitudinal study reporting that the FP response rate had a strong influence on the SAP mean deviation (MD) whereas the role of the FN response rate was negligible (Junoy Montolio et al. IOVS 2012).
The lack of influence of the FP response rate in the current study might be related to the very low median FP response rate of only 1%. The association between a high FN response rate and an abnormal SAP test result triggers the question if these cases were really normal - or is the combination of an elevated FN response rate, an abnormal glaucoma hemifield test, and an abnormal PSD pointing to early glaucoma? Only longitudinal follow-up of either the discs or the fields could settle this issue. The study relies on the assumption that disc abnormalities always precede visual field abnormalities. However, population-based studies have shown that glaucoma with field abnormalities preceding disc abnormalities is not rare (Czudowska et al 2010).
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