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Editors Selection IGR 7-3

Disc Evaluation: Disc photography

Comment by Nicholas Strouthidis on:

22581 Agreement among glaucoma specialists in assessing progressive disc changes from photographs in open-angle glaucoma patients, Jampel HD; Friedman D; Quigley H et al., American Journal of Ophthalmology, 2009; 147: 39-44

See also comment(s) by Douglas Anderson •

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Although the HRT has been available for over a decade, no consensus has been reached as to how best to integrate its use in clinical practice. Most commentators recognize a potential role for detecting structural changes over time. However, a major barrier to acceptability is the fact that its 'true' performance cannot be judged in the absence of an acceptable reference standard. Optic disc stereo-photographs are often touted as the 'gold standard', although this is contentious. The subjective interpretation of stereophotographs is highly variable, even amongst experienced observers. Training of clinicians in this task is not standardized and great experience in disc interpretation by ophthalmoscopy does not necessarily confer an innate ability to interpret stereophotographs reliably and correctly. Given that the subjective evaluation of stereophotographs is so variable, it would seem illogical to adopt the same approach to HRT images. In some respects, using all of the data generated by the HRT to evaluate progression subjectively seems wasteful, when one can use the data to calculate a rate of change, which is an objective measure. Subjective assessment of HRT images was, however, the central conceit of a study by Vizzeri et al. (229) Three different HRT reports were assessed

A logical inference is that defining change solely on the basis of an unsatisfactory reference standard, given that additional data is provided by other methods, should be abandoned

(Moorfields Regression Analysis, Topographical Change Analysis and the Trend Analysis), with stereophotographs used as a reference standard. Agreement as regards progression was 'moderate to good' across all three HRT methods, whilst agreement between each method and stereophotograph assessment was similar but poor. Interestingly, the kappa score for stereophotograph assessment was 0.51 (moderate), which was lower than for most of the HRT comparisons. The authors quite rightly argue that, as different progressing subjects are identified by HRT and by stereophotography, different structural changes are being picked up by both methods. A logical inference is that continuing to define change solely on the basis of an unsatisfactory reference standard, given that additional data is provided by other methods, should be abandoned.

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