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Several systems have been put forth to stage glaucoma severity, though there is no consensus system for staging glaucoma. Kulkarni et al. compare how several staging systems predict glaucoma disability measured using the NEI-VFQ questionnaire and the Assessment of Disability Related to Vision, a scored test of 9 task performance measures. The authors find that better-eye metrics predicted disability better than worse-eye metrics, and the two best metrics for predicting disability were better-eye mean deviation (MD) and integrated visual field loss (IVF) derived from point-wise integration of right and left eye visual field (VF) data. IVF loss and better-eye MD predicted disability to a very similar degree, which is perhaps not surprising given recent work by Asaoka and colleagues that demonstrate that MDs taken from better-eye and integrated VFs differ by less than two dB in over three quarters of glaucoma patients. As such, it is not clear whether better-eye truly predicts disability better than integrated VF loss, or whether both predict disability similarly because they rarely differ.
Better-eye MD is currently the best metric for staging glaucoma given that it is simple to calculate, requires no additional software, and is at least as associated with disability as any other staging system
Staging systems were evaluated for their association with disability using partial Spearman's correlation coefficients, and one should keep in mind that greater association does not necessarily mean that disability is more accurately predicted. Additionally, only the Hodapp-Anderson-Parish system incorporated location of VF loss into the staging, and staging systems which capture both the degree and location of VF loss may predict glaucoma-related disability better than those described here. The authors conclude, and I agree, that better-eye MD is currently the best metric for staging glaucoma given that it is simple to calculate, requires no additional software, and is at least as associated with disability as any other staging system. Given the findings presented, further evidence will be necessary to justify the use of more complex metrics when staging glaucoma.