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Almony et al report in this issue of the BJO (p 569) the use of a threshold Amsler grid (TAG) as a screening tool for asymptomatic patients taking hydroxychloroquine (HCQ). They studied 56 patients taking HCQ and 12 controls. Patients were tested with a “white on black” Amsler grid (AG), a “red on black” AG (RAG), and the threshold AG (TAG). TAG uses cross polarising filters to reduce the perceived luminance of the grid. Scotomas were detected in two patients (3.6%) with the standard AG and five patients (8.9%) with RAG, but 25 (45%) patients with TAG. The TAG testing detected the two positive AG screens and the five positive RAG screens. The authors concluded that TAG has increased sensitivity to the detection of subtle scotomas in patients taking HCQ. Unfortunately, because there is no “gold standard” for HCQ retinopathy in asymptomatic or presymptomatic patients without visible retinopathy the specificity of the TAG results is unknown.
If the scotomas seen on TAG were also detected reproducibly in the same location using another central field test (for example, Humphrey 10-2) this would provide evidence for the specificity of the TAG findings. I would encourage the authors to continue to follow their cohort of HCQ treated patients and perhaps even test the patients with the abnormal TAG findings again with an automated (Humphrey) 10-2 strategy or even …
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