Threshold Amsler grid as a screening tool for asymptomatic patients on hydroxychloroquine therapy

Background/aims: Patients taking hydroxychloroquine (HCQ) are at risk of developing classic bull’s eye maculopathy. Currently, the standard Amsler grid (AG) is one of the most useful methods to identify such lesions. However, AG is a suprathreshold target and may not detect relative central scotomas. The aim of this study was to determine if the threshold Amsler grid (TAG) test, which varies light transmission through two cross polarising filters, allows increased detection of scotomas caused by HCQ toxicity. Methods: 56 rheumatological patients taking HCQ and 12 similar patients not taking HCQ were tested by AG, red Amsler grid (RAG), and TAG. Results: No scotomas were observed in patients never treated with HCQ. Among patients who had been treated with HCQ, AG revealed scotomas in two of 56 (3.64%) patients; in contrast, six (10.7%) and 37 (66.1%) scotomas were identified by RAG and TAG testing respectively. Additionally, the average area of each scotoma detected by all three methods expanded from 34.5 square degrees of central field loss on AG testing to 71 square degrees on RAG and 117 on TAG. Conclusion: By decreasing the perceived luminance of the suprathreshold AG, TAG testing provides a novel alternative to detect shallow scotomas and areas of depressed retinal activity secondary to HCQ toxicity.