RESEARCH - TAG screening for asymptomatic patients on Plaquenil therapy

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British Journal of Ophthalmology 2005;89:569-574

© 2005 BMJ Publishing Group Ltd

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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.

http://bjo.bmjjournals.com/cgi/content/abstract/89/5/569

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