Threshold Amsler Grid as a Screening Tool for Asymptomatic Patients with Hydroxychloroquine Maculopathy

Abstract

Abstract: : Purpose: Patients taking hydroxychloroquine (Plaquenil) to treat inflammatory disorders such as rheumatoid arthritis and systemic lupus erythematosus are at risk of developing bull's eye maculopathy secondary to hydroxychloroquine toxicity. The standard Amsler Grid (AG), used to assess the central 10^o of the visual field, is currently widely implemented to identify such lesions. Unfortunately, AG is a suprathreshold target and may fail to detect relative central scotomas before they become absolute scotomas. The purpose of this study was to determine if the Threshold Amsler Grid (TAG) test, that varies light transmission through two cross-polarizing filters, allows increased sensitivity in the detection of scotomas caused by hydroxychloroquine toxicity. Methods: 57 patients taking hydroxychloroquine medications and 13 control patients were tested by AG, red Amsler Grid (RAG), and TAG. Patients with known visual defects due to other causes were excluded from the study. Results: Control patients who had never been treated with hydroxychloroquine did not reveal scotomas on any of the exams. Patients who were currently taking hydroxychloroquine revealed seven scotomas on AG, 17 scotomas on RAG, and 35 scotomas on TAG testing. The average area of the scotomas detected on standard Amsler Grid expanded from 42 square degrees of central field loss to 63 square degrees on RAG and 113 on TAG. Conclusion: By decreasing the perceived luminance of the suprathreshold Amsler Grid, Threshold Amsler Grid testing provides a novel alternative to detect shallow scotomas and areas of depressed retinal activity secondary to hydroxychloroquine toxicity. These scotomas may go undetected early on using standard or red Amsler Grid testing and lead to irreversible visual changes. TAG offers clinicians an easy to perform, quick, sensitive, and high-yield means to assess the central visual field in patients receiving hydroxychloroquine therapy. In addition, TAG can be used as a quantitative method to monitor the progression of macular changes in these patients. Supported in part by NIH Grant EY03040 and an unrestricted grant from RPB.

Keywords: visual fields • drug toxicity/drug effects • retinal pigment epithelium