Test-retest variability of multifocal electroretinography in normal volunteers and short-term variability in hydroxychloroquine users

PURPOSE: To determine measurement variability of N(1)P(1) amplitudes and the R(1)/R(2) ratio in normal subjects and hydroxychloroquine users without retinopathy. DESIGN: Retrospective, observational study. SUBJECTS: Normal subjects (n=21) and 44 patients taking hydroxychloroquine (n=44) without retinopathy. METHODS: Multifocal electroretinography (mfERG) was performed twice in one session in the 21 normal subjects and twice within 1 year in the hydroxychloroquine users, during which time no clinical change in macular status occurred. MAIN OUTCOME MEASURES: N(1)P(1) amplitudes of rings R(1)–R(5), the R(1)/R(2) ratio, and coefficients of repeatability (COR) for these measurements. RESULTS: Values for N(1)P(1) amplitudes in hydroxychloroquine users were reduced compared with normal subjects by the known effect of age, but R(1)/R(2) was not affected by age. The COR for R(1)–R(5) ranged from 43% to 52% for normal subjects and from 43% to 59% for hydroxychloroquine users; for R(1)/R(2) the COR was 29% in normal subjects and 45% in hydroxychloroquine users. CONCLUSION: mfERG measurements show high test-retest variability, limiting the ability of a single mfERG test to influence a decision to stop hydroxychloroquine; corroborative evidence with a different ancillary test is recommended in a suspicious case.