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

PURPOSE To determine measurement variability of N1P1 amplitudes and the R1/R2 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 N1P1 amplitudes of rings R1-R5, the R1/R2 ratio, and coefficients of repeatability (COR) for these measurements. RESULTS Values for N1P1 amplitudes in hydroxychloroquine users were reduced compared with normal subjects by the known effect of age, but R1/R2 was not affected by age. The COR for R1-R5 ranged from 43% to 52% for normal subjects and from 43% to 59% for hydroxychloroquine users; for R1/R2 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.