To examine the electroretinographic findings derived by full-field electroretinography (ERG) and multifocal electroretinography (mfERG) in patients taking HCQ for different periods of time, including those without clinically visible evidence of toxicity.
The records for 26 consecutive patients (51 eyes, age 19-79) who had used HCQ for 1-30 years and who had an ERG and/or mfERG were reviewed.
The patients fell into 5 groups, according to the results from their electrophysiological and clinical evaluation: no abnormalities (n = 13), cone b-wave delay (n = 2), decreased ERG amplitude (n = 6), borderline toxicity (n = 2) and toxicity (bull's-eye maculopathy; n = 3). Oscillatory potential (OP) amplitudes were decreased in many of the patients, even in the absence of any other clinical or ERG abnormality. MfERGs were normal in these patients without other abnormalities, but showed a bull's eye pattern of damage in a patient with clear toxicity. The full-field ERG parameters (including OPs) showed little relationship to the duration of HCQ usage or the cumulative dose.
A substantial subgroup of patients showed varying degrees of diffuse ERG abnormality despite having no clinical signs (visual or fundus changes) of toxicity, and despite a range of cumulative doses. The mfERG showed toxicity, but its sensitivity in detecting early change remains to be determined. Further work is needed in order to separate pharmacological actions of the drug, retinopathy from the systemic disease, and potential toxic effects.