Characteristic electroretinographic findings in quinine retinal toxicity

Purpose. To describe unique electroretinographic (ERG) findings in a group of patients taking quinine and who report vision loss and night blindness. Method. Careful clinical and electroretinographic evaluations were performed on seven patients who had the common feature of having ingested quinine and reporting visual loss. Electroretinographic evaluations were obtained in a standardized fashion and included a rod-isolated response, a dark-adapted bright flash response, oscillatory potentials, and photopic bright flash and 30 Hz flicker responses. Results. All patients had a distinctive electroretinographic pattern: the photopic bright flash ERG was attenuated, sometimes with missing oscillatory potentials, and significantly reduced to extinguished rod responses. The dark-adapted bright flash response had a characteristic negative waveform; b-wave amplitude reductions in all cases exceeded a-wave amplitude reductions. To index inner- versus outer- retinal dysfunction, b- to a- wave amplitudes were calculated. For this group of patients, median b- to a- wave amplitude ratios were 0.68 (range 0.3 to 1.6). The clinical evaluation typically found that patients complained of nyctalopia, and on fundus examination no patients had a pigmentary retinopathy, but some patients had a diffuse retinal atrophy, mild vascular attenuation, and optic nerve pallor. Discussion. The characteristic electroretinographic pattern in quinine toxicity add to a body of disorders whose differential diagnosis includes negative waveforms. The results are discussed within the context of inner- versus outer- retinal dysfunction.