Early retinal electrophysiology changes in quinine overdose

To report the early and subsequent electrophysiological findings of 2 patients following quinine overdose.

Serial assessments including: Medical history, visual acuity (VA), fundus autofluorescence, spectral-domain macular optical coherence tomography (OCT) and full-field electroretinogram (ffERG) were performed on 2 patients, between 2 and 47 days after quinine overdose.

Both patients experienced a similar clinical course. After almost total vision loss within the first 24 h, VA dramatically improved by day 3. Early OCT changes demonstrated central macula hyperautofluorescence, which coincided with a hyperreflectivity of the macular inner retina on OCT. The initial ffERG findings demonstrated changes consistent with marked inner retinal dysfunction of the cone system, affecting both the cone ON- and OFF-bipolar cell pathways. In contrast, rod bipolar cell function was unaffected in the early phase of toxicity. Between days 10 and 17, the retinal arterioles showed narrowing which coincided with attenuation of ffERG parameters of rod system inner retinal function between days 10-40.

These cases suggest the early stages of quinine toxicity affect function of the presynaptic cone bipolar cell junction. This is then followed by retinal arteriolar attenuation and the well described electronegative scotopic ffERG.