The Pattern electroretinogram as an indirect measure of central dopamine

The retina contains numerous dopamine (DA) receptors as well as dopaminergic amacrine cells and, in animal models, the level of DA in the eye has been shown to be proportional to central DA levels. In this study, we investigated the potential for the pattern electroretinogram to be a sensitive indirect measure of central DA. This was done in the context of understanding the role of variations in DA levels as a function of variations in iron levels in women of reproductive age. Having a reliable indirect measure of DA is motivated by the invasive nature of direct measures. A total of 20 iron deficient non-anemic (IDNA) and 20 iron sufficient women (IS) were recruited and performed four visual tasks: (a) a pattern electroretinogram assessment, (b) a probabilistic selection task, (c) a contrast detection threshold task, and (d) a measure of spontaneous blink rate. Results showed that the latency but not the amplitude of the a- and b-waves of the electroretinogram varied as a function of iron status, with the latencies of both waves being longer for the IDNA than for the IS participants. In addition, contrast detection thresholds were significantly higher for the IDNA than for the IS participants. Critically, the amplitudes and latencies of the a- and b-waves were more strongly correlated with serum ferritin, the storage form of iron critical for DA synthesis and reuptake, than were either spontaneous or task-related blink rate. Finally, the latency of the a-wave was superior to spontaneous blink rate in classifying participants as either IDNA or IS. In sum, the pattern electroretinogram showed itself to be promising as an indirect measure of DA in the context of human iron deficiency.