Possible indication of dopaminergic blockade in man by electroretinography

In view of the finding that dopamine is the principle neurotransmitter in the retina, an attempt was made to demonstrate dopaminergic receptor blockade by means of electroretinography. In an open experimental setting, the effect of 50 mg thioridazine was compared with that of placebo in 2 groups of 10 normal volunteers. In the placebo group, the post-drug scotopic electroretinogram (ERG) was not significantly different from the pre-drug ERG, while in the thioridazine group, the post-drug scotopic ERG showed prolongation of 'a' wave latency time, prolongation of 'b' wave evolution time, and diminution of 'b' wave amplitude.