In this study, the authors have tested the effect of cocaine on light perception using 5dpf zebrafish larvae. This was achieved by bathing larvae in 50 µM cocaine hydrochloride for 8 h and by performing electroretinography to measure the field potential of the retina in response to light. Thus, this work consists of a technically solid three-replica single experiment. However, this is only one concentration and one developmental stage.
Why cocaine would affect retinal processing is much less clear but the authors suggest a possible link with dopamine signaling, based on the fact that cocaine inhibits monoaminergic neurotransmitter reuptake and dopamine is a classical monoamine that is abundant in the retina.
As in fish, consumption of cocaine in humans has been (occasionally) associated with slight vision impairment, however, the underlying mechanisms might differ and directly depend on the mode of administration.