Zebrafish larvae exposed to cocaine accumulate cocaine in the eye. Here we used electroretinography (ERG) to assess the effect of accumulated cocaine on the outer retina function of zebrafish larval eyes. We found a statistically significant increase of the ERG responses at moderate to bright light levels, showing that the presence of cocaine increased retinal responses to light, especially in the bright light range. This increase may be linked to dopamine in the retina, since cocaine is known to increase effective dopamine concentrations in the nervous system.