Dyes such as brilliant blue (BBG) are used during vitreoretinal surgery to visualize anatomical structures. By adding deuterium oxide (D2O), surgeons have tried to create a dye mixture heavier than water to facilitate staining of the inner limiting membrane (ILM) without prior fluid-air exchange. This study investigated the effect of 0.4 ml BBG (Fluoron, Ulm, Germany) mixed with 0.13 ml/ml D2O and D2O on retinal function of a pseudo in vivo model using bovine and human whole mount cultures. Bovine and human retinas were superfused, and the electroretinogram (ERG) was recorded. BBG with 0.13 ml/ml D2O and D2O were applied epiretinally, different staining periods (10, 30, 60 and 120 s) were tested, and ERG recovery was monitored. 1 mM aspartate was added to the nutrient solution to examine the photoreceptor reaction. Reductions of the a- and b-wave amplitudes were found directly after exposure with BBG with 0.13 ml/ml D2O and with D2O in all test series. These effects on the electroretinogram were rapidly and completely reversible within the recovery time for all exposure times. ERG amplitudes measured after dye application at the end of the washout did not differ significantly from those recorded before staining. The clinically used mixture of BBG/D2O seems to be safe for clinical use. Staining periods of more than 120 seconds were not tested.