OBJECTIVE To examine retinal electrophysiological function and retinal thickness in healthy eyes before and after hyperbaric oxygen (HBO) exposure. METHODS The healthy eye in each of six subjects who underwent experimental HBO treatment for branch retinal vein occlusion in the fellow eye was examined using multifocal electroretinography (mfERG) and optical coherence tomography (OCT) at baseline and following a course of five consecutive daily sessions of exposure to HBO at 2.4 atmospheres of absolute pressure lasting 90 min each. RESULTS After HBO, P1 implicit times of the mfERG were significantly shorter than at baseline. The response was delayed, being undetectable on the day treatment concluded, whereas a 2.65% reduction in implicit time was seen 1 week later (p = 0.032). The P1 implicit time remained 2.49% shorter than at baseline 1 month after the end of the HBO sessions (p = 0.020). The bulk of the response to HBO was found in the foveal and parafoveal regions. No detectable change was seen in mfERG amplitudes or in the volume or thickness of the retina. CONCLUSIONS A mfERG component related to bipolar and Müller cell function was accelerated by a short intermittent exposure to HBO. The response developed after the end of the HBO exposure and lasted for at least 3 weeks, suggesting that it was prompted by the withdrawal of HBO rather than the onset and subsequent brief exposure to HBO.