Mathis T, et al. - Authors ascertained and gauged potential mechanisms of proton beam therapy (PBT)–induced phosphenes in a large population of patients undergoing PBT for ocular tumours. A high rate of phosphenes was seen in patients irradiated by PBT for an ocular tumour. The stimulation of S-cones and retinal ganglion cells that reflect the activation of the afferent visual pathway was probably indicated by their blue-violet colour and their relationship with a pupillary constriction. A significant association of irradiation of the macula and/or optic disc with the presence of phosphenes was seen, whereas blue-violet colour was only related to young age and irradiation of macular area.