Occurrence of Phosphenes in Patients Undergoing Proton Beam Therapy for Ocular Tumor

Purpose Phosphenes are frequently reported by patients irradiated in the head and neck area. The aim of the present study was to characterize and investigate potential mechanisms of proton beam therapy (PBT)–induced phosphenes in a large population of patients undergoing PBT for ocular tumors. Design Prospective cohort study. Methods Consecutive patients who underwent PBT in a single center were included. Immediately after the first session, all patients completed a questionnaire collecting information about the presence of phosphenes as well as their color, shape, and duration. Patient, tumor and treatment characteristics (dose volume histograms) were also collected. Results Among the 474 patients included, 62.8% reported phosphenes during the first session of PBT. Reported colors were mainly blue-violet (70.5%) and white (14.1%). The prevalence of phosphenes was higher in younger patients ( P  = .003); other patient or ocular characteristics were not associated with the occurrence of phosphenes. Irradiation of the macula ( P P P  = .04). Pupillary constriction was reported for 57.1% of patients with phosphenes vs 18.5% of patients without ( P P P  = .001) were statistically associated with pupillary constriction. Conclusions The present study reported a high rate of phosphenes in patients irradiated by PBT for ocular tumor. Their blue-violet color and their association with a pupillary constriction probably indicates the stimulation of S-cones and retinal ganglion cells that reflects the activation of the afferent visual pathway.