Mechanisms of phosphenes in irradiated patients

// Thibaud Mathis 1 , Stephane Vignot 2 , Cecila Leal 3 , Jean-Pierre Caujolle 3 , Celia Maschi 3 , Martine Mauget-Faÿsse 4 , Laurent Kodjikian 1 , Stéphanie Baillif 3 , Joel Herault 5 and Juliette Thariat 5, 6 1 Department of Ophthalmology, Croix-Rousse University Hospital, 69004 Lyon, France 2 Department of Medical Oncology, Jean Godinot Institute, 51100 Reims, France 3 Department of Ophthalmology, Pasteur II Hospital, 06000 Nice, France 4 Rothschild Ophthalmologic Foundation, 75019 Paris, France 5 Proton Therapy Center, Université Nice Sophia Antipolis, 06200 Nice, France 6 Department of Radiation Therapy, Centre Francois Baclesse, ARCHADE, 14000 Caen, France Correspondence to: Thibaud Mathis, email: mathisthibaud@hotmail.fr Keywords: phosphenes, radiation therapy, eye tumors, choroidal melanoma, proton beam therapy Received: April 04, 2017      Accepted: May 15, 2017      Published: June 28, 2017 ABSTRACT Anomalous visual perceptions have been reported in various diseases of the retina and visual pathways or can be experienced under specific conditions in healthy individuals. Phosphenes are perceptions of light in the absence of ambient light, occurring independently of the physiological and classical photonic stimulation of the retina. They are a frequent symptom in patients irradiated in the region of the central nervous system (CNS), head and neck and the eyes. Phosphenes have historically been attributed to complex physical phenomena such as Cherenkov radiation. While phosphenes are related to Cherenkov radiation under high energy photon/electron irradiation conditions, physical phenomena are unlikely to be responsible for light flashes at energies used for ocular proton therapy. Phosphenes may involve a direct role for ocular photoreceptors and possible interactions between cones and rods. Other mechanisms involving the retinal ganglion cells or ultraweak biophoton emission and rhodopsin bleaching after exposure to free radicals are also likely to be involved. Despite their frequency as shown in our preliminary observations, phosphenes have been underreported probably because their mechanism and impact are poorly understood. Recently, phosphenes have been used to restore the vision and whether they might predict vision loss after therapeutic irradiation is a current field of investigation. We have reviewed and also investigated here the mechanisms related to the occurrence of phosphenes in irradiated patients and especially in patients irradiated by proton therapy for ocular tumors.