Mechanisms of phosphenes in irradiated patients
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Thibaud Mathis1, Stephane Vignot2, Cecila Leal3, Jean-Pierre Caujolle3, Celia Maschi3, Martine Mauget-Faÿsse4, Laurent Kodjikian1, Stéphanie Baillif3, Joel Herault5 and Juliette Thariat5,6
1Department of Ophthalmology, Croix-Rousse University Hospital, 69004 Lyon, France
2Department of Medical Oncology, Jean Godinot Institute, 51100 Reims, France
3Department of Ophthalmology, Pasteur II Hospital, 06000 Nice, France
4Rothschild Ophthalmologic Foundation, 75019 Paris, France
5Proton Therapy Center, Université Nice Sophia Antipolis, 06200 Nice, France
6Department of Radiation Therapy, Centre Francois Baclesse, ARCHADE, 14000 Caen, France
Thibaud Mathis, email: [email protected]
Keywords: phosphenes, radiation therapy, eye tumors, choroidal melanoma, proton beam therapy
Received: April 04, 2017 Accepted: May 15, 2017 Published: June 28, 2017
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.
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