A Case of Vision Loss From Radiation-Induced Optic Neuropathy Resulting in Charles Bonnet Syndrome

region. The patient underwent a near total resection of the tumor and pathology showed a CNS WHO grade 2 meningioma. One month following surgery, she completed conventionally fractionated radiation therapy to the residual tumor and surrounding high-risk region using proton beam therapy to a total dose of 50.4 cobalt gray equivalents (CGE) in 28 fractions (1.8 CGE per fraction) (Figure 1) . In the absence of an established dose response and given the proximity of the optic apparatus and the emerging uncertainty about proton relative biological effectiveness (RBE) and radiation injury, a dose of 50.4 CGE was used. The maximum (to 0.03 cc volume) and mean doses to the optic nerves and chiasm were: right Abstract Radiation-induced optic neuropathy (RION) is a rare late effect following radiation caused by damage to the optic nerves or chiasm. It is a profound and devastating complication of radiation therapy with no effective treatment and is irreversible. Charles Bonnet syndrome (CBS) is a rare phenomenon characterized by complex visual hallucinations that occur concurrently with visual field loss or visual acuity loss. This case describes a woman with a CNS WHO grade 2 meningioma who received conventionally fractionated radiation therapy with a proton beam to the residual tumor and resection cavity after near total resection. She subsequently developed RION with vision loss and hallucinations and was diagnosed with CBS. We recommend that even though the incidence of RION is rare, patients should be counseled by providers for potential late effects of radiation treatment with surveillance routinely after treatment.