ObjectiveTo observe the clinical and imaging characteristics of radiation optic neuropathy (RION). MethodsA retrospective clinical study. A total of 43 patients (69 eyes) who were diagnosed with RION at the Chinese PLA General Hospital from 2010 to 2021 were included in this study. There were 23 males (36 eyes) and 20 females (33 eyes). The age of patients at the time of radiation therapy was 49.54±13.14 years. The main dose of radiotherapy for lesions was 59.83±14.12 Gy. Sixteen patients were treated with combined chemotherapeutic agents. The clinical details of best corrected visual acuity (BCVA) and color photography of the fundus were collected. Forty-six eyes underwent optical coherence tomography (OCT), visual field were examined in 30 eyes, magnetic resonance imaging (MRI) were performed in 40 eyes. The BCVA examination was performed using Snellen visual acuity chart, which was converted to minimum resolution angle logarithm (logMAR) visual acuity during recording. Hyperbaric oxygen therapy (HBOT) was performed in 10 patients (13 eyes), 9 patients (12 eyes) were treated with intravenous methylprednisolone (IVMP), 12 patients (23 eyes) were treated with HBOT combined with IVMP and control group of 12 patients (21 eyes) were only treated with basal treatment. And grouped accordingly. To observe the changes in onset, recovery, and final BCVA of the affected eye as well as thickness changes of the retinal nerve fiber layer (RNFL) of the optic disc and inner limiting membrane-retinal pigment epithelium (ILM-RPE) layer of the macular area, and final outcome of BCVA with different treatment modalities in affected eyes. The RNFL and ILM-RPE layer thicknesses were compared between patients with different disease duration as well as between treatment regimens using independent samples t-test. ResultsOf the 43 cases, vision loss was monocular in 17 patients (39.53%, 17/43) and binocular in 26 patients (60.47%, 26/43). The latency from radiotherapy to onset of visual loss was 36.33±30.48 months. The duration of RION ranged from 1 week to 10 years, in which the disease duration of 37 eyes ≤2 months. Subacute visual acuity loss was present in 41 eyes. logMAR BCVA＜1.0, 1.0-0.3, ＞0.3 were 45, 15, and 9 eyes, respectively. Optic disc pallor and optic disc edema were found in 10 (27.03%, 10/37), 3 (8.11%, 3/37) eyes, respectively, within 2 months. The superior RNFL [95% confidence interval (CI) 2.08-66.56, P=0.038] and the outer circle of the inner limiting membrane to retinal pigment epithelium (ILM-RPE) (95%CI 4.37-45.39, P=0.021) layer thinned significantly during the first month. The center of the ILM-RPE layer thickened (95%CI －32.95-－4.20, P=0.015) significantly during the first two months. The inner circle temporal quadrant of the ILM-RPE layer thickened (95%CI －42.22-－3.83, P=0.022) significantly from the third to sixth month, and the RNFL except for the temporal quadrants and the average RNFL, inner circle superior quadrant and outer circle of the ILM-RPE layer thinned significantly after 6 months (P＜0.05). Among the 40 eyes that underwent MRI examination, 33 eyes (82.50%, 33/40) were affected by T1 enhancement of optic nerve, including 23 eyes (69.70%, 23/33) in intracranial segment; 12 eyes with thickening and long T2 signal (36.36%, 12/33). After treatment, BCVA was restored in 17 eyes (24.6%, 17/69) and final BCVA improved in 9 eyes (13.0%, 9/69). There was no significant difference between HBOT, IVMP and HBOT combined with IVMP therapy in improving BCVA recovery or final BCVA compared with the control group, respectively (t=－1.04, 0.61, 1.31, －1.47, －0.42, 0.46; P＞0.05). ConclusionsThe structural damage of the RNFL and ILM-RPE layer occurred during the first month, the RNFL showed progressive thinning during the follow-up period, while the ILM-RPE layer showed thinning-thickening-thinning. MRI shows T1 enhancement of the optic chiasma and segments of the optic nerve, and the enhanced segments are usually accompanied by thickening and long T2. HBOT and IVMP have no obvious effect on RION.