Long-Term Visual Function After Fractionated Stereotactic Radiotherapy for Primary Optic Nerve Sheath Meningioma: A Retrospective Analysis of 34 Subjects

Objective: To evaluate long-term visual function after fractionated stereotactic radiotherapy (FSRT) for primary optic nerve sheathMethods: This 22-year retrospective study included 34 subjects (34 affected eyes) with PONSM who were treated with FSRT exclusively. Subjects with a history of biopsy/resection were excluded. Visual function, including visual acuity (VA) and visual field mean deviation (VF MD), was evaluated at presentation (pre-radiotherapy; pre-RT) and at the final follow-up (post-radiotherapy; post-RT); treatment complications were also evaluated. Treatment success was defined as either stabilization or improvement of visual function.Results: The median pre-RT VA and pre-RT VF MD were 0.70 logarithm of the minimum angle of resolution (logMAR; range: 0.0- 2.9 logMAR) and -15.4 decibels (dB) (range: -31.4 to -3.2 dB), respectively. The median total dose of FSRT was 50 Gy (range: 45- 54 Gy) and the median number of fractions was 25 (range: 25-30). The median follow-up interval was 89 months (range: 6-251 months). The median post-RT VA and post-RT VF MD were 0.48 logMAR (range: 0.0-2.9 logMAR) (p = 0.010) and -6.8 dB (range: -20.6 to -1.6 dB) (p = 0.005), respectively. Among the 34 included eyes, VA was successfully treated in 29 eyes (85.3%) and worsened in 5 eyes (14.7%). Of the 14 eyes with both VA and reliable VF MD at pre-RT and post-RT time points, VF MD was successfully treated in 13 eyes (92.8%) and worsened in one (7.2%); overall visual function was successfully treated in 13 eyes (92.8%) and worsened in 1 eye (7.2%). Complications occurred in one subject (2.9%; radiation retinopathy).Conclusion: Approximately 90% of PONSM subjects exhibited long-term treatment success in terms of VA, VF MD, and overall visual function after FSRT. Additionally, the incidence of complications was low. Therefore, FSRT is effective and safe treatment for PONSM.