Objective: Optic pathway glioma (OPG) diagnosed in adults represents a rare and understudied tumor subtype. While pediatric OPGs are typically benign and associated with NF1 and RAS/MAPK pathway dysregulation, less is known about the clinical characteristics and prognostic drivers of OPGs in adults. Methods: A systematic review was conducted in accordance with PRISMA guidelines across multiple databases. Studies reporting patient-level data and follow-up for patients diagnosed with optic pathway glioma at age ≥ 18 years were included. Results: Ninety-six studies comprising 149 adult patients were analyzed. Median patient age was 47 years (range: 18–90), and 51.0% of tumors were high-grade (WHO grade 3–4). Increasing age at diagnosis was significantly correlated with higher WHO grade (ρ = 0.600, p < 0.001), and optic tract involvement was associated with high-grade disease (χ² = 8.08, p = 0.004; ϕ = 0.26). Median follow-up was 12 months, with 74 patients alive and 75 deceased at last follow-up. WHO grade was strongly associated with overall survival (log-rank p < 0.0001), with 24-month survival ranging from 96.9% for grade 1 tumors to 11.3% for grade 4 tumors. Compared with observation or steroid-only management, both surgical and non-surgical oncologic treatments were associated with longer observed survival, although no significant difference was observed between active treatment modalities. Conclusions: Optic pathway gliomas in adults exhibit a multimodal biologic distribution, encompassing both indolent low-grade tumors and aggressive high-grade malignancies. Survival outcomes appear to be primarily driven by tumor biology, with age and anatomic involvement correlating with tumor grade. Prospective, multicenter studies with comprehensive molecular profiling are needed to refine prognostic stratification and guide evidence-based management of this rare disease.