Background <p>Orbital apex syndrome (OAS) is a rare ocular complication characterized by vision loss and ophthalmoplegia from infection, inflammation, trauma, neoplasms, and vascular causes, due to the involvement of ocular motor nerves in the anatomical region of the orbital apex. The epidemiological features of OAS are limited. Therefore, this study aimed to present the clinical features and determine the causes to evaluate the visual prognosis of patients with OAS.</p> Methods <p>A retrospective analysis was conducted on 126 adult patients with clinically confirmed OAS by reviewing the electronic medical records from Beijing Tongren Hospital, Capital Medical University, Beijing, China, between January 2020 and December 2024. Data on demographic information, clinical findings, medical history, laboratory results, radiological findings, diagnosis, treatment, and prognosis were collected. The final cohort comprised 66 patients with OAS (mean age: 54.95 ± 18.48 years; male: 36.36% and female 63.64%).</p> Results <p>All patients presented with unilateral involvement: 25 with right OAS and 41 with left OAS. However, the initial ocular presentations varied: blurred vision was reported in all patients, with 63.64% of them suffering from severe visual function impairment (best-corrected visual acuity, BCVA &lt; 20/200), followed by ophthalmoplegia in 56 patients (84.85%), and headache/facial numbness in 40 patients (60.61%). Inflammation (54.55%) was the most frequent cause for OAS, followed by neoplasm (18.18%), trauma (15.15%), and infection (9.09%). After treatments, we found that the vision of 26 patients (39.39%) improved, the vision of 38 patients (57.58%) remained stable, and the vision of 2 patients (3.03%) worsened to blindness. The mortality in three patients was attributed to the underlying malignancies. Further subgroup analysis revealed that the proportion of patients with BCVA &lt; 20/200 was significantly lower in the inflammatory group compared with the non-inflammatory group (27.78% vs. 66.67%, <i>P</i> = 0.002) after treatments. In the comparison between the inflammatory subgroup and the neoplastic subgroup, we found tha the patients in the inflammatory group were significantly younger than those in the neoplastic group (<i>P</i> = 0.015), the course of disease was significantly shorter (<i>P</i> = 0.020), and the proportion of severe visual function impairment (BCVA &lt; 20/200) was significantly lower in the inflammatory group than in the neoplastic group (27.78% vs. 66.67%, <i>P</i> = 0.036). After adjusting for other confounding factors, etiology was an independent influencing factor for patient improvement (OR = 2.345, 95% CI: 1.126–4.881, <i>P</i> = 0.023).</p> Conclusions <p>The clinical manifestations and etiologies of OAS are heterogeneous. Patients with OAS suffer from severe impairment of visual function, even after undergoing aggressive and comprehensive treatment. Our findings indicated that the inflammation was the most frequent cause of OAS and correlated with better visual outcomes.</p> Clinical trial number <p>Not applicable.</p>