Background <p>Onodi cells (OCs) are clinically significant for a rhinologist owing to their close relationship with the internal carotid artery and optic nerve, enclosing the optic canal. Therefore, pathologies affecting the OC can result in harmful ophthalmologic complications. Optic neuritis resulting from a mucocele within the Onodi cell is a rare condition, and with fewer than thirty cases reported since 1997, and most reports are in the Asian region.</p> Case presentation <p>Here, a 29-year-old man presented with left optic neuropathy attributable to compression from an expanded onodi cell mucocele, which is a rare entity.&#xa0;He underwent endoscopic marsupialization of the mucocele, with subsequent visual acuity improvement from counting fingers at seventy cm to 6/60 uncorrected visual acuity (UCVA) and no recurrence.</p> Conclusion <p>Although Onodi cell mucocele is rare, it should be considered when diagnosing unexplained unilateral vision loss.</p>