Invasive fungal sinusitis (IFS) is rare but potentially fatal in immunocompromised patients. Orbital extension of IFS can cause visual loss or ophthalmoplegia, and the rate of recovery of visual acuity can be low even after treatment with antifungal agents and sinus surgery. In this case, optic nerve decompression with the endoscopic endonasal approach was successful for the treatment of visual loss in a patient with IFS with orbital apex extension. The authors describe the recovery of visual acuity after optic nerve decompression in a patient with IFS who had exhibited visual loss caused by invasion into the orbital apex. The authors also provide an intraoperative video and literature review.