A 73-year-old woman came to ophthalmology with complaining of sudden left visual loss from 7 days ago. On Computed tomograpy, mildly enhanced bulging soft tissue lesion with erosion of skull base and left medial orbital wall. Magnetic resonance image showed expansile cystic lesion in ethmoid sinus that low signal on T1-weighted image and high signal on T2-weighted image. Image studys suggested mucocele. Surgical treatment with an endoscopic sinus approach was performed and pus was drainaged completely. After 1 day of surgery, visual field test result was improved from 0% to 82%. After 1 week of surgery, visual field test was up to 90% and visual acuity test was up to 0.6 from 0.05. ENT doctors and Ophthalmologists should be aware that visual disturbance could be resulted from infected mucocele and early imaging study and prompt surgical treatment are crucial role in recovery of visual function.