Background:To report an unusual case of compressive optic neuropathy secondary to a large onodi air cell.Method:Case report.Results:A 50 year-old gentlemen presented to the eye clinic with left eye painless loss of vision for one day. Visual acuity was counting finger in the left eye with a positive relative afferent pupillary defect (RAPD). Dilated left fundus examination revealed a pale optic disc. A computed tomography of orbit and brain showed a large left sphenoid sinus with onodi-cell-like projection on the left superior margin of left optic canal impinging on the left optic nerve. He was referred to the otorhinolaryngology team and subsequently underwent left optic nerve decompression. Post-operatively, his left visual acuity improved to 6/60 with reversal of RAPD.Conclusion:There are many causes of optic neuropathy and compressive optic neuropathy due to large onodi air cell is uncommon. Acute unilateral loss of vision heralds from a multitude of sinister causes and junior residents should be vigilant that onodi air cell pneumotisation could be one of them.

DATA COLLECTION: (A) Absorbance values of human tenon fibroblast culture after treatment with irradiated riboflavin (raw data): htF: human tenon fibroblast cells IR: irradiated riboflavin (B) Absorbance values of irradiated riboflavin (IR) only: (C) Absorbance values of irradiated culture media only: 0.0644 (D) True absorbance values of human tenon fibroblast cells: To reduce background interference, deduct absorbance values of irradiated riboflavin (B) and of culture media (C) from the raw data (A).