A 30 year old woman with sudden right–sided painful red eye associated with nausea, vomiting and headache. The diagnosis is –

Sudden onset of painful red eye with associated nausea, vomiting and headache suggests the diagnosis of acute congestive glaucoma. Endophthalmitis may also present by sudden onset of severe ocular pain with red eye. But it usually occurs within 7 days of ocular surgery or trauma. There is no history of oculary surgery or trauma in this question.