Corneal ulcer
Keratitis (corneal inflammation e.g. from HSV).
Acute angle-closure glaucoma.
Uveitis
Endophthalmitis
Optic neuritis
Trauma
Giant Cell Arteritis
Factitious
Somatization Syndrome
Conjunctivitis (blurry)
Thining through the Differential Diagnosis
Keratitis produces a sharp superficial pain.
Acute glaucoma produces a deep brow ache with nausea and vomiting.
Endophthalmitis and certain uveitic conditions may also produce a deep boring pain.
Optic neuritis produces pain worse with eye movement.
Other causes of vision loss are typically painless.