- Viral or bacterial conjunctivitis
- Herpes simplex keratitis
- Ophthalmic zoster
- Uveitis
- Scleritis or episcleritis
- Optic neuritits
- Belpharitis, hordeolum, or chalazion
- Dacryocystitis
- Sinusitis
- Temporal arteritis
- Orbital cellulitis
TRAUMATIC/STRUCTURAL
- Acute glaucoma
- Foreign body
- Corneal abrasion
- Trauma to globe
- Entropion
- Decreased tearing (Sjogren's, anticholinergic medications, old age)
OTHER
- Intracranial mass
- Migraine
- Cluster headache