Migraine headache
Tension headache
Cluster headache
Meningitis/encephalitis
Neoplastic meningitis
Myocardial ischemia
Retropharyngeal abscess
Intracranial Hemorrhage (ICH)
SAH / sentinel bleed
Acute obstructive hydrocephalus
Space occupying lesions
CVA
Carbon monoxide poisoning
Basilar artery dissection
Preeclampsia
Cerebral venous thrombosis
Hypertensive emergency
Depression
Neoplastic meningitis
SAH / sentinel bleed<unk>  of temporal artery (temporal arteritis)
Idiopathic intracranial hypertension (Pseudotumor Cerebri)
Acute Glaucoma
Acute sinusitis
Cavernous sinus thrombosis or cerebral sinus thrombosis
Carotid artery dissection
Trigeminal neuralgia
TMJ pain
Post-lumbar puncture headache
Dehydration
Analgesia abuse
Various ocular and dental problems
Herpes zoster ophthalmicus
Herpes zoster oticus
Cryptococcosis
Febrile headache (e.g. pyelonephritis, nonspecific viral infection)
Ophthalmoplegic migraine
Superior Vena Cava Syndrome
Viral
Varicella
Herpes
Enterovirus
West Nile
Tuberculosis
Lyme disease
Syphilis
Leptospirosis
Fungal (AIDS, transplant, chemotherapy, chronic steroid use)
Noninfectious
Sarcoidosis
Vasculitis
Connective tissue disease
Drug induced aseptic meningitis
Varicella
Herpes
Enterovirus
West Nile
Sarcoidosis
Vasculitis
Connective tissue disease
Drug induced aseptic meningitis
Painful
Arteritic anterior ischemic optic neuropathy
Optic neuritis
Temporal arteritis†
Painless
Amaurosis fugax
Central retinal artery occlusion (CRAO)†
Central retinal vein occlusion (CRVO)†
High altitude retinopathy
Open-angle glaucoma
Posterior reversible encephalopathy syndrome (PRES)
Retinal detachment†
Stroke†
Vitreous hemorrhage
Traumatic optic neuropathy (although may have pain from the trauma)
Arteritic anterior ischemic optic neuropathy
Optic neuritis
Temporal arteritis†
Amaurosis fugax
Central retinal artery occlusion (CRAO)†
Central retinal vein occlusion (CRVO)†
High altitude retinopathy
Open-angle glaucoma
Posterior reversible encephalopathy syndrome (PRES)
Retinal detachment†
Stroke†
Vitreous hemorrhage
Traumatic optic neuropathy (although may have pain from the trauma)
†Emergent Diagnosis
Large vessel
Takayasu arteritis<unk> 
Medium vessel
Polyarteritis nodosa
Buerger disease
Kawasaki disease
Granulomatosis with polyangiitis
[[Churg-Strauss syndrome
Microscopic polyangiitis
Small vessel
Essential mixed cryoglobulinemia
Henoch-Schonlein purpura
Behcet disease
Takayasu arteritis<unk> 
Polyarteritis nodosa
Buerger disease
Kawasaki disease
Granulomatosis with polyangiitis
[[Churg-Strauss syndrome
Microscopic polyangiitis
Essential mixed cryoglobulinemia
Henoch-Schonlein purpura
Behcet disease
Giant cell arteritis
Migraine headache
Takayasu arteritis
Tension headache
Cluster headache
Benign paroxysmal positional vertigo
Meningitis/encephalitis
Carotid-cavernous fistula