What are the differential diagnoses for a brief, painless, transient monocular vision loss?

Differential Diagnoses for Transient Painless Unilateral Vision Loss

Transient monocular vision loss (amaurosis fugax) is a retinal TIA and stroke equivalent requiring immediate emergency department referral to a certified stroke center within 24 hours, as stroke risk peaks within the first 7 days even if vision has completely recovered. 1, 2

Vascular Etiologies (Most Common and Urgent)

Retinal Artery Occlusion (Transient or Complete)

• Amaurosis fugax represents transient retinal ischemia lasting seconds to minutes with complete resolution, classically described as a "shade" or "curtain" descending over vision 2, 3
• Up to 25% of patients have concurrent silent brain infarction on MRI, making this a neurological emergency 1
• Caused by emboli (fibrin, cholesterol/Hollenhorst plaques) from ipsilateral carotid atherosclerosis traveling via the ophthalmic artery 2
• Clinically significant carotid stenosis is present in up to 70% of symptomatic cases 1, 2, 3
• Risk factors include hypertension, diabetes, hyperlipidemia, smoking, and cardiovascular disease 1

Critical pitfall: Never assume that complete vision recovery eliminates stroke risk—the 7-day window remains high-risk regardless of symptom resolution 1

Giant Cell Arteritis (GCA)

• Must be considered in all patients over 50 years old with transient vision loss 1, 3
• Associated symptoms include jaw claudication (most specific, LR 4.90), scalp tenderness, temporal tenderness, headaches, and constitutional symptoms 1, 3, 4
• ESR >60 mm/h has high likelihood ratio for diagnosis 1, 3
• Requires immediate empiric high-dose corticosteroids before biopsy to prevent bilateral blindness 1, 2, 4

Critical pitfall: Never delay steroid treatment waiting for temporal artery biopsy results 1

Retinal Vein Occlusion

• Presents with painless vision loss, typically less acute than arterial occlusion 1
• Associated with hypertension, diabetes, hyperlipidemia, and hypercoagulable states 1

Paradoxical Embolism

• Consider patent foramen ovale (PFO) or atrial septal aneurysm as embolic source, particularly in younger patients without typical vascular risk factors 5

Optic Nerve Etiologies

Anterior Ischemic Optic Neuropathy (AION)

• Can be arteritic (from GCA) or non-arteritic 6, 7
• Non-arteritic form associated with vascular risk factors 6

Optic Neuritis

• Approximately 8% of cases are painless (though pain with eye movement is typical) 1
• Features include color desaturation and relative afferent pupillary defect 4
• Associated with multiple sclerosis, neuromyelitis optica, or other demyelinating conditions 1, 4

Retinal Structural Causes

Retinal Detachment

• Presents with curtain-like visual field defect, may have preceding flashes or floaters 1, 4
• Ultrasonography useful when media opacity limits direct visualization 1

Vitreous Hemorrhage

• Can cause sudden vision loss 1
• Diagnosed via ultrasonography when direct visualization is limited 1

Immediate Management Algorithm

Step 1: Confirm Vascular Etiology (Perform in Office)

• Fundoscopic examination to identify Hollenhorst plaques, retinal whitening, or cherry-red spot 2
• Check inflammatory markers (ESR, CRP) in all patients >50 years old regardless of classic GCA symptoms 1, 3

Step 2: Emergency Referral (Do NOT Delay)

• Transfer immediately to certified stroke center ED with note stating "Ocular TIA" or "Ocular Stroke" 1, 2
• Contact receiving stroke center beforehand to prepare team 2
• Do NOT perform extensive ophthalmologic workup before transfer 1, 2

Critical pitfall: Only one-third of ophthalmologists currently follow this immediate referral guideline, despite clear recommendations 2

Step 3: Stroke Center Evaluation (Within 24 Hours)

• Brain MRI with diffusion-weighted imaging to detect concurrent stroke (present in 19-25% of cases) 1, 2, 3
• Vascular imaging (CTA, MRA, or carotid duplex) to assess carotid stenosis 1, 2, 3
• ECG and echocardiography for cardiac embolic sources 2
• Complete blood count, chemistry panel, HbA1c, coagulation studies, fasting lipids 1

Step 4: Time-Sensitive Interventions

• Intravenous tPA may be considered if presenting within 4.5 hours of symptom onset 2
• Carotid endarterectomy for symptomatic stenosis >70% should be performed within 2 weeks for maximal benefit (benefit declines sharply after 2 weeks) 2
• Start antiplatelet therapy immediately 2
• Hyperbaric oxygen therapy (100% oxygen over 9 hours) has demonstrated efficacy in small trials for retinal artery occlusions 2, 8

Risk Stratification for Future Stroke

Vascular Risk Factors*	3-Year Stroke Risk
0-1 factors	1.8%
2 factors	12.3%
3-4 factors	24.2%

*Hypertension, hypercholesterolemia, diabetes, smoking 2

Patients with transient monocular vision loss carry the same cardiovascular risk as those with cerebral TIA and require identical secondary prevention intensity. 2