Minnan Al-Khafaji

Introduction

Transient monocular vision loss (TMVL) is a symptom that demands careful evaluation due to its broad differential diagnosis and potential association with serious systemic disease. Among the most clinically important causes are retinal migraine and amaurosis fugax, which are frequently confused in acute and primary care settings.

Therefore, the distinction is critical, amaurosis fugax represents retinal ischaemia and is considered a transient ischaemic attack (TIA) equivalent with significant risk of future stroke, whereas retinal migraine is generally benign and self-limiting, though rare and often misdiagnosed (1).

This article provides a practical, clinically orientated framework for differentiating these two entities based on history, examination, and appropriate investigation.

Methods

Retinal migraines are a subtype of migraines characterised by transient, fully reversible monocular visual disturbance, typically associated with migraine headache. The pathophysiology is not fully understood but is thought to involve retinal or optic nerve vasospasm. The diagnosis is clinical and requires exclusion of alternative causes.

On the other hand, amaurosis fugax refers to TMVL due to retinal ischaemia, most commonly caused by emboli originating from carotid artery atherosclerosis or the heart. It is classified as a TIA equivalent and carries significant risk of future cerebrovascular events.

In TMVL a careful history remains the most important diagnostic tool in TMVL.

Table 1: Comparison of retinal migraine vs amaurosis fugax

Feature	Retinal migraine	Amaurosis fugax
Typical age	Younger patients	Older patients
Onset	Gradual	Sudden
Duration	5-60 minutes	Seconds to minutes
Visual symptoms	Positive or negative phenomena (scintillations, scotomas)	Negative phenomenon (“curtain” or blackout)
Laterality	Strictly monocular (rarely misperceived)	Monocular
Pain	Often associated with headache	Painless
Frequency	Recurrent stereotyped episodes	May be recurrent but often variable
Vascular risk factors	Usually absent	Typically present (hypertension, diabetes, smoking, hyperlipidaemia)
Systemic risk	Low	High (risk of stroke)

It is important to note the table above is not diagnostic itself and there are common clinical pitfalls to keep in mind. Exercise caution when attributing TMVL in young patients to migraine without exclusion of vascular causes, failing to recognise binocular migraine aura misreported as monocular symptoms, under-investigating older patients with “typical migraine history”, overlooking transient ischaemia in brief episodes (<5 minutes) and not referring suspected amaurosis fugax urgently to stroke services.

Case vignette

A 76-year-old man presents to the emergency department with three episodes of transient loss of vision in the right eye over the past week. Each episode lasted approximately 2 to 3 minutes and was described as a “dark curtain descending” over the visual field. He denies pain or headache. His past medical history includes hypertension, hyperlipidaemia, and a 40 pack year smoking history.

His visual acuity and ophthalmic assessment between episodes are normal. Carotid auscultation reveals a left-sided bruit.

This presentation is highly suggestive of amaurosis fugax rather than retinal migraine and warrants urgent vascular evaluation and TIA clinic referral.

Pathophysiology

The pathophysiology of retinal migraines remains uncertain, some proposed theories include retinal or ophthalmic artery vasospasm, cortical spreading depression with mislocalised monocular perception or neurovascular dysregulation in susceptible individuals. Whilst the underlying mechanism of amaurosis fugax is transient retinal ischaemia, most commonly due to embolic occlusion from carotid artery atherosclerotic plaques, cardioembolic sources such as atrial fibrillation or haemodynamic insufficiency in severe carotid stenosis. (2; 3; 4)

When assessing a patient with TMVL the following red flags suggest amaurosis fugax and must be considered towards prompting urgent vascular work up. Age over 50, vascular risk factors (hypertension, diabetes, smoking, hyperlipidaemia), sudden painless monocular vision loss, “curtain like” visual disturbance, associated neurological symptoms (weakness, dysarthria), carotid bruit (5).

Investigations

If amaurosis fugax is suspected, the patient should be managed as a possible TIA and therefore referred urgently via stroke pathways where the following investigations will be undertaken, carotid doppler ultrasound, ECG, echocardiography if embolic source suspected, blood tests (FBC, lipid profile, glucose), ESR/CRP if giant cell arteritis is suspected and brain imaging (MRI/CT as clinically indicated) (6).

In the absence of the red flag symptoms and with low clinical suspicion, retinal migraines are a more probable diagnosis, keep in mind however this is a diagnosis of exclusion. Neuroimaging is considered in the case of atypical features such as persistent deficit, neurological signs, or a late onset (7).

Management

The management of amaurosis fugax focuses on secondary stroke prevention with treatments including antiplatelet therapy (e.g. aspirin), high intensity statin therapy, aggressive vascular risk factor modification including education, carotid endarterectomy, or stenting if indicated and cardiac rhythm monitoring if an embolic source is suspected (8; 9).

Whereas retinal migraines are generally treated conservatively with education and reassurance, identification and avoidance of triggers, migraine prophylaxis (beta blockers, calcium channel blockers) in recurrent cases and neurology referral in atypical or refractory cases (10).

A practical approach is using the following framework:

1. Confirm monocular vs binocular
2. Determine onset (sudden vs gradual)
3. Characterise visual phenomenon (positive vs negative)
4. Assess duration
5. Evaluate vascular risk factors
6. Identify neurological symptoms
7. If in doubt, treating it as a vascular event until proven otherwise

Conclusion

TMVL is a symptom with important systemic implications. Distinguishing retinal migraine from amaurosis fugax is essential due to their vastly different prognoses and management strategies. Amaurosis fugax represents a vascular emergency requiring urgent stroke assessment, while retinal migraine is a rare benign diagnosis of exclusion. A structured clinical approach based on history and risk stratification improves diagnostic accuracy and patient outcomes.

References

1. Hejazian SS, et al. Risk of Ischemic Stroke After Transient Ischemic Attack in Patients Receiving Comprehensive Versus Noncomprehensive Diagnostic Workup: A Systematic Review and Meta-Analysis. J Am Heart Assoc. 2023.
2. Miller NR, et al. Walsh and Hoyt’s Clinical Neuro-Ophthalmology. 6th ed. Lippincott Williams & Wilkins; 2005.
3. Goadsby PJ, Holland PR, Martins-Oliveira M, et al. Pathophysiology of Migraine: A Disorder of Sensory Processing. Physiol Rev. 2017;97(2):553-622.
4. Easton JD, Saver JL, Albers GW, et al. Definition and Evaluation of Transient Ischemic Attack: A Scientific Statement for Healthcare Professionals From the American Heart Association/American Stroke Association. Stroke. 2009;40(6):2276-2293.
5. The Royal College of Ophthalmologists. Emergency Eye Care Commissioning Guidance. Published 2021. Available at: https://www.rcophth.ac.uk/wp-content/uploads/2021/12/Emergency-Eye-Care-Commissioning-Guidance.pdf
6. EyeWiki. Amaurosis Fugax (Transient Vision Loss). American Academy of Ophthalmology. Available at: https://eyewiki.org/Amaurosis_Fugax_(Transient_Vision_Loss
7. Headache Classification Committee of the International Headache Society (IHS). The International Classification of Headache Disorders, 3rd edition. Cephalalgia. 2018;38(1):1-211.
8. Biousse V, Newman NJ. Transient monocular visual loss. Am J Ophthalmol. 2005;140(4):717-721.
9. Mbonde AA, O’Carroll CB, Dulamea OA, et al. Current Guidelines on Management of Amaurosis Fugax and Transient Ischemic Attacks. Asia Pac J Ophthalmol (Phila). 2022;11(2):168-176.
10. Maher ME, et al. Retinal Migraine: Evaluation and Management. Curr Pain Headache Rep. 2021;25(6):39.