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A

Transient Monocular Blindness


Learning objectives

  • The significance of TMB in terms of carotid disease
  • Important differentials and avoiding misdiagnosis of TIA
  • Value of carotid surgery

About

  • TMB is also called Amaurosis fugax and generally refers to either occlusion or low flow to the ophthalmic artery.
  • Those with TMB may be at increased risk of embolic stroke due to ipsilateral carotid disease and stenosis.

Aetiology

  • Either occlusion or low flow to the ophthalmic artery or ipsilateral carotid disease or Cardioembolism. I suspect low flow gives a more subtle symptom profile than the absolutely loss of vision or curtain effect that an occlusive embolism will give. I have seen very significant stenosis with simple transient blurring.
  • Low flow may be due to systemic blood pressure (vision fades as people faint), ipsilateral carotid stenosis which may be at the bifurcation or higher, raised blood viscosity.
  • A more permanent occlusion may be due to central retinal artery occlusion.
  • Embolism can also in theory and practice give altered vision with blurring or even complete loss of vision

Clinical

  • Classically a curtain descending but in reality can be more subtle with darkening an dimming vision especially when the issue is low flow rather than embolism. If symptoms are present in both eyes unilateral carotid disease seems unlikely.
  • Risk factors for atherosclerosis especially smokers tend to raise red flags and suggest that there may be carotid disease. They key is always to look for alternative diagnoses - migraine will have additional symptoms e.g. headache or nausea or feeling unwell and desire to go lie down and sleep it off.
  • A TIA should be painless and patient should be otherwise well. The other main differential in the older patient is GCA and look for headache, temporal artery tenderness and raised ESR/CRP. The worry with GCA is an arteritic CRAO with mono and binocular visual loss which can be permanent.
  • Non rapidly resolving visual loss: Non-arteritic Central retinal artery occlusion results in severe and permanent visual loss but the acuity does improve in around a quarter. It is quite rare.

Differentials of TMB

DiagnosisComments
TIA Classically embolic to eye from stenosis at bifurcation, Could also be due to low flow to eye from reduced BP or carotid disease or both or increased blood viscosity
(Acephalgic) Migraine with aura Migraine can cause almost any visual disturbance. Classic features include the headache which may be absent and comes on later and associated sickness. Migraine tend to cause dynamic moving visual appearances which are often bright with fortification spectra or swirls. Diagnosis more obvious after multiple transient episodes.
Ophthalmic diseases Retinal detachment or other macular or retinal disease
GCA Patient and ERS > 50 and headache. Visual symptoms may be due to an arteritic CRAO with mono and binocular visual loss which can be permanent. Treat with steroids if diagnosis likely.
Central/Branch venous occlusion Classical findings on fundoscopy. Manage vascular risk factors

Investigations

  • FBC, U&E, LFT, ESR, ECG
  • Carotid ultrasound to look for stenosis, occlusion and/or plaque
  • Echocardiogram
  • 7 day tape ? PAF
  • CT/MRI Brain : may be useful to look for a burden of ispilateral stroke disease

Management (Manage vascular risks)

  • If the diagnosis if central retinal artery occlusion and vision has been recently lost then urgent ophthalmological referral should take place and in some centres thrombolysis would be considered. Take expert guidance. Usual treatments such as reducing intra-ocular pressure, ocular massage, vasodilators, haemodilution, hyperbaric oxygen, steroids, heparin, aspirin have not been proven to be effective with trials and use is very anecdotal. There is a discussion as to whether CRAO should be treated as a disabling stroke with thrombolysis.
  • It is best that all patients go through a formal ophthalmological eye assessment and then come to the TIA clinic just to exclude other causes of altered vision such as retinal detachment or macular disease.
  • Antiplatelet: Aspirin 300 mg OD stat then 75-300 mg OD or Clopidogrel 300 mg stat then 75 mg od
  • Statin: Atorvastatin 20-40 mg OD or Simvastatin
  • Carotid endarterectomy if ipsilateral stenosis > 50% and low peri-operative risk
  • Anticoagulate for Atrial Fibrillation
  • If likely GCA then Locally we refer these to rheumatology for ultrasound or the artery and biopsy as needed after starting Prednisolone 1 mg/kg/d.

References and further reading


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