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Symptom sorter – flashes, floaters and transient visual disturbance


The GP overview

This symptom can be very difficult to fathom, not least because patients often find it nigh on impossible to describe exactly what they’ve experienced. Patience and a painstaking approach are essential – most of the clues are likely to be in the history rather than in the examination. This section does not cover double vision, gradual loss of vision or persistent sudden loss of vision, which are dealt with elsewhere.

Differential diagnosis


  • ‘Normal’ floaters.
  • Migraine.
  • Posterior vitreous detachment.
  • Amaurosis fugax.
  • Retinal detachment.


  • Temporal arteritis.
  • Vasovagals and orthostatic hypotension (commonly cause the symptom but rarely present with it).
  • Vitreous haemorrhage.
  • Medication (for example, transient blurred vision with anticholinergics, blue tinge to vision with sildenafil).
  • Poorly controlled diabetes.
  • TIA.
  • Optic neuritis.


  • Papilloedema.
  • Trauma.
  • Posterior uveitis.
  • Seizures.
  • Psychological.

Ready reckoner

  Normal floaters Migraine Posterior vitreous detachment Amaurosis fugax Retinal detachment
Sudden onset No Yes Yes Yes Yes
Blurred vision No Possible No Yes Possible
Eye symptoms resolve in <one hour No Yes Possible Yes No
Flashing lights No Possible Yes No Possible
‘Curtain’ effect No Possible No Yes Possible

Possible investigations

The GP is highly unlikely to initiate any investigations in this situation – apart, perhaps, from a blood sugar or HbA1c to check for undiagnosed diabetes or an urgent ESR in suspected temporal arteritis. Otherwise, any investigations required would be arranged by the ophthalmologist or neurologist after urgent or routine referral, depending on the clinical picture.

Top tips

  • It is tempting to ‘bounce’ some of these cases to a local optician for assessment. Resist this approach – you may delay an important diagnosis and, besides, even a thorough examination is unlikely to provide anything like as much relevant information as a careful history.
  • Some patients find it easier to ‘draw’ their visual disturbance than describe it.
  • Floaters are a fairly common presentation – one of the key issues to establish is the duration of the symptom. The longer they have been present, the more you can be reassured that they are ‘normal’.
  • Remember that ocular migraine can occur without the ‘usual’ headache.

Red flags

  • A sudden onset of a shower of floaters is significant – especially if accompanied by flashing lights or blurred vision. Refer urgently to exclude a retinal detachment.
  • Do not forget temporal arteritis as a cause of transient visual disturbance, especially in patients aged 50 or over. Treat with high-dose steroids on suspicion of this diagnosis – do not wait for the results of blood tests.
  • Remember to check whether a young woman with migrainous visual disturbance is on the combined contraceptive pill and advise accordingly.
  • Amaurosis fugax is a form of TIA and should be managed as such – apply your local ‘TIA pathway’.


Dr Keith Hopcroft is a GP in Laindon, Essex.

Dr Vincent Forte is a GP in Gorleston, Norfolk.

The fifth edition of Symptom Sorter is available from Radcliffe Publishing for £34.99.

Symptom Sorter 5th edition


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