Red flag symptoms: Blurred vision

It is essential to understand what the patient means by blurred vision, explains Dr Pipin Singh.

Patients with suspected cataract should be referred routinely to opthalamology (SPL)
Patients with suspected cataract should be referred routinely to opthalamology (SPL)
  • Sudden onset
  • Loss of vision
  • Headache or weakness in arm, face or leg
  • Speech disturbance
  • Nausea, vomiting or photophobia
  • Eye painful or red
  • History of trauma
  • Scalp tenderness or jaw claudication
  • New medications
  • Polyuria or polydipsia
  • Problems with bright lights
  • Flashes and floaters

Blurred vision differs from diplopia and it is important to understand what the patient means by blurred vision.

This is not an uncommon presentation and tends to be more common than diplopia. It has a wide range of differential diagnoses.

An understanding of the patient's ideas, concerns and expectations, and of what has caused them to present now, will allow you to formulate a management plan incorporating these factors.


  • What does the patient mean by blurred vision?
  • Is it unilateral or bilateral?
  • When did it start?
  • Did the symptom develop suddenly? If so, what were they doing at the time?
  • If it has developed gradually, over what period of time and does the patient feel it is getting worse?
  • Has there been any associated visual loss? If so, have they presented to their optician? Many patients may have done this and been told to see the GP, so they may have a copy of a formal eye examination report.
  • Has there been any associated eye pain or redness? If so, has there been any associated discharge?
  • Does the patient wear contact lenses?
  • Has the patient noticed any flashes or floaters?
  • Have there been any problems looking at bright lights, for example, with oncoming cars?
  • Have there been any associated headaches? If so, explore them.
  • Has there been any associated weakness of the arm, face or leg?
  • Has there been any speech disturbance?
  • Have they noticed paresthesia in their arms or legs?
  • Have they had this symptom before? Did they seek help from a healthcare professional? If so, it is important to learn the outcome of this assessment, because a series of investigations may already have been undertaken.
  • Has there been any recent change in medication?
  • Does the patient smoke or drink alcohol?
  • Is there any significant family history that the patient may think is related to the symptom?
  • Does the patient work?
  • Do they drive? This symptom may affect the patient's ability to drive and until the cause is established, they may have to stop.
  • What does the patient think is causing the problem? Most patients have researched their symptoms and have their own ideas about what could be causing the difficulty.
  • What led them to present now?
  • How is the symptom affecting them at work or at home?


The examination, which will be guided by the history, needs to be focused. Some or all of the following may be needed.

Note if the patient wears glasses. It may be important to check their vision using a Snellen chart.

Examine the external part of the eye. Is there any redness to the sclera, or pupillary abnormality?

Inspect the eyelashes. You may need to evert the superior tarsal plate. Look for any foreign body. You may need to stain the eye with fluorescein.

Check the pupils. Are they equal and reacting to light and accommodation? Check the red light reflex.

If headaches are associated with blurred vision, it may be necessary to check power and reflexes in the arms and legs and perform fundoscopy. It may also be necessary to palpate the temporal artery.


  • FBC, CRP, ESR, glucose
  • Urine dipstick
  • Staining the eye with fluorescein
  • CT or MRI head (depending on local rules)

When to refer

Urgent same-day ophthalmological assessment may be needed.

If temporal arteritis is suspected, same-day discussion with a vascular surgeon about temporal artery biopsy may be necessary.

Urgent same-day medical admission may be necessary for CT or MRI head. Refer to neurology if you suspect intracranial pathology or a neurological cause.

Refer routinely to ophthalmology if cataract or age-related macular degeneration is suspected.

Possible causes

The cause of blurred vision depends on whether it is painful or painless, unilateral or bilateral, and of sudden or gradual onset. Possible causes include:


  • Corneal ulcer
  • Vitreous haemorrhage
  • Cataract
  • Macular degeneration
  • Conjunctivitis
  • Refractive errors


  • Migraine
  • MS
  • Papilloedema and related causes, for example, space-occupying lesion


  • Central retinal artery or vein occlusion
  • Stroke disease
  • Temporal arteritis


  • Diabetes mellitus
  • Iatrogenic, such as anticholinergics
  • Alcohol intoxication

Dr Singh is a GP in Northumberland

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