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)

Red flag symptoms

  • Sudden onset
  • Loss of vision
  • Associated headache or weakness of the arm, face or leg
  • Speech disturbance
  • Associated nausea, vomiting or photophobia
  • Any history of eye pain or redness
  • 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? Have they already 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 whether 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.


  • Consider FBC, CRP, ESR, glucose
  • HbA1c
  • Staining the eye with fluorescein
  • CT or MRI head (depending on local rules)

When to refer

Urgent same-day ophthalmological assessment may be needed depending on your findings.

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.

Ophthalmological causes

  • Corneal ulcer: generally presents as acute painful red eye, with a history of wearing contact lenses. Normally diagnosed after using fluorescein stain
  • Vitreous haemorrhage: typical symptoms include sudden painless visual loss. Other symptoms may include flashers and floaters
  • Cataract: typical symptoms include gradual loss of vision, glare and possible haloes
  • Macular degeneration: typically involves gradual onset painless loss of vision
  • Conjunctivitis (allergic or infective): typically a sticky, gritty red eye with purulent discharge or excessive watering
  • Refractive errors: typical symptoms include blurred vision when reading - either close up or at a distance. These are easily corrected with appropriate lenses.
  • Glaucoma: this may present with a painful red eye and associated vomiting.
  • Differentiating these diagnoses in primary care without a slit lamp can prove difficult, so a detailed history is crucial to determine the nature of onset and allow an appropriately-timed referral to be made.

Neurological causes

  • Migraine: this may present with flashing lights or loss of vision associated with a headache, nausea, vomiting and photophobia
  • Multiple sclerosis: typical symptoms may include sudden onset painless loss of vision and examination findings may reveal a pale optic disc
  • Papilloedema and related causes, for example, a space-occupying lesion: typical symptoms may include headache, worse in the morning with associated vomiting, and worse when bending forward.

Vascular causes

  • Central retinal artery occlusion or central retinal vein occlusion (CRVO and CVAO): both can present with sudden onset visual loss and require urgent same-day assessment
  • Stroke disease: sudden onset painful visual loss may be accompanied by arm, leg or facial weakness and/or slurred speech. This may represent a transient ischaemic attack (TIA) and fully resolve within 24 hours or longer. Any uncertainty should be discussed with your local on-call stroke team.
  • Temporal arteritis: this may present with blurred vision, headache, scalp tenderness and jaw claudication. Investigations may include an ESR and CRP. Further investigations would include a temporal artery biopsy detecting the presence of skip lesions.

Other causes

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

Dr Singh is a GP in Northumberland

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