Blurred vision - Red flag symptoms

Anatomical and physiological conditions of the eye can cause blurring.

Cataracts typically start with the blurring of night-time vision and progresses into daytime
Cataracts typically start with the blurring of night-time vision and progresses into daytime

Blurred vision is one of the most common eye problems that prompt a patient to seek medical advice. It can be caused by a range of anatomical and physiological conditions of the eye itself, or by underlying systemic medical problems.

Presentations with blurred vision due to normal ageing processes and refraction errors tend to be rare. Some harmless conditions may cause blurring, for example excessive secretions in simple conjunctivitis; but this is usually perceived as mild and temporary.

Red flag symptoms
  • Actual blindness or blind spots (scotomas)
  • Haloes and flashing lights
  • Pain
  • Double vision
  • Redness of the eye or the surrounding skin

History and examination

It is useful to establish the time line of events leading to blurred vision and what the patient actually means by 'blurred vision'.

The minimal external examination of the affected eye(s) in a general practice setting should include: external inspection for redness of eyelids or the eye, evidence of discharge, pus, any obvious visible foreign bodies or any inequalities of appearance and reaction of the pupils; a basic check of visual acuity and visual field; and palpation of the eyeballs and temporal arteries.

Fundoscopy, the use of fluorescein or eyelid eversion are not typically carried out. These investigations could lead to misinterpretation and false reassurance in cases of serious disease if equipment is inappropriate and the examining clinician has insufficient experience of detailed eye examination.

Mechanical (ask about contact lenses) or chemical injuries to the eye are usually suggested by the patient's history. Also, the patient may be familiar with visual symptoms of recurrent migraines. Keep in mind that anticholinergic or other side-effects of various medications may cause blurred vision.

  • Diabetic retinopathy
  • Cataracts
  • Glaucoma
  • Macular degeneration
  • Corneal infection or ulceration
  • Optic neuritis
  • Floaters

Potential causes

Cataracts start with blurring of night-time vision which progresses into daytime. Glaucoma may start similarly but features blind spots and vision loss, mostly of the peripheral visual field, either gradually or as the acute narrow-angle glaucoma, which is a medical emergency.

Retinopathies, in the developed world mostly caused by diabetes, lead to blurred vision due to small bleeds into the retina, and are a frequent cause of blindness.

Loss of light-detecting neurones at the back of the eye in macular degeneration produces blurring, distortion or loss of central vision and fading of colour vision. These symptoms mostly affect patients over the age of 60 and become particularly noticeable during narrow focus activities such as reading.

Optic neuritis, for example as a symptom of multiple sclerosis, can feature pain on pressure to the eyeball or during eye movements and causes blurred vision.

Muscle weakness due to poisoning (for example with botulinum toxin) or occasionally, chronic fatigue syndrome are likely to show during the physical examination and in the context of other symptoms.

Floaters are normally harmless but can cause great concern for patients and in rare cases can be a precursor of retinal detachment.

Retinal detachment classically produces flashes of light across the visual field, or vision loss in the form of a shade or a curtain.

Much rarer causes for blurred vision include haemorrhagic or thrombotic stroke, TIA, and malignant hypertension, occlusions of the central retinal blood vessels, brain tumours, temporal arteritis or thyroid disorders.


Management depends on the proposed cause and could include a recommendation to see an optician, direct referral to an ophthalmologist, or medication, for example a topical antibiotic or artificial tears.

Steroid eyedrops should only be prescribed by eye specialists after a detailed examination to ensure that no damage can occur, namely deep ulceration of the cornea in herpes infection.

As a simple guideline, acute, painful eye conditions with blurred vision or actual vision loss warrant same day referral.

However, it is worth having a low threshold for speaking to the eye department by telephone regarding any patient who presents with blurred vision if there are any doubts about the likely diagnosis or management.

Visit MIMS Learning for an updated version of this article

  • Dr Jacobi is a GP in York

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