Blurred vision: causes, red flags and when to see an optician or doctor

Blurred vision is a loss of sharpness, where things look out of focus or hazy. It may affect near or distance sight, one eye or both, and may be constant, come and go or develop suddenly. The most common reasons are ordinary: a need for glasses or a change in prescription, tired or dry eyes after long screen use, or contact lens problems. The NHS dry eye page lists blurry vision among symptoms of dry eyes, along with itchy, sore, gritty, red, light-sensitive and watery eyes.

But the same symptom can come from the lens of the eye (cataract), the optic nerve (glaucoma), the retina (diabetes), blood vessels (giant cell arteritis, stroke), the brain (migraine aura) or blood sugar swings, so it matters how and when it started.

The table sets out causes named in NHS pages, with what usually distinguishes them.

The NHS stroke page lists blurred vision or loss of sight in one or both eyes among stroke symptoms, alongside face weakness, arm weakness and speech problems, weakness or numbness down one side, confusion, dizziness, severe headache and sickness. It says to call 999 if you think you are having, or have had, a stroke, including signs within the last 24 hours even if they have stopped.

The NHS glaucoma page says that if symptoms of glaucoma develop suddenly, which can include intense eye pain, a red eye, tenderness around the eyes, rainbow-coloured circles around lights, blurred vision, sickness and a headache, it is a medical emergency that may need immediate treatment and to call 999 or go to A&E. For temporal arteritis it advises an urgent GP appointment or 111 and says people with vision problems should have a same-day appointment at a hospital eye department. For diabetes, sudden worsening of eyesight or blurred vision warrants an urgent GP appointment or 111.

The NHS also lists blurred vision and confusion among hypoglycaemia symptoms and among diabetic ketoacidosis symptoms, which need urgent action in someone with diabetes.

• Sudden blurred vision or loss of sight, particularly with face droop, arm weakness or speech trouble.

• Blurred vision with intense eye pain, a red eye, halos around lights or sickness.

• Blurred or lost vision with severe headache, scalp tenderness or jaw pain on chewing.

• Blurred vision with high thirst, passing a lot of urine, fruity breath or confusion in someone with diabetes.

• Double vision or loss of sight in one or both eyes, which the NHS links to stroke and to temporal arteritis.

The questions are: which eye or both, how suddenly, how long, whether near or distance, pain, redness, flashes, floaters, headache, other neurological symptoms, diabetes or blood pressure, medicines, eye injury and family history of glaucoma. An optician tests sight with letter charts, measures the prescription, examines the front and back of the eye and, according to the NHS, checks for glaucoma during routine tests. For diabetes, the NHS describes diabetic eye screening that involves photographs of the back of the eye, offered every 1 or 2 years to people aged 12 and over with diabetes.

A doctor will also check blood pressure, blood sugar, pulse and a neurological examination when the history suggests stroke, and examine the temples when temporal arteritis is possible, as the NHS describes.

Eye tests may include visual acuity, measurement of eye pressure, examination of the optic nerve and retina, and retinal photographs. A blood glucose or HbA1c test checks for diabetes. For suspected temporal arteritis the NHS says blood tests are done and a specialist may arrange an ultrasound of the temples or a small biopsy of the temporal artery. If stroke is suspected, emergency brain imaging in hospital follows. Cataract is assessed by an optician or eye specialist, who may refer for surgery.

For dry or tired eyes the NHS suggests cleaning eyelids daily with a warm, not hot, flannel, taking breaks when using a screen and keeping the screen just below eye level, using a humidifier, and resting contact lenses in favour of glasses. It says not to stop a prescribed medicine without advice, even if you think it is the cause. A pharmacist can suggest eye drops, gels or ointments.

Do not drive when your vision is blurred. If the blur is new, persistent or one-sided, have it checked rather than waiting for it to settle, and keep blood sugar and blood pressure well controlled if you have diabetes or hypertension, as the NHS stresses for diabetic eye disease.

An optician or optometrist for gradual blur or a routine check; a GP, your diabetes team or an optician for eye problems if you have diabetes; an urgent GP appointment or NHS 111 for diabetes with sudden blur or for suspected temporal arteritis; and 999 or A&E for sudden vision loss with stroke features or a sudden painful red eye. The NHS says to see a GP or optician if you have any concerns about your vision.