Blurred Vision

When patients present with a complaint of blurred vision it is first necessary to define exactly what they mean - there may be different understandings of what blurred vision is. History and examination should reveal most causes but it may be necessary to refer to an ophthalmologist for confirmation or management of the problem.

What is the patient complaining of?

• Blurred vision - a single image that is seen indistinctly. Is this at distance, near or both?
• Decrease in peripheral vision - the patient may describe bumping into things or frequent scrapes when parking the car.
• Alteration of a clear image e.g. micropsia/macropsia (image appears smaller or bigger) or metamorphopsia (distorted image).
• Interference with a clear image (e.g. floaters, flashes of light - photopsia).
• Diplopia - monocular (the double vision remains when the uninvolved eye is occluded), binocular (vision returns to normal on covering one eye), horizontal, vertical, oblique.
• Other disturbances of vision e.g. iridescent vision (halos, rainbows), dark adaptation problems or night blindness (nyctalopia), colour vision abnormalities.

History of the presenting complaint

• Is it unilateral or bilateral?
• Was it sudden or gradual in onset? If sudden, what was the patient doing at the time, what have they done recently that may have affected the eyes (e.g. DIY, trauma). If gradual over what period of time?
• Has this happened before? When, what happened, has it been diagnosed?
• Are there any associated factors? Examples include any of the other visual phenomena described above, pain (distinguish between ocular pain and pain in the head), associated ocular complaints (e.g. red eye, discharge, abnormal appearances) or systemic complaints (e.g. headache, other neurological problems, generalised malaise).

Other important factors in the history

• Other ocular history - could this be a worsening of a pre-existing condition (e.g. cataracts that have now become symptomatic) or new condition arising from a recent problem (e.g. infection after cataract surgery)?
• Medical history - many systemic conditions affect the eye and may result in acute or chronic blurring of the vision - see our dedicated article.
• Medication - some drugs may be toxic to the eye or precipitate acute angle closure glaucoma.
• Family history - it is helpful to know about atopy, diabetes, thyroid disease, certain malignancies and any hereditary syndromes.
• Social history - important in many ways, e.g. a metal worker with arc eye, an elderly person whose cataracts are making it difficult for them to cope alone, an HGV driver who needs to contact the DVLA.

Please refer to our article on examination of the eye where there is a comprehensive description of eye examination. The essence of examination involves a look at the eye's structure and at its functioning.

Assessment of structure

• Work from front to back i.e. start with the lids and examine as far back as the instruments you have will permit you to, looking at the anterior segment, lens, vitreous through to the fundus. Don't forget to test for corneal sensation (rolled cotton bud lightly touching the cornea) and then re-examine the cornea using fluorescein.
• Try and decide whether the visual media is clear or not - this will be a good guide as to what the diagnosis might be.
  

  Visual media Light from the outside world has to cross a series of transparent media to reach the retina, namely the cornea, the (crystalline) lens and the vitreous. If you cannot obtain a red reflex, it is likely that the problem lies within one or more of these structures. This may be an intrinsic problem to the structure (e.g. corneal oedema secondary to corneal trauma) or as a result of a more distant problem (e.g. clouding of the lens due to uncontrolled diabetes). If you can obtain red reflex, the problem is more likely to lie at the level of the retina or the optic nerve.

• Look for evidence of trauma, infection or inflammation (generally manifesting themselves as a red eye ± associated features) - be guided by the history.

Assessment of function

• Check visual acuity. This is mandatory in both eyes of all patients. Exact previous visual acuity will probably not be on record but note strength of spectacles if worn. Is visual acuity improved by a pin-hole?
• Examine the pupils: sit the patient in a dimly lit room (to avoid pupillary constriction from the room light over-riding that from your torch) and tell them to look at a far wall to overcome the accommodation reflex. Use a bright light source which should be directed from below to avoid the shadow from the nose. Compare them (size and shape) and assess for a direct response to light, carry out the swinging flashlight test to rule out a relative afferent pupillary defect and look for a light-near dissociation.
• Do a confrontational visual field test
• Assess macular function with an Amsler grid.
• Are the external ocular movements full?

Other examination

This is guided by your history and ocular examination but may include a full neurological exam, examination of the pulse for atrial fibrillation, listen for any carotid bruits and check the blood pressure and check urine for glucose.

This will depend upon what is suspected. It may require urgent (same day) referral to an ophthalmologist for slit lamp examination and a definitive diagnosis. If there is suspicion of giant cell arteritis (temporal arteritis) urgent, same day, CRP and plasma viscosity are required.

It is helpful to divide possible diagnoses into laterality, speed of onset and associated pain. This is for guidance and is not absolute.

Acute angle closure glaucoma may affect both eyes but usually only one at a time has an acute attack. Giant cell arteritis may affect one eye initially and immediate starting of steroids is essential to protect the other eye. Chemicals or foreign bodies in the eye may be unilateral or bilateral (sometimes the symptoms are so intense on one side that the other is not noticed by patient or practitioner until the worse symptoms have subsided - always examine both eyes).

Unilateral, sudden and painful

• Trauma: history, associated injuries, inflammation ± hyphaema.
• Orbital cellulitis: the area surrounding the eye will be hot, red, swollen and tender and the patient will be systemically unwell.
• Endophthalmitis: associated with accidental or surgical trauma which may be recent or old but may also be endogenous. Look for the painful red eye, reduced visual acuity and a hypopyon.
• Corneal problems: trauma, infection, severe dry eye or exposure keratopathy, contact lens problems.
• Anterior uveitis: red eye associated with photophobia, headache, may be previous episodes.
• Acute angle closure glaucoma: often precipitated when pupil in mid-dilation (watching telly in dim conditions), often associated with systemic malaise(headache, nausea, vomiting).
• Arteritic anterior optic neuropathy (giant cell/temporal arteritis): (patients > 50 years old) - the pain is often more a headache than acute eye pain; other features include jaw claudication, scalp tenderness, polymyalgia rheumatica ± anorexia, weight loss, fever.
• Optic neuritis: (can be bilateral) can be a very painful presentation of multiple sclerosis -look for pain particularly on moving the eye. There may be other focal neurological symptoms.
• Migraine: when there are scintillations, the pain in the head often appears when the visual disturbance is ebbing or has disappeared.

Unilateral, sudden and painless

• Vitreous haemorrhage: may also present as sudden floaters. May arise as a result of diabetic retinopathy, a retinal break or detachment, retinal vein occlusion and occasionally, a posterior vitreous detachment or age related macular degeneration. Also consider it in trauma, subarachnoid or subdural haemorrhage, intra-ocular tumours and sickle cell disease. It can occur in other more unusual situations too.
• Central retinal artery occlusion presents with painless, almost instantaneous reduction of vision in one eye. The degree of visual impairment is usually very considerable - there may be a compete loss.
• Central retinal vein occlusion frequently presents with loss of vision or blurred vision, often starting on waking.
• Age-related macular degeneration - in the majority of cases, this is the 'dry' from which is associated with a progressive decrease in visual acuity. However, in about 10% of cases, the 'wet' form occurs where a neovascular membrane forms which may be susceptible to bleeding so causing a dramatic and rapid loss of vision.
• Giant cell (temporal) arteritis - see above - may be associated with a painful or tender head but the eye is not usually painful. There is usually progressive but rapid unilateral loss of vision rather than a complaint of blurred vision.
• Migraine prodrome - this may occur in some people without a following headache. It is usually unilateral but may progress to be homonymous.
• Blurred vision can be part of a toxic illness. It is apparent that the patient is pyrexial and unwell.
• Retinal detachment tends to produce a "curtain" coming across the visual field rather than blurring of vision.

Bilateral, sudden and painful

Arc eye, as in welders. There will probably be a history of welding a number of hours earlier with inadequate protection and often the patient will offer the diagnosis.

Bilateral, sudden and painless

• Cerebrovascular disease may lead to damage to the visual pathways and optic cortex. There may or may not be macular sparing. Visual disturbance is often homonymous
• Drugs - anticholinergic drugs but also sedative drugs like antipsychotics and anticonvulsants.¹ The onset of effect of these drugs can be quite slow.
• Refractive errors tend to change very slowly over years but in poorly controlled diabetes mellitus it may change more rapidly. Drugs like steroids and anticholinergics can also have this effect.

Unilateral or bilateral, gradual and painless

• Refractive errors - hormonal changes such during pregnancy, can affect the refractive error but this reverts on restoration of baseline hormone levels.
• Cataracts - the patient may also complain of dulling of colours (and may be noted by relatives to have a predilection for very bright or gaudy colours!).
• ARMD - dry form (see above).
• Genetic disease - there are many degenerative conditions that can cause blurring of the vision. These may affect the elements of the visual media (e.g. the cornea in keratoconus) or the retina (e.g. Best's disease).
• Drug toxicity e.g. hydroxychloroquine, methanol, ethambutol and more recently it has been described with COX2 inhibitors.²
• Other toxic agents including exposure to organophosphates.³
• Chronic eye strain - as with excessive use of computers under adverse conditions may produce blurred vision.⁴

Unilateral, gradual and painful

Neoplastic or inflammatory disease of the orbit and globe.

Depends upon the cause - see dedicated articles through links. If an adequate diagnosis cannot be made, and often when one can be made, the help of an ophthalmologist is required. As a rule of thumb, acute, painful conditions warrant same day referral. A suspected case of giant cell arteritis (where the patient doesn't necessarily have an eye pain) and central retinal artery occlusion also need prompt referrals.