Blurred vision is the most common visual symptom. It usually refers to a gradual onset decrease in visual clarity and corresponds to reduced visual acuity

Patients with small visual field defects (e.g. caused by a small retinal detachment) may describe their symptoms as blurring.

Aetiology of blurred vision

The most frequent causes of blurred vision include

• Refractive errors (the most frequent cause in general)
• Age-related macular degeneration
• Cataracts
• Diabetic retinopathy

Blurred vision has 4 general mechanisms:

• Opacification of normally transparent structures (cornea, crystalline lens, vitreous) through which light rays must pass to reach the retina
• Pathologies affecting the retina
• Pathologies affecting the optic nerve or its connections
• Refractive errors

Some disorders may have more than one mechanism.

For example, refraction may be impaired by an initial cataract or by reversible swelling of the crystalline lens caused by poorly controlled diabetes.

Patients with certain disorders that cause blurred vision (e.g., acute corneal lesions [such as abrasions], ulcers, herpes simplex keratitis, ophthalmic herpes zoster, acute angle-closure glaucoma) are more likely to present with other symptoms such as eye pain and red eyes.

Rare diseases that can cause blurred vision are hereditary optic neuropathies (e.g. dominant optic atrophy, Leber’s hereditary optic neuropathy) and corneal scarring caused by vitamin A deficiency.

Assessment of blurred vision

Medical history

The history of the current disease should ascertain the onset, duration and progression of symptoms and whether they are bilateral or unilateral.

The symptom should be defined as precisely as possible by asking an open-ended question (e.g., “please describe what you mean by blurred vision”).

For example, a loss of detail is not the same as a loss of contrast.

Furthermore, visual field defects may not be recognised as such by patients, who may instead describe symptoms such as missing a step or inability to see words when reading.

Important associated symptoms include eye redness, photophobia, myodesopsies, sensation of flashes of light (photopsias), and pain at rest or with eye movement.

The effects of darkness (night vision), lights (i.e., causing blurring, starbursts, halos, photophobia), distance from an object, and the use of corrective lenses, and whether central or peripheral vision appears to be more affected, need to be ascertained.

The review of systems includes questions about symptoms of possible causes, such as increased thirst and polyuria (diabetes).

The remote pathological history should draw attention to previous ocular injuries or other diagnosed ocular disorders and investigate disorders known to be risk factors for ocular disease (e.g., hypertension, diabetes, HIV/AIDS, systemic lupus erythematosus, sickle cell anaemia, disorders that could cause hyperviscosity syndrome such as multiple myeloma or Waldenström’s macroglobulinemia).

The pharmacological history should include questions about the use of drugs that could affect vision (e.g., corticosteroids) and treatments for disorders affecting vision (e.g., diabetic retinopathy).

Blurred vision, objective examination

Non-visual symptoms are assessed if necessary; however, eye examination may be sufficient.

Assessing visual acuity is essential.

Many patients do not make a maximal effort.

Allowing enough time and encouraging the patient tends to give more accurate results.

Acuity is ideally measured while the patient stands 6 m from a Snellen board hanging on a wall.

If this test cannot be performed, near acuity can be measured using a board placed 36 cm from the eye.

The measurement of near vision should be performed with the reading correction in place for patients aged > 40 years.

Each eye is measured separately while the other eye is covered with a solid object (not the patient’s fingers, which may be spread apart during the test).

If the patient cannot read the first line of the Snellen chart at a distance of 6 m, visual acuity is tested at 3 m.

If nothing can be read from the table even at the shortest distance, the examiner shows a different number of fingers to the patient to see if he/she can count them.

If this is not the case, the examiner assesses whether the patient can perceive the movement of the hand and a light is projected onto the eye to check whether the light is perceived.

Visual acuity is measured with or without the patient’s spectacles.

If the acuity is corrected with glasses, the problem is a refractive error.

If patients do not have their own spectacles, a pinhole is used.

If a pinhole is not available, one can be made at the patient’s bedside by making holes in cardboard using an 18-gauge needle and varying the diameter of each hole slightly.

Patients choose the hole that best corrects their vision.

Pinhole refraction is a quick and efficient way of diagnosing refractive errors, the most common cause of blurred vision.

However, with pinhole refraction, the best correction is usually only 8/10, not 10/10.

Eye examination is also important.

Direct and consensual pupillary reflexes to light are assessed using the oscillating lamp test.

Visual fields are checked by comparison and with an Amsler grid.

The cornea is examined for opacification, ideally using a slit lamp.

The anterior chamber is examined for cells and luminous bodies using a slit lamp if possible, although the results of this examination are unlikely to explain blurred vision in patients without pain or redness of the eyes.

The crystalline lens is examined for opacity, using either an ophthalmoscope, slit lamp or both.

Ophthalmoscopy is performed using a direct ophthalmoscope.

More detail is visible if the eyes are dilated for ophthalmoscopy with a drop of a sympathomimetic (e.g., phenylephrine 2.5%), cycloplegic (e.g., tropicamide 1% or cyclopentolate 1%), or both; dilation is almost complete after about 20 min.

As much of the fundus as is visible is examined, including the retina, macula, fovea, vessels and optic disc and its margins.

To see the entire fundus (i.e., to see a peripheral retinal detachment), the examiner, usually an ophthalmologist, must use an indirect ophthalmoscope.

Intraocular pressure is measured.

Warning signs

The following findings are of particular concern:

• Sudden change in vision
• Eye pain (with or without eye movement)
• Visual field defects (from history or examination)
• Visible retinal or optic disc abnormality
• HIV/AIDS or other immunosuppressive diseases
• A systemic disorder that could cause retinopathy (e.g., drepanocytosis [sickle cell anaemia], possible hyperviscosity syndrome, diabetes, hypertension)

Interpretation of findings

Symptomatology helps to suggest a cause.

If visual acuity is corrected with spectacles or a pinhole, a simple refractive error is likely to be the cause of the clouding.

Loss of contrast or glare may also be caused by a cataract, which must be considered.

However, warning signs suggest a more serious ophthalmological disorder and the need for a full examination, including slit-lamp examination, tonometry, ophthalmoscopic examination with pupil dilation and, depending on the results, possible immediate or delayed ophthalmological consultation.

Specific retinal signs allow a cause to be suggested (see table Interpretation of retinal findings).

Blurred vision, examinations

If acuity is adequately corrected by refraction, patients are referred to an optometrist or ophthalmologist for a routine formal refractive examination.

If visual acuity is not corrected by refraction, but no warning signs are present, patients are referred to an ophthalmologist for a routine assessment.

With some warning signs, patients are referred for urgent or immediate ophthalmological evaluation.

Patients with symptoms or signs of systemic disease should be referred for appropriate investigations:

• Diabetes: digital or routine blood glucose measurement
• Poorly controlled hypertension and acute hypertensive retinopathy (haemorrhages, exudates, papilledema): urine examination, renal function tests, blood pressure monitoring, and ECG
• HIV/AIDS and retinal abnormalities: HIV serology and CD4+ count
• Systemic lupus erythematosus and retinal abnormalities: antinuclear antibodies, erythrocyte sedimentation rate and blood count with formula
• Waldenström’s macroglobulinemia, multiple myeloma, or drepanocytosis (sickle cell anaemia): complete blood count with differential count and other tests (e.g. serum protein electrophoresis) as clinically indicated

Treatment of blurred vision

The underlying disorders are treated.

Corrective lenses can be used to improve visual acuity, even when the pathology causing clouding is not exclusively a refractive error (e.g. early cataract).

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Source:

MSD