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Blurred Vision

by Kathryn Colby, MD, PhD

Blurred vision is the most common visual symptom. It usually refers to decreased visual acuity of gradual onset. For sudden, complete loss of vision in one or both eyes (blindness), see Acute Vision Loss. Patients with small visual field defects (eg, caused by a small retinal detachment) may describe their symptoms as blurring.

Etiology

The most common causes of blurred vision (see Some Causes of Blurred Vision) include

  • Refractive errors (the most common cause overall)

  • Age-related macular degeneration

  • Cataracts

  • Diabetic retinopathy

Blurred vision has 4 general mechanisms:

  • Opacification of normally transparent ocular structures (cornea, lens, vitreous) through which light rays must pass to reach the retina

  • Disorders affecting the retina

  • Disorders affecting the optic nerve or its connections

  • Refractive errors

Some Causes of Blurred Vision

Cause

Suggestive Findings

Diagnostic Approach

Opacification of eye structures

Cataracts

Gradual onset, often risk factors (eg, aging, corticosteroid use), loss of contrast, glare

Lens opacification on ophthalmoscopy or slit-lamp examination

Clinical evaluation

Corneal opacification (eg, posttraumatic or postinfectious scarring)

Corneal abnormalities on slit-lamp examination

Clinical evaluation

Disorders affecting the retina

Age-related macular degeneration

Gradual onset, central vision affected (central scotoma) without loss of peripheral vision, macular drusen or scarring, neovascular membrane

Fluorescein angiography or other retinal imaging as clinically indicated

Infectious retinitis (eg, cytomegalovirus, Toxoplasma)

Usually HIV infection or other immunosuppressive disorder, often eye redness or pain, abnormal retinal findings

Studies as clinically indicated (eg, anti- Toxoplasma antibodies)

Retinitis pigmentosa

Primarily night blindness, gradual onset, pigmented retinal lesions

Specialized testing by ophthalmologist (eg, dark adaptation, electroretinography)

Retinopathy associated with systemic disorders (eg, hypertension, SLE, diabetes, Waldenström macroglobulinemia, multiple myeloma, or other disorders that could cause hyperviscosity syndrome)

Risk factors, retinal abnormalities detected during ophthalmoscopy (see Interpretation of Retinal Findings)

Testing as indicated for clinically suspected disorders

Disorders affecting the optic nerve or neural pathways

Optic neuritis

Gradual onset unless due to multiple sclerosis (in which onset of optic neuritis is rapid)

Often unilateral or asymmetric

Pain with eye movement,direct pupillary light reflex decreased more than consensual (afferent pupillary defect), sometimes loss of optic disk margins and/or globe tenderness

Often MRI to rule out multiple sclerosis

Disorders affecting focus

Refractive errors

Visual acuity varying with distance from objects, acuity corrected with refraction

Clinical refraction by an optometrist or ophthalmologist

Certain disorders can have more than one mechanism. For example, refraction can be impaired by early cataracts or the reversible lens swelling caused by poorly controlled diabetes.

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

Rare disorders that can cause blurred vision include hereditary optic neuropathies (eg, dominant optic atrophy, Leber hereditary optic neuropathy) and corneal scarring due to vitamin A deficiency.

Evaluation

History

History of present illness should ascertain the onset, duration, and progression of symptoms, as well as whether they are bilateral or unilateral. The symptom should be defined as precisely as possible by asking an open-ended question or request (eg, “Please describe what you mean by blurred vision”). For example, loss of detail is not the same as loss of contrast. Also, visual field defects may not be recognized as such by patients, who may instead describe symptoms such as missing steps or the inability to see words when reading. Important associated symptoms include eye redness, photophobia, floaters, sensation of lightning-like flashes of light (photopsias), and pain at rest or with eye movement. The effects of darkness (night vision), bright lights (ie, causing blur, star bursts, halos, photophobia), distance from an object, and corrective lenses and whether central or peripheral vision seems to be more affected should be ascertained.

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

Past medical history should note previous eye injury or other diagnosed eye disorders and ask about disorders known to be risk factors for eye disorders (eg, hypertension, diabetes, HIV/AIDS, SLE, sickle cell anemia, disorders that could cause hyperviscosity syndrome such as multiple myeloma or Waldenström macroglobulinemia). Drug history should include questions about use of drugs that could affect vision (eg, corticosteroids) and treatments for disorders affecting vision (eg, diabetic retinopathy).

Physical examination

Nonvisual symptoms are evaluated as needed; however, examination of the eyes may be all that is necessary.

Testing visual acuity is key. Many patients do not give a full effort. Providing adequate time and coaxing patients tend to yield more accurate results.

Acuity ideally is measured while the patient stands 6 m (about 20 ft) from a Snellen chart posted on a wall. If this test cannot be done, acuity can be measured using a chart held about 36 cm (14 in) from the eye. Measurement of near vision should be done with reading correction in place for patients > 40 yr. Each eye is measured separately while the other eye is covered with a solid object (not the patient’s fingers, which may separate during testing). If the patient cannot read the top line of the Snellen chart at 6 m, acuity is tested at 3 m. If nothing can be read from a chart even at the closest distance, the examiner holds up different numbers of fingers to see whether the patient can accurately count them. If not, the examiner tests whether the patient can perceive hand motion. If not, a light is shined into the eye to see whether light is perceived.

Visual acuity is measured with and without the patients’ own glasses. If acuity is corrected with glasses, the problem is a refractive error. If patients do not have their glasses, a pinhole refractor is used. If a commercial pinhole refractor is unavailable, one can be made at the bedside by poking holes through a piece of cardboard using an 18-gauge needle and varying the diameter of each hole slightly. Patients choose the hole that corrects vision the most. If acuity corrects with pinhole refraction, the problem is a refractive error. Pinhole refraction is a rapid, efficient way to diagnose refractive errors, which are the most common cause of blurred vision. However, with pinhole refraction, best correction is usually to only about 20/30, not 20/20.

Eye examination is also important. Direct and consensual pupillary light responses are examined using the swinging flashlight test. Visual fields are checked using confrontation and an Amsler grid.

The cornea is examined for opacification, ideally using a slit lamp. The anterior chamber is examined for cells and flare using a slit lamp if possible, although results of this examination are unlikely to explain visual blurring in patients without eye pain or redness.

The lens is examined for opacities using an ophthalmoscope, slit lamp, or both.

Ophthalmoscopy is done using a direct ophthalmoscope. More detail is visible if the eyes are dilated for ophthalmoscopy with a drop of a sympathomimetic (eg, 2.5% phenylephrine), cycloplegic (eg, 1% tropicamide or 1% cyclopentolate), or both; dilation is nearly full after about 20 min. As much of the fundus as is visible, including the retina, macula, fovea, vessels, and optic disk and its margins, is examined. To see the entire fundus (ie, to see a peripheral retinal detachment), the examiner, usually an ophthalmologist, must use an indirect ophthalmoscope.

Intraocular pressure is measured.

Red flags

The following findings are of particular concern:

  • Sudden change in vision

  • Eye pain (with or without eye movement)

  • Visual field defect (by history or examination)

  • Visible abnormality of the retina or optic disk

  • HIV/AIDS or other immunosuppressive disorder

  • A systemic disorder that could cause retinopathy (eg, sickle cell anemia, possible hyperviscosity syndrome, diabetes, hypertension)

Interpretation of findings

Symptoms and signs help suggest a cause (see Some Causes of Blurred Vision).

If visual acuity is corrected with glasses or a pinhole refractor, simple refractive error is the cause of blurring. Loss of contrast or glare may still be caused by cataract, which should be considered.

However, red flag findings suggest a more serious ophthalmologic disorder (see Interpretation of Some Red Flag Findings) and need for a complete examination, including slit-lamp examination, tonometry, ophthalmoscopic examination with pupillary dilation, and, depending on findings, possibly immediate or urgent ophthalmologic referral.

Specific retinal findings help suggest a cause (see Interpretation of Retinal Findings).

Interpretation of Some Red Flag Findings

Findings

Possible Cause

A systemic disorder that could cause retinopathy (eg, sickle cell anemia, possible hyperviscosity syndrome, diabetes, hypertension)

Retinopathy

Bilateral symmetric visual field defects

Lesion affecting cortical visual pathways

Eye pain*

Optic neuritis

HIV/AIDS or other immunosuppressive disorder*

Infectious retinitis

Monocular visual field defect*

Retinal detachment, other retinal abnormality, other optic neuropathy

Retinal or optic disk abnormality

Infectious retinitis,* retinitis pigmentosa, worsening retinopathy* (see Interpretation of Retinal Findings)

Sudden change in vision*

Optic neuritis, sudden worsening of retinopathy, or other physical eye disorder (see Acute Vision Loss)

*Urgent or immediate ophthalmologic referral is usually indicated.

Interpretation of Retinal Findings

Findings

Possible Cause

Arteriolar narrowing, copper wiring, flame hemorrhages, arteriovenous nicking

Hypertensive retinopathy

Dark-pigmented lesions in bone spicule formation in the midperipheral retina (rarely visible with direct ophthalmoscopy)

Retinitis pigmentosa

Diffuse hemorrhages, venous dilation

Hyperviscosity syndrome

Indistinct optic disk margins, suggesting optic nerve swelling

Optic neuritis

Macular hyperpigmentation, loss of pigment in retinal epithelium, drusen, hemorrhage

Age-related macular degeneration

Microaneurysms and neovascularization at posterior retina

Diabetic retinopathy

White retinal infiltrates, sometimes loss of red reflex or visible vitreous inflammation

Infectious retinitis

Toxoplasmosis suggested by retinal infiltrate immediately adjacent to a scar

Testing

If acuity corrects appropriately with refraction, patients are referred to an optometrist or ophthalmologist for routine formal refraction. If visual acuity is not corrected with refraction but there are no red flag findings, patients are referred to an ophthalmologist for routine evaluation. With certain red flag findings, patients are referred for immediate or urgent ophthalmologic evaluation.

Patients with symptoms or signs of systemic disorders should have appropriate testing:

  • Diabetes: Fingerstick or random glucose measurement

  • Poorly controlled hypertension and acute hypertensive retinopathy (hemorrhages, exudates, or papilledema): Urinalysis, renal function testing, BP monitoring, and possibly ECG

  • HIV/AIDS and retinal abnormalities: HIV serology and CD4+ count

  • SLE and retinal abnormality: Antinuclear antibodies, ESR, and CBC

  • Waldenström macroglobulinemia, multiple myeloma, or sickle cell anemia: CBC with differential count and other testing (eg, serum protein electrophoresis) as clinically indicated

Treatment

Underlying disorders are treated. Corrective lenses may be used to improve visual acuity, even when the disorder causing blurring is not purely a refractive error (eg, early cataract).

Geriatrics Essentials

Although some decrease in visual acuity in low light or loss of contrast sensitivity can normally occur with aging, acuity normally is correctable to 20/20 with refraction, even in very elderly patients.

Key Points

  • If visual acuity is corrected with pinhole refraction, refractive error is the problem.

  • If pinhole refraction does not correct acuity and there is no obvious cataract or corneal abnormality, ophthalmoscopy should be done after pupillary dilation.

  • Many abnormalities on ophthalmoscopy, particularly if symptoms are recently worsening, require urgent or immediate ophthalmologic referral.

Resources In This Article

Drugs Mentioned In This Article

  • Drug Name
    Select Trade
  • MYDRIACYL, TROPICACYL
  • No US brand name
  • AKPENTOLATE, CYCLOGYL

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