Blurred vision is the most common visual symptom. It usually refers to decreased visual clarity of gradual onset, and corresponds to decreased visual acuity. Patients with small visual field defects (eg, caused by a small retinal detachment) may describe their symptoms as blurring.
Etiology of Blurred Vision
The most common causes of blurred vision (see table Some Causes of Blurred Vision) include
Refractive errors (the most common cause overall)
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 | ||
Gradual onset, often risk factors (eg, aging, corticosteroid use), loss of contrast, glare Lens opacification on ophthalmoscopy or slit-lamp examination | Ophthalmic evaluation | |
Corneal opacification (eg, posttraumatic or postinfectious scarring) | Corneal abnormalities on slit-lamp examination | Ophthalmic evaluation |
Disorders affecting the retina | ||
Sudden or gradual onset, central vision affected (central scotoma) without loss of peripheral vision, macular drusen or scarring, neovascular membrane | Fundoscopy | |
Infectious retinitis (eg, cytomegalovirus, Toxoplasma) | Usually HIV infection or other immunosuppressive disorder, often eye redness or pain, abnormal retinal findings | Fundoscopy Studies as clinically indicated (eg, anti-Toxoplasma antibodies) |
Primarily night blindness, gradual onset, pigmented retinal lesions | Fundoscopy Specialized testing by ophthalmologist (eg, dark adaptation, electroretinography) | |
Retinopathy associated with systemic disorders (eg, hypertension, systemic lupus erythematosus, diabetes, Waldenström macroglobulinemia, multiple myeloma, or other disorders that could cause hyperviscosity syndrome) | Risk factors, retinal abnormalities detected during ophthalmoscopy (see table Interpretation of Some Red Flag Eye Findings) | Testing as indicated for clinically suspected disorders |
Risk factors (eg, diabetic retinopathy, uveitis, retinal detachment or ocular injury) Blurry or distorted vision (eg, straight lines appear wavy) | Fundoscopy Optical coherence tomography | |
Macular hole | Blurry vision, initially central | Fundoscopy Optical coherence tomography |
Risk factors (eg, hypertension, age, glaucoma) Painless vision loss (usually sudden) Sometimes, blurry vision | Fundoscopy Sometimes, optical coherence tomography | |
Disorders affecting the optic nerve or neural pathways | ||
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 of brain and orbits to rule out multiple sclerosis | |
Disorders affecting focus | ||
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 .
Evaluation of Blurred Vision
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, immunocompromise, systemic lupus erythematosus, sickle cell anemia, disorders that could cause hyperviscosity syndrome such as multiple myeloma or Waldenström macroglobulinemia). Medication history should include questions about use of medications 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.
Visual acuity ideally is measured while the patient wears their own glasses and stands 6 meters (about 20 feet) from a Snellen chart posted on a wall. If this test cannot be done, near acuity can be measured using a near card chart held about 36 centimeters (14 inches) from the eye. Measurement of near vision should be done with reading correction in place for patients > 40 years to account for presbyopia. In the setting of acute illness, presbyopia symptoms can be accentuated in people near the age of 40 who have never needed corrective lenses for reading. Previously unrecognized presbyopia is a common cause of blurred vision in hospitalized adults. 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 meters, acuity is tested at 3 meters (about 10 feet). 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.
If acuity is corrected with the patient's glasses, the problem is likely 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.
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
Immunocompromise
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 table Some Causes of Blurred Vision).
If visual acuity is corrected with glasses or a pinhole refractor, simple refractive error is likely 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 ophthalmic disorder (see table Interpretation of Some Red Flag Eye 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 ophthalmic referral.
Specific retinal findings help suggest a cause (see table ).
Interpretation of Some Red Flag Eye Findings
Findings | Examples of Possible Causes |
|---|---|
Retinopathy | Infections such as HIV or infectious retinitis* and other systemic disorders that can cause retinopathy (eg, sickle cell anemia, hypertension, diabetes, hyperviscosity syndrome) |
Bilateral symmetric visual field defects | Lesion affecting cortical visual pathways |
Eye pain* | |
Monocular visual field defect* | Retinal detachment, other retinal abnormality, other optic neuropathy |
Retinal or optic disk abnormality | Infectious retinitis,* retinitis pigmentosa, worsening retinopathy* (see table 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 |
|---|---|
Dark-pigmented lesions in bone spicule formation in the midperipheral retina (rarely visible with direct ophthalmoscopy) | |
Diffuse hemorrhages, venous dilation | Hyperviscosity syndrome |
Indistinct optic disk margins, suggesting optic nerve swelling | |
Macular hyperpigmentation, loss of pigment in retinal epithelium, drusen, hemorrhage | |
Microaneurysms and neovascularization at posterior retina | |
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 ophthalmic 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, blood pressure monitoring, and electrocardiography (ECG)
HIV/AIDS and retinal abnormalities: HIV serology and CD4+ count
Systemic lupus erythematosus (SLE) and retinal abnormality: Antinuclear antibodies, erythrocyte sedimentation rate (ESR), and complete blood count (CBC)
Waldenström macroglobulinemia, multiple myeloma, or sickle cell anemia: CBC with differential count and other testing (eg, serum protein electrophoresis) as clinically indicated
Treatment of Blurred Vision
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: Blurred Vision
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 older adults.
Key Points
If visual acuity is corrected with pinhole refraction, refractive error is likely 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.
