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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).

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.

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 minutes. 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.

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)

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 ).

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