Blurred vision is the most common vision symptom. When doctors talk about blurred vision, they typically mean a decrease in sharpness or clarity that has developed gradually. Sudden, complete loss of vision in one or both eyes (blindness Sudden Vision Loss Loss of vision is considered sudden if it develops within a few minutes to a couple of days. It may affect one or both eyes and all or part of a field of vision. Loss of only a small part of... read more ) is considered something different.
Causes of Blurred Vision
Blurred vision has 4 general mechanisms:
Disorders affecting the retina, the light-sensing structure at the back of the eye
Clouding of normally transparent eye structures (cornea, lens, and vitreous humor—the jellylike substance that fills the eyeball) that light rays must pass through to reach the retina
Disorders affecting the pathways of nerves that carry visual signals from the eye to the brain (such as the optic nerve)
Imperfect focusing of light rays on the retina (refractive errors Overview of Refractive Disorders In refractive disorders, light rays entering the eye are not focused on the retina, causing blurred vision. The shape of the eye or cornea or age-related stiffness of the lens may decrease the... read more )
An Inside Look at the Eye
Certain disorders can have more than one mechanism. For example, refraction (focusing ability) can be impaired by early cataracts Cataract A cataract is a clouding (opacity) of the lens of the eye that causes a progressive, painless loss of vision. Vision may be blurred, contrast may be lost, and halos may be visible around lights... read more or by the reversible lens swelling caused by poorly controlled diabetes Diabetes Mellitus (DM) Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Symptoms of diabetes may... read more .
Some disorders that cause blurred vision are more likely to cause other symptoms that prompt people to seek medical attention, such as eye pain Eye Pain Eye pain may be severe and seem sharp, aching, or throbbing, or people may feel only mild irritation of the eye surface or the sensation of a foreign object in the eye (foreign body sensation)... read more and eye redness Eye Redness Eye redness refers to a red appearance of the normally white part of the eye. The eye looks red or bloodshot because blood vessels on the surface of the eye widen (dilate), bringing extra blood... read more (for example, acute corneal disorders such as abrasions, ulcers Corneal Ulcer A corneal ulcer is an open sore on the cornea (the clear layer in front of the iris and pupil) that is usually caused by an eye infection. Contact lenses, injuries, disorders, drugs, and nutritional... read more , herpes simplex keratitis Herpes Simplex Keratitis Herpes simplex keratitis is an eye infection that involves the cornea (the clear layer in front of the iris and pupil) and is caused by herpes simplex virus. The infection commonly recurs and... read more , or herpes zoster ophthalmicus Herpes Zoster Ophthalmicus Herpes zoster ophthalmicus is a reactivated infection of the eye caused by the varicella-zoster virus, the virus that causes chickenpox and shingles. Symptoms include pain and tingling of the... read more ).
The most common causes of blurred vision include
What Is Astigmatism?
Astigmatism is an irregularity in the curvature of the cornea or lens. That is, the cornea or lens is curved differently in different directions. This difference causes light traveling in different planes to be focused differently. For example, vertical lines may be in focus when horizontal lines are not (or vice versa). The irregularity can be in any plane, however, and is often different in each eye. A person with astigmatism (each eye should be tested separately) tends to see certain lines more boldly (that is, in better focus) than the others. Astigmatism can be corrected with prescription eyeglasses or contact lenses. It often occurs together with nearsightedness or farsightedness.
The diagram below is of a standard chart used to test for astigmatism in one eye at a time.
Less common causes
Rare disorders that can cause blurred vision include
Inherited disorders affecting the optic nerve, called hereditary optic neuropathies Hereditary Optic Nerve Disorders Dominant optic atrophy and Leber hereditary optic neuropathy are uncommon inherited disorders that damage the optic nerve, causing vision loss. Vision loss affects both eyes and usually develops... read more (for example, dominant optic atrophy and Leber hereditary optic neuropathy)
Corneal scarring due to vitamin A deficiency Vitamin A Deficiency Vitamin A deficiency can result from a diet low in vitamin A or an absorption or liver disorder. Night blindness is an early symptom. Blindness can eventually develop. The eyes, skin, and other... read more (rare in high-income countries)
Evaluation of Blurred Vision
The following information can help people decide when a doctor's evaluation is needed and help them know what to expect during the evaluation.
In people with blurred vision, certain symptoms and characteristics are cause for concern. They include
Sudden change in vision
Severely reduced vision, particularly in only one eye, even if the symptoms began gradually
Loss of a specific area in the field of vision (called a visual field defect)
Conditions that affect the immune system (for example, use of chemotherapy or other immune-suppressing medications)
When to see a doctor
People who have warning signs should usually go to an emergency department right away. People who have a bodywide (systemic) disorder that sometimes causes retinal damage (for example, diabetes, high blood pressure, or sickle cell disease) should see an eye doctor as soon as is practical, usually within a few days. However, if vision has been deteriorating gradually for months or years but has not been severely impaired and there are no warning signs, waiting a week or longer is usually not harmful.
Eye examinations should be done by an ophthalmologist or optometrist. Ophthalmologists are medical doctors who specialize in the evaluation and treatment (surgical and nonsurgical) of all types of eye disorders. Optometrists are health care practitioners who specialize in the diagnosis and treatment of refractive errors Overview of Refractive Disorders In refractive disorders, light rays entering the eye are not focused on the retina, causing blurred vision. The shape of the eye or cornea or age-related stiffness of the lens may decrease the... read more (which are treated by prescribing glasses or contact lenses). However, optometrists can often diagnose certain other eye problems and then refer people to an ophthalmologist for treatment. People should usually see an ophthalmologist if they have warning signs.
What the doctor does
Doctors first ask questions about the person's symptoms and medical history. Doctors then do a physical examination. What they find during the history and physical examination often suggests a cause of the blurred vision and the tests that may need to be done (see table ).
Doctors ask many questions about the person's symptoms because it is important to understand exactly what the person means by blurred vision. For example, people who have actually lost vision in part of their visual field (visual field defect) may describe this sensation only as blurred vision. The presence of other eye symptoms, such as eye redness Eye Redness Eye redness refers to a red appearance of the normally white part of the eye. The eye looks red or bloodshot because blood vessels on the surface of the eye widen (dilate), bringing extra blood... read more , sensitivity to light Light Sensitivity A number of other symptoms and problems can affect the eyes, including changes in the appearance of the eyes, color blindness, dry eyes, glare and halos, impaired depth perception, itchy eyes... read more , floaters Eye Flashes and Floaters Eye flashes are a person's perception of bright flashes of light, flickering lights, or streaks of light that do not correspond to external sources. Eye floaters are specks or strings that appear... read more , a sensation of sudden flashes of light that can look like lightning, spots, or stars (photopsias), and pain at rest or with eye movement, helps doctors determine the cause. Doctors also ask about the effects of darkness (night vision) and bright lights (for example, causing blur, star bursts, or halos) and whether the person wears corrective lenses.
Doctors also ask questions about symptoms of possible causes and about the presence of disorders that are known to be risk factors for eye disorders (for example, high blood pressure, diabetes, HIV infection or AIDS, and sickle cell disease).
Examination of the eyes may be all that is necessary.
Testing visual acuity (sharpness of vision) is the first step. Ideally, acuity is measured while the person stands about 20 feet (6 meters) from a standard eye chart (Snellen chart) posted or projected on a wall. If this test cannot be done, near acuity is measured using a near card chart held about 14 inches (36 centimeter) from the eye. Each eye is measured separately while the other eye is covered. Visual acuity is measured with the person's own glasses, if such are worn. Sometimes the doctor has the person look through a device that has a pinhole. This device can usually correct refractive errors almost completely but does not correct vision that is blurred due to other causes.
The eye examination is also important. The doctor carefully examines the entire eye using an ophthalmoscope What Is a Slit Lamp? (a light with magnifying lenses that shines into the back of the eye), slit lamp Tonometry A person who has eye symptoms should be checked by a doctor. However, some eye disorders cause few or no symptoms in their early stages, so the eyes should be checked regularly (every 1 to 2... read more (an instrument that enables a doctor to examine the eye under high magnification), or both. Often the eyes are dilated for ophthalmoscopy with eye drops. Pressure inside the eye (intraocular pressure) is measured (called tonometry Tonometry A person who has eye symptoms should be checked by a doctor. However, some eye disorders cause few or no symptoms in their early stages, so the eyes should be checked regularly (every 1 to 2... read more ).
Symptoms and findings during the eye examination often help suggest a cause. For example, if visual acuity returns while corrective lenses or a pinhole device is used and the remainder of the eye exam is normal, simple refractive error Overview of Refractive Disorders In refractive disorders, light rays entering the eye are not focused on the retina, causing blurred vision. The shape of the eye or cornea or age-related stiffness of the lens may decrease the... read more is usually the cause of blurring.
In a person who has a sudden, urgent illness, the symptoms of farsightedness may be more noticeable, even in those around age 40 who had never previously needed corrective lenses for reading. Previously unrecognized farsightedness is a common cause of blurred vision in hospitalized people.
Testing depends on the suspected cause of the blurred vision (see table ). People with symptoms of bodywide (systemic) disorders should have appropriate testing. For example, testing might include blood tests for diabetes, systemic lupus erythematosus Systemic Lupus Erythematosus (SLE) Systemic lupus erythematosus is a chronic autoimmune inflammatory connective tissue disorder that can involve joints, kidneys, skin, mucous membranes, and blood vessel walls. Problems in the... read more , or HIV infection, and blood pressure monitoring.
Treatment of Blurred Vision
Essentials for Older Adults: Blurred Vision
Although some decrease in visual acuity normally occurs with aging, in the absence of eye disease, acuity should be correctable to 20/20 with glasses or contact lenses, even in older adults.
Refractive error is the most common cause of blurred vision.
If refractive error is the problem, corrective lenses or surgery (particularly if cataracts are the cause of the change in refractive error) can usually correct the blurriness.
Doctors check visual acuity and determine whether glasses or a pinhole device corrects the problem, and if it does not, they dilate the eye with drops and carefully examine the retina.
People with warning signs should see a doctor as soon as possible.
Because glaucoma is common, intraocular pressure is usually measured.