ConditionEyes & vision
Vision Impairment
Vision impairment is a loss of sight that cannot be fully corrected with ordinary glasses or contact lenses and affects daily activities. It ranges from mild reduction to low vision and blindness. The leading causes in adults are uncorrected refractive error, cataract, age-related macular degeneration, glaucoma and diabetic retinopathy. Many cases are preventable or treatable when caught early. When vision cannot be restored, low-vision rehabilitation and assistive technology help people stay independent.
Also called: Visual impairment, sight loss, reduced vision, low vision, blindness
At a glance
- What it is
- Reduced vision not fully corrected by glasses, affecting daily life.
- Levels
- Mild, moderate and severe impairment, low vision, legal blindness, total blindness.
- Leading causes
- Refractive error, cataract, AMD, glaucoma, diabetic retinopathy.
- Prevention
- Regular eye exams, diabetes and blood pressure control, no smoking, eye protection.
- Red flag
- Sudden vision loss is an emergency.
- Support
- Low-vision rehabilitation, magnifiers, lighting, screen readers, mobility training.
When to get help
Call 911 or go to the ER
- Sudden loss of vision in one or both eyes, even if it comes back
- A curtain or shadow over vision, or a sudden shower of floaters and flashes (possible retinal detachment)
- Vision loss with a severe headache, eye pain, nausea, or a red eye with halos (possible acute glaucoma)
- Vision loss with weakness, numbness, facial drooping or trouble speaking (possible stroke)
- Chemical injury or trauma to the eye
See a doctor within a day or two
- New distortion, a dark spot in central vision, or rapidly worsening blur
- Double vision that is new
- A child with a white pupil, a turned eye or not following objects
Book a routine appointment
- Gradual blurring, glare, difficulty reading or seeing at night
- No eye exam in 1 to 2 years if you have diabetes, glaucoma risk or are over 60
- Vision loss affecting driving, work or daily tasks
Levels of vision impairment
Vision is measured as visual acuity (sharpness) and visual field (how wide you can see).
| Category | Visual acuity in the better eye (with best correction) |
|---|---|
| Mild impairment | Worse than 20/40 |
| Moderate impairment | Worse than 20/70 |
| Severe impairment | Worse than 20/200 |
| Blindness (WHO) | Worse than 20/400, or field under 10 degrees |
In the US, legal blindness means best-corrected vision of 20/200 or worse in the better eye, or a visual field of 20 degrees or less. Low vision is a functional term for vision loss that makes everyday tasks difficult despite glasses, medicine or surgery. See legal blindness and low vision.
Leading causes
| Cause | How it affects vision | Key points |
|---|---|---|
| Refractive errors | Blur at distance or near | Corrected with glasses, contacts or surgery |
| Cataract | Cloudy, glare, faded colors | Cured by surgery |
| Age-related macular degeneration | Central vision loss, distortion | Injections for wet AMD; supplements slow progression |
| Glaucoma | Gradual loss of side vision | Often no symptoms early; drops, laser, surgery |
| Diabetic retinopathy | Blur, floaters, sudden loss | Preventable with control and yearly exams |
| Retinal detachment | Curtain, flashes, floaters | Emergency surgery |
| Stroke and brain injury | Visual field loss | Rehabilitation |
| Childhood causes | Amblyopia, cataracts, retinopathy of prematurity, cortical visual impairment | Early screening matters |
Risk factors
- age over 60
- diabetes
- high blood pressure
- smoking
- family history of glaucoma or macular degeneration
- long-term steroid use
- eye injuries
- prematurity in infants
- limited access to eye care
Symptoms
- blurry vision at distance or near
- difficulty reading, recognizing faces or seeing in dim light
- glare and halos
- loss of central or peripheral vision
- distorted lines
- frequent falls or bumping into objects
- difficulty with driving, stairs or pouring
Diagnosis
A comprehensive eye exam by an optometrist or ophthalmologist includes:
- visual acuity and refraction
- eye pressure measurement
- dilated exam of the retina and optic nerve
- visual field testing
- imaging such as OCT and retinal photography
Treatment and support
Treating the cause
- glasses or contacts for refractive error
- cataract surgery
- anti-VEGF injections for wet AMD and diabetic macular edema
- glaucoma drops, laser and surgery
- laser and surgery for retinal disease
Low-vision rehabilitation
When vision cannot be fully restored, a low-vision specialist can help with:
- magnifiers (handheld, stand, electronic video magnifiers)
- lighting and high-contrast tools such as bold-lined paper and contrasting tape on steps
- technology: screen readers, voice assistants, smartphone magnification and text-to-speech
- orientation and mobility training, white canes and guide dogs
- home safety adjustments to prevent falls
- emotional support: vision loss is linked to depression and isolation, which are treatable
Vision loss with vivid visual hallucinations may be Charles Bonnet syndrome, which is common and not a mental illness.
Prevention
- regular eye exams: adults should have a baseline exam at 40 and follow the schedule advised, more often with diabetes or other risks
- yearly dilated eye exams for people with diabetes
- control blood sugar, blood pressure and cholesterol
- stop smoking
- wear UV-blocking sunglasses and protective eyewear for sports and work
- vision screening for children
Frequently asked questions
What is vision impairment?
Vision impairment is a loss of sight that cannot be fully corrected with glasses or contacts and affects daily tasks. It ranges from mild reduction in sharpness or field of vision to low vision and blindness.
What are the most common causes of vision impairment?
The most common causes are uncorrected refractive errors, cataracts, age-related macular degeneration, glaucoma and diabetic retinopathy. Many are treatable or preventable with early detection through regular eye exams.
What is the difference between low vision and legal blindness?
Low vision means vision loss that makes daily activities hard despite treatment. Legal blindness is a specific definition in the US: best-corrected vision of 20/200 or worse in the better eye, or a visual field of 20 degrees or less. Many legally blind people still have some useful vision.
Is sudden vision loss an emergency?
Yes. Sudden loss of vision, a curtain over vision, new flashes and floaters, or vision loss with headache, eye pain or stroke symptoms needs emergency care. Quick treatment can save sight.
What help is available for people with low vision?
Low-vision rehabilitation offers magnifiers, better lighting, high-contrast tools, screen readers, smartphone accessibility features, mobility training and home safety advice. Many people maintain independence and continue reading, working and hobbies with these tools.
Sources
This guide was written from current patient and clinical guidance, including:
- National Eye Institute: Low vision; Vision impairment and blindness data
- World Health Organization: Blindness and vision impairment fact sheet
- American Academy of Ophthalmology: Low vision and vision rehabilitation
- CDC: Vision Health Initiative
- American Foundation for the Blind: Low vision and legal blindness terms