How common are eye diseases and conditions?

Key facts

  • Vision impairment poses an enormous global financial burden with the annual global costs of productivity losses associated with vision impairment estimated to be US$ 411 billion.
  • The leading causes of vision impairment and blindness are uncorrected refractive errors and cataracts.
  • The majority of people with vision impairment and blindness are over the age of 50 years; however, vision loss can affect people of all ages.
  • Globally, at least 2.2 billion people have a near or distance vision impairment. In at least 1 billion – or almost half – of these cases, vision impairment could have been prevented or has yet to be addressed.

 

Definitions

The International Classification of Diseases 11 (2018) classifies vision impairment into two groups, distance and near presenting vision impairment.

Distance vision impairment:

  • Mild – visual acuity worse than 6/12 to 6/18
  • Moderate – visual acuity worse than 6/18 to 6/60
  • Severe – visual acuity worse than 6/60 to 3/60
  • Blindness – visual acuity worse than 3/60

Near vision impairment:

  • Near visual acuity worse than N6 or M.08 at 40cm.

A person’s experience of vision impairment varies depending upon many different factors. This includes for example, the availability of prevention and treatment interventions, access to vision rehabilitation (including assistive products such as spectacles or white canes), and whether the person experiences problems with inaccessible buildings, transport and information.

Prevalence

Globally, at least 2.2 billion people have a near or distance vision impairment. In at least 1 billion – or almost half – of these cases, vision impairment could have been prevented or has yet to be addressed.

This 1 billion people includes those with moderate or severe distance vision impairment or blindness due to unaddressed refractive error (88.4 million), cataract (94 million), age-related macular degeneration (8 million), glaucoma (7.7 million), diabetic retinopathy (3.9 million) (1), as well as near vision impairment caused by unaddressed presbyopia (826 million) (2).

In terms of regional differences, the prevalence of distance vision impairment in low- and middle-income regions is estimated to be four times higher than in high-income regions (1). With regards to near vision, rates of unaddressed near vision impairment are estimated to be greater than 80% in western, eastern and central sub-Saharan Africa, while comparative rates in high-income regions of North America, Australasia, Western Europe, and of Asia-Pacific are reported to be lower than 10% (2).

Population growth and ageing are expected to increase the risk that more people acquire vision impairment.

Causes

Globally, the leading causes of vision impairment are:

  • age-related macular degeneration
  • cataract
  • diabetic retinopathy
  • glaucoma
  • uncorrected refractive errors

There is substantial variation in the causes between and within countries according to the availability of eye care services, their affordability, and the eye care literacy of the population. For example, the proportion of vision impairment attributable to cataract is higher in low- and middle-income countries than high-income countries. In high income countries, diseases such as glaucoma and age-related macular degeneration are more common.

Among children, the causes of vision impairment vary considerably across countries. For example, in low-income countries congenital cataract is a leading cause, whereas in middle-income countries it is more likely to be retinopathy of prematurity.

As in adult populations, uncorrected refractive error remains a leading cause of vision impairment in all countries amongst children.

Impact of vision impairment

Personal impact

Young children with early onset severe vision impairment can experience delayed motor, language, emotional, social and cognitive development, with lifelong consequences. School-age children with vision impairment can also experience lower levels of educational achievement.

Vision impairment severely impacts quality of life among adult populations. Adults with vision impairment often have lower rates of workforce participation and productivity and higher rates of depression and anxiety.

In the case of older adults, vision impairment can contribute to social isolation, difficulty walking, a higher risk of falls and fractures, and a greater likelihood of early entry into nursing or care homes.

Economic impact

Vision impairment poses an enormous global financial burden with an estimate annual global productivity loss of about US$ 411 billion purchasing power parity (3). this figure far outweighs the estimated cost gap of addressing the unmet need of vision impairment (estimated at about US$ 25 billion).

Strategies to address eye conditions to avoid vision impairment

While a large number of eye diseases can be prevented (such as infections, trauma, unsafe traditional medicines, perinatal diseases, nutrition-related diseases, unsafe use or self-administration of topical treatment), this is not possible for all.

Each eye condition requires a different, timely response. There are effective interventions covering promotion, prevention, treatment and rehabilitation which address the needs associated with eye conditions and vision impairment; some are among the most cost-effective and feasible of all health care interventions to implement. For example, uncorrected refractive error can be corrected with spectacles or surgery while cataract surgery can restore vision.

Treatment is also available for many eye conditions that do not typically cause vision impairment, such as dry eye, conjunctivitis and blepharitis, but generate discomfort and pain. Treatment of these conditions is directed at alleviating the symptoms and preventing the evolution towards more severe diseases.

Vision rehabilitation is very effective in improving functioning for people with an irreversible vision impairment that can be caused by eye conditions such as diabetic retinopathy, glaucoma, consequences of trauma, and age-related macular degeneration.

WHO response

WHO’s work is guided by the recommendations of the WHO World report on vision (2019) and the resolution on “integrated, people-centred eye care, including preventable blindness and vision impairment” that was adopted at Seventy-third World Health Assembly in 2020. The key proposal of the report and resolution is to make integrated people-centred eye care (IPEC) the care model of choice and to ensure its widespread implementation. It is expected that by shaping the global agenda on vision, the report and resolution will assist Member States and their partners in their efforts to reduce the burden of eye conditions and vision impairment and achieve the Sustainable Development Goals (SDGs), particularly SDG target 3.8 on universal health coverage.

Some of WHO’s key areas of work and activities in the prevention of blindness include:

  1. Working with Member States and other partners in the field to monitor the global targets for 2030 on integrated people-centred eye care.
  2. Observing and promoting World Sight Day as an annual advocacy event.
  3. Supporting the integration of eye care in health systems through the implementation of a series of technical tools:
    • eye care in health sytems – Guide for action providing practical, step-by-step support to Member States in the planning and implementation of the recommendations of the World report on vision.
    • package of Eye Care Interventions (PECI): a tool for planning and budgeting for eye care at each level of the health system.
    • Eye Care Competency Framework (ECCF): a planning tool for eye care human resources based on competencies; and
    • mobile health toolkit for myopia to increase awareness and health literacy of modifiable risk factors, potential irreversible consequences of myopia and the importance of spectacle compliance and regular eye examinations.
  4. The development and implementation tools to support countries to assess the provision of eye care services such as:
    • Eye care services assessment tool
    • Tool for Assessment of Diabetes and Diabetic Retinopathy Services
    • Tool for the Assessment of Glaucoma Services
    • Tool for the Assessment of Refractive Services
    • Tool for the Assessment of Rehabilitation Services and Systems

What are some of the most common eye diseases?

The four most common eye conditions leading to loss of vision or blindness are:

  • Cataracts.
  • Diabetes-related retinopathy.
  • Glaucoma.
  • Age-related macular degeneration.

However, there are hundreds of different eye diseases and disorders.

What is macular degeneration?

Macular degeneration (also called age-related macular degeneration or AMD) is an eye disease that affects your central vision. It damages the macula, which is the center area of your retina that allows you to see fine details. It’s the leading cause of vision loss in people over the age of 60.

Macular degeneration can either be wet or dry. Wet AMD happens when abnormal blood vessels grow under the macula and leak blood and fluid. This damages the macula and leads to loss of central vision. Dry AMD results in the thinning of the macula, which blurs your central vision over time. Dry AMD is more common than the wet form, accounting for 70% to 90% of cases.

Symptoms of AMD, which usually aren’t noticed until the disease has progressed, include:

  • Blurred central vision.
  • Black or dark spots in the center part of your field of vision.
  • Wavy or curved appearance to straight lines.

Although there is no cure, treatment can slow the progress of disease or prevent severe vision loss. Recent advances have been made in the treatment of wet AMD using intraocular injections of anti-VEGF medications.

What is a cataract?

A cataract is a clouding of your eye’s lens. This cloudy lens can develop in one or both eyes. Cataracts are the world’s leading cause of blindness. In the U.S., cataracts is the leading cause of reversible vision loss. Cataracts can occur at any age and even be present at birth, but are more common in people over the age of 50.

Symptoms of a cataract include:

  • Cloudy/blurry vision.
  • Glare around lights at night.
  • Trouble seeing at night.
  • Sensitivity to bright light.
  • Need for bright light to read.
  • Changes to the way you see color.
  • Frequent changes to your eyeglass prescription.

Surgery to remove and replace the cloudy lens with an artificial lens is highly successful with more than 90% of people seeing better after cataract removal.

What is diabetes-related retinopathy?

Diabetes-related retinopathy is a common complication of diabetes. It’s one of the leading causes of blindness in adults in the U.S.

Diabetes-related retinopathy is a disease in which there’s ongoing damage to blood vessels in the retina due to long-term unmanaged high sugar (glucose) levels in your blood. Your retina is the light-sensitive tissue in your eye that is needed for clear vision. Most people with diabetes-related retinopathy show no vision changes until the disease is severe. In others, symptoms come and go.

Symptoms include:

  • Blurred or distorted vision.
  • New color blindness or seeing colors as faded.
  • Poor night vision.
  • Small dark spots or streaks in your vision.
  • Trouble reading or seeing faraway objects.

Treatments include injections of a specific type of medication and surgery that addresses repairing or shrinking blood vessels in the retina.

What is glaucoma?

Glaucoma is an eye disease that results from higher-than-normal fluid pressure in the eye. The pressure damages your optic nerve, which affects how visual information is transmitted to your brain. Undetected and untreated glaucoma can lead to vision loss and blindness in one or both eyes. Glaucoma often runs in families.

There are two main types of glaucoma. Open-angle glaucoma develops slowly over time and you may not notice vision change until the disease is far along. Closed-angle glaucoma can happen suddenly. It’s painful and causes loss of vision very quickly.

Symptoms include:

  • Eye pain or pressure.
  • Headaches.
  • Red eyes.
  • Rainbow-colored halos around lights.
  • Low vision, blurred vision, tunnel vision, blind spots.
  • Nausea and vomiting.

Treatments focus on reducing eye pressure and include prescription eye drops, laser therapy and surgery.

What is retinal detachment?

Retinal detachment is a separation or detachment of the retina from its underlying tissues that hold it in place within your eye. This is a serious eye condition that can lead to blindness if not treated.

You may or may not have symptoms, depending on the severity of the detachment. Symptoms include:

  • Seeing flashes of light.
  • Seeing dark spots or squiggly lines drifting across your vision.
  • Darkening/covering of part of your vision or your side vision.

Treatments include laser therapy or different surgical approaches to seal or close the retinal tear and reattach the retina.

What are the most common eye conditions in children?

Eye conditions commonly seen in children include:

  • Amblyopia: Amblyopia (also called “lazy eye”) happens when your child’s brain and one eye aren’t working together properly and the brain favors the other better-seeing eye. They’ll have reduced vision in the non-favored eye. This is the most common cause of vision impairment in children.
  • Strabismus: Strabismus is a lack of coordination between your child’s eyes, which causes the eyes to cross or turn out. Your child’s eyes don’t focus together on a single image at the same time. This can cause reduced 3D vision and/or the brain may favor one eye over the other, which can cause loss of vision in the non-favored eye (amblyopia, see above).
  • Conjunctivitis: Conjunctivitis, also known as pink eye, is an inflammation of the clear tissue that lines the inside surface of your eyelid and the outer coating of your eye. This tissue is called conjunctiva. It helps keep your eyelid and eyeball moist. Pink eye can be highly contagious, especially among children. Although it doesn’t damage vision, it causes itchy, red, blurry, tearing and discharge.

What are refractive eye conditions?

Refractive eye problems cause you to have issues with focus. Light is improperly bent as it passes through your cornea and lens. These refractive errors are the most common eye problems in the U.S. Refractive errors include nearsightedness (myopia), farsightedness (hyperopia) and distorted vision at all distances (astigmatism). These eye conditions can be helped with eyeglasses, contacts or surgery.

What is presbyopia?

Presbyopia is the inability to focus over a range of vision. It’s often confused with farsightedness, but they are not the same conditions. Presbyopia is a natural loss of flexibility of the lens that comes with age. Farsightedness is an abnormal short eye shape that causes light to bend incorrectly after it enters the eye. Presbyopia is treated with corrective lenses (“cheater” eyeglasses).

What are eye floaters?

Eye floaters are clumps or deposits that float in your eye’s vitreous fluid (the clear, jelly-like substance in the middle of your eye). Floaters appear as spots or specks that float by in your field of vision. They are usually harmless, but if they appear suddenly and are joined by other symptoms, such as flashes of light or partial loss of side vision, they can be a sign of a more serious eye condition, such as retinal detachment.

What is dry eye?

Dry eye happens when your tear glands can’t make enough tears or produce low quality tears and can’t adequately lubricate the surface of your eyes. Treatments include artificial tears or tear duct plugs to prevent tear drainage.

What is eye tearing?

Eye tearing happens when your eyes produce more tears than can be drained. This can be from sensitivity to climate elements like wind, sun and temperature changes or to an eye infection or a blocked tear duct.

Can eye diseases be inherited?

Yes, genetic factors can play a role in many kinds of eye disease, some of which are leading causes of blindness in infants, children and adults. More than 60% of cases of blindness among infants are caused by inherited eye diseases, including:

  • Congenital cataracts.
  • Congenital glaucoma.
  • Retinal degeneration.
  • Optic atrophy.
  • Eye malformations.

There is also strong evidence that strabismus (ocular misalignment) has a genetic link. A family history is seen in about one-third of cases. In adults, glaucoma and age-related macular degeneration appear to be inherited in a large portion of cases. Researchers have made significant progress in identifying the genes that cause retinitis pigmentosa, a degenerative disease of the retina that causes night blindness and gradual vision loss. More recently, gene therapy has been used to treat a form of retinitis pigmentosa of early childhood onset.

What common vision problems are inherited?

Researchers now have evidence that some of the most common vision problems among children and adults are genetically determined. These eye problems include:

  • Strabismus (cross-eyes).
  • Refractive errors such as nearsightedness, farsightedness and astigmatism.
  • Retinal degeneration.
  • Glaucoma.

What can I do to keep my eyes as healthy as possible?

There’s a lot you can do to protect your vision. Recommendations include:

  • See your eye care professional at regularly scheduled intervals, even if you don’t have any noticeable changes in your vision. Some eye diseases don’t have early warning signs. Ask your eye care professional how often you should be seen.
  • Know your risk factors for eye diseases. Some include age, family history of eye diseases, your ethnic background or having other health conditions such as high blood pressure or diabetes.
  • Make healthy lifestyle choices. Keeping your body as healthy as possible will lower your risk for eye diseases or vision problems. Maintain a healthy weight, eat healthy foods, exercise for at least 30 minutes a day on most days of the week and stop smoking are some examples of healthy choices.
  • Protect your eyes. Wear sunglasses even on cloudy days to protect your eyes from UVA and UVB light. Wear proper protective eyewear when playing sports or when working on home or industrial projects. Follow instructions for wearing and cleaning contacts. Avoid prolonged computer and phone eye strain. Rest your eyes and focus on distant objects for a minute every 20 minutes.

References

1) GBD 2019 Blindness and Vision Impairment Collaborators; Vision Loss Expert Group of the Global Burden of Disease Study. Causes of blindness and vision impairment in 2020 and trends over 30 years, and prevalence of avoidable blindness in relation to VISION 2020: the Right to Sight: an analysis for the Global Burden of Disease Study. Lancet Glob Health. 2021 Feb;9(2):e144-e160. doi: 10.1016/S2214-109X(20)30489-7.

2) Fricke, TR, Tahhan N, Resnikoff S, Papas E, Burnett A, Suit MH, Naduvilath T, Naidoo K, Global Prevalence of Presbyopia and Vision Impairment from Uncorrected Presbyopia: Systematic Review, Meta-analysis, and Modelling, Ophthalmology. 2018 May 9.

3) Burton MJ, Ramke J, Marques AP, Bourne RR, Congdon N, Jones I, et al. The Lancet Global Health commission on Global Eye Health: vision beyond 2020. Lancet Glob Health. 2021; 9(4):e489–e551.