It is currently estimated that approximately 285 million people across the world have some form of visual impairment. However, this is unevenly distributed, as 90% of the visually impaired are in low and middle-income countries. Strengthening services, improving access, and addressing inequity at the local level are an urgent priority for global eye care. Prevention programmes are essential to achieve these goals and reduce the burden of visual impairment across the world. In this presentation we introduce the epidemiology of blindness and visual impairment. As you watch, try to consider the main causes of visual impairment in your own community and the control strategies that local eye care programmes carry out.
This video is part of the free online course: Global Blindness: Planning and Managing Eye Care Services. We encourage the use and adaptation of this resource for teaching and learning. Find more Open Educational Resources for eye care on our website at http://iceh.lshtm.ac.uk/oer
This presentation on the epidemiology of visual impairment has four learning outcomes: Relate to the epidemiology of blindness and visual impairment Describe the main causes of blindness globally
Explore the trends of blindness with socio-economic variations globally and within a population Apply the global perspective to understand the local burden of visual impairment
We will look at four aspects of the epidemiology of visual impairment: Magnitude: How many are affected? Distribution: Where is it? Determinants - What are the main causes? Control - What can we do about it? We will use these factors to determine appropriate public health control measures.
The magnitude of visual impairment worldwide is currently estimated to be about 285 million people. 39 million people are blind and 246 million have low vision.
When we compare the distribution of visual impairment across the world we find that it is unevenly distributed, with 90% in low- and middle-income countries. The highest prevalence of visual impairment, between 3.34% and 5.61% is found in India, China, the Middle-East and parts of South East Asia. Most of Sub-Saharan Africa has a prevalence of between 3.18% and 3.33%. The lowest prevalence of visual impairment is found in higher income countries and Latin America. Prevalence data is important. It allows health workers to identify the number of blind and visually impaired people in their country or region.
This graph shows the numbers of blind people in each World Health Organization region. You can see that the burden of blindness varies by region.
Africa - which has about 11% of the world’s population - has a disproportionately high number of blind people (about 6 million) compared to China which has 20% of the world population and about 8 million blind people.
The distribution of visual impairment is affected by age.
Globally, 82% of all blind people are aged 50 years and over. The importance of childhood blindness is not in the numbers affected but in the number of years a child has to live with that blindness. This is sometimes referred to as blind years.
Distribution of blindness is affected by gender. Most surveys around the world have found more blind women than men. A study in 2001 estimated the gender distribution of global blindness as 64% women and 36% men. The main reasons for this are: There are more women than men over the age of 50 in most populations Women often do not have equal access to eye care services Women are at a higher risk of blindness from certain conditions, for example trachoma
Image: Thomas Quine CC BY 2.0 flic.kr/p/8SZku
Causes of visual impairment. Global data has identified that refractive errors and cataract cause over 75% of all visual impairment in the world. These two diseases occur across all populations and are closely linked with ageing.
Other causes of visual impairment, such as trachoma, corneal opacities and childhood blindness, occur amongst specific ‘at risk’ populations. Diabetic retinopathy, glaucoma and age-related macular degeneration are diseases that are on the increase globally. Finally, it is difficult to identify a single main cause for about 18% of visual impairment.
Causes of blindness. Globally, cataract is the main treatable cause of blindness as we have a relatively simple, and effective, surgical treatment for it.
Risk of blindness is closely linked to poverty. Very poor individuals and communities are at the highest risk of blindness Poor communities are also more at risk from treatable and preventable causes of blindness To address this issue it is important to ensure that eye care services are accessible by all.
Image : Angela Sevin CC BY-NC 2.0 https://flic.kr/p/9B5h6
Population related risk factors are likely to increase global visual impairment in the future. One risk factor is increasing global population growth. In 1960 the global population was approximately 3 billion people, in 2010 it was 6.9 billion and by 2060 it is predicted to be nearly 10 billion.
A second risk factor is ageing populations. Numbers of people aged over 60 are increasing, especially in low- and middle-income countries. These two issues have huge implications for age-related blindness and appropriate eye health service planning.
Epidemiological data is used to select appropriate control measures for eye disease. Cataract and refractive errors are global diseases and cause 75% of all avoidable visual impairment. There are clear treatment strategies for these two diseases which can be implemented at the local level, alongside practical measures to strengthen eye care services and ensuring access for all.
Corneal blindness, trachoma and childhood blindness are considered ‘focal’ diseases because they affect vulnerable, high risk, groups of people. There are methods in place to treat and, more importantly, to prevent many of these conditions. The challenge here is to find the cases and implement services at a local level. Understanding local needs at the community level is important for developing strong prevention strategies.
Diabetic retinopathy and glaucoma fall into the chronic diseases category. Patients need to be detected early, and treated, to prevent visual impairment. Screening strategies are needed to find the patients as early as possible. Health systems also need to be prepared to appropriately manage cases identified by screening.
To address these conditions, planning appropriate infrastructure for service delivery is a key priority. Implementing these control measures can avoid about 80% of visual impairment.
In summary, epidemiology allows eye health workers to understand the burden of need, and the main causes and determinants of visual impairment at the global and local levels. We know that 80% of visual impairment is due to avoidable causes and that it is mostly found in developing countries. Strengthening services, improving access and addressing inequity at the local level are an urgent priority for global eye care. Prevention programmes are essential to achieve these goals and reduce the burden of visual impairment in the world.
Global Blindness: Epidemiology and visual impairment
Global Blindness: Planning and managing eye care services
Epidemiology and visual impairment
• Relate to the
epidemiology of blindness
and visual impairment
• Describe the main causes
• Explore socio-economic
variations in visual
• Understand the local
burden of visual impairment
Epidemiology of visual impairment
• Magnitude: how many?
• Distribution: where?
• Determinants: main causes?
• Control: what can we do?
285 million people are
globally 246 million have
39 million are blind
90% of visual impairment (VI) is in
low- and middle-income
Low 2.91 - 3.17%
Medium 3.18 - 3.33%
High 3.34 - 5.61%
Burden of blindness varies by region
11% world population
6 million blind
20% world population
8 million blind
Burden of blindness varies by region
Distribution of visual impairment is
affected by age
82% of all blind people are
aged 50 years and over
age 15 - 49
More women aged 50+
Higher risk of blindness
affected by gender
Refractive errors and
cataract cause 75% of
Causes of visual impairment