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Epidemiology and visual impairment
Epidemiology and its specific application to visual impairment.
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. In 2020, 1.1 billion people are affected by some form of visual impairment. An estimated 43 Million are blind and 596 million people had distance vision impairment worldwide, of whom 295 million have a moderate to severe level of distance visual impairment. Another 510 million people had uncorrected near vision impairment, simply because of not having reading spectacles.
The Lancet Commission used data from world bank regions. When we compare the distribution of visual impairment across the world we find that it is unevenly distributed. Globally, 91.75% of people who are blind and 87.68% of those with Moderate to Severe Visual Impairment live in Low and Middle income countries. There are large interregional differences in crude and age standardised prevalence.
Western sub-Saharan Africa has the highest age-standardised prevalence of blindness 1.11% , which means over 1 person in hundred is blind ….Whereas in high-income North America has the lowest prevalence of blindness at 0.12%, approximately 1 in 1000 persons is blind.
The largest number of blind people live in South Asia 11.9 million, followed by East Asia (9.1 million), and southeast Asia (5.9 million), because of the large regional populations. A similar pattern is seen for moderate to severe visual impairment for distance vision. In 2020, of the 43 million estimated blind, over 33 million were aged 50 years and over, highlighting the importance of age related blindness. Data on visual impairment in children and adults under the age of 40 is scarce. Measuring visual acuity in young children is a challenge. Therefore the data is derived from a proxy method using under-5 mortality since 1999.
Using the same method in 2020 it was estimated that 1.02 million children (0-15 years) are blind, representing 4.8 children per 10,000 population. 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 These trends are continuing—largely driven by population ageing and changes in disease patterns.
Globally, for every 100 men with blindness or MSVI there are 108 women with blindness and 112 women with MSVI. These imbalances are attributed to demographic factors as women live longer then men. However, in some the settings the differences are also due to socially determined factors as women often do not have equal access to eye care services and are at a higher risk of blindness from certain conditions, for example trachoma in endemic countries. Gender inequities are an important consideration when pursing universal health coverage.
Vision loss has many causes that require promotional, preventive, treatment, and rehabilitative interventions. Globally, the main causes of Visual Impairment are Cataract, uncorrected refractive error, glaucoma, age related macular degeneration, and diabetic retinopathy . The leading cause of blindness is cataract affecting 17 Million people and Uncorrected refractive error related blindness affecting 3.70 million. Notably, 37% of all blindness affecting over 16 million people are from other causes.
There are regional variation on the main causes of blindness, affected by population demography as well as access to eye health care. Understanding these regional variation in disease patterns allows health systems to prioritise service provision and resource allocation. In South Asia the main cause of blindness is from Cataract and Uncorrected Refractive Error, where as in western Europe the main causes of blindness are due to Glaucoma and Age Related Macular Degeneration. Globally, Cataract is the main treatable cause of blindness as we have a relatively simple, and effective, surgical treatment for it.
In 2020, the leading causes of Moderate to severe visual impairment globally were from uncorrected refractive error affecting the distance vision of over 157·49 million people. Poor eye health and impaired vision have a negative effect on quality of life and restrict equitable access to and achievement in education… …and the workplace. Vision loss has substantial financial implications for affected individuals, families, and communities. Visual Impairment from refractive error is avoidable, by providing a pair of spectacles we have simple and cost effective management. 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.
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 2020 it was 7.8 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. 80% of older people will be living 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 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 in the world.
World Health Organization data from 2010 estimated that approximately 285 million people across the world had some form of visual impairment (Pascolini & Mariotti, 2011). In 2017, a new review of the data by the Vision Loss Expert Group and published in The Lancet Global Health estimated that there were 253 million people with visual impairment in 2015 (Bourne et al. 2017).
90% of visually impaired people 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 step we use the 2010 data to introduce the epidemiology of blindness and visual impairment, looking at four key concepts:
- Magnitude – how many people are affected?
- Distribution – where is it?
- Determinants – what are the main causes?
- Control – what can we do about it?
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 article is from the online course:
Global Blindness: Planning and Managing Eye Care Services
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Global Blindness: Planning and Managing Eye Care Services
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