Common refractive errors
Common forms of refractive error include:
- Myopia: light from distant objects is focussed ‘in front’ of the retina, making it difficult to clearly see objects in the distance. High myopia is a major risk factor for severe conditions such as glaucoma, cataract, retinal detachment and macular degeneration. Myopia is usually due to an excessive elongation of the eyeball. In addition to genetics, eye growth is regulated by visual feedback (environment), and the prevalence of myopia is rising around the world.
- Hyperopia: light from near objects is focussed ‘behind’ the retina. This makes it difficult, particularly for children, to see near objects whilst for adults both near and distance vision may be affected.
- Astigmatism: mostly caused by an irregular-shaped cornea and/or lens which give rise to multiple images that are not focussed on the retina. Both distance and near objects appear blurred and distorted.
- Presbyopia: As part of the ageing process the lens becomes harder and less elastic, making focussing on near objects more difficult. Most people over the age of 40 will have a degree of presbyopia and cannot see near objects clearly. Most people over the age of 40 will have a degree of presbyopia and cannot see near objects clearly.
In addition to genetics, eye growth is regulated by visual feedback (environment). For example, myopia is far more prevalent in urban populations.
Refractive error may result in lost education and employment opportunities, lower productivity and impaired quality of life.
Uncorrected refractive errors, which affect persons of all ages and ethnic groups, are the main cause of vision impairment.
In 2020, it was estimated that 157 million people had significant vision impairment (< 6/18 in the better eye) due to uncorrected refractive errors affecting distance vision, including at least three million people with blindness (< 3/60 in the better eye). In addition, 510 million people were without adequate correction for functional presbyopia in 2020.
The large majority of vision impairment in school aged children is due to uncorrected refractive error (Resnikoff et al., 2008).
The global economic cost in lost productivity due to avoidable distance vision impairment alone was estimated to be I$269 billion (approximately US$202 billion) each year in 2009.
Presbyopia is the most common cause of vision impairment globally.
More than half of those requiring near-vision spectacles globally cannot access them. This is due to factors such as poverty, isolation, poor availability, poor access to eye health facilities and lack of awareness.
The 2020 Vision Loss Expert Group data estimates that in 2020 510 million people had presenting functional presbyopia, or blurred near vision.
Effective coverage of refractive error correction
As discussed in the Lancet Global Health Commission on Global Eye Health, data on effective coverage of refractive error will become increasingly available. Effective Refractive Error Coverage (eREC) was recently proposed and a methodology described (WHO World Report on Vision, 2019, McCormick et al., 2020). The eREC assesses the proportion of people with refractive error who have received and use refractive error correction that achieves a specified VA threshold (e.g. 6/12); it takes into consideration the met, under-met and unmet refractive error need in a population.
This represents a major shift in the way refractive error is reported. Surveys previously focused only on counting unmet need (uncorrected refractive error) and excluded those who already had access to refractive error correction.
Treatment and successes
Refractive error can be treated by well-established and efficacious interventions, but these do not reach all who could benefit with sufficient quality to be effective. Spectacles are the most common and the least expensive method of correcting refractive errors. The two other options are contact lenses (more expensive and not suitable in all settings) and refractive laser surgery.
Refractive error services and public-private collaboration
As discussed in the Lancet Global Health Commission on Global Eye Health, in many regions refractive error and optical services are provided by the private sector. Therefore services largely market-driven, to an extent that other eye care services may not be. This has been a major incentive for service development at scale in some settings, providing well for population needs.
However, where the distribution of refractive error services is influenced by what providers consider a viable return on investment, populations in areas of high deprivation may remain without access to services (Day et al., 2010). The cost of spectacles can vary greatly within settings, but can involve large out-of-pocket expenditure and be unaffordable to many. In some countries there is a large, unregulated market of optical shops which may provide poor quality service (Nie et al., 2020).
The private sector does, however, represent a huge opportunity to bring refractive error services (and primary eye care more broadly) closer to communities. Indeed, given the magnitude of uncorrected refractive error globally, eye health cannot be addressed as part of universal health coverage (UHC) without a major private sector contribution.
However, to truly contribute to delivering eye health within UHC, more consideration needs to be given to developing the right regulatory and market conditions to promote quality, affordable and equitable services.
Economic case for treating refractive error
The economic value of an intervention that eliminated uncorrected refractive error is dwarfed by the humanitarian imperative that is driving efforts to deliver quality eye care to all that need it.
A relatively small investment (compared to the cost) of US$28 billion would establish the eye care services required to provide good vision to people with uncorrected refractive error and create savings of US$202 billion to the global economy annually.
What is myopia and how many people are affected?
Myopia (commonly known as short-sightedness or near-sightedness) is caused by the eye being too long, which results in light focussing in front of the retina, causing blurred distance vision. Myopia commonly onsets in childhood and is corrected using spectacles or contact lenses. However, the condition commonly progresses and the eye continues to grow longer.
As a result of lifestyle changes, including reduced time spent outdoors and increased near-work activities, the number of people with myopia has been estimated to rise from 1.4 billion in 2000 to 2.6 billion in 2020 and 3.4 billion in 2030.
In some Asian countries, 70% of those 17 or above are myopic, as are 97% of 19-year-old male army conscripts in South Korea.
Why should we be concerned about myopia?
Additionally, there is a more sinister side to myopia. High levels of myopia (-5.00 D or worse) increase the risk of sight-threatening conditions including retinal detachment, cataract and glaucoma. In addition, highly myopic eyes are at risk of myopic macular degeneration, a condition fast emerging as a leading cause of blindness in Asia and other parts of the world. There were an estimated 10 million people with vision impairment from MMD in 2015 of whom over 3 million were blind.
Source and references
Future projections of myopia
Approximately half of the world’s population, including children, live in towns and cities; by 2050, nearly 70% will live in urban areas (United Nations).
In 2010, just over 28% of the world’s population were affected by myopia (short-sightedness). This was predicted to rise to 34% by 2020 and nearly 50% by 2050 (Holden el al. 2016). This means the half the world’s population is predicted to have myopia by 2050.
There are significant health and economic implications from the rising prevalence of myopia. Managing the myopia burden requires a co-ordinated effort in prescribing and developing solutions to control onset and progression, and services to manage associated healthcare implications.