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Understanding refractive error

Definition of refractive error in the context of public health and description of its epidemiology.
SPEAKER: Welcome to this presentation on managing refractive error. By the end of it, you should be able to define refractive error and describe its epidemiology, explore considerations for service delivery at the community level, and to appraise school health programmes and their management.
Refractive error in the public health context is defined as a presenting visual acuity of less than 6/18, which can be corrected by refraction or by pinhole. Correctable myopia is defined as worse than minus 1 dioptre. Correctable hyperopia is defined as plus 3 dioptres or more. And it is essential to correct an astigmatism of 1.5 dioptres or more. The patient’s presenting visual acuity is categorised using the World Health Organisation’s International Classification of Disease.
Uncorrected refractive error is the second major cause of blindness and low vision in the world after cataract. Estimates from 2004 indicate that over 8 million people are blind and 145 million are visually impaired because they lack refractive correction. Who is most affected by refractive error? In children aged under 15, the prevalence of refractive error has been found to be higher in urban areas than in rural settings. This is possibly due to a direct cause and effect relationship between access to education and myopia. Refractive error amongst 94 million people aged over 50 includes cataract-related index myopia or even uncorrected aphakia.
The largest burden of refractive error is in India and China. And more research is needed about how and where to identify and treat people with uncorrected refractive error. Some estimates for service coverage shows that urban settings have better services, particularly for children.
Why is there so much uncorrected refractive error? Many settings lack vision testing for children to insure early detection and management. There is a lack of refractive services and limited affordability of spectacle correction, particularly in rural communities. Sometimes spectacles are not regarded as an essential medical intervention. And lastly, there may be cultural disincentives, which means that people choose not to wear or accept correction, especially girls.
Visual impairment from refractive error impacts both individuals and society leading to limited educational performance and success amongst children, social isolation and fewer opportunities for work and education, more exposure to morbidities and higher mortality rates, and generally a lower quality of life and poverty.
There are two strategies for improving access to comprehensive community-based eye care. Static and outreach. Ideally, services are planned for a population of 50,000. And they focus on increasing demand and supply. At a primary level, ophthalmic assistants or nurses can be trained to perform eye examinations and refraction. To minimise referrals, they can also be trained to dispense spectacles directly.
Due to the lack of evidence, we have to use estimates to guide development of refractive error services. Estimating the demand for spectacles can be calculated from prevalence data for the target population or from similar settings. Where no data is available, 20% of the total population is a reasonable estimate. Understanding the demand allows planners and managers to appropriately allocate refraction and dispensing equipment and spectacles, as well as numbers of trained personnel.
Social marketing of refraction services has been a successful model in creating demand and raising awareness. And this has been particularly successful in India through vision centres. School health programmes aimed particularly at the early teenage group have also been shown to be effective. Targeting younger, economically active groups in the workplace or colleges is another option. In the over 50 age group, health promotion and access to services will also improve uptake.
Refraction equipment and spectacle dispensing equipment are both necessary to deliver comprehensive services. A range of lenses and frames suitable for local preferences must also be stocked, particularly for children and girls. Equipment and consumables are managed using an inventory and a reliable supply chain. The priority age group that needs vision testing at least once is children aged 12 to 14 years. This is to detect myopia of puberty. Younger age groups are tested if resources are available. Each eye is tested and vision less than 6/12 in either eye is defined as a case for referral and further testing. Lower cutoff of less than 1 dioptre correction often results in poor adherence to spectacle wearing amongst children.
In some settings, schoolteachers can be trained to do an initial visual assessment within the school. Teachers are provided with a vision kit, referral protocol, and support from local optometry services.
In school vision testing programmes, recruiting science teachers who can explain the benefits to parents are an ideal choice, as are teachers who wear spectacles as they will have an understanding and empathy for a refractive error. The teachers must have the support of school authorities.
The process of vision testing is made as simple as possible. Key points to remember are the teachers must all be trained and supported. Test each eye. Children that fail the 6/12 visual acuity cutoff must be referred using an agreed method. Train teachers to refer each case they identify. All the testing and referral information should be recorded for monitoring and evaluation of the programme. Children who are prescribed spectacles should also be followed up between 3 to 6 months. And lastly, support and counselling must be provided to parents and children.
Management collect data to monitor school vision testing programmes in order to know the coverage. This is the number of children whose vision has been tested by the teachers. Know the uptake of referral. This is how many of the referred children actually present to optometrists. Establish how effective the teacher’s testing is. If there are too many false referrals, retraining may be necessary. And understand the acceptance of refractive correction. This is achieved by revisiting the school 3 to 6 months later and identifying which children are still using their spectacles.
Let’s look at monitoring in more detail using an example. There are 5,000 children in the district schools age 12 to 14, and 3,000 of them undergo vision testing. To calculate the coverage of services, we divide 3,000 by 5,000 and multiply by 100 to get a percentage. This gives us a 60% coverage.
110 children are referred for refraction and 75 of them present to the optometrist. To calculate the uptake of vision testing, we divide 75 by 110 and multiply by 100. This gives us a 68% uptake of the service.
55 children out of the 75 that presented are referred on to be prescribed spectacles. The percentage of correct referrals by teachers is calculated by dividing 55 by 75 and multiplying by 100. This gives a 73% correct referral rate. This is good, but we should also establish why all the children did not come. 40 children are still wearing their spectacles three months later. To work out the acceptance rate, we divide 40 by 55 and multiply by 100. And this gives us a 73% acceptance rate. This data can be monitored on a monthly basis and used by management to adjust the intervention appropriately.
Vision testing in schools is simple to conduct and can have a huge impact on children and their education. Services need to be planned with adequate resources, good monitoring and management, and supported by effective communication between schools and optometry services.
In conclusion, refractive error is the second most important cause of visual impairment and blindness globally. Correction is relatively simple and the challenges are in access, affordability, and acceptance of spectacle correction. To meet the need, comprehensive service delivery at the community level is essential. And school vision testing is an important strategy to address refractive error needs in children, and it can be done by trained and willing teachers.

Uncorrected refractive error is a major cause of visual impairment in the world after cataract. Estimates from 2004 indicate that over 8 million people are blind and over 145 million are visually impaired because they lack refractive correction.

In this step we define refractive error in the context of public health and describe its epidemiology. We then go on to explore the factors which affect refractive error service delivery and school health programmes.

Stakeholders in correction of refractive error

In 2006 the WHO noted that:

“Without appropriate optical correction, millions of children are losing educational opportunities and adults are excluded from productive working lives, with severe economic and social consequences. Individuals and families are frequently pushed into a cycle of deepening poverty because of their inability to see well. At least 13 million children (age 5 to 15) and 45 million working-age adults (age 16 to 49) are affected globally. Fully 90% of all people with uncorrected refractive errors live in low and middle income countries.”

Who are the key stakeholders to involve when attempting to address this situation in a local setting?

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Global Blindness: Planning and Managing Eye Care Services

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