4.2 Understanding Refractive Error

$: 4.2 Understanding Refractive Error$
8/18/2019 4.2 Understanding Refractive Error

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GLOBAL BLINDNESS: PLANNING AND

MANAGING EYE CARE SERVICES

LONDON SCHOOL OF

HYGIENE & TROPICAL MEDICINE

WEEK 4 REFRACTIVE ERRORS AND SCHOOL HEALTH

UNDERSTANDING REFRACTIVE ERROR

SPEAKER: Welcome to this presentation on managing refractive error. By the end ofit, you should be able to define refractive error and describe its epidemiology,

explore considerations for service delivery at the community level, and to appraiseschool health programmes and their management.

Refractive error in the public health context is defined as a presenting visual acuityof less than 6/18, which can be corrected by refraction or by pinhole. Correctablemyopia is defined as worse than minus 1 dioptre. Correctable hyperopia is definedas plus 3 dioptres or more. And it is essential to correct an astigmatism of 1.5dioptres or more.

The patient's presenting visual acuity is categorised using the World HealthOrganisation's International Classification of Disease. Uncorrected refractive error isthe 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 millionare visually impaired because they lack refractive correction.

Who is most affected by refractive error? In children aged under 15, the prevalenceof 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 toeducation and myopia. Refractive error amongst 94 million people aged over 50includes cataract-related index myopia or even uncorrected aphakia.

The largest burden of refractive error is in India and China. And more research isneeded about how and where to identify and treat people with uncorrectedrefractive error. Some estimates for service coverage shows that urban settingshave better services, particularly for children.

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Why is there so much uncorrected refractive error? Many settings lack visiontesting for children to insure early detection and management. There is a lack ofrefractive services and limited affordability of spectacle correction, particularly inrural communities. Sometimes spectacles are not regarded as an essential medical

intervention. And lastly, there may be cultural disincentives, which means thatpeople choose not to wear or accept correction, especially girls.

Visual impairment from refractive error impacts both individuals and society leadingto limited educational performance and success amongst children, social isolationand fewer opportunities for work and education, more exposure to morbidities andhigher mortality rates, and generally a lower quality of life and poverty. There aretwo 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 onincreasing demand and supply. At a primary level, ophthalmic assistants or nursescan 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 ofrefractive error services. Estimating the demand for spectacles can be calculated

from prevalence data for the target population or from similar settings. Where nodata is available, 20% of the total population is a reasonable estimate.Understanding the demand allows planners and managers to appropriately allocaterefraction and dispensing equipment and spectacles, as well as numbers of trainedpersonnel.

Social marketing of refraction services has been a successful model in creatingdemand and raising awareness. And this has been particularly successful in Indiathrough vision centres. School health programmes aimed particularly at the earlyteenage group have also been shown to be effective. Targeting younger,economically active groups in the workplace or colleges is another option. In theover 50 age group, health promotion and access to services will also improveuptake.

Refraction equipment and spectacle dispensing equipment are both necessary todeliver comprehensive services. A range of lenses and frames suitable for localpreferences must also be stocked, particularly for children and girls. Equipment and

consumables are managed using an infantry and a reliable supply chain.

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The priority age group that needs vision testing at least one is children aged 12 to14 years. This is to detect myopia of puberty. Younger age groups are tested ifresources are available.

Each eye is tested and vision less than 6/12 in either eye is defined as a case forreferral and further testing. Lower cutoff of less than 1 dioptre correction oftenresults 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 localoptometry services.

In school vision testing programmes, recruiting science teachers who can explainthe benefits to parents are an ideal choice, as are teachers who wear spectacles asthey will have an understanding and empathy for a refractive error. The teachersmust have the support of school authorities.

The process of vision testing is made as simple as possible. Key points to rememberare the teachers must all be trained and supported. Test each eye. Children that failthe 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 6months. And lastly, support and counselling must be provided to parents andchildren.

Management collect data to monitor school vision testing programmes in order toknow the coverage. This is the number of children whose vision has been tested bythe teachers. Know the uptake of referral. This is how many of the referred childrenactually 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 refractivecorrection. This is achieved by revisiting the school 3 to 6 months later andidentifying which children are still using their spectacles.

Let's look at monitoring in more detail using an example. There are 5,000 children inthe 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 toget a percentage. This gives us a 60% coverage.

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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 prescribedspectacles. The percentage of correct referrals by teachers is calculated by dividing55 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 theexceptions 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 adjustthe intervention appropriately. Vision testing in schools is simple to conduct andcan have a huge impact on children and their education. Services need to beplanned with adequate resources, good monitoring and management, andsupported 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 thechallenges are in access, affordability, and acceptance of spectacle correction. Tomeet the need, comprehensive service delivery at the community level is essential.And school vision testing is an important strategy to address refractive error needsin children, and it can be done by trained and willing teachers.

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4.2 Understanding Refractive Error

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