Detection of uncorrected refractive error in developing
The proportion of children who are blind or visually impaired due to refractive errors can be used to assess the level of development of eye care services in a country.
Vision testing in children is undertaken to improve early detection, prognosis, and reduce eventual disability. The word ‘screening’ has a very precise meaning in public health, with clearly defined criteria that should be applied before any screening programme is established.
When considering the detection of refractive errors, the term ‘screening’ does not really apply: ‘vision testing’ is perhaps a better term.
Assessment of need
There is limited global epidemiological data available and variable from place to place. However, at least 2000 children / million population have refractive errors greater than -1.00D in both eyes. These are the children who should be the focus of attention in any school vision testing programme.
Fig 1 shows how refractive error varies across the different age groups in
Planning a vision testing programme for children
Several questions need to be addressed and answered when planning a vision testing programme for children. The most important is to decide the aim of the programme or why the programme is being set up. The flow chart below shows the decisions that need to be made when planning Vision testing programmes.
Aim of vision testing programme
If the aim is to detect and treat conditions that may lead to amblyopia (i.e., refractive errors, eye disease causing visual impairment, and strabismus) the programme must focus on preschool-age children. Where and how will these young children can be tested raise logistical challenges and are therefore also not established in many industrialised countries.
If the aim is to detect and treat ‘significant’ uncorrected refractive errors the older children can be targeted, e.g. testing of 12-14-year-olds to detect myopia of puberty. The frequency of vision testing also needs to be linked to the availability of resources. If conditions are favourable, children should be screened once during the primary school years (6-11 years) and once during early adolescence (12-14 years).
School vision testing in resource-limited settings: how and who?
The initial vision examination identifies children who ‘fail’ the test and require refraction and detail examination. Decisions need to be made around whether to test vision in each eye separately or with both eyes open. The level of acuity that denotes ‘failure’ also has to be decided.
If the cut off level of acuity is too high e.g. 6/9, then a high proportion of children may be detected who may not benefit or accept glasses. If the level is set too low (e.g. <6/60 in the better eye), only those with severe visual impairment will be detected.
To increase the cost-effectiveness of a school vision testing programme, a cut off at <6/12 in the better eye is suggested as it may result in better compliance with spectacle use. Children failing this test are referred for refraction.
The method of vision testing needs to be valid (see figure. 3). There should be a balance between sensitivity and specificity so as to easily detect the children who will benefit from treatment and avoid overloading the services with false negatives.
Vision testing does not require highly trained eye workers and school teachers, with one day of training and equipped with a vision kit, as in India, are often best placed to test the children.
Vision testing procedure in schools
Vision testing can be carried out at a suitable time in the academic year. The procedure for testing should be explained, e.g. an ‘E’ cut out at 6/12 optotype is shown and the direction of the ‘limbs’ explained. If the child already wears glasses, vision should be recorded with the spectacles and not in crowds, as children tend to assist each other. Rotation prevents
memorising. Good lighting is important and testing outdoors is possible.
The vision for each child is recorded, and a referral list made of all the children who fail vision testing. If children are tested and there is no referral system, the programme will fail. Parents should be involved so they can participate in the process.
Service provision and follow up
Good quality, low-cost spectacles should be available for parents to buy. Every child should be re-examined at intervals of 1-2 years by the optometrist/ophthalmologist as myopia may be progressive.
Monitoring, evaluation, and impact
School vision testing programmes do not end with the provision of spectacles as it is important to evaluate the benefit of the programme. Regular monitoring ensures that the programme runs well. The evaluation may highlight direct and indirect impact of the programme with wider educational, social, and economic benefits resulting from improved vision in school children and also extended to their families and communities.
In conclusion, school vision testing programmes are simple to conduct, need minimal resources, greatly benefit children with significant refractive errors and have an impact on concerned communities by increasing their knowledge of vision disorders and how to manage them. However, they need careful planning and resourcing.