2. General background on child vision and hearing screening programmes

Chapter editors: Jill Carlton, Allison Mackey

a. Criteria for responsible screening

In 1968, the WHO published the following ten “principles of early disease detection”1:

  • The condition sought should be an important health problem
  • There should be an accepted treatment for patients with recognized disease
  • Facilities for diagnosis and treatment should be available
  • There should be a recognizable latent or early symptomatic stage
  • There should be a suitable test or examination
  • The test should be acceptable to the population
  • The natural history of the condition, including development from latent to declared disease, should be adequately understood
  • There should be an agreed policy on whom to treat as patients
  • The cost of case-finding (including diagnosis and treatment of patients diagnosed) should be economically balanced in relation to possible expenditure on medical care as a whole
  • Case-finding should be a continuing process and not a ‘once and for all’ project

It is important to notice that the authors of this report considered the above principles as a preliminary checklist. That is, when these criteria are not met, there is no justification or rationale to  start a screening programme. When these criteria are met, further research is warranted to determine whether or not it is appropriate to start a screening programme.

Forty years after the publication of the original principles, the WHO published a “synthesis of emerging screening criteria”2:

  • The screening programme should respond to a recognized need
  • The objectives of screening should be defined at the outset
  • There should be a defined target population
  • There should be scientific evidence of screening programme effectiveness
  • The programme should integrate education, testing, clinical services and programme management
  • There should be quality assurance, with mechanisms to minimize potential risks of screening
  • The programme should ensure informed choice, confidentiality and respect for autonomy
  • The programme should promote equity and access to screening for the entire target population
  • Programme evaluation should be planned from the outset
  • The overall benefits of screening should outweigh the harm

In 2020, the WHO published a short guide offering operational advice for designing and managing screening programme.

 

b. Effectiveness and cost-effectiveness of vision and hearing screening programmes

i. Vision

Vision screening has been shown to be effective in reducing the prevalence of amblyopia among adults. In Denmark, following the implementation of a national preschool vision screening programme, the prevalence of undetected or unsuccessfully treated amblyopia decreased fourfold: the prevalence dropped from 1.8% in the group that was not screened to 0.4% in the screened group3.  An earlier, longitudinal and retrospective study in Sweden found that with screening and subsequent diagnosis and treatment, the prevalence of severe amblyopia (visual acuity ≤0.3) was reduced from 2% to 0.2%4.

Amblyopia fulfils most of the WHO criteria as a target condition for screening, but there are many other childhood visual defects, such as refractive error, strabismus, weak stereovision, and poor convergence. They can be detected in early childhood, and would be monitored or treated if presented to an eyecare professional, but they fulfil fewer of the WHO criteria e.g. later treatment may be just as effective, and there may not be a consensus on who to treat as patients. The evidence in terms of better long-term public health outcomes is less clear for population screening to detect and treat for these often mild and asymptomatic conditions. If screening also targets these conditions (as the EUSCREEN Country Reports suggest is common), costs increase and cost-effectiveness may reduce. It is very important that the target condition for the screening is clearly identified from the outset. Each country must decide whether screening is to detect any visual defect outside normal ranges, even if it may be mild with little proven adverse impact on development or long term outcome, or to detect only severe cases where the evidence is clearer. Countries with different economic or health priorities may make very different decisions.

Research has shown that the cost-effectiveness of screening for amblyopia is dependent on the long-term effects of unilateral vision loss on the quality of life, but that even a small effect would mean that screening would be cost-effective5. Other research has indicated that unilateral amblyopia indeed negatively affects the quality of life6. Children with unsuccessful treatment for amblyopia have a seven months longer period of bilateral vision loss at the end of life, compared to children without amblyopia or with successfully treated amblyopia7. The loss in utility in these seven months is measured in elderly people with bilateral vision loss to be 0.08 (8% loss in quality of life)8. Using the same time trade-off methods, the effect of unilateral vision loss measured in 40-year olds was 0.037 (3.7% loss in quality of life)9. However, since this figure for unilateral vision loss is considered high compared to the 0.08 utility loss for bilateral vision loss and since only 37% of the people with unilateral vision loss accepted a death risk according to the standard gamble method also used in the study, we can assume a loss in utility for unilateral vision loss of 0.01.

 

ii. Hearing

The earlier a child’s hearing impairment is discovered, the less affected language and speech development will be. Early intervention, before the first birthday, has been shown to prevent disabilities to a much larger degree than interventions at later ages10 11. Early hearing loss detection and intervention dramatically improves outcome measures for infants and young children with hearing loss. Therefore, the Joint Committee on Infant Hearing recommends benchmarks, that hearing loss be identified before the age of one month, with audiological evaluation and intervention before three and six months, respectively12. The introduction of universal newborn hearing screening (NHS) programmes has been instrumental in reducing the age of identification13.

Healthcare policy-makers must make decisions on how to allocate resources within the healthcare system. Cost-effectiveness analyses are useful in the decision-making process. A systematic review found 29 studies that evaluated the cost-effectiveness of universal newborn hearing screening and concluded that universal NHS is cost-effective14. This is particularly true when assuming long-term positive effects of early intervention on speech and language development and education15 16. Universal NHS is cost-effective when compared to selective (high-risk) screening; however, cost-effectiveness is affected by programme quality measures such as the rate of false referrals and loss to follow-up to diagnostics and intervention17

Because a considerable number of children (an additional 50-90% relative to children identified by newborn screening) will develop hearing loss in the postnatal years, studies have advocated for the universal hearing screening of preschool and school-aged children18. Only some EU countries have established programmes. Despite the encouragement from European experts to initiate programmes19, there is limited evidence showing the societal benefit and cost-effectiveness of childhood hearing screening in countries or regions with existing newborn hearing screening. There is currently a lack of good quality data available20. 

It should be noted that the situation may be different in countries or regions where there is no NHS.

 

c. Benefits versus harms of vision and hearing screening programmes

i. Vision

If left untreated, amblyopia nearly doubles the lifetime risk of bilateral visual impairment21. Also, amblyopia, significant refractive errors, and non-obvious strabismus (which would not be detected without screening) can affect health, the ability to play sports, development, and academic, occupational and social functioning22. Since vision screening can detect these disorders, there is a broad consensus that paediatric vision screening is beneficial.

Even so, issues such as what age to screen, which test to use and how often to screen, remain subject to debate. In the US, the US Preventive Services Task Force (an independent, volunteer panel of national experts in disease prevention and evidence-based medicine) recommends vision screening at least once (but preferably yearly) in all children aged three to five years to detect amblyopia or its risk factors23.

A study in Ontario found that the vast majority of children surveyed (90%) perceived vision screening as a game that they enjoyed24Nevertheless, preschool or school-aged vision screening could have possible adverse effects such as unnecessary referrals, overdiagnosis and unnecessary treatment25, as well as an increased risk of being bullied because of glasses or therapeutic eye patches26 and a lower self-perception of social acceptance because of patches27. Skin irritation because of patching has also been reported, although this affected only a small portion of children28. The use of eye drops to blur vision in the better seeing eye (BSE), instead of patching, may cause more frequent minor adverse effects, such as light sensitivity29.

Amblyopic children themselves have reported that treatment did not significantly affect their quality of life30.

 

ii. Hearing

The long-term benefits of early detection and intervention have been documented by the literature, showing that intervention for hearing impairment before six months of age leads to long-term positive benefits for speech and language development, and improved quality of life and improved educational success31. Early intervention is made possible due to newborn hearing screening programmes. The long-term benefits of preschool or school-age hearing screening have not yet been clearly established, particularly in areas with newborn hearing screening in place.

No physical long- or short-term harms have been reported in the literature or by expert experience for newborn or preschool/school-age hearing screening. No harms have been reported from the screening devices used. Despite some evidence of mild parental anxiety after newborn hearing screening positives (whether true or false), no long-term emotional distress has been reported due to a false positive result from newborn hearing screening32

 

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