Chapter 123 What is a sensible screening program in paediatric ophthalmology?
Young children do not report reliably changes in vision to one or both of their eyes. There are a limited range of professionals who are able to perform an eye examination on children, and this number is possibly reducing. For these reasons many pediatric eye disorders present late. A need for screening is recognized and has led to the detection by screening of over 50% of pediatric eye conditions affecting the child’s sight, usually by pediatricians or family doctors.1
“Screening is the systematic application of a test or inquiry to identify individuals at sufficient risk of a specific disorder to benefit from further investigation or direct preventive action, among persons who have not sought medical attention on account of symptoms of that disorder”.2 Screening detects individuals within a population who have a disease before they develop signs or symptoms. Alternatively, screening can be used to detect a risk factor for future or asymptomatic disease.
Box 123.1 World Health Organization criteria for screening
Is screening feasible and acceptable to those being screened? (criteria 4,5,6). A test is required that can be performed prior to the development of symptomatic disease that might detect a risk factor for the disease or allow diagnosis at a symptomless stage. The test requires sufficient sensitivity and specificity to be useful, validated, and safe.
Is the disease understood, is treatment possible, is there consensus on who to treat and how, and are facilities in place for investigation and treatment? (2,3,7,8) Understanding of and consensus on the natural history of the disease is necessary to judge the chance of the disease progressing from the asymptomatic screened stage to symptomatic disease. Treatment should be possible, available, and agreed widely. Screening for untreatable disease, especially in children too young to give consent, carries the risk of significant harm.
Is there a program for widespread and continuing implementation of screening? (1) Screening is complex and it creates expectations of availability. Inequality of access leads to non-participation of those most likely to benefit.
What is the cost utility of the whole program, including subsequent investigations and treatments, and how does this relate to resources available for other medical conditions? (1,9) Cost-utility analysis is required. Cost-benefit should exceed that of alternatives − public education via awareness campaigns, medical surveillance to facilitate early detection of symptomatic disease, or increased treatment resources.
The identification of a person affected by a disease prompts testing of relatives at risk; it is the chief form of screening in clinical genetics. Cascade screening is of heightened value in consanguineous families. In other families, benefit rapidly decreases as testing moves away from the proband, when it detects only a small percentage of the total number of carriers within the wider population.
The prevalence of underlying disease in primary screening is low; for example, hundreds of neonatal red reflex examinations will be needed to detect an abnormality and WHO guidelines need to justify screening. When the chance of positive findings within a targeted population is high, then active surveillance is used instead of screening (Fig. 123.1).
The special and changing nature of genetics screening is recognized in program assessment criteria.4 As costs reduce there is increasing pressure from individuals, families, patient support groups and commercial interests for testing in specific gene disorders or for gene markers of complex traits.5