Skip to 0 minutes and 12 secondsIn public health, secondary prevention aims to detect disease in its earliest stages, often when it is still without symptoms and offer an appropriate intervention to slow or prevent progression of the disease. Screening is a case finding public health service offered to people in a defined population - for example people with diabetes - who may or may not perceive they are at risk of a disease or its complications. They are offered a simple and acceptable test which identifies those individuals who are likely to benefit from further tests and/or treatment to reduce the risk of irreversible complications (such as blindness). A case here is referred to as a person with the condition. Not all diseases or their complications are suitable for screening.

Skip to 0 minutes and 58 seconds40 years ago, Wilson and Junger set out a list of ten criteria that need to be met in order to implement a public health screening programme. First, the condition or disease must be a public health problem affecting a defined population. Second, there should be a recognisable latent or early symptomatic stage. Third, the natural progression of the condition from latent to declared disease must be adequately understood. Fourth, there should be a suitable test or examination to identify the condition. Fifth, the suitable test should be acceptable to the population. Sixth, facilities for diagnosis and treatment should be available. Seventh - there should be an accepted treatment for patients with recognised disease.

Skip to 1 minute and 46 secondsEighth, there should be an agreed policy on whom to treat as patients. Ninth, the cost of case finding should be economical. And tenth, case finding should be a continuous process for chronic conditions and not a once and for all project. If we examine diabetic retinopathy

Skip to 2 minutes and 6 secondsagainst Wilson and Jungers criteria we can see that: Epidemiological studies have shown that diabetic retinopathy is a public health problem with a rising prevalence due to the increasing number of people with diabetes.

Skip to 2 minutes and 21 secondsThe natural course of diabetic retinopathy progression is well understood. It has a clear latent, early stage that can be adequately identified on examination and classified into background and even pre-proliferative retinal changes. So diabetic retinopathy meets Wilson and Jungers second and third criteria for screening. We are able to detect its early signs and intervene with treatment to prevent visual impairment and blindness from the disease.

Skip to 2 minutes and 48 secondsThe screening test for diabetic retinopathy is carried out by trained personnel who examine a persons retina using a suitable method. The retinal fundus examination is generally simple, non-invasive and acceptable. However, the most appropriate examination method has to be determined locally as it is based on available resources (human, infrastructure and financial) for screening and treatment within the health system. Once a person with diabetes has a positive referral outcome (a case) they must be referred in a timely manner for further examination, diagnosis and treatment using an established referral protocol. Wilson and Jungers sixth, seventh and eighth criteria address this by requiring that policies, facilities and trained personnel for the diagnosis and acceptable treatment of diabetic retinopathy are available.

Skip to 3 minutes and 38 secondsA public health screening service for diabetic retinopathy needs to invest in appropriate laser facilities as a minimum requirement and in the capacity to provide, or refer for, vitreo-retinal treatment. These facilities and their trained personnel should be ideally established prior to the roll out of a diabetic retinopathy screening programme. Many eye health settings face challenges in meeting these criteria due to shortages in facilities, trained personnel and equipment. Criteria 9 addresses the key issue of the cost of screening, which has to be both acceptable to the patient and sustainable within the health system. Some health systems may provide diabetic health care schemes or insurance towards direct screening costs.

Skip to 4 minutes and 22 secondsHowever, there may also be a range of indirect costs to patients to attend screening, which become additional barriers for acceptance and uptake. Wilson and Jungers 10th criteria for a diabetic retinopathy screening programme is that case finding has to be an ongoing process throughout the life of each person with diabetes. In the UK, after a lot of co-ordinated efforts, the annual coverage for diabetic retinopathy screening is above 80%. However, many places face multiple geographical, economical and social challenges to achieving good coverage in diabetic retinopathy screening. For example, women may not be able to attend screening on their own.

Skip to 5 minutes and 1 secondIn these settings, it may be best to put opportunistic screening in place, at least initially, until a clear pathway for systematic screening can be found. In summary. The Wilson and Junger criteria for screening are, in principle, fully applicable to diabetic retinopathy. However, the local conditions affecting a health system - in terms of health care facilities, equipment and personnel - will determine whether a systematic diabetic retinopathy screening programme can be rolled out. Once a diabetic retinopathy screening programme is in place, individual patient acceptance and adherence to screening is key to achieving high coverage.

Principles of screening for diabetic retinopathy

The aim of screening is to prevent disease from progressing to a stage where treatment is less likely to succeed or impossible, resulting in permanent damage or even death. However, not all conditions or diseases are suitable for screening and there are many implications for a health service when it undertakes screening.

Public health screening programmes are based on epidemiological evidence and a clear understanding of disease progression and treatment.

Screening interventions are designed to:

  • Reduce the risk of a disease or a condition in a clearly defined population
  • Detect signs that a disease or condition that might develop in people who otherwise feel entirely well or have no symptoms (are asymptomatic).

Screening tests look for risk markers that indicate a disease might develop or has just started to develop. For this reason, screening programmes will not help most of the people who take part in them as they would not have developed the disease looked for, although they remain at risk. Additionally, for a variety of reasons, some people who do develop the disease unfortunately also may get missed by the screening test.

When screening for a disease is introduced into a health system it is important that medical researchers and policymakers monitor results on the programme’s overall benefits and risks. Implementing screening is a long term undertaking within a health system and requires careful planning. The cost of screening (human and financial) and the resulting required treatments must be considered. Screening must be constantly monitored and revised: a better test may come into existence or new evidence may arise about the relevance and impact of the screening approach being used in the local setting.

Watch the video to learn more about the key public health principles behind screening and how it is applied to control diabetic retinopathy. As you watch, consider how other screening services in your setting compare to what is required for diabetic retinopathy?

Share this video:

This video is from the free online course:

Diabetic Eye Disease: Building Capacity To Prevent Blindness

London School of Hygiene & Tropical Medicine