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Towards evidence based public health
Readers of the BJO will be aware that cataract is the leading cause of blindness in Africa, affecting an estimated half of the seven million blind people in that continent.1 This number is likely to increase substantially, as approximately 600 000 Africans become blind from cataract each year. Despite the enormity of the problem, few cataract operations are performed in Africa. The cataract surgery rate (CSR), a measure of the volume of cataract surgery performed in a population, is about 500 per million per year in Africa. To tackle cataract blindness, the Vision 2020 initiative, a programme involving the World Health Organization, the International Agency for Prevention of Blindness, and various governmental and non-governmental organisations, aims to increase the CSR in Africa to about 2000 per million per year.2
Substantial progress has been made on several fronts over the past few years. There has been a steady stream of information on the epidemiology, distribution, and impact of cataract in different parts of Africa.3,4 There is also increasing evidence that well designed and well executed cataract surgery programmes can provide effective high volume and high quality cataract surgical services in selected communities in Africa.5
Despite encouraging signs, there remain significant challenges and barriers. Thus, there may be important lessons in the few “successful” cataract surgery programmes that emerge from Africa. In this month’s issue of the BJO (p 1237), Lewallen and colleagues share their experience of two such programmes, both of which appeared to have contributed towards a significant increase in the number of cataract surgeries performed in their communities. Since the introduction of these programmes, the authors estimate that CSR have risen to 1583 per million in the Kwale District in Kenya, and 1165 per million in the Kilimanjaro Region in Tanzania in 2004. These are remarkable figures, all the more so given that previous estimates of the CSR were approximately 644 per million in Kenya and 313 per million in Tanzania in 2002.
What were the key lessons learnt from these “successful” cataract surgery programmes? The authors describe several. These include a close link between the community screening programmes and the hospital services that provide the cataract surgery services, a seamless “patient friendly” referral chain, the utilisation of a community screening examination team that has appropriate ophthalmic expertise to identify people most likely to benefit from cataract surgery, and selecting populations that both need the services and have the ability to sustain such programmes. None of these concepts is very new, of course. Indeed, many of the features described in this article have been proposed in other African communities, and apply elsewhere in other developing countries (for example, India).6
Like changes in clinical practice resulting from a heightened awareness of evidence based medicine, evidence based public health is necessary in ensuring the major paradigm changes needed in public health practice
A unique aspect of this study was using a quantitative outcome (in this case, the CSR) to qualify the success for the programme, information that many previous descriptive studies have lacked.7 None the less, there are several limitations in this study that may serve as areas for future research. For example, the authors argue in their article that one of the key lessons of the cataract surgery programme was to “make specific changes at the hospital essential to providing more service.” A list of these changes is described in the article. However, the study lacked more quantitative analyses on the specific changes described, which may make it difficult to translate these features to other programmes. Future studies should more precisely quantify the specific features or processes of a programme, and whether one feature or process is independent of and, more important, relative to others. Secondly, although the article attributes the high CSR in the two communities to the introduction of the cataract surgery programmes, it would have been vastly more instructive to have data on the actual change in CSR over time (that is, before and after the introduction of the programme).
Some of this information will not be readily available, given the resources and situation. Indeed, we recognise that evaluating the effectiveness of cataract surgery programmes is challenging enough, even in the most ideal circumstances in developed Western countries. However, it is crucial for public health ophthalmology to move away from purely descriptive, experience based case studies towards evidence based public health.
What is evidence based public health? It is a variation of evidence based medicine, focusing instead on a public health intervention.8 Evidence based public health seeks to answer several questions regarding the usefulness of an intervention.9 Firstly, has the research performed been sufficiently valid to support a decision on whether or not to implement an intervention (in this case, a particular cataract surgery programme)? Secondly, have all the important research outcomes been evaluated (CSR is one example, post-cataract surgery visual outcome would be another)? Thirdly, is the research applicable to the potential recipients of the intervention (would such cataract surgery programme be transferable to other African communities and settings)? Although these questions are similar in many respects to the evaluation of evidence in medicine, there are some differences. Compared to a treatment in clinical medicine, public health interventions tend to be multifaceted, more complex, and more dependent on specific situations.10 Thus, it is more critical to distinguish between the efficacy of an intervention, and the effectiveness of an intervention in terms of delivery and execution.
Evidence based public health is but one factor in the process of translating a research observation into broad policy decisions regarding the implementation of a particular intervention. Like changes in clinical practice resulting from a heightened awareness of evidence based medicine, evidence based public health is necessary in ensuring the major paradigm changes needed in public health practice. For public health ophthalmology, it will be the first step towards the elimination of avoidable blindness from cataract in Africa and other developing countries.
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Towards evidence based public health
Competing interests: none declared