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The order is rapidly fadin’
  1. J D Chidambaram1,
  2. T M Lietman1,2
  1. 1FI Proctor Foundation, University of California, San Francisco, CA, USA
  2. 2Institute for Global Health, and Department of Ophthalmology, University of California, San Francisco, CA, USA
  1. Correspondence to: Dr Thomas M Lietman FI Proctor Foundation, Room 307, 95 Kirkham Street, University of California San Francisco, San Francisco, CA 94143-0944, USA; tmlitsa.ucsf.edu

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Onchocerciasis and trachoma may become historical diseases within our lifetime

In this issue of the BJO (p 796), Egbert et al utilise a case-control design to demonstrate that onchocerciasis and glaucoma are associated in an area of Ghana. Perhaps this is not surprising, as onchocerciasis is known to cause anterior segment inflammation and peripheral anterior synechiae, which can in turn lead to increased intraocular pressure. However, this association had never really been proved in the past, in part because reliable glaucoma data in the developing world have been difficult to come by. Interestingly, as glaucoma has become more recognised, onchocerciasis has become less so—glaucoma has moved up to number two in the WHO’s latest rankings, while onchocerciasis may have made the list for the last time at number 8 (table 1).1 This may be the ideal time to make such an association between these two diseases when awareness of both diseases is relatively high—it would have been difficult in the past or the future.

Table 1

 Global blindness rankings for 1994 and 2002

Many factors go into the disease rankings. To some extent, they reflect the efficacy of treatment. Programmes have had remarkable success with those diseases amenable to mass drug distributions (neonatal ophthalmia, xerophthalmia, onchocerciasis, and trachoma). In fact, onchocerciasis and trachoma may become historical diseases within our lifetime. As developing countries become wealthier with improved diet and longer life expectancies, we expect worldwide rankings to reflect diseases now found often in the developed countries. Worldwide, diabetes is increasing at an alarming rate, and diabetic retinopathy is now fifth on the list. Older populations are more susceptible to age related macular degeneration (AMD), now third.1 Both diabetic retinopathy and AMD had not even appeared on previous rankings.2 This echoes what has been previously been noted with mortality statistics, where projected worldwide rankings are similar to current rankings in developed countries.3 Difficulties in the diagnosis of disease also come into play. Some diseases are easily found on the external examination (trachoma), or at least with an undilated examination (mature cataract). Others, such as glaucoma, require equipment and dilated examination—the harder people look, the more glaucoma they find. Glaucoma moved up to third in the 1990s2 and to second in the most recent survey,1 in part the result of better diagnosis. There are also fluctuations in the awareness and politics of disease. More than one country has been reluctant to attribute blindness to trachoma, since it had been declared eliminated in the past. To some extent, the changes in rankings reflect secular, socioeconomic trends. Trachoma is disappearing in much of the world, even in the absence of programmes specifically targeting the disease. This may be the result of better hygiene, fewer flies, and perhaps even widespread use of antibiotics for other purposes that incidentally cover chlamydia.4 The rankings also reflect the vagaries of estimation. In the past decade trachoma has gone from second to seventh in the rankings, in part because of mass treatment programmes, the presence of a secular trend, and the realisation that previous estimates of the burden of trachomatous blindness were just too high.

Associations between diseases and rankings of their importance worldwide are not just curiosities. They can be of great practical importance. Programmes targeting onchocerciasis, trachoma, lymphatic filariasis, and schistosomiasis all distribute antimicrobials to large segments of the population. Groups are beginning to study how the geographical distributions of these infections overlap. Immunisation campaigns have already demonstrated that mass administrations can be used for the delivery of other preventive health services such as vitamin A distribution. Synergy in surgical programmes may exist as well; for example, trachoma programmes often pick up more mature cataracts than trichiasis. As programmes expand, it will be important to integrate, so as not to overburden public health programmes with limited resources. Just as important is not to overburden rural, subsistence farmers with requests to attend separate onchocerciasis days, trachoma days, polio days, etc. The rankings of the major causes of blindness not only appeal to our love of lists, but also help to set priorities and demonstrate our long term successes and failures. The recent rankings may serve to alert the international community that not enough is being done for management of some diseases. Diabetes and AMD researchers can be forgiven if they tout the newly recognised importance of their diseases in papers and grant applications. Likewise onchocerciasis and trachoma programmes can be forgiven if they take some of the credit for the decline of their diseases, and now brag that they are number 8.

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Onchocerciasis and trachoma may become historical diseases within our lifetime

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