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Leprosy is one of the oldest scourges of humankind. Accurate portrayals of the disease in Chinese medical treatises date from 400 bc, and classic descriptions in ancient Indian literature occur even earlier.1 In our western tradition the fear and loathing directed towards the disease come directly from the bible. Leprosy was the “disease of the soul”, the “punishment for sin”. By the dawn of the Middle Ages the leper had become the universal symbol of persecution, the diseased and disenfranchised outcast of Western society.2 Even though the prevalence of leprosy steadily declined in Western Europe after a peak in the 14th century, it became epidemic in other parts of the world, especially in Asia, Africa, and South America. Until the introduction of dapsone in the 1940s there was no effective treatment for leprosy, and infected individuals were routinely isolated and segregated from all contact with society. In some areas of the world this approach continued until well into the 1980s, even after a number of highly effective antileprosy drugs had been developed.
Today the prevalence of this ancient disease is rapidly declining in most countries around the world. This decline is a direct result of the widespread administration by public health workers of multidrug therapy (MDT), a combination of rifampin, dapsone, and clofazimine. The introduction of MDT by the World Health Organization in 1982 for the treatment of multibacillary leprosy has led to a shortened treatment time of 2 years and a high degree of bacterial eradication (99.9%). It is felt that MDT for 2 years in almost all cases is adequate for producing a complete bacteriological cure of the disease and for preventing the emergence of drug resistant strains ofMycobacterium leprae.3 In spite of this optimistic assessment leprosy still affects 10–12 million people worldwide, the majority of whom are found in Africa and in the southern portion of the Indian subcontinent.4 The disease invariably causes many visually disabling sequelae, and it is estimated that 3.2% of all leprosy patients are ultimately blinded by long term ocular complications.5 Several recent studies have documented the main causes of blindness in leprosy.4 5-12 These causes include iritis, posterior synechia, cataract, lagophthalmos, corneal ulceration, and all of the complications associated with corneal hypaesthesia and exposure. However, none of the studies has addressed the question of whether or not the sight threatening complications of leprosy continue to develop after the infectious component of the disease has been adequately treated.
We have had a highly effective treatment programme for leprosy for almost 20 years, and the treatment regimen, MDT, has been proved to be almost 100% effective in eliminating M leprae in infected patients. But the ocular complications of the disease remain a major cause of blindness worldwide, and we still do not understand how, why, or to what extent eye disease in “cured” leprosy patients continues to progress. Until we understand this phenomenon we will not be able to adequately address the eyecare needs of leprosy patients.
Lewallen et al (see p 817, this issue) have examined this question in an exhaustive study that spans an 11 year period from 1988 to 1999 and documents ocular changes in leprosy patients in eight resettlement villages in South Korea. Of 501 patients examined in 1988 the authors were able to find 270 for re-examination in 1999, a remarkable follow up effort. Eighty four of the patients had died. It is known that patients who are blind from leprosy have a 4.8-fold excess risk of death compared with their non-blind peers of the same age.13 Lewallen and colleagues found that, over the 11 year period, of the patients with no sight threatening leprosy related ocular diseases (lagophthalmos, posterior synechia, keratitis, etc) in 1988, 14.7% had developed one or more of these conditions in 1999. Similarly, of those with no signs of cataract in 1988, 26.4% had developed a vision reducing cataract in at least one eye at the follow up examination. Overall, 14.3% of the patients developed visual impairment and 5.7% became blind in the intervening 11 years.
These findings are a sobering reminder that even though patients may be cured bacteriologically, leprosy related ocular lesions can slowly cause visual impairment that ultimately leads to blindness. Lewallen et al did not find any ocular lesions caused by active infection by M leprae. Instead, they found that progressive visual loss occurred as a result of chronic nerve damage that led to lagophthalmos, entropion, ectropion, corneal exposure, and keratitis. Small pupils, posterior synechia, and cataracts were frequently associated with a smouldering “chronic iritis”. This phenomenon has been commonly described in “cured” leprosy patients and is felt to be caused by damage to the sympathetic nerves. Therefore, Lewallenet al concluded that all of the progressive long term blinding complications in these bacteriologically cured leprosy patients, with the exception of trichiasis, were the direct result of chronic nerve damage.
From a public health point of view this study documents for the first time the progressive nature of the blinding complications of leprosy long after a “cure” has been effected. This conclusive evidence should have a profound influence on the planning of future strategies for blindness prevention in leprosy treatment programmes. Improved methods for managing the ocular complications of leprosy are currently being proposed.14 Any future recommendations for the worldwide eradication of leprosy and the treatment of the ocular complications of the disease should take into consideration the findings of this important study.