Childhood Blindness: More Useful Evidence From Blind School Survey.

T he latest World Health Organization (WHO) data show that childhood blindness (BL) accounts for 4% of the causes of BL globally. Although the prevalence of BL among children is estimated to be approximately 0.75%, which is only one tenth of that in adults, its impact can be detrimental in the way that it affects educational opportunities, employment, and personal and social disability throughout life. Childhood BL is the second greatest cause of blind-person years; with around 1.4 million blind children worldwide, approximately 70 million blind-person years are caused by childhood BL. Of these blind children, 93.5% live in middleand low-income countries. Previous research has shown that up to 50% of childhood BLworldwide might be either avoidable or even treatable. Thus, the control of childhood BL has been identified as a priority of the WHO global initiative for the elimination of avoidable BL by the year 2020. Substantial regional differences have been identified in the major causes of childhood BL. The leading cause of BL in low-income countries is corneal opacification caused by a combination of measles, xerophthalmia, and the use of traditional eyemedicine, whereas in high-income countries, lesions of the optic nerve and higher visual pathways predominate as the causes of BL. Socioeconomic development, mortality rates for children younger than age 5, and the availability of primary health care and eye care services are important determinants for the prevalence and distributions of major causes of childhood BL. An accurate estimation of the prevalence, magnitude, and causes of childhood BL and severe visual impairment (SVI), especially in middleand low-income countries, is very important for health policy planners. Proper methodology is the prerequisite in efforts to obtain accurate and comparable information. For many years, a standard methodology using a reporting form developed by the International Centre for Eye Health, London, in collaboration with the WHO, has been widely used. The causes are classified according to the main anatomical site of the abnormality and the underlying etiology. In this issue of the Asia-Pacific Journal of Ophthalmology, Farmer and colleagues reported and compared the findings of the causes of childhood BL/SVI from their studies in 1 school for the blind in Bhutan and another school for the blind in Laos. A total of 30 children in Bhutan and 23 children in Laos younger than age 16 with best-corrected visual acuity of less than 6/36 were enrolled in the study. Detailed ophthalmic examinations were performed according to WHO standards, and pathology was categorized both anatomically and etiologically in all participants. In the Bhutanese sample, 20 children were found to have BL/SVI. The leading causes of BL were hereditary disease (65%), lenticular abnormality (25.0%), and whole globe abnormality (20.0%). In the Laotian sample, hereditary disease accounted for 9 (39%) of 23 BL/SVI, and corneal abnormality (30.5%) was most frequently seen. Avoidable causes were identified in 18 (62.0%) of the children studied. Bhutan and Laos are both low-income countries in Asia. A detailed comparison between the distributions of the causes of childhood BL/SVI was presented. Possible explanations for the discrepancy between the proportions of corneal abnormality in the 2 samples and the relatively high rate of hereditary disease in the Bhutanese sample were discussed. This study may provide useful information on the causes of BL/SVI in these countries, and some findings deserve further discussion. Measles and vitamin A deficiency remain the leading causes of BL because of corneal scarring among children in low-income countries and are totally preventable. However, in the report, Bhutanese children showed a low rate of corneal scarring. This finding deviates from other studies of low-income regions but was consistent with the lowered rate of measles infection in the country during the previous decades. There are very few data available on the prevalence of childhood BL/SVI from population-based studies, as childhood BL is a very rare disease and therefore would require a very large sample. The fact