Academic journal article Bulletin of the World Health Organization

Global Data on Blindness

Academic journal article Bulletin of the World Health Organization

Global Data on Blindness

Article excerpt

Introduction

The number of blind in the world is not accurately known, but it has been estimated at various times by WHO. Thus, in 1972, it was reported that there might be 10-15 million blind globally. In the same year, when a WHO Study Group on the Prevention of Blindness was convened, this value was recognized to be an underestimate, even though based on information provided by Member States[1]. The Study Group recommended and made a great contribution to the future collection of data on blindness by proposing uniform definitions of blindness and visual impairment, which have been included in the International Statistical Classification of Diseases, and Related Health Problems, tenth revision ICD-10).

When the WHO Programme for the Prevention of Blindness (PBL) was established in 1978, its priority was to obtain more detailed knowledge about blindness and its causes worldwide. A Task Force on Data on Blindness was therefore convened and this developed an epidemiological model for blindness estimates in relation to the developmental stage of the country[2].

The programme has, from its outset, developed a simplified population-based assessment methodology for visual loss and its causes[3]; this has resulted in a standard form and method for low-cost, small-scale field surveys that can be conducted mainly by trained non-specialist staff. The application of this methodology in an increasing number of countries had led to a gradual accumulation of epidemiologically reliable data.

In addition to the WHO Global Data Bank on Blindness (BDB) for the collection and dissemination of epidemiological information and trends assessment, work was undertaken in 1993, in collaboration with the World Bank, to measure the burden of blindness. For this purpose, PBL provided estimates of the prevalence and incidence of the following blinding diseases: cataract, glaucoma, trachoma, and onchocerciasis. The global burden of disease approach combines the premature loss of life with the loss of healthy life years from a disability; the global burden of disease is measured in units of disability-adjusted life years (DALYs)[4].

This review reports on and discusses the available information on the prevalence, distribution, and causes of blindness in the world. Described also are the trends in the prevalence of blindness over the last two decades. Attention is drawn to some of the assumptions made and the methodological issues involved in the calculation of the data. Finally, areas are identified that require further investigation.

Methods

Definitions

In this article, the definitions of blindness and visual impairment used follow those included in ICD-10.

* Blindness is defined as visual acuity of less than 3/60 (0.05) or corresponding visual field loss in the better eye with best possible correction (visual impairment categories 3, 4, and 5 in ICD-10). This corresponds to loss of walk-about vision.

* Low vision corresponds to visual acuity of less than 6/18 (0.3) but equal to or better than 3/60 (0.05) in the better eye with best possible correction (visual impairment categories 1 and,2 in ICD-10).

Data collection

The background information for this article was obtained from selected, epidemiologically sound data on blindness and visual impairment. Two main sources were used to identify relevant existing information as outlined below.

* Routine periodic computerized search of relevant information carried out as part of an ongoing updating of the BDB. This involves a three-step process. First, all abstracts are scanned to identify subject matter of interest. Next, all relevant materials are reviewed in depth and a checklist is used for eligibility criteria for inclusion. Finally, an in-house discussion is held to arrive at a consensus for inclusion of the new data in the bank.

For this purpose, the following inclusion criteria have been established:

- Clear, unequivocal definitions of blindness and low vision have to be stated (preferably according to the ICD-10 categorization). …

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