2002 global update of available data on visual impairment: a compilation of population-based prevalence studies.

PURPOSE: For the past 25 years, the WHO Programme for the Prevention of Blindness and Deafness has maintained a Global Data Bank on visual impairment with the purpose of storing the available epidemiological data on blindness and low vision. The Data Bank has now been updated to include studies conducted since the last update in 1994. METHODS: An extensive literature search was conducted in international and national scientific and medical journals to identify epidemiological studies that fulfilled basic criteria for inclusion in the Data Bank, namely a clearly stated definition of blindness and low vision, and prevalence rates derived from population-based surveys. Sources such as National Prevention of Blindness Programmes, academic institutions or WHO country or regional reports were also investigated. RESULTS: Two-hundred-and-eight population-based studies on visual impairment for 68 countries are reported in detail, providing an up-to-date, comprehensive compilation of the available information on visual impairment and its causes globally.

Proposed international clinical diabetic retinopathy and diabetic macular edema disease severity scales.

PURPOSE: To develop consensus regarding clinical disease severity classification systems for diabetic retinopathy and diabetic macular edema that can be used around the world, and to improve communication and coordination of care among physicians who care for patients with diabetes. DESIGN: Report regarding the development of clinical diabetic retinopathy disease severity scales. PARTICIPANTS: A group of 31 individuals from 16 countries, representing comprehensive ophthalmology, retina subspecialties, endocrinology, and epidemiology. METHODS: An initial clinical classification system, based on the Early Treatment Diabetic Retinopathy Study and the Wisconsin Epidemiologic Study of Diabetic Retinopathy publications, was circulated to the group in advance of a workshop. Each member reviewed this using e-mail, and a modified Delphi system was used to stratify responses. At a later workshop, separate systems for diabetic retinopathy and macular edema were developed. These were then reevaluated by group members, and the modified Delphi system was again used to measure degrees of agreement. MAIN OUTCOME MEASURES: Consensus regarding specific classification systems was achieved. RESULTS: A five-stage disease severity classification for diabetic retinopathy includes three stages of low risk, a fourth stage of severe nonproliferative retinopathy, and a fifth stage of proliferative retinopathy. Diabetic macular edema is classified as apparently present or apparently absent. If training and equipment allow the screener to make a valid decision, macular edema is further categorized as a function of its distance from the central macula. CONCLUSIONS: There seems to be a genuine need for consistent international clinical classification systems for diabetic retinopathy and diabetic macular edema that are supported with solid evidence. The proposed clinical classification systems provide a means of appropriately categorizing diabetic retinopathy and macular edema. It is hoped that these systems will be valuable in improving both screening of individuals with diabetes and communication and discussion among individuals caring for these patients.

Blindness prevention programmes: past, present, and future.

Blindness and visual impairment have far-reaching implications for society, the more so when it is realized that 80% of visual disability is avoidable. The marked increase in the size of the elderly population, with their greater propensity for visually disabling conditions, presents a further challenge in this respect. However, if available knowledge and skills were made accessible to those communities in greatest need, much of this needless blindness could be alleviated. Since its inception over 50 years ago, and beginning with trachoma control, WHO has spearheaded efforts to assist Member States to meet the challenge of needless blindness. Since the establishment of the WHO Programme for the Prevention of Blindness in 1978, vast strides have been made through various forms of technical support to establish national prevention of blindness programmes. A more recent initiative, "The Global Initiative for the Elimination of Avoidable Blindness" (referred to as "VISION 2020--The Right to Sight"), launched in 1999, is a collaborative effort between WHO and a number of international nongovernmental organizations and other interested partners. This effort is poised to take the steps necessary to achieve the goal of eliminating avoidable blindness worldwide by the year 2020.

Global data on blindness.

Globally, it is estimated that there are 38 million persons who are blind. Moreover, a further 110 million people have low vision and are at great risk of becoming blind. The main causes of blindness and low vision are cataract, trachoma, glaucoma, onchocerciasis, and xerophthalmia; however, insufficient data on blindness from causes such as diabetic retinopathy and age-related macular degeneration preclude specific estimations of their global prevalence. The age-specific prevalences of the major causes of blindness that are related to age indicate that the trend will be for an increase in such blindness over the decades to come, unless energetic efforts are made to tackle these problems. More data collected through standardized methodologies, using internationally accepted (ICD-10) definitions, are needed. Data on the incidence of blindness due to common causes would be useful for calculating future trends more precisely.

Epidemiologic aspects of global blindness prevention.

The number of blind persons in the world is not accurately known. However, taking into account previous estimates by the World Health Organization and adjusting to the world population of 1990, it is likely that there are at least 35 million blind people if we apply the internationally accepted definition of blindness as vision less than 3/60 ( less than 20/400 or 0.05) in the better eye. If the threshold of vision less than 6/60 ( less than 20/200 or 0.1) is applied, the above figure can be increased by roughly 50%, ie, going well beyond 50 million blind people. To this somber picture should be added the effects of aging on populations in both developed and developing countries. Longer life expectancy is going to dramatically increase the need for eye care to prevent visual loss from such conditions as cataract, glaucoma, diabetic retinopathy, and macular degenerations. Corneal blindness, resulting mainly from trachoma and other infections, is apparently showing a downward trend, but there are still foci of severe disease. Thus the need for trichiasis surgery remains, and some recently evaluated techniques offer particularly good results. On the other hand, xerophthalmia due to vitamin A deficiency is still a major public health problem, causing both visual loss and increased mortality. It should be possible, by targeting ivermectin distribution programs to high-risk populations, to gradually eliminate onchocerciasis as a cause of blindness; however, the long-term sight-saving effect of ivermectin in cases of established ocular lesions needs to be confirmed.

[Epidemiological surveillance of trachoma: evaluation and perspective]. / La surveillance épidémiologique du trachome: bilan et perspective.

World Health Organization (W.H.O.) carried out a survey recently. This survey consisted in a questionnaire to some of its Member States to try to define the importance and world distribution of trachoma. The answers which have been sent by ocular health advisers and/or persons in charge of national ophthalmological institutes showed a systemic lack of significant data to be used for planning or for epidemiological surveillance. Nevertheless, the analysis of this survey seems to lead to the conclusion that trachoma is not still the main cause of blindness in some countries who used to be famous because of an important endemicity. However, trachoma is still a real ocular health and public health problem in numerous other countries, mainly in rural areas and- or areas which are away from socio-sanitary development areas. To have a better quality concerning epidemiological data and to obtain an easier regularity in their collecting, W.H.O. Program for the Blindness Prevention proposed a simplified coding system of trachoma and its complications (S.S.C.T.C.). If this system was accepted by numerous countries it would allow: the use of a simple, reliable and cheap tool to collect epidemiological informations which would constitute an help to take decisions to be able to, give a second start to epidemiological surveillance of trachoma, to have a better idea of the localization of endemic centres of the disease and of this impact on population, to define the needs concerning collective and individual medical and surgical treatments.

Epidemiology of blindness in Nepal.

This report presents the major findings of the Nepal Blindness Survey, the first nationwide epidemiological survey of blindness, which was conducted in 1979-80. The survey was designed to gather data that could be used to estimate the prevalence and causes of blindness in the country. Ancillary studies were conducted to obtain information on socioeconomic correlates and other risk factors of blinding conditions and patterns of health care utilization.The nationwide blindness prevalence rate is 0.84%. Cataract is the leading cause of blindness, accounting for over 80% of all avoidable blindness. Trachoma is the most prevalent blinding condition, affecting 6.5% of the population. Very few cases of childhood blindness were detected.The implications of the survey findings for programme planning, health manpower development, and health education are discussed.

Associations among cataract prevalence, sunlight hours, and altitude in the Himalayas.

The relationship between cataract prevalence, altitude, and sunlight hours was investigated in a large national probability sample survey of 105 sites in the Himalayan kingdom of Nepal, December 1980 through April 1981. Cataract of senile or unknown etiology was diagnosed by ophthalmologists in 873 of 30,565 full-time life-long residents of survey sites. Simultaneously, the altitude of sites was measured using a standard mountain altimeter. Seasonally adjusted average daily duration of sunlight exposure for each site was calculated by a method which took into account latitude and obstructions along the skyline. Age- and sex-standardized cataract prevalence was 2.7 times higher in sites at an altitude of 185 meters or less than in sites over 1000 meters. Cataract prevalence was negatively correlated with altitude (r = -0.533, p less than 0.0001). However, a positive correlation between cataract prevalence and sunlight was observed (r = 0.563, p less than 0.0001). Sites with an average of 12 hours of sunlight exposure had 3.8 times as much cataract as sites with an average of only seven hours of exposure. Sunlight was blocked from reaching certain high altitude sites by tall neighboring mountains.