A population based eye survey of older adults in Tirunelveli district of south India: blindness, cataract surgery, and visual outcomes.

AIMS: To assess the prevalence of vision impairment, blindness, and cataract surgery and to evaluate visual acuity outcomes after cataract surgery in a south Indian population. METHODS: Cluster sampling was used to randomly select a cross sectional sample of people > or =50 years of age living in the Tirunelveli district of south India. Eligible subjects in 28 clusters were enumerated through a door to door household survey. Visual acuity measurements and ocular examinations were performed at a selected site within each of the clusters in early 2000. The principal cause of visual impairment was identified for eyes with presenting visual acuity <6/18. Independent replicate testing for quality assurance monitoring was performed in subjects with reduced vision and in a sample of those with normal vision for six of the study clusters. RESULTS: A total of 5795 people in 3986 households were enumerated and 5411 (93.37%) were examined. The prevalence of presenting and best corrected visual acuity > or =6/18 in both eyes was 59.4% and 75.7%, respectively. Presenting vision <6/60 in both eyes (the definition of blindness in India) was found in 11.0%, and in 4.6% with best correction. Presenting blindness was associated with older age, female sex, and illiteracy. Cataract was the principal cause of blindness in at least one eye in 70.6% of blind people. The prevalence of cataract surgery was 11.8%-with an estimated 56.5% of the cataract blind already operated on. Surgical coverage was inversely associated with illiteracy and with female sex in rural areas. Within the cataract operated sample, 31.7% had presenting visual acuity > or =6/18 in both eyes and 11.8% were <6/60; 40% were bilaterally operated on, with 63% pseudophakic. Presenting vision was <6/60 in 40.7% of aphakic eyes and in 5.1% of pseudophakic eyes; with best correction the percentages were 17.6% and 3.7%, respectively. Refractive error, including uncorrected aphakia, was the main cause of visual impairment in cataract operated eyes. Vision <6/18 was associated with cataract surgery in government, as opposed to that in non-governmental/private facilities. Age, sex, literacy, and area of residence were not predictors of visual outcomes. CONCLUSION: Treatable blindness, particularly that associated with cataract and refractive error, remains a significant problem among older adults in south Indian populations, especially in females, the illiterate, and those living in rural areas. Further study is needed to better understand why a significant proportion of the cataract blind are not taking advantage of free of charge eye care services offered by the Aravind Eye Hospital and others in the district. While continuing to increase cataract surgical volume to reduce blindness, emphasis must also be placed on improving postoperative visual acuity outcomes.

[The use of state of the art statistical methodology in biomedical research: the example of methodology for interim analyses in clinical trials]. / El uso de metodología estadística actualizada en la investigación biomédica: el ejemplo de metodología para análisis interino en ensayos clínicos.

BACKGROUND: Clinical research stresses the need for evidence as a basis for setting research agendas. The extent to which current clinical research involves recent advances in biostatistics is not well known. AIM: This manuscript focuses on the use of interim analyses accumulating data in clinical trials. MATERIAL AND METHODS: A PubMed search was conducted for the period 1990-2000. Keywords used included 'interim analysis', 'alpha-spending function', and 'early termination', after subsetting to 'randomised controlled trials (RCT)' that were 'multicenter' since these particular studies are more likely to have external monitoring boards conducting interim analyses. Studies were grouped by clinical discipline and also by journals of high or low impact index. RESULTS: Thirteen thousand two hundred eighty two articles with both 'RCT' and 'multicenter' were found. Of these, the 'interim analysis' keyword yielded 879 articles, of which only 163 (19%) studies reported their methodology. The percentages varied by clinical discipline and by journal type. A 25% random sample of the articles were further reviewed to investigate the appropriateness of the interim analysis methods used. DISCUSSION: Recent articles in the medical literature attempt to make the interim analysis methods more accessible to clinicians. However, further training of statisticians involved in clinical trials is needed as well.

Growth in indigenous and nonindigenous Chilean schoolchildren from 3 poverty strata.

OBJECTIVES: This study sought to determine whether the short stature of Mapuche children, an indigenous group in Chile, reflects poverty or genetic heritage and whether the international reference population, derived from studies of US children of mostly European origin, is appropriate for assessing growth failure in indigenous peoples of the Americas. METHODS: The study assessed 768 schoolchildren of Mapuche and non-Mapuche ancestry, aged 6 to 9 years, living under conditions of extreme, medium, and low poverty. RESULTS: Growth retardation was strongly related to poverty in both ethnic groups. Within poverty levels, there were no significant differences in stature between ethnic groups, and in low-poverty areas in Santiago, the capital city, mean stature was only slightly less than in the reference population. CONCLUSIONS: Poverty, not ancestry, explains the short stature of Mapuche children, and use of the international reference to assess growth in this population is appropriate.

A population-based eye survey of older adults in a rural district of Rajasthan: I. Central vision impairment, blindness, and cataract surgery.

PURPOSE: To assess the prevalence of central vision blindness and cataract surgery in older adults in rural northwest India. DESIGN: Population-based, cross-sectional study. PARTICIPANTS: A total of 4284 examined persons 50 years of age or older. METHODS: A random selection of village-based clusters was used to identify a population sample in the predominantly rural Bharatpur district of Rajasthan. Eligible subjects in the 25 selected clusters were enumerated through a door-to-door household survey and invited to village sites for visual acuity testing and eye examination early in 1999. The principal cause of reduced central vision was identified for eyes that had visual acuity worse than 6/18. Independent replicate testing for quality assurance monitoring took place in participants with reduced vision and in a sample of those with normal vision in five of the study clusters. MAIN OUTCOME MEASURES: Presenting and best-corrected visual acuity and lens status. RESULTS: A total of 4728 eligible persons in 2821 households were enumerated, and 4284 (90.6%) were examined. The prevalence of presenting and best-corrected visual acuity worse than 6/60 in both eyes was 11.9% (95% confidence interval: 10.0%-13.9%) and 6.1% (95% CI: 4.7%-7.4%), respectively. Presenting blindness was associated with increasing age, female gender, lack of schooling, and rural residence. Cataract was the principal cause of blindness in one or both eyes in 67.5% of blind persons, with uncorrected aphakia and other refractive error affecting 18.4% in at least one eye. The prevalence of cataract surgery was 12.8% (95% CI: 11.6%-14.0%), with an estimated 65.7% of the cataract blind operated on; low surgical coverage was associated with lack of schooling. CONCLUSIONS: Blindness, particularly blindness because of cataract, continues to be a significant problem among the elderly living in remote areas of rural northwest India. Increased attention should be given to reaching women and the illiterate.

Refractive Error Study in Children: results from Shunyi District, China.

PURPOSE: To assess the prevalence of refractive errors and vision impairment in school-age children in Shunyi District, northeast of Beijing, the Peoples Republic of China. METHODS: Random selection of village-based clusters was used to identify a sample of children 5 to 15 years of age. Resident registration books were used to enumerate eligible children in the selected villages and identify their current school. Ophthalmic examinations were conducted in 132 schools on children from 29 clusters during May 1988 to July 1998, including visual acuity measurements, cycloplegic retinoscopy, cycloplegic autorefraction, ocular motility evaluation, and examination of the external eye, anterior segment, media, and fundus. Independent replicate measurements of all children with reduced vision and a sample of those with normal vision were done for quality assurance monitoring in three schools. RESULTS: A total of 6,134 children from 4,338 households were enumerated, and 5,884 children (95.9%) were examined. The prevalence of uncorrected, presenting, and best visual acuity 0.5 (20/40) or worse in at least one eye was 12.8%, 10.9%, and 1.8%, respectively; 0.4% had best visual acuity 0.5 or worse in both eyes. Refractive error was the cause in 89.5% of the 1,236 eyes with reduced vision, amblyopia in 5%, other causes in 1.5%, with unexplained causes in the remaining 4%. Myopia -0.5 diopter or less in either eye was essentially absent in 5-year-old children, but increased to 36.7% in males and 55.0% in females by age 15. Over this same age range, hyperopia 2 diopters or greater decreased from 8.8% in males and 19.6% in females to less than 2% in both. Females had a significantly higher risk of both myopia and hyperopia. CONCLUSIONS: Reduced vision because of myopia is an important public health problem in school-age children in Shunyi District. More than 9% of children could benefit from prescription glasses. Further studies are needed to determine whether the upward trend in the prevalence of myopia continues far beyond age 15 and whether the development of myopia is changing for more recent birth cohorts.

Refractive Error Study in Children: results from Mechi Zone, Nepal.

PURPOSE: To assess the prevalence of refractive error and vision impairment in school age children in the terai area of the Mechi zone in Eastern Nepal. METHODS: Random selection of village-based clusters was used to identify a sample of children 5 to 15 years of age. Children in the 25 selected clusters were enumerated through a door-to-door household survey and invited to village sites for examination. Visual acuity measurements, cycloplegic retinoscopy, cycloplegic autorefraction, ocular motility evaluation, and anterior segment, media, and fundus examinations were done from May 1998 through July 1998. Independent replicate examinations for quality assurance monitoring took place in all children with reduced vision and in a sample of those with normal vision in seven villages. RESULTS: A total of 5,526 children from 3,724 households were enumerated, and 5,067 children (91.7%) were examined. The prevalence of uncorrected, presenting, and best visual acuity 0.5 (20/40) or worse in at least one eye was 2.9%, 2.8%, and 1.4%, respectively; 0.4% had best visual acuity 0.5 or worse in both eyes. Refractive error was the cause in 56% of the 200 eyes with reduced uncorrected vision, amblyopia in 9%, other causes in 19%, with unexplained causes in the remaining 16%. Myopia -0.5 diopter or less in either eye or hyperopia 2 diopters or greater was observed in less than 3% of children. Hyperopia risk was associated with female gender and myopia risk with older age. CONCLUSIONS: The prevalence of reduced vision is very low in school-age children in Nepal, most of it because of correctable refractive error. Further studies are needed to determine whether the prevalence of myopia will be higher for more recent birth cohorts.

Refractive Error Study in Children: results from La Florida, Chile.

PURPOSE: To assess the prevalence of refractive errors and vision impairment in school-age children in a suburban area (La Florida) of Santiago, Chile. METHODS: Random selection of geographically defined clusters was used to identify a representative sample of children 5 to 15 years of age. Children in the 26 selected clusters were enumerated through a door-to-door survey and invited to report to a community health clinic for examination. Visual acuity measurements, cycloplegic retinoscopy, cycloplegic autorefraction, ocular motility evaluation, and examination of the external eye, anterior segment, media, and fundus were done from April through August 1998. Independent replicate examinations of all children with reduced vision and a sample of those with normal vision were done for quality assurance monitoring in six clusters. RESULTS: A total of 6,998 children from 3,830 households were enumerated, and 5,303 children (75.8%) were examined. The prevalence of uncorrected, presenting, and best visual acuity 0.50 (20/40) or worse in at least one eye was 15.8%, 14.7%, and 7.4%, respectively; 3.3% had best visual acuity 0.50 or worse in both eyes. Refractive error was the cause in 56.3% of the 1,285 eyes with reduced vision, amblyopia in 6.5%, other causes in 4.3%, with unexplained causes in the remaining 32.9%. Myopia -0.50 diopter or less in either eye was present in 3.4% of 5-year-old children, increasing to 19.4% in males and 14.7% in females by age 15. Over this same age range, hyperopia 2.00 diopters or greater decreased from 22.7% to 7.1% in males and from 26.3% to 8.9% in females. Females had a significantly higher risk of hyperopia than males. CONCLUSIONS: Refractive error, associated primarily with myopia, is a major cause of reduced vision in school-age children in La Florida. More than 7% of children could benefit from the provision of proper spectacles. Efforts are needed to make existing programs that provide free spectacles for school children more effective. Further studies are needed to determine whether the upward trend in myopia continues far beyond 15 years of age.

A survey of blindness and cataract surgery in Doumen County, China.

PURPOSE: To assess blindness prevalence and that caused specifically by cataract in rural southern China. DESIGN: Population-based, cross-sectional study. PARTICIPANTS: A total of 5342 persons older than 50 years of age. METHODS: Visual acuity and eye examinations were performed in the summer of 1997 in a random sample of villages in Doumen County. Differences in blindness prevalence associated with age, gender, and education were explored using logistic regression. The survey was preceded by a pilot study in which operational methods were refined and quality assurance measures were performed. MAIN OUTCOME MEASURES: Distance visual acuity and lens status. RESULTS: Bilateral blindness (presenting visual acuity < 0.10) was found in 4.37% (95% confidence interval, 3.67%-5.06%). Blindness was associated with increasing age (P < 0.001) and with the lack of education (P < 0.01). Cataract was the principal cause of blindness in at least one eye in 61.5% of blind people, with refractive error responsible for another 10%. An estimated 40% of the cataract blind were operated on; surgical coverage was lowest among the elderly, women, and those without schooling, although not at statistically significant levels. CONCLUSIONS: Despite the increased attention given to eye care in Doumen County, blindness remains a major public health problem. Cataract surgery is reaching fewer than half of those who could benefit from it.

Visual acuity and quality of life in patients with cataract in Doumen County, China.

PURPOSE: To evaluate the effectiveness of cataract surgery in achieving sight restoration and vision-related quality-of-life (QOL) in patients from rural southern China. DESIGN: Population-based, cross-sectional study. PARTICIPANTS: A total of 109 cataract operated persons (152 eyes) and 654 unoperated persons. METHODS: Cluster sampling was used in identifying a random sample of 5342 persons 50 years of age and older for visual acuity and eye examinations. Visual functioning (VF) and QOL questionnaires were administered to aphakic and pseudophakic individuals, unoperated persons with presenting visual acuity less than 0.10 in either eye, and a sample of those with normal vision. MAIN OUTCOME MEASURES: Distance visual acuity, VF, and QOL questionnaire scores. RESULTS: Among the cataract operated participants, 43 (39.4%) were bilaterally operated on, 32.1% had presenting visual acuity less than 0.10 in both eyes with 8.3% greater than or equal to 0.32 in both eyes. Of operated eyes, 52.6% presented with visual acuity less than 0.10, 23.7% greater than or equal to 0.32; with best correction, the corresponding percentages were 21.1% and 42.1%. Uncorrectable aphakia due to surgical complications was common. In a multivariate regression model, better visual acuity outcomes were associated with higher level surgeon practice settings and recent surgery. On a 0 to 100 scale, mean VF and QOL scores for the cataract operated population were 41.6 and 54.5, respectively. Mean scores ranged from 84.4 and 93.4, respectively, for the unoperated persons with normal vision, to 14.6 and 31.2, respectively, for those with visual acuity less than 0.05 in both eyes. The VF and QOL scores were closely correlated with presenting visual acuity in both cataract operated and unoperated populations (r = 0.49-0.64). Scores among the cataract operated population were not influenced by age, gender, or education level. Among the unoperated population, lack of education was associated with lower VF and QOL scores (P = 0.017 and P = 0.005, respectively), and older age was associated with lower QOL scores (P < 0.001). CONCLUSION: Patients in rural southern China are not realizing the full sight-restoring potential of modern-day cataract surgery. Remedial efforts are needed to improve the performance of local eye surgeons.

[Measurement of reliability and validity of clinical instruments]. / Medición de confiabilidad y validez en instrumentos clínicos.

In biomedical measurement, comparisons between two instruments or between a new instrument and the gold standard is commonly needed to evaluate the reliability and validity of the instruments. Such studies are frequently analyzed using statistics that are inappropriate for studying concordance. This article reviews the appropriate statistical techniques and provides a current methodological guide for the evaluation of reliability and validity of instruments used in the measurement of biomedical variables. The techniques are illustrated using real data from a pilot study comparing four instruments for measuring cholesterol.

[The case-control design in medical research]. / El diseño de casos y controles en la investigación médica.

The aim of this paper is to present a conceptual and practical framework of the case-control design in medical research. To illustrate this method, practical examples directed to clinicians and other health professionals interested in medical research are presented. The case-control method is very versatile and allows for multiple applications. Guidelines for the selection of cases and controls, and some considerations on sample size are presented. In the statistical analysis we use concrete examples of how to estimate odds ratios, confidence intervals, and methods to control for potential confounders, from stratified analysis to logistic regression.

Nonfatal and fatal firearm injuries in a rural county.

OBJECTIVE: To measure the incidence of fatal and nonfatal firearm injuries in a rural setting. DESIGN: A prospective, population-based surveillance system using information from medical and legal records, newspapers, and members of the community. SETTING: A rural county in North Carolina. MAIN OUTCOME MEASURES: Incidence rates and case-fatality ratios (fatal:non-fatal). RESULTS: Of the 114 firearm injuries detected by the surveillance system from January 1, 1990, through December 31, 1991, nearly two thirds were nonfatal. The overall age-adjusted annual incidence of firearm injuries was 66.4 per 100 000 population, and the incidence of nonfatal firearm injuries was 41.2 per 100 000 population. Subgroup annual incidence rates were greatest for African Americans. The overall case-fatality ratio was 1:1.8 (fatal:nonfatal). CONCLUSIONS: Incidence rates and case-fatality ratios for firearm injury in this rural setting were greater than expected, based on national estimates, perhaps because of greater proportions of rifle injuries and self-inflicted injuries.

[Sample size for estimating attributable risk in cross-sectional studies]. / Tamaño de muestra para estimar riesgo atribuible en estudios transversales.

The prevalence of a variety of risk factors and their strength of association with a disease can vary greatly among apparently similar communities. In small communities, risk estimates can also vary from year to year. An identification of important risk factors in each community is then needed, so that interventions can be specifically oriented towards the needs of each specific community. The attributable risk is the adequate measure of association for these purposes. The purpose of this paper is to determine the minimum sample size required to detect a given attributable risk in cross-sectional studies. A table was constructed, presenting the number of exposed subjects necessary to detect a given attributable risk for different combinations of prevalence of disease and prevalence of exposure to a given risk factor, with a power of 0.80 and alpha of 0.05.

Bacterial cell wall polymers (peptidoglycan-polysaccharide) cause reactivation of arthritis.

Intraperitoneal (i.p.) injection of peptidoglycan-polysaccharide derived from group A streptococci (PG-APS) causes chronic arthritis with spontaneous remissions and exacerbations. We hypothesized that, following i.p. injection, PG-APS released from hepatic stores mediated spontaneous recurrences of arthritis. We tested whether transplanted livers with large amounts of PG-APS were able to reactivate quiescent arthritis. Saline-loaded (group 1) or PG-APS-loaded (group 2) livers were transplanted into rats which had been injected intra-articularly 10 days earlier with PG-APS in one joint and saline in the other. A comparison was made with the arthritis that occurred in rats injected i.p. with PG-APS which did not receive transplants (group 3). Arthritis was monitored by serial measurement of joint diameters. Transplantation of saline-loaded livers (group 1) caused no reactivation of arthritis. However, transplantation of PG-APS-loaded livers (group 2) reactivated arthritis (P < 0.0001). Injection of PG-APS i.p. (group 3) induced the most-severe arthritis. PG-APS levels in plasma decreased with time, and PG-APS accumulated in the spleen in groups 2 and 3. Plasma and hepatic levels of PG-APS in rats injected i.p. with PG-APS were greater than levels in rats transplanted with PG-APS-loaded livers, which in turn were greater than levels in rats with saline-loaded livers. Plasma tumor necrosis factor did not correlate with recurrence of arthritis. Transplantation with PG-APS-loaded livers induced reactivation of arthritis in preinjured joints. The extent of arthritis was proportional to hepatic PG-APS content. Reactivation of arthritis may be mediated by slow release of liver-sequestered PG-APS or cytokines (not tumor necrosis factor) released by the liver.