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PubMed2006

Who is blinded in randomized clinical trials? A study of 200 trials and a survey of authors.

BACKGROUND: Insufficient blinding of persons involved in randomized clinical trials is associated with bias. The appraisal of the risk of bias is difficult without adequate information in trial reports. PURPOSE: We wanted to study how blinding is reported in clinical trials and how lack of reporting relate to lack of blinding. METHODS: A cohort study of 200 blinded randomized clinical trials published in 2001 randomly sampled from the Cochrane Central Register of Controlled Trials, and a questionnaire survey of the trial authors. RESULTS: One-hundred and fifty-six (78%) articles described trials as 'double blind'. In three (2%) of such articles the blinding status of patients, health care providers and data collectors was explicitly described. Eighty-eight (56%) articles did not describe the blinding status of any trial person, and 41 articles (26%) reported no blinding relevant information at all beyond the trial being 'double blind'. One-hundred and thirty (65%) surveyed authors responded. Patients were blinded in 101 (97%) 'double blind' trials, and health care providers in 93 (89%). Twenty (19%) 'double blind' trials had not blinded either patients, health care providers or data collectors. Survey responders provided 15 different operational meanings of the term 'double blind', and typically felt that their preferred definition was the most widely used. LIMITATIONS: The proportions in the author survey may be too optimistic due to reporting bias. It is not known how the increased use of the CONSORT guidelines may have affected reporting in years after 2001. CONCLUSIONS: The blinding status of key trial persons was incompletely reported in most randomized clinical trials. Unreported blinding may be frequent, but one of five 'double blind' trials did not blind either patients, treatment providers or data collectors. Authors, referees, and journal editors could improve the completeness of reporting of blinding, eg, by adhering to the CONSORT statement. It is inappropriate to presume blinding of key trial persons based only on the ambiguous term 'double blind'.

Double-Blind Method↗
PubMed2002

Blinding in randomised trials: hiding who got what.

Blinding embodies a rich history spanning over two centuries. Most researchers worldwide understand blinding terminology, but confusion lurks beyond a general comprehension. Terms such as single blind, double blind, and triple blind mean different things to different people. Moreover, many medical researchers confuse blinding with allocation concealment. Such confusion indicates misunderstandings of both. The term blinding refers to keeping trial participants, investigators (usually health-care providers), or assessors (those collecting outcome data) unaware of the assigned intervention, so that they will not be influenced by that knowledge. Blinding usually reduces differential assessment of outcomes (information bias), but can also improve compliance and retention of trial participants while reducing biased supplemental care or treatment (sometimes called co-intervention). Many investigators and readers naïvely consider a randomised trial as high quality simply because it is double blind, as if double-blinding is the sine qua non of a randomised controlled trial. Although double blinding (blinding investigators, participants, and outcome assessors) indicates a strong design, trials that are not double blinded should not automatically be deemed inferior. Rather than solely relying on terminology like double blinding, researchers should explicitly state who was blinded, and how. We recommend placing greater credence in results when investigators at least blind outcome assessments, except with objective outcomes, such as death, which leave little room for bias. If investigators properly report their blinding efforts, readers can judge them. Unfortunately, many articles do not contain proper reporting. If an article claims blinding without any accompanying clarification, readers should remain sceptical about its effect on bias reduction.

Double-Blind Method↗
PubMed1999

Mortality in blind subjects. A population-based study on social security files from Baden-Württemberg.

BACKGROUND: Previous studies indicated that mortality is increased in blind subjects. However, no detailed analysis with respect to causes of blindness and the effect of additional diseases has been performed. The present study was undertaken to examine these questions. MATERIALS AND METHODS: The investigation is based on social security files from the Württemberg-Hohenzollern region (population 5.5 millions) in Germany. In total, 571 files of blind subjects whose blindness benefits terminated (mostly due to death) in 1994 were included. Medical opinions on ophthalmological status and general health were extracted from the files. Standardised mortality ratios (SMRs) on the basis of life tables of former West Germany were calculated using maximum likelihood methods taking into account censoring. RESULTS: Most subjects in our study had one or more additional diseases at onset of blindness (74%). The SMR in all blind is 1.41 [95% CI (confidence interval) = 1.28-1.54; n= 571]. Mortality of blind subjects is increased if subjects suffer from multiple disease at onset of blindness: the SMR in blind with multiple diseases is 1.76 (95% CI = 1.58-1.94; n = 421) versus 0.85 (CI = 0.70-1.0; n = 150) in otherwise healthy blind subjects. In cases where specifically ocular diseases were responsible for the visual loss, the symbol [M] indicates that the blind subject suffered from multiple disease at onset of blindness and [E] denotes that this was not the case. The SMRs for main causes of blindness are: macular degeneration [M] 1.5 (CI = 1.3-1.8; n = 123), [E] 1.1 (CI = 0.8-1.5; n = 43); glaucoma [M] 1.6 (CI = 1.3-2.1; n = 65), [E] 1.0 (CI = 0.6-1.5; n = 26); high myopia [M] 1.2 (CI = 0.8-1.7; n = 32), [E] 0.8 (CI = 0.5-1.2; n = 21); optic atrophy [M] 1.1 (CI = 0. 6-1.8; n = 19), [E] 1.4 (CI = 0.4-3.2; n = 4), and tapetoretinal degeneration [M] 2.3 (CI = 1.1- 4.2; n = 10), [E] 0.9 (CI = 0.4-1.8; n = 12). The SMR of cases of blindness in conjunction with other diseases was fairly high for diabetic retinopathy: 5.5 (CI = 4.4-6. 8; n = 81). Central-nervous-system-triggered blindness led to an SMR of 1.5 (CI = 1.0-2.2; n = 37). DISCUSSION: According to the results of the present study mortality is significantly increased in blind subjects. However, increased mortality in cases of blindness due to specifically ocular disease (e.g. macular degeneration) is associated with the presence of multiple (extra-ocular) diseases at onset of blindness.

Adolescent↗
PubMed2001

Blindness in the Indian state of Andhra Pradesh.

PURPOSE: To determine the current prevalence and causes of blindness in the Indian state of Andhra Pradesh to assess if blindness has decreased since the last survey of 1986-1989. METHODS: A population-based epidemiology study, using a stratified, random, cluster, systematic sampling strategy, was conducted in the state of Andhra Pradesh in India. Participants of all ages (n = 10,293), 87.3% of the 11,786 eligible, from 94 clusters in one urban and three rural areas representative of the population of Andhra Pradesh, underwent interview and a detailed dilated ocular evaluation by trained professionals. Blindness was defined as presenting distance visual acuity < 6/60 or central visual field < 20(o) in the better eye. RESULTS: Two hundred seventy-five participants were blind, a prevalence of 1.84% (95% confidence interval, 1.49%-2.19%) when adjusted for the age, sex, and urban-rural distribution of the population in 2000. The causes of this blindness were easily treatable in 60.3% (cataract, 44%; refractive error, 16.3%). Preventable corneal disease, glaucoma, complications of cataract surgery, and amblyopia caused another 19% of the blindness. Blindness was more likely with increasing age and decreasing socioeconomic status, and in female subjects and in rural areas. Among the 76 million population of Andhra Pradesh, 714,400 are estimated to have cataract-related blindness (615,600 cataract, 53,200 cataract surgery-related complications, 45,600 aphakia), and 228,000 refractive error-related blindness (159,600 myopia, 22,800 hyperopia, 45,600 refractive error-related amblyopia). If 95% of the cataract and refractive error blindness in Andhra Pradesh had been treated effectively, 3.4 and 7.4 million blind-person-years, respectively, could have been prevented. If 90% of the blindness due to preventable corneal disease and glaucoma had been prevented, another 2.7 million blind-person-years could have been prevented. CONCLUSIONS: The prevalence of blindness in this Indian state has increased from 1.5% in the late 1980s to 1.84% currently, as against the target of the National Program for Control of Blindness to reduce the prevalence to 0.3% by 2000. The number of people with cataract-related blindness has not reduced even with the eye care policy focus on cataract. Reduction of blindness in India will require strategies that are more effective than those that have been pursued so far.

Adolescent↗
PubMed2002

[Prevalence of blindness among adults aged 40 years or above in Linzhou county of Lasa].

OBJECTIVE: To estimate the prevalence of blindness among older adults aged >/= 40 years in Linzhou county, Lasa, China. METHODS: Cluster sampling was used in randomly selecting individuals aged >/= 40 years in 44 villages in Linzhou county in May, 2000. A total of 3 153 individuals were examined for visual acuity and eye condition. The prevalence of blindness was calculated according to the pinhole vision with WHO blindness criterion (criterion A) and presenting vision with blindness criterion (criterion B). RESULTS: The individuals examined were enumerated. The response rate was 97.4% (3 071/3 153). When the bilateral pinhole vision < 3/60 was defined as the blindness criterion, the prevalence of blindness was 2.3% [95% confidence interval (CI), 1.8 - 2.8]. The blindness prevalence was increased with age (P < 0.001). Men had a higher prevalence of blindness than women (P > 0.05). After adjusting for age, the difference had statistical significance (P < 0.05). Prevalence of blindness was higher among the illiterate persons than among those with 1 or more years of schooling (P < 0.001). But after adjusting for age, the difference had no statistical significance (P > 0.05). When the bilateral presenting vision < 6/60 was defined as the blindness criterion, the prevalence of blindness was 3.2% (95% CI, 2.6 - 3.8). The blindness prevalence was increased with age (P < 0.001). Men had a higher prevalence of blindness than women. The crude male-to-female odds ratio for moderate and severe blindness was 1.17 (P > 0.05). After adjusting for age, the difference had no significance too (P > 0.05). Prevalence of blindness was higher among the illiterate persons than among those with 1 or more years of schooling (P < 0.001). But after adjusting for age, the difference had no statistical significance (P > 0.05). CONCLUSIONS: The prevalence of blindness is higher in the area of plateau. The principal cause of blindness is cataract.

Adult↗
PubMed2003

Blindness in patients with treated open-angle glaucoma.

PURPOSE: To investigate blindness in patients with treated open-angle glaucoma (OAG) and risk factors for blindness. DESIGN: Retrospective observational case series. PARTICIPANTS: One hundred eighty-six patients seen between April and November 2000 at the University of Washington Medical Center Eye Clinic, diagnosed in 1975 or later, and treated for at least 2 years for OAG. METHODS: Chart review with evaluation of visual acuity and visual field. Kaplan-Meier survival analysis was used to estimate the risk of blindness in one and both eyes. Variables considered to be possible risk factors for blindness were evaluated using chi-square test, t test, and Cox proportional hazards regression analysis. MAIN OUTCOME MEASURES: Blindness, defined as visual acuity of 20/200 or worse, and/or continuous constriction of the visual field to 20 degrees or less in all four quadrants with a size III4e Goldmann stimulus or the equivalent on automated perimetry, allowing a higher threshold level on one point in one quadrant on automated perimetry. RESULTS: The mean duration of disease was 10.2 +/- 4.9 years. Twelve patients were blind in at least one eye from OAG at diagnosis. Nineteen other patients became blind in at least one eye from OAG, and three patients became bilaterally blind from OAG. The Kaplan-Meier estimate for blindness at 15 years in one eye was 14.6%, and in both eyes was 6.4%. Noncompliance with the treatment regimen (P = 0.016) and worse initial visual field loss (P < 0.0001) were significantly associated with development of blindness. Nonwhite race was associated with blindness (P = 0.014) when all blindness, including that found at diagnosis, was considered in the analysis. CONCLUSIONS: Bilateral blindness from chronic OAG was uncommon in this population of treated patients diagnosed in 1975 or later. Of patients with a blind eye, 39% were blind at diagnosis, and worse visual field loss at diagnosis and noncompliance were associated with development of blindness.

Blindness↗
PubMedDate not supplied

Perceived length across the physiological blind spot.

Objects falling across the physiological blind spot appear "complete" despite the absence of photoreceptors. Completion of objects may occur across the blind spot because (1) the blind spot is filled in with the background (the associative explanation); (2) the opposite sides of the blind spot may be contiguously represented in the cortex (i.e. the blind spot is simply sewn up-the retinotopic explanation); or (3) the blind spot may be sewn up, with compensatory expansion occurring around the blind spot (the compensation explanation). These theories would predict no size distortions regardless of object size; constant size distortions regardless of object size; and distortions that depend on the size of the object, respectively. To evaluate these explanations, we measured size distortions at the blind spot. We measured length distortions at the blind spot using a criterion-free two-alternative forced-choice method with feedback. Observers compared the lengths of test bars presented across the blind spot with lengths of reference bars presented at the corresponding location in the fellow eye. Test bar lengths ranged from 7-14 deg. Reference bar lengths were in the range of +/- 3 deg of test bar length. From the observers' responses the perceived length of each bar at the blind spot was estimated. Estimates of the precision of length discrimination at the blind spot were also obtained. Our results were consistent with the associative explanation. In all seven observers, length distortions at the blind spot were smaller than 1 deg (< 20% of the vertical height of the blind spot) for all bar lengths tested. For bars that were presented across the blind spot, the precision with which observers could discriminate length was comparable to that of normal periphery (Weber fraction approximately 20%). Both the veridicality and precision of perceived length are preserved around the blind spot.

Distance Perception↗
PubMed2006

Methods of blinding in reports of randomized controlled trials assessing pharmacologic treatments: a systematic review.

BACKGROUND: Blinding is a cornerstone of therapeutic evaluation because lack of blinding can bias treatment effect estimates. An inventory of the blinding methods would help trialists conduct high-quality clinical trials and readers appraise the quality of results of published trials. We aimed to systematically classify and describe methods to establish and maintain blinding of patients and health care providers and methods to obtain blinding of outcome assessors in randomized controlled trials of pharmacologic treatments. METHODS AND FINDINGS: We undertook a systematic review of all reports of randomized controlled trials assessing pharmacologic treatments with blinding published in 2004 in high impact-factor journals from Medline and the Cochrane Methodology Register. We used a standardized data collection form to extract data. The blinding methods were classified according to whether they primarily (1) established blinding of patients or health care providers, (2) maintained the blinding of patients or health care providers, and (3) obtained blinding of assessors of the main outcomes. We identified 819 articles, with 472 (58%) describing the method of blinding. Methods to establish blinding of patients and/or health care providers concerned mainly treatments provided in identical form, specific methods to mask some characteristics of the treatments (e.g., added flavor or opaque coverage), or use of double dummy procedures or simulation of an injection. Methods to avoid unblinding of patients and/or health care providers involved use of active placebo, centralized assessment of side effects, patients informed only in part about the potential side effects of each treatment, centralized adapted dosage, or provision of sham results of complementary investigations. The methods reported for blinding outcome assessors mainly relied on a centralized assessment of complementary investigations, clinical examination (i.e., use of video, audiotape, or photography), or adjudication of clinical events. CONCLUSIONS: This review classifies blinding methods and provides a detailed description of methods that could help trialists overcome some barriers to blinding in clinical trials and readers interpret the quality of pharmacologic trials.

Double-Blind Method↗
PubMed1998

An ethnographic study of night blindness "ratauni" among women in the Terai of Nepal.

Night blindness is the most common ocular condition representing moderate-to-severe vitamin A deficiency in children. Very little, however, is known about maternal night blindness, which has recently been reported to occur frequently during pregnancy in parts of south-east Asia. In Nepal, the prevalence of night blindness is reported to be 16%. We carried out an ethnographic study of night blindness during pregnancy in the south-eastern, rural plains of Nepal as preliminary research for a case-control study of the determinants of this condition. The purpose of the research was to identify local terms and concepts of night blindness and to examine women's perceptions of its causes, symptoms, severity, and consequences during pregnancy. Data collection involved in-depth interviews, case studies, unstructured observations and structured anthropologic methods, such as free listing and quick sort ranking. Women considered night blindness to be an important illness of pregnancy, ranking it second (to vaginal bleeding) in perceived severity from a list of 15 "women's illnesses". Local terms for night blindness were identified in three different languages from the region. Informants described a complex ethnomedical model of night blindness that included causes, symptomatology, and treatment alternatives. However, there was no perceived link between food intake and the occurrence of night blindness. The major causes of night blindness were attributed to pregnancy, weakness, or "hotness". Some women sought treatment for the condition but most women chose not to treat it since they believed that it was a transient condition of pregnancy. Interviews with women who had previously experienced night blindness and home-based observations of women exhibiting concurrent night blindness showed that it adversely affected their activity patterns, especially those related to child care and food preparation. Night blindness increased reliance on family members to perform various domestic chores and was also associated with personal injury and accidents. The findings of this study have relevance for women's reproductive health and nutrition throughout the Indian sub-continent. A simple history of night blindness may be a practical tool to identify women with nutritional and health risks. Maternal night blindness should be more routinely investigated in vitamin A deficient areas of the world, both to define the magnitude of the problem, and to develop programs/interventions that specifically target this population.

Anthropology, Cultural↗
PubMedDate not supplied

[Ocular disorders causing blindness in working-age outpatients: a prospective study at the African Institute of Tropical Ophthalmology (IOTA, Bamako, Mali)].

UNLABELLED: The objective of this study was to determine the different groups of ocular disorders causing low vision or blindness among working-age patients consulting at the African Institute of Tropical Ophthalmology (IOTA) in Bamako, Mali. METHODS: This prospective study took place from 1 February through 8 April, 2003, at IOTA. It included all new patients aged between 18 and 50 years, regardless of whether they worked, but excluding students. RESULTS: 828 patients were recruited: 384 men (46.4%) and 444 women (53.6%). The average age was 35.7 years. The rate of bilateral blindness was 5.8%, of low vision 8.5%, and of blindness in one eye 11.5%. Men and women did not differ significantly in rates of bilateral blindness (p = 0.77) or low vision (p = 0.24), but blindness in a single eye affected men (67.4%) more often than women (32.6%, p = 0.01). While the frequency of bilateral blindness and low vision increased with age, blindness in one eye affected all ages. We observed no significant differences according to ethnic group in the prevalence of bilateral blindness and low vision, both observed most frequently among housewives, farmers and low-income workers, most illiterate. The major causes of bilateral blindness were cataracts 29.2%, glaucoma 22.9%, trachoma 14.6%, ocular manifestations linked to HIV/AIDS 8.3%, and non-glaucomatous optical neuropathies 8.3%. Half the cases (50.5%) of blindness in one eye resulted from ocular trauma, and five cases from HIV/AIDS (5.3%). Low vision resulted from impaired refraction 22.9%, cataract 17.2%, trachoma 15.7%, glaucoma 10% and corneal opacities 5.7%. DISCUSSIONS: The high rate of blindness and low vision are associated with the study site: a reference center whose population was composed completely of patients with vision problems. The causes of blindness and low vision have not changed over time except for the ocular manifestations of HIV/AIDS, which is among the most important current causes of blindness, because of the lack of antiretroviral treatments in sub-Saharan Africa. If nothing stops this pandemic, it will soon modify epidemiological data about blindness. CONCLUSION: Blindness and visual deficiencies, already a public health problem, will become an important socioeconomic burden in sub-Saharan Africa and may even stop progress among low-income countries.

Adolescent↗
PubMed2001

The prevalence and causes of bilateral and unilateral blindness in an elderly urban Danish population. The Copenhagen City Eye Study.

PURPOSE: To study the prevalence and causes of bilateral and unilateral blindness in an elderly urban Danish population. METHODS: Data originated from a Danish epidemiologic cross-sectional random sample population eye survey conducted during the years 1986-1988. The population consisted of 1,000 inhabitants aged 60 to 80 years in Copenhagen. The participants underwent an extensive ophthalmologic examination. A participation rate of 96.9% was achieved. Any blindness was defined as best-corrected visual acuity (VA) worse than 0.05 (the WHO criteria) and VA of 0.1 or worse (the National criteria (NC) of blindness). RESULTS: The prevalence rates of bilateral and unilateral blindness were, respectively, 0.53% and 3.38% according to WHO, but 1.06% and 4.44% using NC. Bilateral blindness rose significantly with age (p=0.02). According to NC, age-related macular degeneration (AMD) was the leading cause of bilateral blindness, accounting for 60% of all blind persons. Glaucoma, myopic macular degeneration, cataract and retinitis pigmentosa were jointly the second most common cause, each accounting for 10% of all bilaterally blind persons. Diabetic retinopathy was not a cause of bilateral blindness. Amblyopia was the most frequent, AMD the second most frequent, and diabetic retinopathy was among the third most common cause of unilateral blindness accounting for, respectively, 28.60%, 16.66% and 9.52% of all unilateral blindness. CONCLUSIONS: Blindness was associated with increasing age. A calculation indicates that among Danes aged 60 to 80 years 7,736 are bilaterally blind and 35,503 suffer from unilateral blindness. This study highlights AMD as the most important cause.

Aged↗