The National Blindness and Low Vision Prevalence Survey of Bangladesh: Research design, eye examination methodology and results of the pilot study

Abstract

PURPOSE To describe the research design and eye examination protocol of The National Blindness and Low Vision Prevalence Survey of Bangladesh and to present the main results of the rural pilot study. METHODS A thorough description of the sampling strategy, eye examination protocol and operational definitions are presented. Multi-stage stratified (rural/urban) cluster random sampling, with probability proportional-to-size procedures, will be used for selection of a cross-sectional, nationally representative sample (12,900 subjects) of the population aged > or = l30 years. Each subject will be tested for visual acuity, auto-refracted and undergo optic disc examination. Those with <6/12 visual acuity in either eye will be re-tested with their refractive correction, dilated and examined for anterior and posterior segment disease. A preliminary, separate rural pilot survey sample was conducted according to the eye examination procedures, with results reported herein. RESULTS Two-hundred-and-four (73.1%) of 279 eligible subjects were examined for the rural pilot. Forty-eight persons had presenting visual acuity worse than 6/12 in either eye. The presenting visual acuity of the better eye was used to group the subjects into the following WHO categories (brackets enclose the number of subjects after refractive correction): Blind: 4 [4]; Visually impaired: 29 [14]; Sighted: 171 [186], of whom 3 [3] were unilaterally blind. Cataract was the main cause of visual acuity of less than 6/12, followed by refractive error, and age-related macular degeneration. CONCLUSIONS The pilot survey demonstrated that the proposed examination process for the main survey was both feasible and appropriate for the purposes of this study. Particular strengths of the pilot and subsequent main survey include the use of logMAR visual acuity testing and auto-refraction of all subjects. The pilot study reveals the burden of cataract and refractive error, which are two of the five diseases specifically targeted by the WHO global blindness initiative 'Vision 2020'.

Prevalence, Causes, and Risk Factors for Functional Low Vision in Nigeria: Results from the National Survey of Blindness and Visual Impairment

“…These charts have been used in other national surveys of visual impairment (Bangladesh and Pakistan surveys). 17,18 VA was measured in a shaded area outdoors and individuals who could not read at least two letters on the top line of the chart at 4 meters were retested at 1 meter. Those who could not read any letters at 1 meter were tested for counting fingers, hand movements, and perception of light by an ophthalmologist.…”

The Pakistan National Blindness and Visual Impairment Survey—Research Design, Eye Examination Methodology and Results of the Pilot Study

“…21 Prior to this study, the chart had been extensively validated in clinic-based 22 and population-based studies 23 in advance of its use in the National Blindness and Low Vision Survey of Bangladesh. 3,4 The RLM chart is based on the illiterate E, a necessity in a population with only 47% adult literacy. The 'E' optotypes are arranged according to the logMAR scale with three letters per line, each with a different directional orientation.…”

“…Following several years of implementing expanded eye care services in Pakistan, it was felt for a number of reasons that a more detailed survey was required. A survey with more diagnostically rigorous methodology was needed, with one which would detect diseases of the posterior segment, the importance of which has been highlighted in two recent low vision and blindness surveys in Bangladesh 3,4 and India. 5−7 Based on the results of the original survey, the eye services were adapted to meet the identified need for expanded cataract surgical service delivery.…”

Rapid assessment of avoidable blindness and needs assessment of cataract surgical services in Satkhira District, Bangladesh

“…2 A nationally representative sample of 11 624 adults aged >30 years underwent detailed ophthalmic examination, of whom 1.4% were blind (95% confidence intervals (CI) 1.2% to 1.6%), most of which was due to cataract. 3 The prevalence of blindness in the poorest divisions was twice as high as that in the richest divisions.…”