The Pakistan National Blindness and Low Vision Prevalence Survey – research design, eye examination protocol and results of the pilot study

Abstract

Abstract: : Purpose: To identify the age– and sex–specific prevalence percentages and the causes for blindness and low vision in adults aged 30 years of age and older in Pakistan. Methods: A nationally representative sample of adults (16,600 subjects) was selected using multi–stage, stratified (rural/urban), cluster random sampling, with probability proportional–to–size procedures. Each subject underwent: a demographic interview, presenting visual acuity testing with a validated logMAR ‘E’ chart, auto–refraction with keratometry, A–scan ultrasound and optic disc assessment. Those that saw less than 6/12 in either eye underwent: corrected visual acuity and a dilated posterior segment examination. Digital fundus imaging, optic nerve head tomography (HRT–II) and visual field analysis were performed in those subjects further suspected of posterior segment disease. The results of a pilot survey are reported. Results: A total of 164 adult subjects were examined in the two rural pilot sites (82% response rate). Fifty percent of the subjects were male. A sub–total of 37 persons (23.3%) saw worse than 6/12 in either or both eye(s). Two subjects were blind (based on the best corrected visual acuity) in the better eye, and 11 were visually impaired. Refractive error was the main cause of less than 6/12 visual acuity (in 22 eyes (39% of total of 56 eyes)), followed by cataract (12 eyes), uncorrected aphakia (6 eyes) and age–related macular disease (3 eyes). Conclusions: This national blindness and low vision survey is the first of its kind conducted in Pakistan. Particular strengths of this survey include: the large, representative sample, use of reduced logMAR visual acuity testing and auto–refraction of all subjects, a dilated posterior segment examination, and the use of a 'less than 6/12' threshold for further examination. The sampling strategy and examination protocol implemented in the study are indicative of the scientific value of the study; the pilot survey demonstrated the feasibility of the survey despite the comprehensive nature of the eye examinations. The findings regarding the prevalence and causes of visual impairment will be used to further develop eye health service provision in Pakistan in line with the principles of Vision 2020.

Keywords: clinical (human) or epidemiologic studies: prevalence/incidence • clinical (human) or epidemiologic studies: biostatistics/epidemiology methodology • cataract