| [Background] Blindness and low vision are serious public health and social economic problem in the world. Worldwide, an estimated 37 million people are blind, and an additional 124 million are severely visually impaired. According to WHO's statistics,80% of blindness are avoidable. If correct methods are adopted, blindness caused by cataract, refractive error, etc. can be prevented or controlled. Therefore, WHO, international blindness prevention institution and non-government organization proposed a global initiative:vision 2020, the right to sight, to eliminate avoidable blindness of the world in 2020. In many regions of the world, uncorrected refractive error becomes the main reason of visual impairment. By the data of 2008, there are 145 million low vision persons and 8 million blind persons caused by uncorrected refractive error. Our country is one of the most serious blindness and low vision country of the world including 5 million blind persons and 7.1 million low vision persons. The criteria of blindness and low vision according to best-corrected distance visual acuity (BCVA) were introduced by WHO in 1973. The new criteria of blindness and low vision according to presenting distance visual acuity (PVA) were introduced by WHO in 2003.[Purpose] Describe the prevalence of blindness and low vision with presenting and best-corrected distance VA among older adults in rural populations in Tengzhou and Huaiyin.[Design] Population-based, cross-sectional study. [Methods] Geographically defined cluster sampling was used in randomly selecting a cross-section of residents from a representative rural county including Rushan, Tengzhou, Juancheng and Huaiyin within Shandong Province in mainland China. Epidemiological investigation of blindness and low vision among adults aged 50 years and above was carried out in Tengzhou and Huaiyin from April to July,2008. Participants were enumerated through village registers. Eligible persons were invited to local examination sites for visual acuity (VA) testing and eye examination. Main outcome measures were presenting and best-corrected distance VA. Based on WHO's blindness and low vision criteria (1973), bilateral blindness was defined as BCVA of less than 0.05 in both eyes; unilateral blindness was defined as BCVA of less than 0.05 in one eye, equal or more than 0.05 in the other eye; bilateral low vision was defined as BCVA of less than 0.3, equal or more than 0.05 in both eyes; unilateral low vision was defined as BCVA of less than 0.3 and equal or more than 0.05 in one eye, equal or more than 0.3 in the other eye. Prevalence and causes of bilateral and unilateral blindness and low vision were respectively calculated and analyzed based on BCVA and PVA criteria.Of 8933 enumerated eligible persons,7956 (89.06%) were examined and tested for VA. Based on criteria of BCVA, the prevalence of bilateral blindness, unilateral blindness, bilateral low vision and unilateral low vision were 1.34%,4.47%,1.97% and 4.27%, respectively. Bilateral and unilateral blindness and low vision were associated with older age with best-corrected VA(P<0.01). There were no differences in prevalence of bilateral blindness, unilateral blindness and unilateral low vision among male and female (P>0.05). The prevalence of bilateral low vision was higher in female than male (P<0.05). There were no differences in prevalence of bilateral blindness and bilateral low vision between Tengzhou and Huaiyin (P>0.05). The prevalence of unilateral blindness and unilateral low vision in Tengzhou were significantly higher than in Huaiyin (P<0.01). The first five causes of bilateral blindness were cataract, corneal opacity, glaucoma, macular degeneration, optic atrophy; the first five causes of unilateral blindness were cataract, corneal opacity, eyeball absence or atrophy, refractive error and amblyopia, macular degeneration; the fist five causes of bilateral low vision were cataract, refractive error and amblyopia, macular degeneration, optic atrophy, other retinal and choroidal disorders; the first five causes of unilateral low vision were cataract, refractive error and amblyopia, macular degeneration, corneal opacity, optic atrophy.With presenting VA, the prevalence of bilateral blindness, unilateral blindness, bilateral low vision and unilateral low vision were 1.58%,5.09%,3.51%,6.83%, respectively. Bilateral and unilateral blindness and low vision were associated with older age with presenting VA (P<0.01). There were no differences in prevalence of bilateral blindness and unilateral low vision among male and female (P>0.05). The prevalence of unilateral blindness and bilateral low vision were higher in female than male (P<0.05). There were no differences in prevalence of bilateral blindness between Tengzhou and Huaiyin (P>0.05). The prevalence of unilateral blindness, bilateral low vision and unilateral low vision in Tengzhou were higher than in Huaiyin (P<0.05). The first five causes of bilateral blindness were cataract, corneal opacity, macular degeneration, refractive error and amblyopia, glaucoma; the first five causes of unilateral blindness were cataract, refractive error and amblyopia, corneal opacity, eyeball absence or atrophy, macular degeneration; the first five causes of bilateral low vision were cataract, refractive error and amblyopia, macular degeneration, optic atrophy, other retinal and choroidal disorders; the first five causes of unilateral low vision were refractive error and amblyopia, cataract, macular degeneration, corneal opacity, optic atrophy.There were no differences in prevalence of bilateral blindness and unilateral blindness between best-corrected VA and presenting VA (P>0.05). The prevalence of bilateral low vision and unilateral low vision based on presenting VA were significantly higher than those based on best-corrected VA (P<0.01).[Conclusion] Among older adults in rural populations in Tengzhou and Huaiyin, the prevalence of blindness and low vision was associated with older ages. Blindness prevention programs targeting the rural elderly should be expanded. Cataract was the leading cause of bilateral and unilateral blindness and low vision with best-corrected VA, and was the leading cause of bilateral and unilateral blindness, bilateral low vision with presenting VA. While refractive error and amblyopia were the leading cause of unilateral low vision with presenting VA. Greater attention should also be given to correction of refractive error.
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