***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: 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 r and om 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 OBJECTIVE To perform a reference case cost-utility analysis of  second-eye cataract surgery  by using the current literature on cataract outcomes and complications . DESIGN Computer-based econometric modeling . METHODS Visual acuity data of patients treated and observed over a 4-month postoperative period were obtained from the U.S. National Cataract Patient Outcomes Research Team report . The results from this prospect i ve study were combined with those of other studies that investigated the complication rates of cataract surgery to complete the cohort of patients and outcomes . These synthesized data were incorporated with time trade-off utility values , which accounted for prior successful cataract surgery in the fellow eye . Cost-utility determinations were made with decision analysis , and present value modeling was used to account for the time value of money and health state consequences . MAIN OUTCOME MEASURES The number of quality -adjusted life-years ( QALYs ) gained was calculated for the study group undergoing second-eye cataract surgery  , assuming that the postoperative vision in the second eye was equivalent to the vision in the first eye after surgery ( 20/27 ) . This was divided into the cost of the procedure to find the number of year 2001 nominal U.S. dollars spent per QALY gained . RESULTS Second-eye cataract surgery , as compared with unilateral pseudophakia , result ed in a mean gain of 1.31 undiscounted QALYs per patient treated . A 3 % annual discount rate , dependent on the duration of benefit , was used , yielding 0.92 discounted QALYs gained over a 12-year life expectancy . The mean discounted cost of treatment for each patient totaled 2509 US dollars . The cost divided by the QALYs gained ( benefit ) result ed in 2727 US dollars per QALY gained for this procedure . Sensitivity analysis varying costs and utility values revealed a range from 2045 US dollars to 3649 US dollars per QALY gained . CONCLUSIONS Second-eye cataract surgery is an extremely cost-effective procedure when compared with other interventions across medical specialties . The cost-effectiveness of second-eye surgery diminishes only slightly from the 2023 US dollars per QALY gained from first-eye cataract surgery . This suggests that patients with good vision in one eye and visual loss from cataract in the fellow eye derive substantial benefit from cataract extraction R and om sample s of people aged 40 years and over were drawn from lists of patients registered with two neighbouring inner-city general practice s : one predominantly with Asian patients and the other predominantly with European patients . The people selected were invited to attend specially arranged eye clinics for examination by an ophthalmologist and an optician . We examined 377 people and found that , compared to people of European descent , Asians had a significantly higher prevalence of age-related cataract : 30 % compared to 3 % in people aged under 60 years and 78 % compared to 54 % in those aged 60 years and over . The age of onset of cataract seems to be earlier in Asians . After adjustment for age , there were no statistically significant ethnic differences in the prevalences of open-angle glaucoma , macular degeneration or diabetic retinopathy AIMS A population based cross sectional survey was conducted to determine the magnitude of cataract blindness and the barriers to uptake of  cataract services  in a rural community of northern Nigeria . METHODS 1461 people out of 1924 registered eligible people were examined . The study population was chosen by two stage cluster r and om sampling . In the first sampling stage 15 villages were r and omly chosen while in the final stage 170 people who were 40 years and over were selected in each village . Each selected person had visual acuity recorded for both eyes . Those with vision of less than 3/60 in the better eye were assessed for cataract . People with cataract were asked why they had not sought medical attention . RESULTS A blindness prevalence of 8.2 % ( 95 % CI 5.8%–10.5 % ) was found among the sample d population . Cataract was responsible for 44.2 % of the blindness . Thus , a cataract blindness prevalence of 3.6 % was found . The  cataract surgical coverage ( people ) was 4.0 % and the couching coverage ( people ) was 18 % . The main barrier to seeking cataract surgery was cost of the service ( 61 % ) . CONCLUSION Some regions of the world still have high burden of cataract blindness that needs attention . Such areas need an effective free cataract outreach programme OBJECTIVE To estimate the prevalence of cataract , the rate of  cataract surgical coverage rate  , and the rate of cataract-blindness social burden  among older adults aged 50 years or above in Qidong City of Jiangsu Province , China , in 2006 . METHODS Cluster sampling was used in r and omly selected 5662 individuals aged 50 years or above in 16 clusters in Qidong City . 5141 individuals received visual acuity and eye examination from September to December 2006 .  Lens and cataract operation status were evaluated by slit lamp . Multiple logistic regression analysis was employed to analyzed the prevalence of cataract , cataract surgical coverage rate , cataract blindness social burden rate and outcomes of surgery among different ages , sex and educational background . RESULTS In 5141 individuals , 1098 cases of cataract were found , the prevalence of cataract was 21.35 % among adults aged 50 or above . The prevalence of cataract was higher in the aged , female , illiterate persons ( P < 0.01 ) . In 89 eyes with cataract surgery  , 25.84 % and 42.70 % of eyes were performed by the modern extra-capsular surgery and Phacoemulsification respectively . The rate of intraocular lens implantation  was 69 . 66 % . Post-operative presenting and best corrected visual acuity more than 0.7 was 24.70 % and 48.31 % of operated eyes respectively . The main causes of the post-operated eyes with worse visual acuity were retinal disorders post-capsular opacity and glaucoma . The cataract surgical coverage rate was 37.96 % , and the cataract blindness social burden rate was 2.10 % . The cataract blindness social burden rate was higher in the aged persons ( P < 0.01 ) . CONCLUSIONS Cataract is the most common and important eye disease that may lead into blindness and severe visual impairment among older adults aged 50 years or above . The cataract surgical coverage rate is not so high in Qidong City , and even lower in the aged persons . The first important task in blindness prevention still is the elimination of cataract blindness . The visual outcomes of the cataract surgery should be further improved in the future Purpose To describe the prevalence of cataract in older people in 2 areas of north and south India . Design Population -based , cross-sectional study . Participants R and omly sample d villages were enumerated to identify people aged ≥60 years . Of 7518 enumerated people , 78 % participated in a hospital-based ophthalmic examination .  Methods The examination included  visual acuity measurement , dilatation , and anterior and posterior segment examination . Digital images of the lens were taken and grade d by type and severity of opacity using the Lens Opacity Classification System III ( LOCS III ) . Main Outcome Measures Age- and gender-st and ardized prevalence of cataract and 95 % confidence intervals ( CIs ) . We defined type of cataract based on the LOCS III grade in the worse eye of : ≥4 for nuclear cataract , ≥3 for cortical cataract , and ≥2 for posterior subcapsular cataract ( PSC ) . Any unoperated cataract was based on these criteria or ungradable dense opacities . Any cataract was defined as any unoperated or operated cataract . Results The prevalence of unoperated cataract in  people aged ≥60  was 58 % in north India ( 95 % CI , 56–60 ) and 53 % ( 95 % CI , 51–55 ) in south India ( P = 0.01 ) . Nuclear cataract was the most common type : 48 % ( 95 % CI , 46–50 ) in north India and 38 % ( 95 % CI , 37–40 ) in south India ( P<0.0001 ) ; corresponding figures for PSC were 21 % ( 95 % CI , 20–23 ) and 17 % ( 95 % CI , 16–19 ; P = 0.003 ) , respectively , and for cortical cataract 7.6 % ( 95 % CI , 7–9 ) and 10.2 % ( 95 % CI , 9–11 ; P<0.004 ) . Bilateral aphakia/pseudophakia was slightly higher in the south ( 15.5 % ) than in the north ( 13.2 % ; P<0.03 ) . The prevalence of any cataracts was similar in north ( 73.8 % ) and south India ( 71.8 % ) . The prevalence of unoperated cataract increased with age and was higher in women than men ( odds ratio [ OR ] , 1.8 ) . Aphakia/pseudophakia was also more common in women , either unilateral ( OR , 1.2 ; P<0.02 ) or bilateral ( OR , 1.3 ; P<0.002 ) . Conclusions We found high rates of unoperated cataract in older people in north and south India .  Posterior subcapsular cataract was more common than in western studies . Women had higher rates of cataract , which was not explained by differential access to surgery . Financial Disclosure(s ) The authors have no proprietary or commercial interest in any of the material s discussed in this article Purpose To investigate the prevalence and visual acuity ( VA ) outcomes of  cataract surgery in adults of the Bai Nationality population s in rural China . Methods We conducted a population -based cross-sectional survey ( from r and omly selected block groups ) of Chinese Bai Nationality aged ≥50 years in southwestern China . Presenting visual acuity ( PVA ) , best corrected visual acuity ( BCVA ) were recorded and a detailed eye examination was carried out . For all aphakic and pseudophakic subjects identified , information on the date , setting , type , and complications of cataract surgery were recorded . In eyes with VA < 20/63 , the principal cause of visual impairment was identified . Results Of 2133 ( 77.8 % of 2742 ) subjects , 99 people ( 129 eyes ) had undergone cataract surgery . The prevalence of cataract surgery was 4.6 % . Surgical coverage among those with PVA < 20/200 in both eyes because of cataract was 52.8 % . Unoperated cataract was associated with older age . The main barrier to cataract surgery  was lack of awareness and knowledge , cost , and fear . Among the 129 cataract-operated eyes , 22.5 % had PVA of ≥20/32 , 25.6 % had PVA of 20/40 to 20/63 , 23.3 % had PVA < 20/63 to 20/200 , and 28.7 % had PVA<20/200 . With BCVA , the percentages were 42.6 % , 23.3 % , 10.9 % , and 23.3 % , respectively . Aphakia ( odds ratio [ OR ] , 8.49 ; P<0.001 ) and no education ( OR , 10.18 ; P = 0.001 ) or less education ( OR , 6.49 ; P = 0.014 ) were significantly associated with postoperative visual impairment defined by PVA , while aphakia ( OR , 8.49 ; P<0.001 ) and female gender ( OR , 4.19 ; P = 0.004 ) were significantly associated 
    Output:
    
Conclusions The prevalence of cataract and cataract blindness  in China was unmasked .