***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 Dry eye syndrome ( DES ) is believed to be one of the most common ocular problems in the United States ( US ) , particularly among older women . However , there are few studies describing the magnitude of the problem in women and how this may vary with demographic characteristics . DESIGN Cross-sectional prevalence survey . METHODS STUDY POPULATION we surveyed 39,876 US women participating in the Women 's Health Study about a history of diagnosed DES and dry eye symptoms . MAIN OUTCOME MEASURE we defined DES as the presence of clinical ly diagnosed DES or severe symptoms ( both dryness and irritation constantly or often ) . We calculated the age-specific prevalence of DES and adjusted the overall prevalence to the age distribution of women in the US population . We used logistic regression to examine associations between DES and other demographic factors . RESULTS The prevalence of DES increased with age , from 5.7 % among women < 50 years old to 9.8 % among women aged > or = 75 years old . The age-adjusted prevalence of DES was 7.8 % , or 3.23 million women aged > or = 50 in the US . Compared with Whites , Hispanic ( odds ratio [ OR ] = 1.81 , confidence interval [ CI ] = 1.18 - 2.80 ) and Asian ( OR = 1.77 , CI = 1.17 - 2.69 ) women were more likely to report severe symptoms , but not clinical ly diagnosed DES . There were no significant differences by income ( P([trend ] ) = .78 ) , but more educated women were less likely to have DES ( P([trend ] ) = .03 ) . Women from the South had the highest prevalence of DES , though the magnitude of geographic differences was modest . CONCLUSIONS Dry eye syndrome leading to a clinical diagnosis or severe symptoms is prevalent , affecting over 3.2 million American women middle-aged and older . Although the condition is more prevalent among older women , it also affects many women in their 40s and 50s . Further research is needed to better underst and DES and its impact on public health and quality of life Purpose To study the prevalence and associations of dry eye symptoms in adult Chinese . Methods The Beijing Eye Study is a population -based study in northern China , which included 4439 of 5324 subjects invited to participate with an age of 40 + years ( response rate : 83.4 % ) . For the present study , a r and om sample was taken consisting of 1957(44.1 % ) subjects ( 1112 women ; 56.9 % ) .  Dry eye symptoms were evaluated with ( 1 ) an  interviewer-assisted question naire ; ( 2 )  measurement of the tear-film break-up time ; ( 3 ) assessment of the fluorescein staining of the cornea ; ( 4 ) slit-lamp-based examination of a meibomian gl and dysfunction ;  and ( 5 ) Schirmer 's test .  Results Symptoms of a dry eye felt ‘ often ’ or ‘ at all times ’ were present in 411 subjects ( 21.0 % ) . In a multivariate analysis , dry eye symptoms were significantly associated with age ( P<0.001 ) , female gender ( P<0.001 ; odds ratio ( OR ) : 1.56 ; 95 % confidence intervals ( CI ) : 1.23 , 1.98 ) , urban region ( P<0.001;OR : 1.89 ; 95 % CI : 1.46 , 2.48 ) , low degree of nuclear cataract ( P=0.02 ) , and undercorrection of refractive error ( P=0.005 ; OR : 1.42 ; 95 % CI : 1.11 , 1.82 ) . All tests for dry eye did not vary significantly between the dry eye group and the normal group . Conclusions The dry eye symptoms as evaluated subjectively in a question naire occurred in about 21 % of the adult population in China , with associations to age , female gender , urban region , and undercorrection of a refractive error . Measurement of the tear-film break-up time , assessment of the corneal fluorescein staining , slit-lamp-based examination of a meibomian gl and dysfunction , and Schirmer 's test were not significantly associated with dry eye symptoms Purpose : To determine the prevalence of dry eye syndrome , analyze the relationship between dry eye symptoms and signs , and identify associated risk factors for dry eye syndrome in an elderly Tibetan population at high altitude . Methods : A population -based survey was conducted from October 2006 to December 2006 . A stratified , clustered , r and om sampling procedure was used to select 2632 native Tibetan people ≥40 years of age . Symptoms of dry eye were assessed by using a 6-item vali date d question naire . Dry eye syndrome was diagnosed in those subjects having 1 or more symptoms often or all the time . Positive signs included a tear film breakup time of ≤10 seconds in 1 or both eyes , a Schirmer test score of ≤5 mm , or a fluorescein score of ≥1 . Correlations between symptoms and signs were analyzed . Results : Of a total of 2632 eligible subjects , 2229 ( 84.69 % ) were examined . The data of 1840 participants were analyzed . Of 1840 participants , 52.4 % ( 95 % confidence interval : 50.2 - 54.7 ) were symptomatic . The tear film breakup time of ≤10 seconds was seen in 35.3 % ( 95 % confidence interval : 33.1 - 37.5 ) , a Schirmer test score of ≤ 5 mm was seen in 24.7 % ( 95 % confidence interval : 22.8 - 26.7 ) , and a fluorescein score of ≥1 was seen in 5.8 % ( 95 % confidence interval : 4.7 - 6.9 ) . The correlations between dry eye symptoms and signs were statistically significant . Independent risk factors for dry eye syndrome were positive dry eye signs , increased age , low education level and socioeconomic status , and higher altitude . Conclusions : This study shows a high prevalence rate of dry eye syndrome in elderly Tibetans , representing an important health problem OBJECTIVE To evaluate the prevalence of and risk factors for dry eye disease ( DED ) in an elderly Korean population . METHODS This population -based study in Yongin , Korea , included 657 individuals 65 years or older r and omly selected from an official household registration data base .  Dry eye symptoms were assessed using a 6-item question naire , and DED was defined as having 1 or more dry eye symptoms often or all the time .  Dry eye tests  , including the Schirmer test , tear film break-up time measured using fluorescein , cornea fluorescein staining , and examination for meibomian gl and dysfunction  , were performed . RESULTS The crude prevalence of DED was 30.3 % , and the age- , sex- , and region ( urban vs rural)-adjusted prevalence was 33.2 % . Women ( P = .01 ) and urban dwellers ( P = .001 ) were more likely to have DED . Of those with DED , 85.1 % had tear film break-up time of 10 seconds or less , 54.1 % had meibomian gl and dysfunction , 39.2 % had a fluorescein score of 1 or greater , and 32.8 % had a Schirmer test score of 5 mm or less . A low Schirmer score was correlated with increased prevalence of DED , although sensitivity was low . CONCLUSIONS Dry eye disease is common in elderly Koreans ; female sex and living in an urban region were strongly correlated with its frequency . We also noted a positive correlation between low Schirmer test scores and symptom-based DED OBJECTIVE To investigate the prevalence of dry eye in population s equal or over 20 years old in Jiangning District , Shanghai , China . METHODS This was a cross-sectional study . From September 2008 to January 2009 , 6 small districts including 21,102 people of Jiangning District were r and omly selected as survey venues by Department of Ophthalmology in First People 's Hospital affiliated to Shanghai Jiaotong University . Then , 1266 people as the selected residents were enrolled , which was figured out through the r and om cluster sampling procedure . Every participant completed  dry eye question naire , the  ocular surface disease index ( OSDI ) , and a series of examination including slit-lamp microscope , tear-film break-up time ( BUT ) , Schirmer I test , and fluorescein staining of the cornea ( F1 ) .  The diagnosis of dry eye was referred to the well-accepted domestic diagnostic criteria The SPSS11 . 0 software was used to analyze the data base , t . test , chi2 test , one-way-ANOVA and Logistic regression were used for analysis . RESULTS One thous and and eighty five residents finally took part in this study , and the inclusion ratio was 85.70 % . Three hundred and twenty six individuals , including 101 men and 225 women , were diagnosed as dry eye , and the prevalence rate was 30.05 % . The prevalence of dry eye in the female ( 33.78 % ) was higher than that of the male ( 24.11 % ) ( chi2 = 11.46 , P < 0.01 ) . The prevalence of dry eye in people over 50 years old was higher than that under 50 years ( chi2 = 94.50 , P < 0.01 ) . The figure of Schirmer I test and BUT decreased in elder people , at the same time the scores of Fl and MGD increased . Meanwhile , the score of OSDI in dry eye patients was significantly higher than that in non-dry eye individuals . The relative risk factors of dry eye were gender , age , wearing contact lens , long-time using of eye solutions , taking anti-allergy drugs . CONCLUSIONS The prevalence of dry eye in female is higher than that in the male . And the prevalence of dry eye increases following the aging process . Relative risk factors of dry eye are gender , age , wearing contact lens , long-time using of eye solutions , taking anti-allergy drugs 
    Output:
    
Patients with diabetes were also found to be more vulnerable to DES .
The pooled prevalence rate of DES in mainl and China was lower than that in other Asian regions and countries .
A remarkable discrepancy in the prevalence in different geographic regions was noted .
Aging , female gender , and diabetes were found to be risk factors for DES in China