dry eye is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort , visual disturbance , and tear film instability with potential damage to the ocular surface . dry eye could be either a separated clinical entity or a condition associated with other systemic or ocular surface diseases . currently , it belongs to the most frequently encountered ocular problems in clinical practice . as the definition of dry eye is still under constant revision , the lack of a the international dry eye workshop recommended confirming the diagnosis of dry eye based on a combination of symptoms and objective clinical tests . accordingly , the chinese diagnostic criteria of dry eye were published by the corneal disease study group of chinese ophthalmological society in 2013 , offering a more defined standard . the subjective symptoms of dry eye , along with certain risk factors , were advised to be screened by validated questionnaires . as one of the most long - standing instruments , the mcmonnies questionnaire is widely used in numerous prevalence studies [ 46 ] and clinical trials [ 79 ] . it contains 14 questions that revolve around the risk factors of dry eye , including age , gender , previous dry eye treatments , dry eye - related symptoms ( both primary and secondary to environmental triggers ) , and systemic conditions associated with dry eye ( dryness of mucous membranes , arthritis , thyroid disease , and medication use ) . previous analyses [ 1114 ] revealed varying values of sensitivity ( 34%98% ) and specificity ( 36%97% ) for the mcmonnies questionnaire . moreover , this instrument was originally devised from a sample of australian women aged above 45 years with or without keratoconjunctivitis sicca syndrome [ 10 , 11 ] . subsequent studies [ 1214 ] evaluating the reliability and validity of the instrument continued to focus on non - asian populations . thus , it is anticipated that variations in the diagnostic efficacy are likely to occur when applying the instrument to a chinese cohort . therefore , we carried out a study in multiple ophthalmological centers across china to investigate the diagnostic performance of the mcmonnies questionnaire as a screening survey for dry eye in chinese outpatients . the study was carried out in 94 ophthalmological centers , distributed in 45 cities , 23 provinces across china . consecutive outpatients in general eye clinics were enrolled from july to november , 2013 , if they presented with one or more of the following chief complaints : dryness , grittiness , burning sensation , tiredness , soreness , and visual disturbance . participants are excluded if they exhibited any active infection of the eye , evidence of ocular chemical or thermal burn , ocular surgeries within 6 months before the screening , and pregnancy or lactation . the research was approved by peking university third hospital medical ethics committee and consistent with the tenets of the declaration of helsinki . the mcmonnies questionnaire , translated into mandarin in advance , was self - administered by all participants . all subjects were required to remove their contact lens and discontinue any artificial tears for at least 2 hours before the assessment . information on ophthalmic and systemic disease was collected.tear break - up time ( tbut ) . a standard fluorescein stripe was moistened and used to lightly touch the inferior palpebral conjunctiva . blue light of a slit - lamp , the time interval between the last blink and the appearance of the first desiccation spot would be recorded as tbut.keratoconjunctival staining . after tbut test , any fluorescein staining of the corneas and interpalpebral conjunctiva was also recorded.schirmer i test . without anesthesia , a precalibrated standard stripe was placed in the lateral one - third of each lower fornix for 5 minutes . during this time , the patients were instructed to look downward or gently close their eyes . the length of the wetting was measured after removing the stripe.slit-lamp exam . eyelid margins , including meibomian gland orifices and secretions , were evaluated under slit - lamp for pathological changes . a standard fluorescein stripe was moistened and used to lightly touch the inferior palpebral conjunctiva . blue light of a slit - lamp , the time interval between the last blink and the appearance of the first desiccation spot would be recorded as tbut . after tbut test , any fluorescein staining of the corneas and interpalpebral conjunctiva was also recorded . a precalibrated standard stripe was placed in the lateral one - third of each lower fornix for 5 minutes . during this time , the patients were instructed to look downward or gently close their eyes . the length of the wetting was measured after removing the stripe . slit - lamp exam . eyelid margins , including meibomian gland orifices and secretions , were evaluated under slit - lamp for pathological changes . diagnoses were established according to the chinese diagnostic criteria of dry eye : ( 1 ) presence of dry eye symptoms ( dryness , grittiness , burning sensation , tiredness , soreness , or visual disturbance ) , with tbut  5  s or schirmer i test  5  mm/5  min ; ( 2 ) presence of dry eye symptoms , with 5  s < tbut  10  s or 5  mm/5  min < schirmer i test  10  mm/5  min , accompanied by positive keratoconjunctival staining with fluorescein . subjects conformed to either of the two criteria were clinically diagnosed with dry eye ; otherwise they were classified as non - dry eye ( control ) . data analyses were performed using statistical package for the social sciences software , version 22.0 ( spss inc . , chicago , il ) . a p value less than 0.05 was considered statistically significant , and 95% confidence intervals ( cis ) were tabulated . the kaiser - meyer - olkin measure was first calculated to test the degree of common variance , an assessment of whether the sample is adequate for factor analysis . any value below 0.50 the bartlett test of sphericity was also conducted to determine whether the items were sufficiently intercorrelated for factor analysis . after weighing the adequacy , factor analysis with varimax rotation was performed to find out whether the items of the mcmonnies questionnaire tend to cluster into certain domains . the internal reliability of the mcmonnies questionnaire was evaluated by cronbach . generally , an  value greater than 0.70 is acceptable to indicate that the items of the instrument are measuring the same thing . it should be noted that the cronbach  coefficient is an index dependent on the number of items in an instrument . therefore , the average interitem correlation was also calculated , which is not affected by the number of items . due to the large sample size of our study concurrent validity was assessed by examining the correlation between scores of the questionnaire and 2 quantitative dry eye test results ( i.e. , tbut and the schirmer i test ) using spearman 's rank correlation . discriminant validity was evaluated using 2-sample t - test to determine the differences in scores between the dry eye and the control group . in order to maximize the diagnostic efficacy of the mcmonnies questionnaire , receiver - operating characteristics ( roc ) curves of both the entire sample and different gender and age groups roc curves express the diagnostic accuracy of a test variable by plotting the sensitivity of the test against the specificity at all possible thresholds . this method was employed to select the most appropriate cut - off point for our study population . the area under the roc curve ( auc ) is an index for diagnostic value : 0.5 means no discrimination between the affected and the control groups , while 1.0 indicates perfect discrimination . we compared the roc curves of different gender and age groups using z tests to see if the diagnostic performance is compromised when applying the instrument to certain subpopulations . we also summarized the positive likelihood ratio ( lr+ ) of the mcmonnies questionnaire in different groups , which is a measure that indicates how much the odds of the disease increase when a test is positive . this study recruited 31,124 outpatients from the ophthalmology departments of 94 tertiary hospitals , distributed in 45 cities , 23 provinces across china . among these participants , 27,999 ( 90.0% ) the majority of our sample ( 44.6% ) belonged to the age group of 2545 years , whereas participants less than 25 years old made up the smallest portion ( 22.2% ) . the overall prevalence of dry eye according to the chinese diagnostic criteria was 58.8% ( 16,468 ) , with the remaining 41.2% ( 11,531 ) classified as the control group . prevalence of dry eye in each gender / age subgroup is also revealed in table 1 . the kaiser - meyer - olkin measure of sampling adequacy was 0.62 , and the bartlett test of sphericity was significant ( p < 0.001 ) , indicating sufficiency for factor analysis . exploratory factor analysis of the mcmonnies questionnaire revealed four potential factors , explaining only 47% of the cumulative variance . for instance , one factor was composed of the question regarding a history of thyroid abnormality and the question about sleeping with eyes partly open . therefore , the attempt to further analyze the questionnaire by domain was denied . the cronbach  based on standardized items for the mcmonnies questionnaire was 0.37 , indicating poor internal consistency . similarly , the average interitem correlation was 0.046 ( range , 0.132 to 0.328 ) , implying that each item refers to relatively independent aspects of the instrument 's objective ( i.e. , screening dry eye ) . the correlations between the scores of the mcmonnies questionnaire and both dry eye test results were significant . the spearman coefficient for the questionnaire and tbut was 0.322 ( p < 0.001 ) and 0.370 ( p < 0.001 ) for schirmer i test . also , the mean scores were 17.27  5.33 for the dry eye group and 12.82  5.21 for the control group , respectively . the scores of the two groups were statistically different from each other ( 2-sample t - test , t = 69.51 , p < 0.001 ) . the roc curves of the mcmonnies questionnaire in the entire sample as well as in various gender / age subgroups are shown in figures 1 and 2 . the sensitivity , specificity , and lr+ values at a cut - off point of 14.5 as recommended   are listed in table 2 , along with the aucs of each group . the overall auc of mcmonnies questionnaire is 0.729 ( 95% ci , 0.7230.735 ) , indicating moderate discrimination . all aucs of each group were significantly different from that of the entire sample ( z test , p < 0.001 ) , as the discriminating ability declined with age . likewise , sensitivity , specificity , and lr+ all varied considerably among these cohorts . since the mcmonnies questionnaire is used mainly as a screening method for dry eye , it is appropriate to maximize the sensitivity value , so as to avoid missed diagnosis . we also select separate cut - off points for each gender / age subpopulation with the highest specificity after setting the sensitivity at a value above 0.80 , that is , those with the sensitivity values most approximate to 0.80 ( table 4 ) . to our knowledge , this is the first multicenter study with a large sample investigating the diagnostic efficacy of the mcmonnies questionnaire . our results suggest that the instrument shows poor internal consistency , excellent validity , and moderate discriminating ability as a screening survey for dry eye in chinese outpatients . the mcmonnies questionnaire was initially developed by reviewing literature , and scores of each item were tabulated based on clinical experience . mcmonnies and ho   tested the instrument in 100 women aged above 45 years with or without keratoconjunctivitis sicca and achieved 98% sensitivity and 97% specificity . the results were deemed biased , because they were derived from the same sample from which the cut - off value was determined . so they reassessed on an independent sample of 50 women with sjgren syndrome and 124 normal controls , all over 45 years of age , and found a sensitivity of 92% and specificity of 93% with a weighted - scale algorithm . still , the data were affected by spectrum bias , since the severity of the disease in the study population was highly selective . later on , nichols et al .   reported a sensitivity and specificity of 82% and 36% , respectively , by identifying various degrees of dry eye severity in a sample without normal controls . moreover , differences in the diagnostic criteria of dry eye used in these studies made it challenging to compare the results . nonetheless , certain psychometric properties of the mcmonnies questionnaire can be compared with other studies , because they are irrelevant to diagnostic criteria . in our study , the questionnaire showed poor internal consistency as indicated by the cronbach  and average interitem correlation . such low internal reliability implies that each item of the instrument measures rather independent aspects of dry eye . this is also why the items failed to cluster into any logical domains by factor analysis . the authors inferred that the poor internal consistency would undermine the power associated with statistical significance tests , when comparing the scores between different groups or over time . similar conclusions have been made using rasch analysis , suggesting that the mcmonnies questionnaire does not function as a measure . unlike previous studies , the instrument was found to have fine validity in our study population . the scores not only differed significantly between the dry eye and control groups but also strongly correlated with the results of tbut and schirmer i test . several prevalence studies [ 16 , 17 ] have indicated poor correlations between dry eye symptoms and objective clinical tests . even so , we would argue that the mcmonnies questionnaire is comprised of many aspects of dry eye rather than symptoms . it is possible that the objective test results are correlated with some unknown factors such as age , gender , or secondary symptoms caused by environmental triggers . after all , the schirmer i test without anesthesia is technically a stimulus to the subjects ' eyes . besides , hong et al .   reported that the schirmer i test values were correlated with age in a chinese cohort , while tbut results were not . differences in the ethnicity of the study populations may also contribute , which is beyond the scope of our study . further analysis of the roc curves revealed varying discriminating abilities among different gender and age subgroups , as the aucs decreased with age . this is a bit surprising , since the instrument was originally developed and adjusted with subjects over 45 years old . again , variations in experimental samples and criteria used for disease diagnosis should be taken into account here . the differences in diagnostic efficacy among each subgroup are substantial , especially when applied with the same threshold of 14.5 ( table 2 ) . it even resulted with some lr+ values lower than 1.0 , which meant that the odds of dry eye actually reduced after the scores of the questionnaire were deemed positive . therefore , we believe it is necessary to assign separate cut - off values for different gender and age subpopulation . as a screening method for dry eye , the mcmonnies questionnaire is extremely cost - effective as it could be conducted in a self - administered manner by patients . this is particularly appropriate when the patients could be further assessed with routine ophthalmic examinations to reach a final diagnosis in clinics . based on these reasons , we consider a sensitivity value over 0.80 acceptable for the screening purpose . the diagnostic performances of each subgroup showed less diversity with newly proposed cut - off points as depicted in table 4 . nevertheless , we need to stress that these cut - off points were derived from selected chinese outpatients with at least one of the typical dry eye complaints . further studies are required to assess these proposed cut - off points for their efficacy on independent samples . our data suggest that the mcmonnies questionnaire demonstrate poor internal consistency , fine validity , and moderate accuracy as a screening survey for dry eye in chinese outpatients . it is recommend to become a routine process for dry eye diagnosis in the clinical practice of ophthalmologists .
purpose . to evaluate the diagnostic performance of the mcmonnies questionnaire as a screening survey for dry eye in chinese outpatients 
 . methods . 
 the questionnaire was self - administered by 27,999 patients with dry eye symptoms . 
 a thorough ophthalmic examination including tear break - up time ( tbut ) , fluorescein staining , and schirmer i test was completed to make a clinical diagnosis of dry eye . reliability , validity , and accuracy of the mcmonnies questionnaire were assessed . results . 
 the mcmonnies questionnaire showed poor internal consistency ( cronbach  = 0.37 ) , but excellent validity as the scores correlated with tbut ( spearman test , r = 0.322 , p < 0.001 ) and schirmer i test ( spearman 's test , r = 0.370 , p < 0.001 ) , and significantly differed between the dry eye and control groups ( 2-sample t - test , t = 69.51 , p < 0.001 ) . 
 the area under the receiver - operating characteristics ( roc ) curve ( auc ) was 0.729 , suggesting moderate accuracy in identifying dry eye and non - dry eye patients . however , the aucs varied significantly in different gender and age subgroups ( z test , p < 0.001 ) , as the discriminating ability declined with age . 
 analysis of the roc curves also revealed that different cut - off points should be employed for each subgroup to achieve the same level of accuracy . 
 conclusions . 
 the mcmonnies questionnaire demonstrates moderate diagnostic value , and different cut - off points should be selected for various study populations .