this study used a population - based prevalence survey to examine the rates of glaucoma among residents of oeso - myeon , sangju city , an inland , rural , agricultural area of 88.19 km located in central south korea who were aged greater than 50 years . this city was selected for the survey because of its stable , older population and its socioeconomic profile which is representative of rural areas of south korea . residents aged 50 years or older who had lived in the city for more than 1 year were selected for participation in the study . using the household resident register record kept by the district government , households with eligible participants were identified according to address , name of the head of the household , name of the potential participant , and the potential participant 's date of birth . potential participants were invited to the base clinic to complete a survey and ocular examinations . informed consent was obtained after providing the potential participant with a description of the purpose of the study . the study was carried out in accordance with the guidelines set forth by the world medical association 's declaration of helsinki and the municipal laws of sangju city . a site was developed in the community for the examinations which was less than thirty minutes walking distance for most potential participants . a standard questionnaire was administered by a trained interviewer in order to obtain detailed information regarding the participant 's family history of glaucoma and ocular disease , surgical history , general medical history , income , and education history . visual acuity was measured using the hahn chun suk eye chart as well as the korean version of the snellen chart with a standard illumination box at 4 meters . for those participants who presented with visual acuity score of less than 0.6 , refraction was measured with a handheld auto - refractor ( ark-30 ; nidek corp . , gamagori , japan ) . for those participants with corrected visual acuity of less than 0.8 , intraocular pressure was measured using goldmann applanation tonometry under local anesthesia resulting in two independent measurements for each eye which were obtained from right to left . a slit lamp examination was completed to identify abnormalities of the anterior segment , including iris changes and lens opacities . gonioscopy was performed using a sussman 4-mirror lens when the angle width measured by the van herick technique was less than  the angle depth . the optic disc was determined using a + 90 diopters ( d ) lens at 16  magnification without the use of pupil dilatation . the vertical cup - to - disc ratio ( vcdr ) was used as the index for structural glaucomatous change . if the stereo view was not satisfactory due to the opacity of the lens or due to restrictions of pupil size , then the pupil was dilated using 0.5% tropicamide and 0.5% phenylephrine hydrochloride , and the optic disc was examined with an indirect ophthalmoscope using a + 20 d lens . refractive correction at near or full threshold perimetry ( n-30 strategy ) was performed if the vcdr was larger than 0.6 or the vcdr asymmetry was larger than 0.2 or iop  21 mm hg , using frequency doubling technology ( fdt ; zeiss humphery system , dublin , ca , usa ) . these tests were considered reliable when fixation loss was less than 50 percent and the false - positive and false - negative error rates were under 50 percent . abnormal examination results were defined as the presence of 2 or more points having a p < 5% on the pattern deviation plot [ 10 - 11 ] . glaucoma was diagnosed according to the criteria described by isgeo ( table 1 ) . in this study , a cup disc ratio ( cdr ) equal to or greater than the 97.5 percentile was roughly 0.6 , and a cdr equal to or greater than the 99.5 percentile was roughly 0.9 . all participants were classified into the following groups : normal , poag with low iop ( iop  21 mmhg ) , poag with high iop ( iop > 21 mmhg ) , primary angle closure glaucoma ( pacg ) , and secondary glaucoma . poag with low iop was defined as open angle glaucoma with an iop of 21 mmhg or less while not taking medication for the treatment of glaucoma . a diagnosis of pacg was assigned on the basis of these criteria as well as the use of gonioscopically occludable angles ( invisible trabecular meshwork 270 without indentation or peripheral anterior synechiae ) . eyes with a history of significant ocular trauma , iridocyclitis , or the presence of new vessels on the iris or chamber angle or other ocular findings which may cause glaucomatous optic discs or visual field changes were classified as secondary glaucoma . all information was maintained in accordance with the protection of the participants ' privacy at severance hospital , yonsei university college of medicine . the prevalence of the different forms of glaucoma and their 95% confidence intervals were calculated using sas ver . the prevalence of glaucoma and 95% confidence interval ( ci ) were calculated individually for each age group . this study used a population - based prevalence survey to examine the rates of glaucoma among residents of oeso - myeon , sangju city , an inland , rural , agricultural area of 88.19 km located in central south korea who were aged greater than 50 years . this city was selected for the survey because of its stable , older population and its socioeconomic profile which is representative of rural areas of south korea . residents aged 50 years or older who had lived in the city for more than 1 year were selected for participation in the study . using the household resident register record kept by the district government , households with eligible participants were identified according to address , name of the head of the household , name of the potential participant , and the potential participant 's date of birth . potential participants were invited to the base clinic to complete a survey and ocular examinations . informed consent was obtained after providing the potential participant with a description of the purpose of the study . the study was carried out in accordance with the guidelines set forth by the world medical association 's declaration of helsinki and the municipal laws of sangju city . a site was developed in the community for the examinations which was less than thirty minutes walking distance for most potential participants . a standard questionnaire was administered by a trained interviewer in order to obtain detailed information regarding the participant 's family history of glaucoma and ocular disease , surgical history , general medical history , income , and education history . visual acuity was measured using the hahn chun suk eye chart as well as the korean version of the snellen chart with a standard illumination box at 4 meters . for those participants who presented with visual acuity score of less than 0.6 , corrected visual acuity was measured using auto - refraction . refraction was measured with a handheld auto - refractor ( ark-30 ; nidek corp . , gamagori , japan ) . for those participants with corrected visual acuity of less than 0.8 , intraocular pressure was measured using goldmann applanation tonometry under local anesthesia resulting in two independent measurements for each eye which were obtained from right to left . a slit lamp examination was completed to identify abnormalities of the anterior segment , including iris changes and lens opacities . gonioscopy was performed using a sussman 4-mirror lens when the angle width measured by the van herick technique was less than  the angle depth . the optic disc was determined using a + 90 diopters ( d ) lens at 16  magnification without the use of pupil dilatation . the vertical cup - to - disc ratio ( vcdr ) was used as the index for structural glaucomatous change . if the stereo view was not satisfactory due to the opacity of the lens or due to restrictions of pupil size , then the pupil was dilated using 0.5% tropicamide and 0.5% phenylephrine hydrochloride , and the optic disc was examined with an indirect ophthalmoscope using a + 20 d lens . refractive correction at near or full threshold perimetry ( n-30 strategy ) was performed if the vcdr was larger than 0.6 or the vcdr asymmetry was larger than 0.2 or iop  21 mm hg , using frequency doubling technology ( fdt ; zeiss humphery system , dublin , ca , usa ) . these tests were considered reliable when fixation loss was less than 50 percent and the false - positive and false - negative error rates were under 50 percent . abnormal examination results were defined as the presence of 2 or more points having a p < 5% on the pattern deviation plot [ 10 - 11 ] . glaucoma was diagnosed according to the criteria described by isgeo ( table 1 ) . in this study , a cup disc ratio ( cdr ) equal to or greater than the 97.5 percentile was roughly 0.6 , and a cdr equal to or greater than the 99.5 percentile was roughly 0.9 . all participants were classified into the following groups : normal , poag with low iop ( iop  21 mmhg ) , poag with high iop ( iop > 21 mmhg ) , primary angle closure glaucoma ( pacg ) , and secondary glaucoma . poag with low iop was defined as open angle glaucoma with an iop of 21 mmhg or less while not taking medication for the treatment of glaucoma . a diagnosis of pacg was assigned on the basis of these criteria as well as the use of gonioscopically occludable angles ( invisible trabecular meshwork 270 without indentation or peripheral anterior synechiae ) . eyes with a history of significant ocular trauma , iridocyclitis , or the presence of new vessels on the iris or chamber angle or other ocular findings which may cause glaucomatous optic discs or visual field changes were classified as secondary glaucoma . all information was maintained in accordance with the protection of the participants ' privacy at severance hospital , yonsei university college of medicine . the prevalence of the different forms of glaucoma and their 95% confidence intervals were calculated using sas ver . 9.1 ( sas inc . , cary , nc , usa ) . the prevalence of glaucoma and 95% confidence interval ( ci ) were calculated individually for each age group . among the identified potential participants older than 50 years , 1,118 were eligible to participate in this study . of these , 671 ( 264 males and 407 females ) participated in the examination , which is an overall response rate of 60.0% . table 2 reports the age and sex distributions for the town 's residents and the participants of this study . female participation rates were greater in all age groups with the exception of the , group with an age of older than 80 years . the female age group with the highest participation rate ( 69.1% ) was the group aged 50 to 59 years . the male group with the highest participation rate ( 65.0% ) was the group between 70 and 79 years old . the group over 80 years old had the lowest participation rate for both males and females . 1 shows the distribution of intraocular pressure for all participants and glaucoma patients . there were no differences between levels of the iop in the right and left eyes or between the age groups . the mean iop for the full sample was 13.5  2.9 mmhg , and the iop for the participants in the 99.5th percentile was 19 mmhg . 2 shows the distribution of the vertical cdr for all participants and glaucoma patients . the 97.5th percentile and 99.5th percentile were 0.6 and 0.9 , respectively ; thus , these values were applied to the glaucoma diagnostic categories 1 and 2 , respectively . table 3 reports the prevalence of glaucoma based on age and sex . as the age increased , there additionally , there was no statistically significant difference in the prevalence of glaucoma for men and women . 23 of the participants received a diagnosis of glaucoma with of those 15 participants being placed in category 1 and 8 participants being placed in category 2 . the prevalence of glaucoma increased from 2.2% in the group aged 50 to 59 years to 3.1% in the group aged 60 to 69 years . the prevalence rate then increased to 4.5% for the group aged 70 to 79 years , and then , increased to 13.0% in the group aged 80 years and older . among females , the prevalence rates of those participants in their 50 's and 60 's were similar , and then , the prevalence rates increased in association with each advancing decade of life . table 4 reports the ratio of each type of glaucoma to the total of all the forms of glaucoma . open angle glaucoma ( oag ) was the most common form at 74.0% of the total , and the poag with low iop group included 94.4% of the total number of patients in the oag group . the mean intraocular pressure for the normal population was 13.4  2.5 mmhg , and it was 13.9  2.1 mmhg for patients with poag with low iop . in this study this is the first population - based epidemiological report regarding the prevalence of glaucoma in korea . the glaucoma prevalence was determined to be 3.4% of the population aged 50 years and older , which is similar to the prevalence reported in other east asian countries [ 12 - 15 ] . the prevalence of poag with low iop in the study outlined by tajimi was 92.4% , and this prevalence was 94.4% in this study . this result differs from results based on chinese , indonesia , and mongolian data , which described a higher prevalence rate of poag with high iop [ 12 - 15 ] . the similar ethnic and cultural backgrounds of korea and japan may contribute to the similarities in prevalence of glaucoma in the two countries ( table 6 ) [ 3,13 - 20 ] . the average iop for all participants in this study was 13.5  2.9 mmhg , which is lower than that observed in most other surveys ( 12.5 to 18.7 mmhg ) . therefore , the low mean iop likely plays a role in the higher prevalence of poag with low iop observed in this study . however , the low average iop in the poag participants and the high prevalence of poag with low iop , do not necessarily mean that the iop value was not related to poag . the prevalence of pacg has been reported to range from 0.6% to 1.4% in other asian countries [ 12 - 13,16,23 - 25 ] . the prevalence of angle closure glaucoma ( 0.46% ) was significantly lower than that observed in other east asian or japanese studies . the results of this stuy may have been underestimated as only the van herick method was used in the screening of acg , and this screening only included the cases which met criteria for isgeo . although there have been several reports on the prevalence and composition of glaucoma in korea [ 4 - 8 ] , many of these reports have been hospital or health center - based studies . in a hospital - based study , the overall incidence of glaucoma was determined to be 4.7% of new patients visiting the ophthalmology outpatient clinic , and poag with high iop was determined to be the most common form of glaucoma , accounting for 37.7% of all cases of glaucoma . and choe and hong   found that normal - tension glaucoma ( poag with low iop ) was the most common type of glaucoma in korean popykatuibs , based on the results of two health center studies . according to these studies , the prevalence rates of all types of glaucoma were 2.67%   and 2.04% , with oag with low iop comprising 2.04%   and 1.71% , respectively . the prevalence of glaucoma is known to increase with age , and this was also shown in the data of this study . the average age of the participants in this study was 64.1 years , while the average age of the population over 50 years old in south korea was 62.6 years at the end of 1998 . the older average age of the residents in this rural area , compared with those in urban areas and the entire nation , may have increased the prevalence of glaucoma observed in the present study . individuals aged 80 years or more showed an especially low participation rate ( 26.4% ) , which may reflect the limited mobility and poorer physical health observed in this population . there are several methodological limitations associated with this study . in particular , random sampling was not performed and the participation rate was relatively low , about 60.0% . additionally , visual field testing was not performed on all subjects as the glaucoma grading scheme required an enlarged vcdr for individuals to be classified as having glaucoma . however , it is possible that some participants experiencing subtle optic nerve changes may have been missed due to visual fields which would not have been examined in these individuals . furthermore , visual field measurements were performed using a full threshold of n-30 of the frequency doubling test rather than humphrey visual field analyzer . the fdt perimetry was used instead of the humphrey visual field because the fdt perimetry can be performed easily in a few minutes with a screening method , and the device is portable and relatively inexpensive . there are many other epidemiologic studies using only the fdt , which have reported that the results of the fdt were almost identical to that of the humphery exam . despite the limitations , this is the first population - based epidemiological study in a rural area of south korea , reporting that poag with low iop is the most common form of glaucoma . these results imply that there are unique characteristics of glaucoma in korea and japan and that specific race - based factors may contribute to the pathogenesis of glaucoma . in conclusion , the prevalence of glaucoma in the rural korean area was 3.4% and the prevalence of poag with low iop was 2.8% , which was similar to that observed in japanese studies . the prevalence of pacg in korea was relatively lower than those of other asian countries . a large - scale epidemiologic study , the nam - il study , is being conducted in korea , which will allow for validation of this study and its findings .
purposethe purpose of this study was to investigate the prevalence and characteristics of glaucoma in the population of the rural korean town , sangju.methodsresidents of sangju aged greater than 50 years old were included in this study . 
 participants completed an interview examining their medical and ophthalmic history information was collected on the participants ' uncorrected and best corrected vision scores , slit lamp examination results , angle width measurements using the van herick technique , gonioscopy if the angle width was less than 1 / 4 angle , intraocular pressure ( iop ) assessed with the goldmann applanation tonometry , optic disc examination results , and a visual field test results using frequency - doubling perimetry in cases in which glaucoma was suspected . 
 glaucoma was diagnosed according to the criteria described by the international society for geographic and epidemiological ophthalmology.results1,118 residents aged greater than 50 years were examined initially from a population of 2,984 people . 
 of these , 671 subjects ( 60% ) participated in this study . 
 the prevalence of glaucoma was determined to be 3.4% ( 95% confidence interval [ ci ] , 2.1 - 4.8 ) . 
 open - angle glaucoma with low iop was determined to be the most common form with a prevalence rate as high as 2.5% ( 95% ci , 1.8 - 3.7 ) . additionally , primary angle closure glaucoma was determined to have a prevalence rate of 0.3% ( 95% ci , 0.1 - 0.9 ) . 
 open - angle glaucoma with low iop accounted for 94.4% of the open - angle glaucoma cases.conclusionsthe prevalence of glaucoma among the population of rural sangju was 3.4% , and open - angle glaucoma with low iop was the most common form accounting for 94.4% of the total number of cases .