May 2012
Volume 53, Issue 6
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Clinical and Epidemiologic Research  |   May 2012
The Prevalence of Glaucoma in Adult Rural Chinese Populations of the Bai Nationality in Dali: The Yunnan Minority Eye Study
Author Affiliations & Notes
  • Hua Zhong
    State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China;
  • Jun Li
    State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China;
  • Cairui Li
    The Hospital Affiliated to Dali College, Dali, China; and
  • Tao Wei
    Kunming Medical University, Kunming, China.
  • Xueping Cha
    State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China;
  • Ning Cai
    State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China;
  • Tinghao Luo
    State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China;
  • Minbin Yu
    State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China;
  • Yuansheng Yuan
    State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China;
  • *Each of the following is a corresponding author: Yuansheng Yuan, Department of Ophthalmology, The First Affiliated Hospital of Kunming Medical University, No. 295 Xichang Road, Kunming 650032, People's Republic of China; Telephone (86) 13708718520; Fax (86) 871 5394669; 1119abcd@163.com.  
  • Minbin Yu, Department of Glaucoma, Department of Optometry, Zhongshan Ophthalmic Center, Guangzhou 510060, People's Republic of China; Telephone (86) 20 87331545; Fax (86) 20 87333271; max-yu@tom.com
Investigative Ophthalmology & Visual Science May 2012, Vol.53, 3221-3225. doi:10.1167/iovs.11-9306
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      Hua Zhong, Jun Li, Cairui Li, Tao Wei, Xueping Cha, Ning Cai, Tinghao Luo, Minbin Yu, Yuansheng Yuan; The Prevalence of Glaucoma in Adult Rural Chinese Populations of the Bai Nationality in Dali: The Yunnan Minority Eye Study. Invest. Ophthalmol. Vis. Sci. 2012;53(6):3221-3225. doi: 10.1167/iovs.11-9306.

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Abstract

Purpose.: We evaluated the prevalence of glaucoma in adults of the Bai Nationality populations in rural China.

Methods.: A population-based survey of Chinese Bai Nationality aged ≥50 years from randomly selected block groups in southwestern China was conducted. Eligible persons were invited to local examination sites for a complete ophthalmic examination. Glaucoma was diagnosed using the International Society of Geographical and Epidemiological Ophthalmology Classification scheme.

Results.: In the study, 2133 subjects (77.8% participation rate) were examined, with a crude prevalence of all glaucoma of 2.2% (95% confidence interval [CI] 1.6%–2.9%). Primary open angle glaucoma (POAG) was found in 1.0% of cases (95% CI 0.6%–1.6%) and primary angle-closure glaucoma (PACG) in 0.9% (95% CI 0.6%–1.4%). The prevalence of all glaucoma was significantly higher in older people and women. Mean intraocular pressure (IOP) was 16.17 ± 3.74 mm Hg (97.5th and 99.5th percentiles, 24 mm Hg and 30 mm Hg, respectively). The mean vertical cup-to-disc ratio (VCDR) was 0.43 ± 0.17 (97.5th and 99.5th percentiles 0.7 and 0.8, respectively). Unilateral blindness was found in 80% of PACG, compared to only 36.3% of POAG cases.

Conclusions.: Prevalence of POAG is similar to PACG in the ethnic Bai population living in rural southwestern China. PACG has a worse visual impairment and prognosis compared to POAG.

Introduction
Glaucoma is considered the world's leading cause of irreversible blindness, and it affects approximately 70 million people. 1,2 Many studies suggest that Asian ethnic groups are more susceptible to primary angle closure glaucoma (PACG) than primary open-angle glaucoma (POAG). 35 In China, an Asian country with the largest population in the world, a 1990 survey by Hu et al. found that PACG was the most common form of glaucoma. 6  
In the past 20 years, the definition and diagnosis of glaucoma have changed considerably. The diagnostic criteria and methods were not described clearly and appear not to conform to current international standards in most studies. Recently, a study using the general accepted International Society of Geographical and Epidemiological Ophthalmology (ISGEO) classification scheme was performed in Southern Chinese. 7 The results showed that POAG is seen more frequently than PACG in this population. The study challenges the traditional view on the prevalence of primary glaucoma in China. Direct comparison of the past results may not be possible because of the differences in diagnostic criteria for glaucoma among the studies. More studies should be performed to explore the prevalence of glaucoma in Chinese using the ISGEO criteria. 8  
China is a vast country that includes many different nationalities, ethnic groups, and living environments. Of the preceding studies, none focused on the Chinese ethnic minorities. Our study, which is called the Yunnan Minority Eye Study (YMES), was designed to determine the prevalence and impact of eye diseases among rural southwestern Chinese populations of the minority nationality (including the Bai, Dai, and Yi nationalities). As a part of YMES, we report the initial results of the prevalence of glaucoma to enumerate those potentially at risk in the Bai nationality. The ISGEO scheme was used in our study. 
Methods
Sampling and Enumeration
Ethical approval was obtained from the Kunming Medical University Ethics Review Board. The study was conducted in accordance with the tenets of the World Medical Association's Declaration of Helsinki. 
Study subjects were enrolled in a randomly selected sample of individuals in Dali (a County-level city). Dali is one of 12 counties in Dali Bai Nationality Autonomous Prefecture. The decision to select this district for the survey was due to the fact that more than 80% of the population of the Bai nationality in China live in the Dali Prefecture, and it is a socioeconomic profile that is representative of the Bai nationality as a whole. 9  
The sampling frame was constructed using geographically defined clusters based on village register data. Cluster boundaries were defined such that each cluster would have a population of approximately 1000 individuals (all ages). Cluster sampling was used to divide Dali County into 259 areas. Sample size was based on estimating an anticipated 3.5% prevalence for glaucoma with 95% confidence interval (CI). Assuming an examination response rate of 80%, and a design effect of 1.25 to account for inefficiencies associated with the cluster sampling design, a sample of 2118 persons ≥50 years old was required for each village. Depending on the percentage of the population ≥50 years old, 12 to 14 clusters were selected randomly (with equal probability) by specialists of Zhongshan Ophthalmic Center (MH and JZ).  
Field work was performed over a 4-month period, beginning in January 2010. Listing of households with the names of residents ≥50 years old were obtained from the village registers, followed by door-to-door household visits conducted by enumeration teams. Those ≥50 years old were enumerated by name, sex, age, education (using graduation levels), and spectacle use. Individuals temporarily absent at the time of the household visit were included in the enumeration. Unregistered adults ≥50 years old were enumerated and included in the study sample if they had been living in the household for 6 months. 
An examination site was set up in the local community facilities within 15 minutes' walking distance for most subjects. Study participants were examined on a prescheduled date established at the time of enumeration. Identity of the subjects was verified using the subjects' official photo identity cards. Those who did not appear at the examination site were revisited, repeatedly if necessary, by a member of the enumeration team to encourage participation. 
A standard questionnaire was administered by a trained interviewer to collect details of ophthalmic history, general medical history, income, and education. Two optometrists used an auto refractometer (RM-8000; Topcon Corp., Tokyo, Japan) to measure the noncycloplegic refraction. Distance visual acuity was measured using a retro-illuminated logarithm of the minimum angle of resolution tumbling E chart (wh06; Wehen Vision Technology Co., Ltd., Guangzhou, China) at a distance of 4 meters, and at 1 meter for those failing to read the top line (20/200). Visual acuity was recorded as the smallest line read with 1 or no errors. Testing for counting fingers, hand movement, or light perception was performed on those unable to read the top line at 1 meter. Each eye was measured separately, with glasses if worn for distance correction. The presenting visual acuity (VA) with habitual correction was recorded. In those presenting with VA <20/25 in either eye, best-corrected VA was assessed using the results of autorefraction and subjective refinement.  
Ophthalmic examination of the eyelid, globe, and pupillary reflex was done by an experienced ophthalmologist. Slit-lamp examination (model SL-1E; Topcon, Tokyo, Japan) then was performed to identify abnormalities of the anterior segment, including evidence of ischemic sequelae of angle-closure, secondary glaucoma, and lens opacity. For those with aphakia/pseudophakia, surgical history (year and place) was obtained, with clinical details pertaining to the type of surgery and surgical complications noted during the examination. Direct ophthalmoscopy and slit-lamp biomicroscopy with a 90 diopter (D) lens without a graticule were used to assess vitreous and retina situations of all participants. 
Intraocular pressure (IOP) was measured by a study ophthalmologist using a handheld tonometer (TONO-PEN AVIA; Reichert Inc., New York, NY) device after instilling topical anesthesia (0.4% Benoxil; Oxybuprocaine, Santen, Japan). The measurement was repeated if the SE of the measurement was more than 5%. One measurement was taken and recorded for each eye. Goldmann applanation tonometry was performed on an optional basis for all glaucoma suspects. Also, gonioscopy was performed in all glaucoma suspects with a G-4 Four-Mirror Glass Gonio Lens (Volk Optical Inc., Mentor, OH) at ×16 magnification with low ambient illumination by the same observer. A narrow vertical beam 1 mm in length was offset vertically for superior and inferior quadrants, and horizontally for nasal and temporal quadrants. Care was taken to avoid light falling on the pupil. Small movements of the lens were allowed to visualize the drainage angle, but large movement was avoided because of the possibility of indentation. Dynamic examination with the lens was performed after the static gonioscopy of four quadrants were completed. The Spaeth grading system was used to record the results. 10  
The optic disc was evaluated using a +90 D lens at ×16 magnification without pupil dilation, and digital fundus photographs of the optic disc were taken using a fundus camera (APS-A; KangHua CO., LTD, Chongqing, China). The vertical cup-to-disc ratio (VCDR) was used as the key index of structural glaucomatous change. Measurement of VCDR excluded parapapillary atrophy and the scleral ring of Elschnig. The margins of the cup were defined by stereoscopic view as the point of maximum inflection of the vessels crossing the neuroretinal rim. Disc hemorrhage and focal enlargement of cup (notching) were recorded. If the optic disc was not visible despite pharmacological dilation, “fundus not seen” was recorded. 
Those people with any of the following signs were identified as glaucoma suspects: VCDR ≥0.7 in either eye, VCDR asymmetry ≥0.2, or a neuroretinal rim width reduced to <0.1 CDR (between 11 and 1 o'clock or 5 and 7 o'clock), IOP >21 mm Hg, optic disc hemorrhage, notch and nerve fiber layer defect. All suspects were asked to return for visual field (VF) testing on a designated day. White-on-white automated perimetry (Humphrey 750; Carl Zeiss Meditec, Inc., Dublin, CA) was performed with near refractive correction. The SITA-Fast 24-2 mode was used throughout. Tests were rated as having good reliability if no more than 20% of fixation losses, 33% of false-positives and false-negatives were observed. If the reliability of the field test was not satisfactory or there was a defect compatible with glaucoma, the participants were invited for a second field test on another day.  
Diagnostic Definition
The definitional criteria developed by ISGEO were used in the our study. In that definition, criteria for a category 1 diagnosis (structural and functional evidence) were a VCDR or an inter-eye asymmetry in the VCDR of ≥97.5th percentile for the normal population, or a neuroretinal rim width reduced to ≤0.1 VCDR (between 11 and 1 o'clock or 5 and 7 o'clock), in addition to a definite visual field defect consistent with glaucoma. Criteria for the category 2 diagnosis (advanced structural damage with unproven visual field loss) were a VCDR or a VCDR asymmetry ≥99.5th percentile for the normal population. Criteria for a category 3 diagnosis (for eyes the optic nerve head of which could not be examined or for which a visual field examination was not possible) were a visual acuity <3/60 combined with either an intraocular pressure >99.5th percentile or definite glaucoma medical records, such as filtering surgery history. 
The differentiation between open-angle glaucoma and primary angle closure glaucoma was based on the gonioscopic findings. For subjects with unilateral pseudophakia or aphakia, the angle of the contralateral eye was used to define the angle status. For those with bilateral pseudophakia and/or aphakia, we could not classify the eye's primary angle status before surgery. Therefore, it was defined as underdetermined. All glaucoma suspects were classified finally as normal, or having ocular hypertension, POAG (with high or normal IOP), primary angle-closure glaucoma, and secondary glaucoma. 
Results
A total of 2742 persons aged ≥50 years was enumerated, and 2133 participants (77.8%) were examined. Table 1 shows the distribution across age, sex, and education. The mean age of the enumerated population was 64.6 years. Overall, 36.1% were male. Examination response was associated with older age and being female; 35.6% of those enumerated had no education and 23.7% had an education of secondary or higher level. 
Table 1.  
 
Demographic Comparison of Enumerated and Examined Subject
Table 1.  
 
Demographic Comparison of Enumerated and Examined Subject
Enumerated No. (%) Examined No. (%) % Examination Response Rate
Age group:
 50–59 1123 (41) 715 (33.5) 63.7
 60–69 867 (31.6) 775 (36.3) 89.4
 70–79 607 (22.1) 525 (24.6) 86.5
  >80 145 (5.3) 118 (5.5) 81.4
Sex:
 Male 1315 (48.0) 769 (36.1) 58.5
 Female 1427 (52.0) 1364 (63.9) 95.6
Education:
 None 994 (36.3) 759 (35.6) 76.4
 Primary 1095 (40.0) 868 (40.7) 79.3
 Secondary 554 (20.2) 427 (20.0) 77.1
 Postsecondary 99 (3.6) 79 (3.7) 79.8
Totals 2742 (100) 2133 (100) 77.8
The distribution of VCDR in right and left eyes with normal visual fields was similar, with the median of 0.3, and 97.5th and 99.5th percentiles of 0.7 and 0.9, respectively (Table 2). As for the absolute value of difference of the VCDR between right and left eyes, the mean 97.5th and 99.5th percentiles for this asymmetry were 0, 0.1, and 0.3, respectively. 
Table 2.  
 
VCDR in Normal Subjects*
Table 2.  
 
VCDR in Normal Subjects*
Right CDR Left CDR Asymmetry†
N (CDR measurements) 1952 1935 1850
 0.5th percentile 0.2 0.2 0
 2.5th percentile 0.2 0.2 0
  Median 0.3 0.3 0
 97.5th percentile 0.7 0.7 0.1
 99.5th percentile 0.9 0.9 0.3
IOP was 14.4 ± 3.3 mm Hg (SD) in the whole population, 14.7 ± 3.4 mm Hg in the men, and 14.3 ± 3.3 mm Hg in the women (P > 0.05). Distribution of IOP (as measured by the handheld tonometer) in both eyes generally was similar, with mean, median, and 97.5th and 99.5th percentiles being 14, 14, 20, and 21 mm Hg, respectively (Table 3). The 99.5th percentile (21 mm Hg) was used as the cutoff value for the category-3 definition. IOP values were missing in 27 right and 26 left eyes (1%), mainly because of the corneal disease and participants who were difficult to examine. 
Table 3.  
 
Intraocular Pressure in Normal Subjects*
Table 3.  
 
Intraocular Pressure in Normal Subjects*
Right IOP (mm Hg, 95% CI†) Left IOP (mm Hg, 95% CI†)
N (IOP measurements) 2060 2060
  Mean 14.19 14.38
 0.5th percentile 6 6
 2.5th percentile 8 8
  Median 14 14
 97.5th percentile 20 20
 99.5th percentile‡ 21 21
Table 4 gives the demographic characteristics of people with glaucoma and relative rates of blindness. A total of 47 people had glaucoma, including 22 (46.8%) with POAG, 20 (42.5%) with PACG, and 5 (10.6%) with secondary glaucoma (Table 4). Of 29 people classified as having POAG, eight had an IOP level higher than 21 mm Hg in the affected eyes, and two had normal pressure after surgical trabeculectomy. Therefore, 55% of untreated open-angle glaucoma cases could be classified as “normal-tension” disease. Among all the PACG cases, 10 (50%) had been diagnosed and treated, and 16 patients (80%) were blind in at least one eye, but there was only one case of bilateral blindness. By contrast, among the 22 POAG cases, only 2 (9%) had been diagnosed and treated previously, and eight (36.3%) had unilateral blindness. 
Table 4.  
 
Mechanism and Characteristics of Glaucoma
Table 4.  
 
Mechanism and Characteristics of Glaucoma
Diagnosis Sex Ratio (M:F) Median Age (Range) Diagnostic Category* Blind† in at Least 1 Eye (% of Total) Previously Diagnosed (%)
1 2 3
POAG 12:10 66 (51–78) 14 6 2 8 (36) 2 (9)
PACG‡ 3:17 71 (54–85) 9 5 6 14 (70) 10 (47.6)
Secondary 1:4 70 (57–82) 0 2 3 5 (100) 1 (20)
Totals 16:31 69 (51–85) 23 13 11 27 (57) 13 (27.7)
Table 5 summarizes the number and diagnostic category of all the glaucoma cases, giving the age-specific rates of disease. The crude prevalence of glaucoma was 2.2% (95% CI 1.6–2.9%), with an age- and sex-standardized prevalence of 2.0%. The crude prevalence of POAG and PACG was 1.0% (95% CI 0.6–1.6%) and 0.9% (95% CI 0.6–1.4%), respectively, with age- and sex-standardized prevalences being 1.1% and 0.7%, respectively. The prevalence of glaucoma increased significantly with age. In a logistic regression model, the adjusted odds ratios (ORs) for 60–69, 70–79, and ≥80 versus the 50–59 age groups were 4.0 (95% CI 1.5–10.7), 4.5 (95% CI 1.6–12.5), and 6.3 (95% CI 1.8–22.1), respectively. However, the glaucoma prevalence was not significantly different between male and female sex (P = 0.598). 
Table 5.  
 
Prevalence of All Glaucoma by Age and Sex*
Table 5.  
 
Prevalence of All Glaucoma by Age and Sex*
Age (yrs.) Men Women Totals
(n) Diagnostic Category† Prevalence (95% CI) (n) Diagnostic Category† Prevalence (95% CI) (n) Prevalence (95% CI)
1 2 3 1 2 3
50–59 220 3 0 0 1.4 (0.3–3.9) 495 2 1 0 0.6 (0.1–1.8) 715 0.8 (0.3–1.8)
60–69 308 5 3 0 2.6 (1.1–5.1) 468 5 4 3 2.6 (1.3–4.4) 776 2.6 (1.6–3.9)
70–79 203 4 1 0 2.5 (0.8–5.7) 321 2 4 5 3.4 (1.7–6.0) 524 3.1 (1.8–4.9)
≥80 39 0 0 0 0.0 (0.0–9.0) 79 2 0 3 6.3 (2.1–14.1) 118 4.2 (1.4–9.6)
All 769 12 4 0 2.1 (1.2–3.4) 1364 11 9 11 2.3 (1.6–3.2) 2133 2.2 (1.6–2.9)
Discussion
The Bai ethnic group is a major component of Chinese minority nationality. The majority of Bai people live in the Dali Bai Autonomous Prefecture of Yunnan Province. Archaeological finds from Canger and Haimenkou show that the Erhai area was inhabited as early as the Neolithic Age. The Bai ethnic have their own language derived from the Zang-Mian Austronesian family of Sino-Tibetan Phylum. The Bai area is crisscrossed with rivers. The area around Lake Erhai in the autonomous prefecture has a mild climate and fertile land yielding two crops a year. Therefore, the Bai people mainly are occupied with agriculture. As a whole, the Bai ethnic group and the majority of Chinese ethnic groups differ in genetic origin, inhabited environment, economy, and customs. 
The prevalence of glaucoma shows wide regional and racial variations. PACG used to be considered as the most common type of primary glaucoma in Asia, especially in China. The prevalence of angle-closure glaucoma varied between 1.0 and 2.00% in the Chinese rural adult population, 11,12 1.4% in a rural population in Mongolia, 4 0.9% in a Thailand urban population, 13 and 0.87% in an Indian rural population. 14 The prevalence of open-angle glaucoma was much lower than PACG in Chinese people in previous studies. However, recent research has changed this traditional view. The Liwan Eye Study in Guangzhou/South China reported a glaucoma prevalence of 3.8%, with 2.1% for POAG and 1.5% for PACG, respectively. 7 To our knowledge, the study is the first population-based study to report that POAG affects more people than PACG in adult Chinese population. Similarly, the Beijing Eye Study and Handan Eye Study reported that the ratio of open-angle glaucoma to primary angle-closure glaucoma was 2.6:1 and 2:1, respectively. 1517 The reasons for the discrepancies between the recent studies and the past investigation have been attributed to differences in the examination techniques, variations in the definition of glaucoma, and regional differences between the provinces of China, leading to variations in climate, lifestyle, and ethnic background. 6,7,11,12,15 In our study, glaucoma was diagnosed in 47 subjects (2.2%, 95% CI 2.1–3.2%), in which POAG, PACG, and SG accounted for 1.0% (95% CI 2.1–3.0%), 0.9% (95% CI 0.7–1.3%), and 0.2% (95% CI 0–0.1%), respectively. The prevalence of glaucoma for the age groups of 50–59, 60–69, and above 70 years was 2.5%, 4.4%, and 9.5%, respectively. 
In this southwest China minority nationality eye study, the prevalence of glaucoma was lower than in Handan, Liwan, and Beijing. The discrepancy could be explained partly by regional and ethnic differences in lifestyle or genetic drift. Other sources of the discrepancy could originate from the differences in perimetry techniques, screening methods for glaucoma, and subjective interpretation of examination data. The method using a graticule with slit-lamp microscopy is more accurate and objective, and it should be taken into account in our further study. More epidemiological data about Chinese minority eye diseases would be obtained to compare in our further study in the Yi and Dai minority. 
The ratio of open-angle glaucoma to primary angle-closure glaucoma was 1.0:0.9. The prevalence of POAG is higher than PACG, and this trend undoubtedly is due at least partly to advances in diagnostic technology, which have led to earlier and more reliable identification of POAG cases. The ISGEO classification developed by Foster et al. 8 also has a vital role. According to the ISGEO system most glaucoma cases are assigned to categories 2 and 3. The lower prevalence of PACG is due partly to the adoption of more stringent criteria for the diagnosis of this form of glaucoma. 18 Another reason may be that earlier cataract surgery prevented the development of angle-closure glaucoma because of higher education and economic level in Dali.  
Of 22 people classified as having POAG, two had been diagnosed previously and were on irregular medication, with higher IOP (>21 mm Hg) in both eyes. The rest all were undiagnosed and untreated; 11 POAG patients (55%) had an IOP lower than 21 mm Hg in both eyes. The high prevalence of POAG with normal IOP in Chinese people was reported in the Liwan eye study, which obtained data similar to that found in Japan and Korea. 19,20 Furthermore, as in the Tajimi study, the low average IOP in POAG subjects and the high prevalence of POAG with normal IOP do not mean that IOP was not related to POAG. The average IOP in POAG with high or normal IOP subjects was 25.3 ± 6.2 mm Hg or 15.2 ± 2.3 mm Hg, respectively. Both were higher than that in nonglaucomatous subjects (14.5 ± 3.4 mm Hg), and the POAG prevalence rate was high among subjects with higher IOP. 
Many published studies reported that most of glaucoma cases had not been diagnosed previously. This was noted first in the Ferndale study, where two-thirds of the POAG and three-quarters of the PACG cases were undiagnosed. 21 In our study, over 90% of POAG and 50% of PACG cases were undiagnosed previously. These rates are comparable to those in Liwan, Guanzhou (93.1% and 66.7%, respectively) and higher than those found in other population-based studies in Europe and America. Of the 20 PACG cases nine (45%) had a history and consistent clinical signs of an acute, symptomatic attack, among which six had been diagnosed and treated with surgery. POAG was diagnosed previously very poorly, at even less than one-fifth of the PACG diagnosis rate. The reason for this may be that some PACG subjects had an acute symptomatic attack. Diagnosis of PACG may be relatively easier in rural medical establishments than for POAG, because a shallow anterior chamber and high IOP could be found without sophisticated devices and experienced ophthalmologists. Such high prevalence of undiagnosed patients highlights the need to develop and assess early detection and screening methods of glaucoma, especially POAG. 
The prevalence of glaucomatous bilateral blindness in our study population was low (0.2%), while the prevalence of unilateral blindness was higher (1.3%). POAG was associated with a lower rate of unilateral blindness (36% of persons with POAG) than was PACG (70%), and secondary glaucoma was the most visually destructive form of glaucoma (100% were blind in at least 1 eye). This suggests that PACG has a worse visual impairment and prognosis compared to POAG, although the prevalence of POAG was higher than that of PACG. 
In our study, the ISGEO criteria were taken for field testing and glaucoma screening. The effect of variation in diagnostic criteria showed great influence on glaucoma prevalence. 22 The ISGEO system is intended to standardize diagnostic procedures and definitions for glaucoma, and make the population surveys be subjected to meaningful comparison. Potential limitations in the ISGEO system using VCDR as a defining feature for glaucoma include variation in the size of the optic disc between individuals. 8 The Handan Study reported that 32.3% of subjects with POAG by expert consensus had a cup-to-disc ratio under the 97.5th percentile. These strict criteria were designed to be highly specific, but more early glaucoma cases are likely to have been excluded than studies using inclusive criteria. 23 Therefore, our glaucoma subjects were more likely to have advanced disease, and using the cutoff values might have underestimated the prevalence of POAG. However, the Rotterdam study showed the 97.5th percentile of the VCDR was similar for right and left eyes, and differed 0.05 between the lowest and highest quartiles of disc area. 22 The definition similar to the ISGEO classification was recommended to implement and the ISGEO systems should be validated in future studies. 
In summary, using the ISGEO criteria, the glaucoma prevalence was 2.2% in the adult Bai nationality population of Dali, Yunnan. The ratio of open-angle glaucoma was similar to primary angle-closure glaucoma of 1.0:0.9, which is different from conventional views. Most persons with POAG and half with PACG were not diagnosed previously. PACG and secondary glaucoma had greater contribution to glaucoma-related blindness than POAG. The prevalence of angle-closure glaucoma was greater than that reported in Caucasian subjects and the disease usually was asymptomatic. These data indicate that there is a large burden of glaucoma in Chinese people. This condition should be the focus of public health initiatives and promote efforts to prevent glaucoma blindness as soon as possible. 
Acknowledgments
Geoffrey Arden, City University London, and Yinfeng Zheng, Zhongshan Opthalmic Center, revised the article. Mingguang He and Jian Zhang provided suggestions on study sampling and statistical analysis. 
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Footnotes
 Supported by the National Natural Science Foundation of China Grants 30860309 and 81160121, and Yunnan Province Science and Technology Project Grant 2009CA007.
Footnotes
5  These authors contributed equally to the work presented here and should therefore be regarded as equivalent first authors.
Footnotes
 Disclosure: H. Zhong, None; J. Li, None; C. Li, None; T. Wei, None; X. Cha, None; N. Cai, None; T. Luo, None; M. Yu, None; Y. Yuan, None
Table 1.  
 
Demographic Comparison of Enumerated and Examined Subject
Table 1.  
 
Demographic Comparison of Enumerated and Examined Subject
Enumerated No. (%) Examined No. (%) % Examination Response Rate
Age group:
 50–59 1123 (41) 715 (33.5) 63.7
 60–69 867 (31.6) 775 (36.3) 89.4
 70–79 607 (22.1) 525 (24.6) 86.5
  >80 145 (5.3) 118 (5.5) 81.4
Sex:
 Male 1315 (48.0) 769 (36.1) 58.5
 Female 1427 (52.0) 1364 (63.9) 95.6
Education:
 None 994 (36.3) 759 (35.6) 76.4
 Primary 1095 (40.0) 868 (40.7) 79.3
 Secondary 554 (20.2) 427 (20.0) 77.1
 Postsecondary 99 (3.6) 79 (3.7) 79.8
Totals 2742 (100) 2133 (100) 77.8
Table 2.  
 
VCDR in Normal Subjects*
Table 2.  
 
VCDR in Normal Subjects*
Right CDR Left CDR Asymmetry†
N (CDR measurements) 1952 1935 1850
 0.5th percentile 0.2 0.2 0
 2.5th percentile 0.2 0.2 0
  Median 0.3 0.3 0
 97.5th percentile 0.7 0.7 0.1
 99.5th percentile 0.9 0.9 0.3
Table 3.  
 
Intraocular Pressure in Normal Subjects*
Table 3.  
 
Intraocular Pressure in Normal Subjects*
Right IOP (mm Hg, 95% CI†) Left IOP (mm Hg, 95% CI†)
N (IOP measurements) 2060 2060
  Mean 14.19 14.38
 0.5th percentile 6 6
 2.5th percentile 8 8
  Median 14 14
 97.5th percentile 20 20
 99.5th percentile‡ 21 21
Table 4.  
 
Mechanism and Characteristics of Glaucoma
Table 4.  
 
Mechanism and Characteristics of Glaucoma
Diagnosis Sex Ratio (M:F) Median Age (Range) Diagnostic Category* Blind† in at Least 1 Eye (% of Total) Previously Diagnosed (%)
1 2 3
POAG 12:10 66 (51–78) 14 6 2 8 (36) 2 (9)
PACG‡ 3:17 71 (54–85) 9 5 6 14 (70) 10 (47.6)
Secondary 1:4 70 (57–82) 0 2 3 5 (100) 1 (20)
Totals 16:31 69 (51–85) 23 13 11 27 (57) 13 (27.7)
Table 5.  
 
Prevalence of All Glaucoma by Age and Sex*
Table 5.  
 
Prevalence of All Glaucoma by Age and Sex*
Age (yrs.) Men Women Totals
(n) Diagnostic Category† Prevalence (95% CI) (n) Diagnostic Category† Prevalence (95% CI) (n) Prevalence (95% CI)
1 2 3 1 2 3
50–59 220 3 0 0 1.4 (0.3–3.9) 495 2 1 0 0.6 (0.1–1.8) 715 0.8 (0.3–1.8)
60–69 308 5 3 0 2.6 (1.1–5.1) 468 5 4 3 2.6 (1.3–4.4) 776 2.6 (1.6–3.9)
70–79 203 4 1 0 2.5 (0.8–5.7) 321 2 4 5 3.4 (1.7–6.0) 524 3.1 (1.8–4.9)
≥80 39 0 0 0 0.0 (0.0–9.0) 79 2 0 3 6.3 (2.1–14.1) 118 4.2 (1.4–9.6)
All 769 12 4 0 2.1 (1.2–3.4) 1364 11 9 11 2.3 (1.6–3.2) 2133 2.2 (1.6–2.9)
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