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Clinical and Epidemiologic Research  |   September 2013
Seven-Year Incidence of Age-Related Cataracts Among an Elderly Chinese Population in Shihpai, Taiwan: The Shihpai Eye Study
Author Affiliations & Notes
  • Tung-Mei Kuang
    Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan
  • Su-Ying Tsai
    Department of Health Management, I-Shou University, Kaohsiung, Taiwan
  • Catherine Jiu-Ling Liu
    Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan
    National Yang-Ming University, School of Medicine, Taipei, Taiwan
  • Yu-Chieh Ko
    Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan
    National Yang-Ming University, School of Medicine, Taipei, Taiwan
  • Shui-Mei Lee
    Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan
    National Yang-Ming University, School of Medicine, Taipei, Taiwan
  • Pesus Chou
    Community Medicine Research Center and Institute of Public Health, National Yang-Ming University, Taipei, Taiwan
  • Correspondence: Pesus Chou, Community Medicine Research Center and Institute of Public Health, National Yang-Ming University, No. 155, Sec. 2, Linong Street, Taipei, 112 Taiwan; pschou@ym.edu.tw
Investigative Ophthalmology & Visual Science September 2013, Vol.54, 6409-6415. doi:10.1167/iovs.13-12582
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      Tung-Mei Kuang, Su-Ying Tsai, Catherine Jiu-Ling Liu, Yu-Chieh Ko, Shui-Mei Lee, Pesus Chou; Seven-Year Incidence of Age-Related Cataracts Among an Elderly Chinese Population in Shihpai, Taiwan: The Shihpai Eye Study. Invest. Ophthalmol. Vis. Sci. 2013;54(9):6409-6415. doi: 10.1167/iovs.13-12582.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose.: To report the 7-year incidence of age-related cataracts in a metropolitan Chinese elderly population.

Methods.: The Shihpai Eye Study 2006 included 460 (55.8%) of 1361 participants in the 1999 baseline survey for a follow-up eye examination. Cataract was graded by one ophthalmologist using the Lens Opacities Classification System III.

Results.: The 7-year incidence of pure nuclear opacity was 18.5% (95% confidence interval [CI]: 12.7%–24.3%)]; 34.7% (95% CI: 27.6%–41.8%) for cortical opacity; and 0.6% (95% CI: 0%–1.8%) for posterior subcapsular opacity. On the other hand, 11.6% (95% CI: 6.8%–16.4%) participants developed both nuclear and cortical opacity, 3.5% (95% CI: 0.8%–6.2%) nuclear and posterior subcapsular opacity; and 1.7% (95% CI: 0%–3.6%) cortical and posterior subcapsular opacity. A total of 3.5% (95% CI: 0.8%–6.2%) of participants developed all three types of cataract. Nuclear cataract was significantly associated with current smoking (P = 0.04; relative risk [RR]: 2.05; 95% CI: 1.05–3.99). Males were almost half as likely (P = 0.04; RR: 0.57; 95% CI: 0.34–0.97) to develop cortical opacity, whereas participants with a history of diabetes were approximately twice as likely to develop cortical opacity (P = 0.05; RR 2.43; 95% CI: 1.02–5.81). A higher level of education (P = 0.03; RR: 0.40; 95% CI: 0.18–0.91) and a higher body mass index (P = 0.02; RR: 0.28; 95% CI: 0.10–0.79) was protective of posterior subcapsular cataract.

Conclusions.: This study indicated a high incidence of cortical opacities and lower incidence of nuclear opacities compared with Caucasians. Posterior subcapsular opacity incidence and cataract surgery rate were comparable.

Introduction
Age-related cataracts are a major cause of blindness worldwide. 1 4 A mission of the World Health Organization VISION 2020: the Right to Sight is to eliminate avoidable blindness globally to ensure the best possible vision for all people, making cataracts a main target. Although not fatal, age-related cataracts cause visual impairment, 5 decrease quality of life, 6 and negatively impact daily and social activities. 7  
Few longitudinal studies provide information on the incidence of age-related cataracts, 8 16 especially in the Asian population. 17 Moreover, the longitudinal effects of some predictors of age-related cataracts, such as body mass index (BMI) 18 20 and increased systolic blood pressure, 21,22 are controversial. The purpose of the present study was to investigate the incidence of different types of age-related cataracts in a metropolitan elderly Chinese population in Shihpai, Taipei, Taiwan, with follow-up at 7 years, and to identify risk factors for various types of age-related cataracts, including demographic variables, lifestyle, and medical history. 
Materials and Methods
The Shihpai Eye Study 23 was a community-based, cross-sectional survey of vision and eye diseases among noninstitutionalized subjects aged 65 years and older in Shihpai, Taipei, Taiwan. Residents aged 65 years and older were identified using the household registration system. This system officially registers personal information such as date of birth, sex, and home address, as well as family members and relations. According to the official household registration in 1999, the total number of residents aged 65 years and older in Shihpai was 4750; 3746 persons were eligible, and 2045 of these were randomly selected to be invited to participate in the study. Of the 2045 subjects, 1361 (66.6%) participated in both the questionnaire and eye examination. The baseline examination was conducted between July 1, 1999, and December 31, 2000. Follow-up examination of the eye condition of the fixed cohort was conducted from March 25, 2006, and ended December 31, 2007. We planned to invite the 1361 participants in the baseline examination for the follow-up study. A structured questionnaire similar to the baseline survey 23 was conducted by intensively trained interviewers. The questionnaire obtained information on demographics (age, sex, locality, marital status, and education); personal medical history; and lifestyle (smoking and alcohol intake). Participants' self-reported demographic data were assessed. Personal medical history was assessed by a checklist. Participants were asked whether they had been diagnosed by a physician with a chronic disease such as diabetes (yes/no). Cigarette smoking history was scored as smoker, passive smoker, ex-smoker, or never-smoker. Alcohol consumption was limited to wine and hard alcohol and was scored as no consumption (or frequency of alcohol consumption only once a week) or habit of alcohol consumption (frequency of alcohol consumption more than once a week). Women were also asked whether they ever used estrogen replacement therapy or other hormones (yes/no). Subjects that were interviewed were invited to participate in a comprehensive ophthalmic examination conducted at the Taipei Veterans General Hospital. Ophthalmologists conducted the examinations according to a standardized protocol. Informed consent was obtained from each subject after explaining the purpose and procedure of the study. The survey followed the tenets of the Declaration of Helsinki. 
This study was approved by the Institutional Review Board of the Taipei Veterans General Hospital. 
Definitions
Three major types of age-related cataracts (nuclear, cortical, and posterior subcapsular) were assessed based on the Lens Opacity Classification system III (LOCS III) by one ophthalmologist at the slit-lamp under maximum dilatation with tropicamide. Subjects were categorized as having an age-related cataract if any type of opacity with an LOCS III grade >2 was present in one or both eyes. We chose grade >2 as the cutoff, because this grade was used in our prevalence analysis 23 and it is also the definition of cataracts adopted by previous major population-based studies. 12,13,15 The intraobserver kappa statistics for reproducibility of grading cataracts (grade >2 versus grade ≤2 ) were 0.86 for cortical opacity, 0.84 for posterior subcapsular opacity, and 0.87 for nuclear opacity. 
Incidence was estimated by participants without any type of opacity (grade ≤2) in both eyes at baseline that developed lens opacity (grade >2) in either eye at the 7-year follow-up, and were categorized into pure form of lens opacity, mixture of two types of opacity, and presence of all three types of opacities. In cases of discordance between eyes, the eye with more types of lens opacity was taken as the cataract type for that participant. 
For comparison with other population-based studies, the development of any cortical, nuclear, or posterior subcapsular opacity (grade >2) in at least one eye among persons without that opacity type (grade ≤2) at baseline was also calculated. An eye that had one opacity type at baseline was considered to be at risk for the other incident opacity types. Participants who were pseudophakic or aphakic at baseline were excluded. Participants that had cataract surgery during this period were excluded in the incidence analysis, but were assessed separately for the cataract surgery rate. 
Height and weight were measured and BMI was calculated by the formula weight in kilograms divided by the square of the height in meters (kg/m2) and was dichotomized into overweight and not overweight according to World Health Organization criteria (overweight, ≥25 kg/m2 versus not overweight, <25 kg/m2). Three consecutive seated blood pressure readings, at least 5 minutes apart, were taken from the right arm and averaged. Waist girth was measured at the minimum circumference, whereas hip girth was measured at the maximum circumference. The definition of regional or central obesity by waist-to-hip ratio was ≥0.92 for men or ≥0.88 for women. 24  
Statistical Analysis
Dependent variables in the analysis were incidence of nuclear, cortical, or posterior subcapsular opacities. Independent variables tested were age (≥80 years vs. 72–79 years); sex (female versus male); education (high school and above versus secondary school and below); marital status (married and living with spouse versus single/separated/divorced/widowed), BMI (≥25 vs. <25); waist-to-hip ratio (high: waist-to-hip ratio ≥0.92 for males, ≥0.88 for females versus normal: <0.92 for males, <0.88 for females); systolic blood pressure (≥160 mm Hg versus <160 mm Hg); history of hypertension (yes/no); diabetes (yes/no); cardiovascular disease (yes/no); stroke (yes/no); smoking history (current smoking versus nonsmoking; ex-smoking versus nonsmoking); alcohol drinking (yes/no); and history of hormone use (yes/no) among women. Univariate analysis was performed to test for an association between each independent variable and dependent variable by χ2 analysis. Generalized estimating equations were used to fit the best model for independent variables. Models were developed separately for each type of opacity—that is, those with grade ≤2 at baseline for one type of opacity that developed to grade >2 at follow-up, regardless of the status of the other two types of opacity. Another analysis was performed with the dependent variable as pure incident nuclear opacity and pure incident cortical opacity, controls were participants without any type of lens opacity (grade ≤2 for all three types of opacity) in both eyes at baseline and follow-up. For posterior subcapsular opacity, because incident case number was small, mixture of posterior subcapsular opacity with nuclear and/or cortical opacity were also included as cases. Sex and age as well as independent variables with a P value of <0.20 under univariate analysis were analyzed in the multivariate models. A P value of <0.05 was considered to be statistically significant. 
Statistical analysis was performed using commercial software (SAS 6.12; SAS Institute, Cary, NC). 
Results
Of the 1361 participants who attended the baseline examination, 205 (15.1%) residents died before they were interviewed, 301 (22.1%) residents moved away, and 31 (2.3%) were institutionalized, thus 824 (60.5%) subjects were eligible for the study, 725 (87.4%) of whom agreed to be interviewed for the questionnaire. Among those interviewed, 460 (55.8% of those eligible, or 39.8% of survivors) participated in the ophthalmic examination. A comparison of the demographics and some of the variables in subjects with and without the eye examination are shown in Table 1. Participants were younger (78.1 ± 4.1 years versus 80.4 ± 5.4 years, P < 0.001), more likely to be male (P < 0.01), married and living with spouse (P < 0.001), and were more highly educated (P < 0.001). Participants were less likely to have a history of stroke (P = 0.03) and more likely to be current smokers (P = 0.03). 
Table 1
 
Descriptive Characteristics of Participants in Shihpai, Taipei, Taiwan, 2006 to 2007
Table 1
 
Descriptive Characteristics of Participants in Shihpai, Taipei, Taiwan, 2006 to 2007
Characteristic Participants,
n = 460
Non participants, n = 265 P Value
Age, y
 72–79 333 150 <0.001*
 ≥80 127 115
Sex
 Male 304 128 <0.001*
 Female 156 137
Education
 Secondary education and below 251 191 <0.001*
 High school and above 209 74
Marital status†
 With spouse 365 191 0.03*
 Without spouse 95 74
BMI, kg/m2
 <25 292 158 0.30
 ≥25 168 107
History of hypertension
 Yes 213 138 0.53
 No 208 122
History of diabetes
 Yes 85 53 0.99
 No 331 206
History of cardiovascular disease
 Yes 167 85 0.06
 No 249 173
History of stroke
 Yes 14 18 0.03*
 No 407 241
Smoking (current vs. never)
 Yes 43 14 0.03*
 No 335 218
Ex-smoking (quit vs. never)
 Yes 46 29 0.90
 No 335 218
Alcohol
 Yes 20 7 0.10
 No 322 233
Among the participants, males were significantly more highly educated (P < 0.001) and married, living with their spouse (P < 0.001) than female participants. There was no significant difference among other demographic variables for participants. 
The number of participants without any type of opacity in both eyes at baseline that participated in the follow-up was 184. After excluding subjects who were unable to cooperate, declined slit-lamp biomicroscopy, or had undergone cataract surgery, information on 173 participants was assessed. A total of 32 (18.5%; 95% confidence interval [CI]: 12.7%–24.3%) participants had incident pure nuclear opacity; 60 participants (34.7%; 95% CI: 27.6%–41.8%) had incident pure cortical opacity; and 1 participant (0.6%; 95% CI: 0%–1.8%) developed incident pure posterior subcapsular opacity. On the other hand, 20 (11.6%; 95% CI: 6.8%–16.4%) participants had both nuclear and cortical opacity; 6 (3.5%; 95% CI: 0.8%–6.2%) had a mixture of nuclear and posterior subcapsular opacity; and 3 (1.7%; 95% CI: 0%–3.6%) participants developed both cortical and posterior subcapsular opacity; 6 (3.5%; 95% CI: 0.8%–6.2%) participants developed all three types of cataract after a 7-year follow-up. 
When analyzed according to eyes, 27.1% (95% CI: 22.2%–32.6%) of the right eye, 21.8% of the left eye (95% CI: 17.4%–27.0%), and 29.4% (95% CI: 24.6%–34.8%) for either eye developed nuclear opacity. For cortical cataract, the percentage was 44.5% (95% CI: 38.9%–50.3%) for the right eye, 41.0% (95% CI: 35.5%–46.7%) for the left eye, and 49.1% (95% CI: 44.3%–55.1%) for either eye. For posterior subcapsular cataract, 5.9% (95% CI: 3.8%–8.9%) of the right eye, 5.8% (95% CI: 3.7%–8.8%) for the left eye, and 8.1% (95% CI: 5.7%–11.3%) for either eye developed posterior subcapsular cataract. The distribution of cataracts among participants is shown in Table 2. During this period of time, 41 (10.6%; 95% CI: 7.9%–14.1%) right eyes and 38 (9.8%; 95% CI: 7.2%–13.2%) left eyes received cataract surgery. 
Table 2
 
Seven-Year Incidence of Each Type of Age-Related Cataract in Either Eye in Shihpai, Taipei, Taiwan, 2006 to 2007
Table 2
 
Seven-Year Incidence of Each Type of Age-Related Cataract in Either Eye in Shihpai, Taipei, Taiwan, 2006 to 2007
Type of Cataract Male Female Total
n % n % n %
Nuclear cataract 65/220 29.6 26/89 29.2 91/309 29.4
Cortical cataract 102/228 39.8 60/98 49.7 162/326 49.1
Posterior subcapsular cataract 20/252 7.9 10/120 8.3 30/372 8.1
Pseudophakia 27/255 10.6 30/132 22.7 57/387 14.7
In univariate analysis, nuclear cataract was significantly associated with smoking (P = 0.04). Females (P = 0.01) were more likely to have cortical cataracts than males. Moreover, alcohol drinking (P = 0.01) and a history of diabetes (P = 0.04) were also significantly associated with cortical opacity. For posterior subcapsular cataract, BMI (P = 0.01) was a significant predisposing factor (Table 3). 
Table 3
 
Univariate Analysis on Age-Related Cataracts Among Residents in Shihpai, Taipei, Taiwan, 2006 to 2007
Table 3
 
Univariate Analysis on Age-Related Cataracts Among Residents in Shihpai, Taipei, Taiwan, 2006 to 2007
Variable Nuclear Cortical Posterior Subcapsular
n P Value n P Value n P Value
Age, y
 72–79 71/236 0.66 116/243 0.23 20/280 0.25
 80–93 20/73 46/83 10/92
Sex
 Male 65/220 0.95 102/228 0.01* 20/252 0.90
 Female 26/89 60/98 10/120
Education
 ≤Secondary 45/154 0.93 81/160 0.74 20/195 0.10
 ≥High school 46/155 81/166 10/177
BMI, kg/m2
 <25 56/193 0.83 102/199 0.48 25/230 0.01*
 ≥25 35/116 60/127 5/142
Waist-to-hip ratio†
 High 29/97 0.91 40/96 0.06 10/112 0.69
 Not high 62/212 122/230 20/260
Systolic blood pressure, mm Hg
 ≥160 9/25 0.45 10/25 0.31 3/33 0.82
 <160 82/284 152/301 27/339
Smoking
 Current 23/56 0.04* 33/62 0.58 7/68 0.44
 Never 52/195 99/201 17/230
Smoking
 Past 15/54 0.87 28/59 0.81 6/67 0.67
 Never 52/195 99/201 17/230
Alcohol
 Yes 12/43 0.73 14/44 0.01* 5/49 0.58
 No 76/249 140/266 24/306
Hypertension history
 Yes 36/118 0.75 62/119 0.51 14/140 0.29
 No 55/191 100/207 16/232
Diabetes history
 Yes 10/38 0.69 21/31 0.04* 5/47 0.46
 No 78/265 138/288 24/318
Cardiovascular disease history
 Yes 25/80 0.62 35/83 0.11 10/92 0.17
 No 64/226 126/241 18/276
Stroke history
 Yes 2/8 0.78 3/8 0.48 1/11 0.90
 No 89/301 159/318 29/361
History of hormone use in women
 Yes 6/24 0.57 12/23 0.48 3/28 0.63
 No 20/64 46/73 7/90
In multivariate analysis, nuclear cataract was significantly associated with smoking (P = 0.04; relative risk [RR]: 2.05; 95% CI: 1.05–3.99). On the other hand, males were almost half as likely to develop cortical opacity compared with females (P = 0.04; RR: 0.57; 95% CI: 0.34–0.97) and those with a history of diabetes were 2.43 times (P = 0.05; RR 2.43; 95% CI: 1.02–5.81) more likely to have cortical opacity. For posterior subcapsular cataract, a higher level of education was protective against posterior subcapsular cataract (P = 0.03; RR: 0.40; 95% CI: 0.18–0.91) and a higher BMI was associated with a lower risk of developing posterior subcapsular opacity (P = 0.02; RR 0.28; 95% CI: 0.10–0.79) (Table 4). 
Table 4
 
Multivariate Analysis on Age-Related Cataracts Among Residents in Shihpai, Taipei, Taiwan, 2006 to 2007
Table 4
 
Multivariate Analysis on Age-Related Cataracts Among Residents in Shihpai, Taipei, Taiwan, 2006 to 2007
Variable Nuclear Cortical Posterior Subcapsular
RR (95% CI) P Value RR (95% CI) P Value RR (95% CI) P Value
Age, y
 80–93 vs. 72–79 0.84 (0.43–1.64) 0.60 1.23 (0.71–2.12) 0.47 1.24 (0.52–3.00) 0.63
Sex
 Male vs. female 0.85 (0.46–1.57) 0.60 0.57 (0.34–0.97) 0.04* 1.24 (0.54–2.81) 0.61
Education
 ≥High school vs. ≤secondary 0.40 (0.18–0.91) 0.03*
BMI, kg/m2
  ≥25 vs. <25 0.28 (0.10–0.79) 0.02*
Waist-to-hip ratio†
 High vs. not high 0.63 (0.37–1.07) 0.09
Smoking
  Current vs. never smoking 2.05 (1.05–3.99) 0.04*
Alcohol
 Yes vs. no 0.53 (0.26–1.07) 0.08
History of diabetes
 Yes vs. no 2.43 (1.02–5.81) 0.05*
History of cardiovascular disease
 Yes vs. no 0.68 (0.39–1.18) 0.17 1.88 (0.80–4.43) 0.15
Separate multivariate analysis performed for the development of a pure type of lens opacity showed that results were generally consistent with the previous analysis. Smoking (P = 0.01; RR 5.87; 95% CI: 1.53–22.48) was a significant predictor for nuclear opacity. For cortical opacity, age (P = 0.03; RR 4.01; 95% CI: 1.16–13.84) was a significant predictor, whereas sex (P = 0.87) became statistically insignificant. Diabetes mellitus (P = 0.05; RR: 6.63; 95% CI: 1.01–45.88) was borderline significant. For posterior subcapsular opacity, BMI (P = 0.03; RR 0.15; 95% CI: 0.03–0.80) became the only significant predictor. 
Discussion
The Shihpai Eye Study provides the longest follow-up data on the natural history of cataract development in a Chinese elderly population. A particularly high incidence of cortical opacity was noted in our study. This observation was very similar to the Barbados Eye Study. 12,13 When compared with the Beaver Dam Eye Study 8 10 and the Blue Mountains Eye Study 11 (Table 5), whites had a much higher incidence of nuclear opacity and a lower incidence of cortical opacity. Interestingly, even among different races, posterior subcapsular opacity had the lowest incidence of the three types of cataract. 
Table 5
 
Incidence of Various Types of Age-Related Cataract and Cataract surgery in Population-Based Studies
Table 5
 
Incidence of Various Types of Age-Related Cataract and Cataract surgery in Population-Based Studies
Study Race Follow-up Years Age at Baseline Baseline Examination Grading System Nuclear Cortical Posterior Subcapsular Surgery
At Risk, n % At Risk, n % At Risk, n % At Risk, n %
Beaver Dam Eye Study8 Caucasians 4.8 65–74 1988–1990 Wisconsin 565 40.2 582 18.9 647 7.6 909 11.2
(either eye) ≥75 107 55.1 121 26.5 158 11.4 314 15.0
Beaver Dam Eye Study9 Caucasians 10 65–74 1988–1990 Wisconsin 566 53.3 584 36.9 712 12.9 909 26.4
(either eye) ≥75 107 72.7 123 48.2 194 14.0 314 29.8
Blue Mountains Eye Study11 Caucasians 5 65–74 1992–1994 Wisconsin 407 35.1 563 14.6 679 4.9 847 7.3
(persons) >74 99 61.6 146 21.2 214 6.1 296 16.6
Blue Mountains Eye Study11 Caucasians 10 65–74 1992–1994 Wisconsin 407 54.2 563 33.9 679 12.9 847 28.0
(persons) >74 99 78.7 146 50.8 214 15.1 296 45.4
Barbados Eye Study12 African descent 4 60–69 1987–1992 LOCS II 567 18.9 343 40.5 681 3.8
(persons) 70+ 251 41.8 135 56.3 473 10.4
Barbados Eye Study13 African descent 9 60–69 1987–1992 LOCS II 610 81.9 365 55.7 732 9.1 779 5.7
(persons) 70+ 262 94.6 141 72.9 494 21.2 602 14.4
Los Angeles Latino Eye Study16 Latinos 4 60–69 2000–2003 LOCS II 701 26.5 553 17.2 711 4.9 3668 1.48
(either eye) 70+ 194 53.6 170 25.9 271 10.3 (all age groups)
Beijing Eye Study17 Chinese 5 65−74 2001 AREDS 362 16.9 485 29.1 536 15.5 5.4
(either eye) 75+ 24 33.3 65 24.6 75 25.3 9.5
This Study Chinese 7 65−74 1999–2000 LOCS III 236 29.6 243 48.5 280 6.5 12.6
(either eye) >74 73 28.9 83 55.4 92 15.4 24.6
The incidence of different types of cataract differed between our study and the Beijing Eye Study, 17 although the two studies included subjects of the same race. There are several possible explanations. First, different grading systems were used (AREDS in the Beijing Eye study 17 and LOCS III in our study). Second, the definition of cataract development differed. Third, the target population in our study was aged 65 and older at baseline, whereas the recruitment age for the Beijing Eye Study was 40 years and older. The elderly group, especially those aged 75 years and older, represented only a small proportion in the age structure of their participants. Hence, one subject might contribute to a substantial percentage in the incidence rate. Moreover, the follow-up period was 5 years in their study as opposed to 7 years in our survey. Environmental and lifestyle factors may play a role as well. A higher incidence of nuclear and cortical opacity was observed in our study compared with the Beijing Eye Study. 17 On the other hand, the incidence of posterior subcapsular cataract was much lower in our population. The cataract operation rate was approximately double in our participants compared with the Beijing Eye Study (Table 5). The cataract surgery rate in our population was comparable with the Beaver Dam Eye Study 8,9 and higher than the Barbados Eye Study. 12,13 Posterior subcapsular opacity is more visually disturbing than the other two types of cataract and thus participants might be more inclined to undergo cataract operation. 
Among the potential risk factors, our study revealed that current smokers had a higher chance of developing nuclear opacity compared with nonsmokers. On the other hand, there was no significant difference in the risk of developing all three types of cataract between previous smokers and nonsmokers. This finding was largely confirmed by earlier studies. 23,25 31 Our results based on longitudinal follow-up of a fixed cohort further suggested a possible effect that smoking imposed on the development of nuclear cataract. However, a higher proportion of current smokers participated in the eye examination, which may have biased the strength of the relationship between current smoking and nuclear cataracts in our study. 
On the other hand, female sex and a history of diabetes were associated with a higher risk of cortical opacity. This finding was concordant with the Los Angeles Latino Eye Study 25 and most other population-based studies. 18,21,23  
Our findings indicated that having a higher level of education and higher BMI were protective of posterior subcapsular opacity. One possible reason is that lower levels of education might be related to lower income and a higher probability of outdoor jobs 30 and hence more UV-light exposure. Moreover, a lower income might also lead to a low diet quality with insufficient antioxidants and vitamins. 30,32  
In our study, higher BMI was noted to be protective of posterior subcapsular opacity. Higher education provides a better chance of indoor jobs and a more sedentary lifestyle. Hence, this may be related to a lower chance of UV-light exposure as well as a higher chance of a greater BMI. Interestingly, there are abundant studies in the literature suggesting that BMI is related to age-related cataract, although the pathway is unclear. Moreover, the relationship is inconsistent with regard to the type of cataract involved as well as the direction of the relationship. 18 20,33 Because BMI is a modifiable risk factor, however, this aspect deserves further evaluation and analysis. 
There were some limitations to our study. The response rate in our study was relatively low (55.8% of those eligible). Obtaining population-based prevalence estimates of eye disease among elderly persons is challenging because this group of individuals is less likely to participate in research studies. 34 The inclusion rate in the Rotterdam Study 35 ranged from 59% in the group aged 75 to 84 years to 28% in the group aged 85 years and older. Similarly, in the Baltimore Study, 36 inclusion rates were 48% in the group aged 70 to 79 years and 21% in the group aged 80 years and older. Another potential reason for the low participation rate is that lack of utilization of ophthalmologic care for prevention and treatment has created the impression that loss of vision is expected in senior life and the idea that nothing can be done to improve the situation among elderly people, particularly among the less-educated. 23  
Nonparticipants were older, more likely to be female or illiterate, and more likely to have a history of stroke and to be current smokers. These unexamined subjects remain a potential source of bias. Our study populations were noninstitutionalized survivors; excluding those who are inpatients or who have paralysis or disability in the survey probably removes a disproportionate number of potential participants with functional or physical impairment and/or declining health-related quality of life and might bias the results of the study. Furthermore, mortality of nonparticipants might lead to an underestimation of the incidence rate. Third, the assessment of comorbidities by adopting a dichotomized classification was simplistic. Moreover, the possibility of a chance finding cannot be completely excluded. 
On the other hand, interobserver agreement of graders between baseline and follow-up was unavailable. The interobserver reproducibility of lens grading between two study ophthalmologists at baseline 23 was 0.86 for cortical opacity, 0.82 for posterior subcapsular opacity, and 0.85 for nuclear opacity. The intraobserver agreement for reproducibility of grading cataracts was 0.83 for cortical opacity, 0.80 for posterior subcapsular opacity, and 0.86 for nuclear opacity for one ophthalmologist and 0.87, 0.85, and 0.84, respectively, for the other ophthalmologist. The possibility of a contemporaneous variability and temporal drift in lens grading cannot be eliminated. A previous study 37 showed that when temporal drift was present, baseline scores tended to be higher than subsequent scores for eyes with higher severity grades at baseline. Hence, the effect on our study should be minimal. 
In conclusion, the incidence of cortical opacity is highest among the three types of cataract after a follow-up of 7 years in our urban elderly Chinese population, followed by nuclear opacity, then the incidence of posterior subcapsular opacity. Understanding the incidence of various types of cataracts and their risk factors can facilitate the development of educational programs and campaigns to prevent and delay the onset of cataracts and the impact it may bring to the quality of life of the elderly. 
Acknowledgments
Supported by a grant from Taipei Veterans General Hospital, Taipei, Taiwan (V95S3-001). The authors alone are responsible for the content and writing of the paper. 
Disclosure: T.-M. Kuang, None; S.-Y. Tsai, None; C.J.-L. Liu, None; Y.-C. Ko, None; S.-M. Lee, None; P. Chou, None 
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Table 1
 
Descriptive Characteristics of Participants in Shihpai, Taipei, Taiwan, 2006 to 2007
Table 1
 
Descriptive Characteristics of Participants in Shihpai, Taipei, Taiwan, 2006 to 2007
Characteristic Participants,
n = 460
Non participants, n = 265 P Value
Age, y
 72–79 333 150 <0.001*
 ≥80 127 115
Sex
 Male 304 128 <0.001*
 Female 156 137
Education
 Secondary education and below 251 191 <0.001*
 High school and above 209 74
Marital status†
 With spouse 365 191 0.03*
 Without spouse 95 74
BMI, kg/m2
 <25 292 158 0.30
 ≥25 168 107
History of hypertension
 Yes 213 138 0.53
 No 208 122
History of diabetes
 Yes 85 53 0.99
 No 331 206
History of cardiovascular disease
 Yes 167 85 0.06
 No 249 173
History of stroke
 Yes 14 18 0.03*
 No 407 241
Smoking (current vs. never)
 Yes 43 14 0.03*
 No 335 218
Ex-smoking (quit vs. never)
 Yes 46 29 0.90
 No 335 218
Alcohol
 Yes 20 7 0.10
 No 322 233
Table 2
 
Seven-Year Incidence of Each Type of Age-Related Cataract in Either Eye in Shihpai, Taipei, Taiwan, 2006 to 2007
Table 2
 
Seven-Year Incidence of Each Type of Age-Related Cataract in Either Eye in Shihpai, Taipei, Taiwan, 2006 to 2007
Type of Cataract Male Female Total
n % n % n %
Nuclear cataract 65/220 29.6 26/89 29.2 91/309 29.4
Cortical cataract 102/228 39.8 60/98 49.7 162/326 49.1
Posterior subcapsular cataract 20/252 7.9 10/120 8.3 30/372 8.1
Pseudophakia 27/255 10.6 30/132 22.7 57/387 14.7
Table 3
 
Univariate Analysis on Age-Related Cataracts Among Residents in Shihpai, Taipei, Taiwan, 2006 to 2007
Table 3
 
Univariate Analysis on Age-Related Cataracts Among Residents in Shihpai, Taipei, Taiwan, 2006 to 2007
Variable Nuclear Cortical Posterior Subcapsular
n P Value n P Value n P Value
Age, y
 72–79 71/236 0.66 116/243 0.23 20/280 0.25
 80–93 20/73 46/83 10/92
Sex
 Male 65/220 0.95 102/228 0.01* 20/252 0.90
 Female 26/89 60/98 10/120
Education
 ≤Secondary 45/154 0.93 81/160 0.74 20/195 0.10
 ≥High school 46/155 81/166 10/177
BMI, kg/m2
 <25 56/193 0.83 102/199 0.48 25/230 0.01*
 ≥25 35/116 60/127 5/142
Waist-to-hip ratio†
 High 29/97 0.91 40/96 0.06 10/112 0.69
 Not high 62/212 122/230 20/260
Systolic blood pressure, mm Hg
 ≥160 9/25 0.45 10/25 0.31 3/33 0.82
 <160 82/284 152/301 27/339
Smoking
 Current 23/56 0.04* 33/62 0.58 7/68 0.44
 Never 52/195 99/201 17/230
Smoking
 Past 15/54 0.87 28/59 0.81 6/67 0.67
 Never 52/195 99/201 17/230
Alcohol
 Yes 12/43 0.73 14/44 0.01* 5/49 0.58
 No 76/249 140/266 24/306
Hypertension history
 Yes 36/118 0.75 62/119 0.51 14/140 0.29
 No 55/191 100/207 16/232
Diabetes history
 Yes 10/38 0.69 21/31 0.04* 5/47 0.46
 No 78/265 138/288 24/318
Cardiovascular disease history
 Yes 25/80 0.62 35/83 0.11 10/92 0.17
 No 64/226 126/241 18/276
Stroke history
 Yes 2/8 0.78 3/8 0.48 1/11 0.90
 No 89/301 159/318 29/361
History of hormone use in women
 Yes 6/24 0.57 12/23 0.48 3/28 0.63
 No 20/64 46/73 7/90
Table 4
 
Multivariate Analysis on Age-Related Cataracts Among Residents in Shihpai, Taipei, Taiwan, 2006 to 2007
Table 4
 
Multivariate Analysis on Age-Related Cataracts Among Residents in Shihpai, Taipei, Taiwan, 2006 to 2007
Variable Nuclear Cortical Posterior Subcapsular
RR (95% CI) P Value RR (95% CI) P Value RR (95% CI) P Value
Age, y
 80–93 vs. 72–79 0.84 (0.43–1.64) 0.60 1.23 (0.71–2.12) 0.47 1.24 (0.52–3.00) 0.63
Sex
 Male vs. female 0.85 (0.46–1.57) 0.60 0.57 (0.34–0.97) 0.04* 1.24 (0.54–2.81) 0.61
Education
 ≥High school vs. ≤secondary 0.40 (0.18–0.91) 0.03*
BMI, kg/m2
  ≥25 vs. <25 0.28 (0.10–0.79) 0.02*
Waist-to-hip ratio†
 High vs. not high 0.63 (0.37–1.07) 0.09
Smoking
  Current vs. never smoking 2.05 (1.05–3.99) 0.04*
Alcohol
 Yes vs. no 0.53 (0.26–1.07) 0.08
History of diabetes
 Yes vs. no 2.43 (1.02–5.81) 0.05*
History of cardiovascular disease
 Yes vs. no 0.68 (0.39–1.18) 0.17 1.88 (0.80–4.43) 0.15
Table 5
 
Incidence of Various Types of Age-Related Cataract and Cataract surgery in Population-Based Studies
Table 5
 
Incidence of Various Types of Age-Related Cataract and Cataract surgery in Population-Based Studies
Study Race Follow-up Years Age at Baseline Baseline Examination Grading System Nuclear Cortical Posterior Subcapsular Surgery
At Risk, n % At Risk, n % At Risk, n % At Risk, n %
Beaver Dam Eye Study8 Caucasians 4.8 65–74 1988–1990 Wisconsin 565 40.2 582 18.9 647 7.6 909 11.2
(either eye) ≥75 107 55.1 121 26.5 158 11.4 314 15.0
Beaver Dam Eye Study9 Caucasians 10 65–74 1988–1990 Wisconsin 566 53.3 584 36.9 712 12.9 909 26.4
(either eye) ≥75 107 72.7 123 48.2 194 14.0 314 29.8
Blue Mountains Eye Study11 Caucasians 5 65–74 1992–1994 Wisconsin 407 35.1 563 14.6 679 4.9 847 7.3
(persons) >74 99 61.6 146 21.2 214 6.1 296 16.6
Blue Mountains Eye Study11 Caucasians 10 65–74 1992–1994 Wisconsin 407 54.2 563 33.9 679 12.9 847 28.0
(persons) >74 99 78.7 146 50.8 214 15.1 296 45.4
Barbados Eye Study12 African descent 4 60–69 1987–1992 LOCS II 567 18.9 343 40.5 681 3.8
(persons) 70+ 251 41.8 135 56.3 473 10.4
Barbados Eye Study13 African descent 9 60–69 1987–1992 LOCS II 610 81.9 365 55.7 732 9.1 779 5.7
(persons) 70+ 262 94.6 141 72.9 494 21.2 602 14.4
Los Angeles Latino Eye Study16 Latinos 4 60–69 2000–2003 LOCS II 701 26.5 553 17.2 711 4.9 3668 1.48
(either eye) 70+ 194 53.6 170 25.9 271 10.3 (all age groups)
Beijing Eye Study17 Chinese 5 65−74 2001 AREDS 362 16.9 485 29.1 536 15.5 5.4
(either eye) 75+ 24 33.3 65 24.6 75 25.3 9.5
This Study Chinese 7 65−74 1999–2000 LOCS III 236 29.6 243 48.5 280 6.5 12.6
(either eye) >74 73 28.9 83 55.4 92 15.4 24.6
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