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Six-Year Incidence of and Risk Factors for Cataract Surgery in a Multi-ethnic Asian Population
Six-Year Incidence of and Risk Factors for Cataract Surgery in a Multiethnic Asian Population The Singapore Epidemiology of Eye Diseases Study Ava Grace Tan, MAIT, MPH,1 Annette Kifley, MAppStat, PhD,1 Yih-Chung Tham, PhD,2 Yuan Shi, PhD,2 Miao Li Chee, BSc,2 Charumathi Sabanayagam, MD, PhD,2,3,4 Nicholas Yi Qiang Tan, MA, BM BCh,2 Kah Hie Wong, MBBS,2,4 Paul Mitchell, MD, PhD,1 Robert G. Cumming, MPH, PhD,5 Tien Yin Wong, MD, PhD,2,3,4 Jie Jin Wang, MMed, PhD,1,6,* Ching-Yu Cheng, MD, PhD2,3,4,* Purpose: To report the 6-year incidence of cataract surgery in an Asian population-based cohort of Malay, Indian, and Chinese persons living in Singapore and factors associated with undergoing cataract surgery over the follow-up period. Design: Population-based prospective cohort study. Participants: From 2004 through 2011, 10 033 participants (3280 Malays, 3400 Indians, and 3353 Chinese) 40 years of age or older participated in the Singapore Epidemiology of Eye Diseases Study. Six years later, 6762 participants (78.7% of those eligible, including 1901 Malays [72.1% of eligible], 2200 Indians [75.5% of eligible], and 2661 Chinese [87.7% of eligible]) were re-examined. Methods: Detailed eye examinations including slit-lamp biomicroscopy were conducted at both visits. Logistic regression models were used to assess factors associated with cataract surgery after adjusting for age, gender, socioeconomic status, and other risk factors. Main Outcome Measure: Incident cataract surgery. Results: The age-adjusted 6-year incidence of cataract surgery was 11.0% (9.5%, 12.6%, and 11.1% for Malays, Indians, and Chinese, respectively) and was strongly age related (P < 0.001 for trend). After adjustment, baseline factors associated with incident cataract surgery included older age (odds ratio [OR], 1.13 per 1-year increase; 95% confidence interval [CI], 1.11e1.14), diabetes (OR, 1.90; 95% CI, 1.54e2.33), myopia (OR, 1.78; 95% CI, 1.44e2.20), and baseline presence of any cataract, including nuclear cataract (OR, 3.78; 95% CI, 2.91e4.89), cortical cataract (OR, 3.01; 95% CI, 2.45e3.71), and posterior subcapsular cataract (OR, 5.00; 95% CI, 3.91e6.41). The population attributable risks of cataract surgery related to diabetes and myopia were 17.6% and 19.1%, respectively. Conclusions: One in 10 Malay, Indian, and Chinese Singaporeans 40 years of age or older underwent cataract surgery in at least 1 eye over 6 years. In Asian populations, diabetes and myopia, 2 well-known factors associated with cataract prevalence, are significant and potentially modifiable factors associated with the need for cataract surgery. Ophthalmology 2018;-:1e10 ª 2018 by the American Academy of Ophthalmology Supplemental material available at www.aaojournal.org.
Age-related cataract remains the leading causes of blindness (35%) and visual impairment (25%) among older people globally.1 Cataract surgery currently is the only effective treatment for cataract.2 In addition to improved visual function, cataract surgery is associated with benefits on other health and social outcomes, including emotional well being, quality of life, economic benefits and productivity, and improved survival of elderly who are visually impaired because of cataract.3e7 However, cataract surgery requires significant investment in terms of the number of ophthalmologists needed and the ª 2018 by the American Academy of Ophthalmology Published by Elsevier Inc.
set-up of clinic and operating theater resources. To plan for such health care and ophthalmic care resources, longitudinal data are needed to determine the number of new cataract surgery cases needed in the population and to identify persons at risk of cataract surgery. Although the incidence of cataract surgery is well documented in Western countries,8e13 there are fewer reports from Asian populations14e17 (Table S1, available at www.aaojournal.org). The use of incidence rates from other countries may provide an estimate; however, it may limit the ability of policy makers and governments to plan adequately for https://doi.org/10.1016/j.ophtha.2018.07.026 ISSN 0161-6420/18
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Ophthalmology Volume -, Number -, Month 2018
The SEED Study is a population-based cohort study of common eye diseases in residents of Singapore 40 years of age and older among 3 major ethnic groups: Malay, Indian, and Chinese. The baseline examinations for each ethnic group were as follows: 3280 (78.7% of eligible) Malay participants were recruited from 2004 through 2006, 3400 (75.6% of eligible) Indian participants were recruited from 2007 through 2009, and 3353 (72.8% of eligible) Chinese participants were recruited from 2009 through 2011. Overall response rate at baseline for the SEED Study was 75.6%. For the 6-year follow-up visits, we re-examined 1901 (72.1% of eligible) Malay participants from 2011 through 2013, 2200 (75.5% of eligible) Indians from 2013 through 2015, and 2661 (87.7% of eligible) Chinese from 2015 through 2017. The study adhered to the principles of the Declaration of Helsinki. Ethics approval was obtained from the Singapore Eye Research Institute Institutional Review Board. Written informed consent was obtained from each participant.
participants with an intact lens in both eyes at baseline were considered at risk. For eye-specific analysis, any eye with an intact lens at baseline was considered at risk of incident cataract surgery. In addition, incident unilateral and bilateral cataract surgery were defined as cataract surgery performed in one eye only and in both eyes, respectively, during the 6-year follow-up period. Interviews were conducted in participants’ choice of English, Chinese, Malay, or Tamil. Information collected from intervieweradministered questionnaires included socioeconomic status (such as education level and income levels), occupation, medical history, medication use, and smoking status. Participants also were asked whether they used any glasses and, if so, how often they visited optometrists, opticians, or ophthalmologists to have their glasses checked. Blood pressure was measured after the participant was seated and rested for 5 minutes using a digital sphygmomanometer (Dinamap model Pro Series DP110X-RW, 100V2; GE Medical Systems Information Technologies, Inc., Milwaukee, WI). Hypertension was defined as systolic blood pressure of 140 mmHg or more, diastolic blood pressure of 90 mmHg or more, physiciandiagnosed hypertension, or self-reported history of hypertension. Smoking status was defined as current and noncurrent smoking. Low socioeconomic status (SES) was defined as having primary or lower education, individual monthly income less than SG$2000, and a 1- to 2-room Housing and Development Board flat. Nonfasting blood samples were collected and processed the same day at the Singapore General Hospital Laboratory. Serum glucose levels were assessed on the Beckman Coulter Unicel DxC 800 analyzer using the oxygen rate method. Diabetes was defined as random glucose level of 11.1 mmol/l or more, use of diabetic medication, or self-reported history of diabetes. Presenting visual acuity (PVA) and best-corrected visual acuity (BCVA) were measured for each eye using a logarithm of the minimum angle of resolution number chart (Lighthouse International, New York) at 4 m. PVA was measured with walk-in optical correction (glasses or contact lenses), if any. BCVA was measured as the best possible correction obtained with subjective refraction conducted by study optometrists. Myopia was defined as spherical equivalent (SE) refraction of less than 0.5 diopters (D). High myopia was defined as less than e5.0 D. Axial length was measured using a noncontact partial coherence laser interferometer (IOLMaster version 3.01; Carl Zeiss, Meditec AG Jena, Germany).
Examination Procedures and Definitions
Statistical Analysis
Similar examination procedures were followed for all ethnic groups for both the baseline and follow-up examinations. Details of the methodology have been reported previously.19e22 Briefly, each participant underwent a detailed eye examination, including slitlamp biomicroscopy (model BQ-900; Haag-Streit, Switzerland) and slit-lamp photography of the lens using digital slit-lamp (Topcon model DC-1 with FD-21 flash attachment; Topcon, Tokyo, Japan) and retroillumination (Nidek EAS-1000; Nidek, Tokyo, Japan) cameras. Cataract was graded from baseline photographs using the Wisconsin Cataract Grading system. Nuclear cataract was defined as grade 4 or more, cortical cataract was defined as 5% or more of the total lens area with cortical opacity involved, and posterior subcapsular (PSC) cataract was defined as any such opacity present. Any cataract refers to the presence of cataract in either eye. Cataract surgery status was defined as the presence of an intraocular lens implant (pseudophakia) or the absence of the natural lens (aphakia), determined from the slit-lamp biomicroscopy examination during the study visit, from the grading of lens photographs, or both. Incidence of cataract surgery was defined as pseudophakia or aphakia at follow-up among participants with an intact lens at baseline. For person-specific analysis,
All analyses were performed using SAS version 9.3 (SAS Institute, Inc., Cary, NC). Findings from each ethnic group were presented separately as well as in combination as the SEED Study population. Differences in baseline characteristics were tested using an independent t test for continuous variables and Pearson’s chisquare test for categorical variables. Age-adjusted incidence for the 3 ethnic groups and the combined SEED Study population was calculated using direct age standardization to the 2010 Singapore Population Census.23 Logistic regression models (person-specific analysis) and generalized estimating equations logistic regression models (eyespecific analysis) were used to determine factors associated with incident cataract surgery after adjusting for baseline age, gender, ethnicity, smoking status, hypertension, diabetes, SES, and myopia. In the person-specific analysis, for the continuous variables PVA, BCVA, and axial length, we used PVA and BCVA from the worse eye (eye with poorer visual acuity) and the mean axial length of the right and left eyes for each person. For the eyespecific analyses, we used variables specific to each eye. We also compared the mean ages at follow-up among those who had incident cataract surgery by the presence versus absence of diabetes and myopia. We determined the proportion of incident
sufficient eye care resources in Asia. Providing geographicand ethnic-specific incidence rates for cataract surgery will aid in planning and allocating resources more accurately. Singapore is a small city-state but has a multiethnic Asian population comprising 3 major ethnic groups: Chinese, Malays, and Indians. Cataract surgical rates among Malay, Indian, and Chinese Singaporeans were evaluated previously almost 2 decades ago based on health expenditure data from the Medisave scheme, a governmentadministered medical savings scheme in Singapore.18 This database does not have factors associated with cataract surgery, nor does it cover private insurance, which is increasingly used to pay for cataract surgery.18 Hence, we investigated the 6-year incidence rates and associated factors of cataract surgery in Singapore’s multiethnic Asian population using recent data from the Singapore Epidemiology of Eye Diseases (SEED) Study.
Methods Study Populations
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Table 1. Baseline Characteristics of Participants and Nonparticipants in 6-Year Follow-up Examinations from the Singapore Epidemiology of Eye Diseases Study Ethnic Groups: Malays, Indians, and Chinese
Baseline Characteristics
Participants
Nonparticipants P Value
2200 <0.001 56.5 (9.2) <0.001 1113 (50.6) <0.001 293 (13.3) <0.001 1168 (53.2) <0.001 671 (31.6) <0.001 62 (2.9) <0.001 0.3 (0.4) <0.001 0.1 (0.3) <0.001 1741 (79.2) 0.56 393 (22.7) <0.001 202 (10.9) <0.001 409 (20.5) <0.001 157 (7.8) <0.001 253 (11.5) <0.001 96 (4.4) <0.001 157 (7.1) 0.005 696 (32.8) 0.04 83 (3.9) <0.001 23.4 (1.1)
Nonparticipants P Value 1200 60.1 (11.1) 581 (48.4) 206 (17.2) 761 (63.6) 458 (40.2) 70 (6.0) 0.4 (0.4) 0.2 (0.4) 857 (71.5) 192 (22.5) 197 (21.0) 300 (30.1) 143 (14.5) 232 (19.5) 80 (6.7) 152 (12.7) 395 (35.5) 50 (4.6) 23.3 (1.1)
<0.001 0.23 0.003 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.91 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.11 0.38 0.08
Participants 2661 58.4 (11.2) 1365 (51.3) 333 (12.5) 1481 (55.7) 345 (13.5) 35 (1.36) 0.3 (0.4) 0.2 (0.3) 2279 (85.7) 340 (15.0) 299 (12.9) 560 (23.0) 219 (9.1) 278 (10.5) 110 (4.1) 168 (6.3) 1248 (48.1) 246 (9.6) 24.0 (1.4)
Nonparticipants P Value 692 64.5 (9.2) 326 (47.1) 109 (15.8) 501 (72.4) 142 (22.1) 23 (3.44) 0.5 (0.4) 0.3 (0.4) 531 (76.7) 78 (14.9) 155 (29.4) 187 (33.5) 119 (22.0) 168 (24.4) 69 (10.0) 99 (14.3) 325 (49.5) 47 (7.4) 23.8 (1.4)
<0.001 0.05 0.02 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.96 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.52 0.09 <0.001
Participants 6762 57.4 (9.5) 3515 (52.0) 972 (14.4) 3876 (57.5) 1414 (21.7) 294 (4.5) 0.3 (0.4) 0.1 (0.3) 5369 (79.5) 922 (17.3) 778 (13.2) 1478 (23.6) 581 (9.4) 658 (9.8) 266 (3.9) 392 (5.8) 2504 (38.0) 419 (6.4) 23.7 (1.3)
Non-participants P Value 3271 62.0 (11.4) 1575 (48.2) 631 (19.4) 2291 (70.3) 971 (31.3) 334 (10.4) 0.5 (0.5) 0.3 (0.4) 2257 (69.3) 383 (17.3) 740 (28.0) 977 (34.3) 534 (19.0) 557 (17.2) 219 (6.7) 338 (10.3) 1179 (38.1) 140 (4.6) 23.5 (1.1)
<0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.94 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.93 <0.001 <0.001
AL ¼ axial length; BCVA ¼ best-corrected visual acuity (logarithm of the minimum angle of resolution); PSC ¼ posterior subcapsular; PVA ¼ presenting visual acuity (logarithm of the minimum angle of resolution); SES ¼ socioeconomic status (low ¼ primary or lower education, individual monthly income <$2000 [Singapore], and 1e2 room Housing and Development Board flat). Boldface values are statistically significant. Data presented as mean (standard deviation) or number (percentage) accordingly. *Cataract presence is in unoperated eyes at baseline.
Cataract Surgery Incidence in Singapore
1379 62.3 (11.5) 668 (48.4) 316 (23.1) 1029 (75.0) 371 (28.1) 241 (17.7) 0.5 (0.5) 0.3 (0.4) 869 (63.7) 113 (13.4) 388 (33.0) 490 (37.8) 272 (21.2) 157 (11.5) 70 (5.1) 87 (6.3) 459 (34.6) 43 (3.3) 23.5 (1.0)
Participants
Combined Singapore Epidemiology of Eye Diseases Study (n [ 10 033)
Chinese (n [ 3353)
Total no. 1901 Age (yrs), mean (SD) 56.9 (10.1) Female, n (%) 1037 (54.6) Current smokers, n (%) 346 (18.2) Hypertension, n (%) 1227 (64.9) Diabetes, n (%) 398 (21.8) SES (low), n (%) 197 (10.5) PVA, mean (SD) 0.3 (0.4) BCVA, mean (SD) 0.1 (0.3) Wears glasses, n (%) 1349 (71.3) Annual glasses check, n (%) 189 (14.3) Nuclear cataract,* n (%) 277 (16.11) Cortical cataract,* n (%) 509 (27.7) PSC cataract,* n (%) 205 (11.2) Any previous cataract surgery, n (%) 127 (6.7) Unilateral surgery, n (%) 60 (3.2) Bilateral surgery, n (%) 67 (3.5) Myopia, n (%) 560 (29.9) High myopia, n (%) 90 (4.8) AL (mm), mean (SD) 23.6 (1.1)
Indians (n [ 3400)
Tan et al
Malays (n [ 3280)
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Ophthalmology Volume -, Number -, Month 2018 Table 2. Incident Cataract Surgery Stratified by Age Groups in the Singapore Epidemiology of Eye Diseases Study Ethnic Groups: Malays, Indians, and Chinese Malays Baseline Variable
No./Total*
Incidence (%)
Age group (yrs) 40e49 9/536 50e59 37/651 60e69 73/380 70 55/198 y P value (for trend) Crude 174/1765 9.5 Age-adjusted (95% CI)z
Indians No./Total*
Chinese
Incidence (%)
1.7 15/662 5.7 57/724 19.2 99/451 27.8 42/103 <0.001 9.9 213/1940 (8.1e10.9)x 12.6
No./Total*
Incidence (%)
2.3 13/602 2.2 7.9 40/933 4.3 22.0 116/604 19.2 40.8 100/239 41.8 <0.001 <0.001 11.0 269/2378 11.3 (10.9e14.3)x 11.1 (9.8e12.5)x
Combined Singapore Epidemiology of Eye Diseases Study No./Total*
Incidence (%)
37/1800 134/2308 288/1435 197/540
2.1 5.8 20.1 36.5 <0.001 10.8 11.0 (10.2e11.8)
656/6083
CI ¼ confidence interval. Boldface values are statistically significance. *Number of cases/number at risk. y CochrandArmitage trend test. z Standardized to 2010 Singapore population census. x P values for age-adjusted incidence between the 3 ethnic groups are: Malays vs. Indians, P < 0.001; Indians vs. Chinese, P < 0.001; Malays vs. Chinese, P ¼ 0.002.
cataract surgery cases in the population attributable to modifiable risk exposures (or population attributable risk [PAR]) using the following equation24: ðPrevalence of exposure in the populationÞ ðRisk ratio 1Þ : 1 þ ðPrevalence of exposure in the populationÞ ðRisk ratio 1Þ The adjusted odds ratios (ORs) determined from the logistic regression models and the published prevalence of diabetes and myopia in the SEED Study25e29 were used to calculate the 2 PARs. To determine whether there were factors particularly contributing to risk of bilateral surgery, additional analyses limiting to unilateral versus bilateral incident cataract surgery as outcomes were conducted using logistic regression models. Odds ratios and 95% confidence intervals (CI) are presented. In all statistical analyses, a P value of less than 0.05 was considered statistically significant.
Results A total of 6762 (78.7% of eligible) SEED Study participants were re-examined at the 6-year follow-up visit. Table 1 compares baseline characteristics of participants and nonparticipants at the 6-year follow-up examinations for each ethnic group in the SEED Study. Overall, compared with those who participated, nonparticipants were older, more likely to be men, more likely to be current smokers, and more likely to have hypertension, diabetes, cataract, previous cataract surgery, low SES, and poorer PVA and BCVA and were less likely to have glasses (Table 1). Of the 1901, 2200, and 2661 re-examined Malay, Indian, and Chinese participants, respectively, we excluded 415 participants who had undergone cataract surgery in both eyes before baseline (n ¼ 392) or who had missing baseline (n ¼ 15) or follow-up (n ¼ 8) lens status for one or both eyes. Thus, there were 1765 Malay participants (92.8%), 1940 Indian participants (88.1%), and 2378 Chinese participants (89.4%) with 2 phakic eyes at baseline who were at risk of incident cataract surgery in either eye (i.e., both eyes were at risk). For the entire SEED Study, there were 6083 participants (90.0%) with 2 phakic eyes at baseline who were at risk of incident cataract surgery in either eye. In addition, there were 59 Malay participants (3.1%), 95 Indian participants (4.3%), and 110
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Chinese (4.1%; 264 participants [3.9%] in the SEED Study) who had undergone cataract surgery in 1 eye before baseline and were at risk of incident cataract surgery in the second eye. The overall 6-year incidence of cataract surgery in the SEED Study was 10.8% (Malay, 9.9%; Indian, 11.0%; and Chinese, 11.3%). Age-adjusted incidence for the SEED Study was 11.0% (95% CI, 10.2%e11.8%; Table 2). The age-adjusted incidences for Malay, Indian, and Chinese participants were 9.5% (95% CI, 8.1%e10.9%), 12.6% (95% CI, 10.9%e14.3%), and 11.1% (95% CI, 9.8%e12.5%), respectively (Table 2). The incidence rate in Malays was the lowest and was significantly different from that in Indians (P < 0.001) and Chinese (P ¼ 0.002; Table 2). The incidence of cataract surgery increased with increasing age in the SEED Study from 2.1% among those 40 to 49 years of age, 5.8% for those 50 to 59 years of age, 20.1% for those 60 to 69 years of age, and 36.5% for those 70 years of age or older (P < 0.001 for trend), with a similar trend for each ethnic group (Table 2). Of the 264 participants with previous unilateral cataract surgery, 148 (56.1%) underwent incident cataract surgery in the second eye (26 eyes in the Malay group, 57 in the Indian group, and 65 in the Chinese group, respectively). Table 3 presents the crude incidence of cataract surgery by baseline characteristics. In the SEED Study sample (combined 3 ethnic groups), there was a significantly higher incidence of cataract surgery among those with diabetes, myopia, high myopia, and cataract at baseline and in those who had their glasses checked annually (Table 3). Baseline factors associated with increased cataract surgery incidence were similar across the 3 ethnic groups, except for hypertension being significant among Chinese participants, but diabetes was not, and an annual glasses check was not significant among Malays and Chinese (Table 3). In a person-specific model including baseline age, gender, ethnicity, smoking status, hypertension, diabetes, SES, and myopia, baseline factors that were associated significantly with increased likelihood of cataract surgery were age, diabetes, visual acuity (PVA or BCVA), yearly glasses check, myopia, high myopia, axial length, and the presence of nuclear, cortical, or PSC cataract at baseline (Table 4). These baseline factors and the magnitude of their associations with incident cataract surgery were similar across the 3 samples, with the exception of the Malay sample, in which yearly glasses check was not a risk
Tan et al
Cataract Surgery Incidence in Singapore
Table 3. Incident Cataract Surgery by Baseline Characteristics in the Singapore Epidemiology of Eye Diseases Study Ethnic Groups: Malays, Indians, and Chinese Malays (n [ 174/1765)* Baseline Characteristics Age (yrs), mean (SD) Gender (%) Male Female Smoking status (%) Nonsmoker Current smoker Hypertension (%) Absent Present Diabetes (%) Absent Present Socioeconomic status (%) High Low PVA, mean (SD) BCVA, mean (SD) Wears glasses (%) No Yes Annual glasses check (%) No Yes Any nuclear (%) No Yes Any cortical (%) No Yes Any PSC (%) No Yes Myopia (%)z Absent Present High myopia (%)x Absent Present AL (mm), mean (SD)
Indians (n [ 213/1940)*
Chinese (n [ 269/2378)*
% with Incident % with Incident % with Incident Surgery P Valuey Surgery P Valuey Surgery P Valuey 64.6 (8.4)
62.8 (8.3)
65.9 (8.0)
Combined Singapore Epidemiology of Eye Diseases Study (n [ 656/6083)* % with Incident Surgery
P Valuey
64.6 (8.3)
8.8 10.7
0.06
11.7 10.3
0.98
11.6 11.0
0.49
10.9 10.7
0.23
10.3 8.0
0.77
11.5 8.2
0.82
11.6 9.2
0.83
11.2 8.5
0.89
5.9 12.2
0.90
7.6 14.5
0.68
5.7 16.3
0.01
6.4 14.4
0.09
8.0 17.0
<0.001
7.3 18.8
<0.001
10.3 18.3
0.06
8.8 18.1
<0.001
9.6 12.2 0.6 (0.5) 0.4 (0.5)
0.60
11.0 21.3 0.5 (0.4) 0.3 (0.4)
0.95
11.3 21.4 0.6 (0.4) 0.3 (0.4)
0.94
10.7 14.9 0.6 (0.4) 0.4 (0.4)
0.35
8.8 10.3
0.73
10.9 11.0
0.24
10.0 11.5
0.47
9.8 11.0
0.22
10.0 11.2
0.14
10.4 13.2
0.02
11.2 13.7
0.20
10.6 13.0
<0.001
5.3 32.7
<0.001
6.2 49.7
<0.001
6.1 46.7
<0.001
5.9 42.4
<0.001
4.9 23.3
<0.001
6.4 29.3
<0.001
6.1 30.8
<0.001
5.9 27.8
<0.001
6.4 40.6
<0.001
7.4 57.3
<0.001
8.6 44.0
<0.001
7.6 46.2
<0.001
7.8 13.2
<0.001
8.8 13.7
<0.001
9.3 12.4
<0.001
8.7 12.9
<0.001
8.9 17.4 23.7 (1.3)
<0.001
9.8 20.8 23.5 (1.4)
<0.001
10.1 12.8 24.0 (1.5)
<0.001
9.6 15.4 23.7 (1.2)
<0.001
AL ¼ axial length; BCVA ¼ best-corrected visual acuity (logarithm of the minimum angle of resolution); PSC ¼ posterior subcapsular cataract; PVA ¼ presenting visual acuity (logarithm of the minimum angle of resolution); SD ¼ standard deviation. Boldface values are statistically significant. *Number of incident cataract surgery cases/total number in population. y Age-adjusted P value. z Myopia defined as spherical equivalent refraction <0.5 diopter. x High myopia defined as spherical equivalent
factor, and the Chinese sample, in which hypertension was a significant risk factor, but diabetes and a yearly glasses check were not (Table 4). Eye-specific analysis showed similar associations between baseline ocular characteristics and incident cataract surgery in the same eye (Table 5). The 2 significant modifiable risk factors of incident cataract surgery were diabetes and myopia. Among participants who had incident cataract surgery, the mean ages at follow-up were significantly younger among those with diabetes than those without
among Malays (mean age, 69.4 years vs. 73.2 years; P ¼ 0.005) and among those with myopia than those without among Indians and Chinese or among the SEED Study population (Indians: 67.6 years vs. 70.0 years [P ¼ 0.04]; Chinese: 69.9 years vs. 74.0 years [P < 0.001]; SEED: 69.4 years vs. 72.0 years [P < 0.001]). The proportion of the risk of having cataract surgery in the SEED Study population attributable to diabetes (i.e., PAR) was 17.6% (21.6%, 24.0%, and 5.7% for Malay, Indian, and Chinese groups, respectively). The PAR for myopia was 19.1% (15.8%,
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Ophthalmology Volume -, Number -, Month 2018 Table 4. Association between Baseline Demographic, Systemic, and Ocular Factors with Incident Cataract Surgery (in Either Eye) Using Person-Specific Analysis in the Multiethnic Singapore Epidemiology of Eye Diseases Study
Baseline Characteristics Age, per year Gender Male Female Smoking status Nonsmoker Current smoker Hypertension Absent Present Diabetes Absent Present Socioeconomic status High Low PVA, per 0.1 unit BCVA, per 0.1 unit Wears glasses No Yes Annual glasses check No Yes Cataract typey Any nuclear Any cortical Any PSC Myopiaz Absent Present High myopiaz Absent Present AL per mmz
Malays (n [ 1765), Multivariate Adjusted Odds Ratio (95% Confidence Interval)
Indians (n [ 1940), Multivariate Adjusted Odds Ratio (95% Confidence Interval)
Chinese (n [ 2378), Multivariate Adjusted Odds Ratio (95% Confidence Interval)
Combined Singapore Epidemiology of Eye Diseases Study (n [ 6083), Multivariate Adjusted* Odds Ratio (95% Confidence Interval)
1.11 (1.09e1.14)
1.12 (1.10e1.15)
1.15 (1.13e1.17)
1.13 (1.11e1.14)
1.00 (ref) 1.48 (0.98e2.22)
1.00 (ref) 0.96 (0.67e1.36)
1.00 (ref) 1.26 (0.92e1.73)
1.00 (ref) 1.18 (0.96e1.44)
1.00 (ref) 1.42 (0.80e2.50)
1.00 (ref) 0.90 (0.50e1.60)
1.00 (ref) 1.13 (0.68e1.87)
1.00 (ref) 1.12 (0.82e1.52)
1.00 (ref) 0.97 (0.62e1.52)
1.00 (ref) 0.95 (0.66e1.38)
1.00 (ref) 1.45 (1.02e2.05)
1.00 (ref) 1.13 (0.91e1.40)
1.00 (ref) 2.13 (1.46e3.11)
1.00 (ref) 1.92 (1.36e2.71)
1.00 (ref) 1.40 (0.94e2.08)
1.00 (ref) 1.90 (1.54e2.33)
1.00 0.76 1.08 1.19
1.00 1.08 1.19 1.29
1.00 1.34 1.20 1.32
1.00 0.84 1.16 1.26
(ref) (0.43e1.32) (1.02e1.14) (1.10e1.28)
(ref) (0.45e2.56) (1.13e1.26) (1.20e1.39)
(ref) (0.43e4.22) (1.15e1.26) (1.22e1.42)
(ref) (0.55e1.29) (1.12e1.19) (1.21e1.31)
1.00 (ref) 1.30 (0.84e2.01)
1.00 (ref) 0.95 (0.61e1.48)
1.00 (ref) 1.34 (0.83e2.18)
1.00 (ref) 1.18 (0.91e1.53)
1.00 (ref) 1.36 (0.75e2.44)
1.00 (ref) 1.60 (1.05e2.44)
1.00 (ref) 1.17 (0.74e1.83)
1.00 (ref) 1.39 (1.06e1.82)
2.93 (1.75e4.88) 3.14 (2.11e4.67) 4.78 (3.13e7.31)
5.66 (3.55e9.02) 2.77 (1.89e4.04) 11.24 (6.98e18.09)
3.47 (2.33e5.17) 3.25 (2.35e4.49) 3.29 (2.17e4.99)
3.78 (2.91e4.89) 3.01 (2.45e3.71) 5.00 (3.91e6.41)
1.00 (ref) 1.76 (1.17e2.64)
1.00 (ref) 1.82 (1.24e2.67)
1.00 (ref) 1.98 (1.42e2.76)
1.00 (ref) 1.78 (1.44e2.20)
1.00 (ref) 2.25 (1.07e4.72) 1.30 (1.10e1.54)
1.00 (ref) 3.85 (1.90e7.80) 1.26 (1.09e1.46)
1.00 (ref) 2.36 (1.41e3.97) 1.18 (1.04e1.33)
1.00 (ref) 2.44 (1.71e3.49) 1.20 (1.10e1.30)
AL ¼ axial length; BCVA ¼ best corrected visual acuity (logarithm of the minimum angle of resolution); PSC ¼ posterior subcapsular cataract; PVA ¼ presenting visual acuity (logarithm of the minimum angle of resolution). Boldface values are statistically significant. Models adjusting for age, gender, current smoking, hypertension, diabetes, socioeconomic status, and myopia unless otherwise indicated. *Model additionally adjusted for ethnicity. y Each individual cataract type was assessed separately in each model (e.g., analysis for nuclear cataract only had that type of cataract with full model adjustment). z Model adjusted for age, gender, current smoking, hypertension, diabetes, socioeconomic status, and nuclear cataract.
17.6%, and 27.9% for Malay, Indian, and Chinese groups, respectively). Of the 656 incident cataract surgery cases, 368 (56.1%) underwent bilateral incident cataract surgery (85 Malays, 131 Indians, and 152 Chinese). Participants with bilateral cataract surgery were slightly older than those who undergone unilateral surgery in all 3 cohorts. Risk factors for bilateral cataract surgery differed among the 3 ethnic groups (Table S2, available at www.aaojournal.org). Overall in the SEED Study samples combined, compared with unilateral cataract surgery cases, age, female gender, nuclear and PSC cataract, and high myopia were associated with an increased risk of bilateral cataract surgery, whereas low SES was associated with decreased risk of bilateral surgery.
6
Discussion In this population-based cohort study of 3 major ethnic groups in Singapore, we report an overall (person-specific) age-adjusted 6-year incidence of cataract surgery of 11.0% in the SEED Study. Incidence of cataract surgery increased with age in all cohorts from 2.1% among those 40 to 49 years of age up to 36.5% among those 70 years of age or older. Aside from age and presence of cataract at baseline, diabetes and myopia were 2 significant and potentially modifiable risk factors for incident cataract surgery. Among
Tan et al
Cataract Surgery Incidence in Singapore
Table 5. Association between Baseline Ocular Factors with Incident Cataract Surgery Using Eye-Specific Analysis in the Multiethnic Singapore Epidemiology of Eye Diseases Study
Baseline Characteristics PVA, per 0.1 unit BCVA, per 0.1 unit Cataract typey Any nuclear Any cortical Any PSC Myopiaz High myopiaz Axial length, per mmz
Malays (n [ 3589), Multivariate Adjusted Odds Ratio (95% Confidence Interval)
Indians (n [ 3975), Multivariate Adjusted Odds Ratio (95% Confidence Interval)
Chinese (n [ 4866), Multivariate Adjusted Odds Ratio (95% Confidence Interval)
Combined Epidemiology of Eye Diseases Study (n [ 12 430), Multivariate Adjusted* Odds Ratio (95% Confidence Interval)
1.07 (1.00e1.14) 1.19 (1.11e1.28)
1.16 (1.10e1.21) 1.22 (1.13e1.33)
1.21 (1.16e1.26) 1.30 (1.18e1.44)
1.44 (1.11e1.18) 1.23 (1.17e1.29)
1.94 2.40 5.52 1.70 2.52 1.31
3.04 2.43 6.42 1.81 3.51 1.24
2.87 2.16 3.68 1.69 3.12 1.24
2.55 2.25 4.77 1.67 2.84 1.21
(1.29e2.91) (1.68e3.43) (3.82e7.97) (1.21e2.38) (1.30e4.88) (1.12e1.52)
(2.03e4.56) (1.81e3.25) (4.27e9.66) (1.32e2.48) (2.00e6.17) (1.07e1.43)
(2.06e4.02) (1.69e2.76) (2.63e5.16) (1.29e2.22) (2.08e4.67) (1.11e1.38)
(2.05e3.16) (1.91e2.66) (3.86e5.88) (1.40e1.98) (2.13e3.81) (1.12e1.30)
BCVA ¼ best-corrected visual acuity (logarithm of the minimum angle of resolution, per 0.1-unit increase); PSC ¼ posterior subcapsular cataract; PVA ¼ presenting visual acuity (logarithm of the minimum angle of resolution, per 0.1-unit increase). Boldface values are statistically significant. Models adjusted for age, gender, current smoking, hypertension, diabetes, socioeconomic status, and myopia unless otherwise indicated. *Model additionally adjusted for ethnicity. y Each individual cataract type was assessed separately in each model (e.g., analysis for nuclear cataract only had that type of cataract with full model adjustment). z Model adjusting for age, gender, current smoking, hypertension, diabetes, socioeconomic status, and nuclear cataract.
Malays and Indians, diabetes was a more important determinant of incident cataract surgery; in contrast, among Chinese, myopia was a more important determinant of cataract surgery. Female gender was associated with greater risk of bilateral cataract surgery, whereas low SES was associated with less likelihood of bilateral cataract surgery, when compared with incident unilateral cataract surgery. Although direct comparison between studies is difficult because of differing age ranges, durations of follow-up, and periods when previous studies were conducted, the overall incidence of cataract surgery observed in our Singapore cohorts (11.0%) is comparable and within the higher end of the ranges reported by previous studies of similar age groups (40þ years; Table S1). Previously reported cataract surgery incidence rates varied from a 4-year incidence of 1.5% in the Los Angeles Latino Eye Study13 of Latinos 40 years of age or older to a 7-year incidence of 14.7% in the Shihpai Eye Study15 of Taiwanese persons 65 years of age or older (Table S1). In a previous study conducted in Singapore using data from Medisave,18 the average annual rate of cataract surgery for all ages from 1991 through 1996 was 356.4 per 100 000 persons. Because of different study designs and different age ranges of the 2 samples, we cannot compare our findings from this population-based cohort with that from the previous Medisave data. Nevertheless, differences in cataract surgery incidence between our cohort and other population-based cohorts of similar age range may be explained by the advances in cataract surgical technologies and techniques over the past decades, leading to substantial improvements in patient safety and surgical outcomes30 and to lowering visual impairment thresholds for surgery.30 Age is a consistent risk factor for cataract surgery among the 3 cohorts of the SEED, in keeping with findings from
other populations.9e12,14,17 We observed an increasing trend of incident cataract surgery with age from 2.1% among those 40 to 49 years of age up to 36.5% among those 70 years of age or older. This equates to roughly 12 782 persons 40 to 49 years of age and up to 81 708 persons 70 years of age or older, for a total of 186 000 undergoing cataract surgery over 6 years (approximately 30 000 per year) for persons 40 years of age or older, when extrapolating to the Singapore population using numbers from the last census. This is consistent with the reported 48 000 surgeries from 2006 through 2010 (approximately 12 000 per year) performed in the Singapore National Eye Centre, where 40% of the total volume of cataract surgeries in Singapore were performed.31 As expected, of the factors that determine the need for cataract surgery, the presence of cataract at baseline was a major factor. Of the types of cataract, the risk magnitude was highest for PSC cataract, followed by nuclear and cortical cataract. This is consistent with findings from the Beaver Dam Eye Study and the Blue Mountains Eye Study, where the presence of PSC cataract at baseline was the most important ocular risk factor for incident cataract surgery.9,10 This is consistent with the impact of PSC cataract on central vision. Our reported incidence of cataract surgery for Malays, Indians, and Chinese (9.5%, 12.6%, and 11.1%, respectively) was higher than the proportions of SEED Study participants with an unmet need for cataract surgery services at baseline, based on presence of visually significant cataract (7.2%, 4.9%, and 5.8%, respectively).32 However, the higher incidence of cataract surgery reported is consistent with an expected increase in the need for cataract surgery services over time because of factors that affect cataract formation such as age and diabetes.
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Ophthalmology Volume -, Number -, Month 2018 The impact of diabetes and myopia on incident cataract surgery in the SEED Study is considerable, estimated at 17.6% and 19.1% of incident cataract surgery cases attributable to diabetes and myopia, respectively. Diabetes is a well-established risk factor for cataract. Myopia has been documented consistently to be associated with cataract33,34 and cataract surgery.10,33,35,36 In addition, persons with diabetes or myopia may make more frequent visits to doctors and so be more likely to have cataract detected earlier compared with persons without these conditions. Our finding of increased incidence of cataract surgery among those who undergo a yearly glasses check supports this. The burden of these 2 diseases is substantial; in the SEED Study, the overall prevalences of diabetes and myopia were 23.7%25 and 38.9%,28 respectively, with comparable prevalences reported in similar ethnic populations living in37,38 and outside of29,39,40 Singapore. With an increasing prevalence of diabetes41 and myopia28 in Singapore, ensuring adequate resources allocated and patient access to eye care services is needed. We also found significant ethnic differences. Among Malays and Indians, diabetes was a more important determinant of incident cataract surgery (accounting for 21.6% and 24%, respectively, of cataract surgery). In contrast, myopia was a more important determinant of cataract surgery among Chinese, accounting for 27.9% of incident cataract surgery. Strategies to mitigate increasing prevalence of diabetes and myopia in these ethnic groups may help to reduce eye health care burden resulting from early onset of agerelated cataract associated with these 2 common conditions. We observed an increased likelihood of undergoing bilateral cataract surgery among women overall in the SEED Study compared with men, and this seems to be driven by an increased risk of bilateral surgery among Indian women compared with Indian men. This is in keeping with findings of a previous study that, in Singapore, the highest rate of cataract surgery was observed among Indian women.18 Low SES was associated with lower likelihood of having bilateral cataract surgery compared with unilateral surgery overall in the SEED Study, which also seemed to be driven by an association seen in Indians. We speculate that persons who are less comfortable financially delay having secondeye surgery as long as possible. High myopia was associated with a 2-fold increased risk of bilateral cataract surgery compared with unilateral surgery. This may be the result of patients wanting to minimize postoperative anisometropia after unilateral cataract surgery,42 which would be marked in those with high myopia (
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to have a history of hypertension or diabetes, more likely to have cataract at baseline, and had lower SES at baseline, each of which could have led to an underestimation of incident cataract surgery in our study population. Lack of association found between current smoking and incident cataract surgery may be confounded by lower participation rates among current smokers at follow-up. Although the 3 substudies of the SEED Study were conducted in different periods over a span of 7 years, the eye health care practice pattern and the overall health care provision system in Singapore has not changed during this period.43 Therefore, we do not anticipate that there would be apparent cohort effect on cataract surgery incidence rates of the 3 ethnic populations. In conclusion, our study documented that in an urban city-state Asian setting, 1 in 10 Malay, Indian, and Chinese Singaporeans 40 years of age or older had undergone incident cataract surgery in at least 1 eye over 6 years. Apart from age and the presence of cataract at baseline, diabetes and myopia were significant and potentially modifiable risk factors for incident cataract surgery. Our findings provide greater insights on the trends of cataract surgery uptake over time and will inform planning of future provision of eye care services to target at-risk sectors of the Singapore population. Furthermore, our incident cataract surgery rates are substantially higher than those reported from less developed Asian communities, and thus provide further evidence of the need to improve access to cataract surgery in large parts of Asia, home to more than 3 billion people.
References 1. Flaxman SR, Bourne RRA, Resnikoff S, et al. Global causes of blindness and distance vision impairment 1990e2020: a systematic review and meta-analysis. Lancet Glob Health. 2017;5:e1221ee1234. 2. Liu YC, Wilkins M, Kim T, et al. Cataracts. Lancet. 2017;390: 600e612. 3. Essue BM, Li Q, Hackett ML, et al. A multicenter prospective cohort study of quality of life and economic outcomes after cataract surgery in Vietnam: the VISIONARY study. Ophthalmology. 2014;121:2138e2146. 4. Finger RP, Kupitz DG, Fenwick E, et al. The impact of successful cataract surgery on quality of life, household income and social status in South India. PLoS ONE. 2012;7: e44268. 5. Fong CS, Mitchell P, Rochtchina E, et al. Visual impairment corrected via cataract surgery and 5-year survival in a prospective cohort. Am J Ophthalmol. 2014;157:163e170. 6. Fong CS, Mitchell P, Rochtchina E, et al. Correction of visual impairment by cataract surgery and improved survival in older persons: the Blue Mountains Eye Study Cohort. Ophthalmology. 2013;120:1720e1727. 7. Tseng VL, Yu F, Lum F, Coleman AL. Cataract surgery and mortality in the United States Medicare population. Ophthalmology. 2016;123:1019e1026. 8. Leske MC, Wu SY, Nemesure B, et al. Incidence and progression of lens opacities in the Barbados Eye Studies. Ophthalmology. 2000;107:1267e1273.
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9. Klein BE, Klein R, Moss SE. Incident cataract surgery: the Beaver Dam Eye Study. Ophthalmology. 1997;104:573e580. 10. Panchapakesan J, Mitchell P, Tumuluri K, et al. Five year incidence of cataract surgery: the Blue Mountains Eye Study. Br J Ophthalmol. 2003;87:168e172. 11. McCarty CA, Mukesh BN, Dimitrov PN, Taylor HR. Incidence and progression of cataract in the Melbourne Visual Impairment Project. Am J Ophthalmol. 2003;136:10e17. 12. Koo E, Chang JR, Agron E, et al. Ten-year incidence rates of age-related cataract in the Age-Related Eye Disease Study (AREDS): AREDS report no. 33. Ophthalmic Epidemiol. 2013;20:71e81. 13. Varma R, Richter GM, Torres M, et al. Four-year incidence and progression of lens opacities: the Los Angeles Latino Eye Study. Am J Ophthalmol. 2010;149:728e734. 14. Zhang JS, Xu L, Wang YX, et al. Five-year incidence of agerelated cataract and cataract surgery in the adult population of greater Beijing: the Beijing Eye Study. Ophthalmology. 2011;118:711e718. 15. Kuang TM, Tsai SY, Liu CJ, et al. Seven-year incidence of age-related cataracts among an elderly Chinese population in Shihpai, Taiwan: the Shihpai Eye Study. Invest Ophthalmol Vis Sci. 2013;54:6409e6415. 16. Panday M, George R, Asokan R, et al. Six-year incidence of visually significant age-related cataract: the Chennai Eye Disease Incidence Study. Clin Exp Ophthalmol. 2016;44: 114e120. 17. Huang W, Zheng Y, Wang L, et al. Five-year incidence and postoperative visual outcome of cataract surgery in urban southern China: the Liwan Eye Study. Invest Ophthalmol Vis Sci. 2012;53:7936e7942. 18. Wong TY. Cataract extraction rates among Chinese, Malays, and Indians in Singapore: a population-based analysis. Arch Ophthalmol. 2001;119:727e732. 19. Foong AW, Saw SM, Loo JL, et al. Rationale and methodology for a population-based study of eye diseases in Malay people: the Singapore Malay Eye Study (SiMES). Ophthalmic Epidemiol. 2007;14:25e35. 20. Lavanya R, Jeganathan VS, Zheng Y, et al. Methodology of the Singapore Indian Chinese Cohort (SICC) eye study: quantifying ethnic variations in the epidemiology of eye diseases in Asians. Ophthalmic Epidemiol. 2009;16:325e336. 21. Rosman M, Zheng Y, Wong W, et al. Singapore Malay Eye Study: rationale and methodology of 6-year follow-up study (SiMES-2). Clin Experiment Ophthalmol. 2012;40:557e568. 22. Sabanayagam C, Yip W, Gupta P, et al. Singapore Indian Eye Study-2: methodology and impact of migration on systemic and eye outcomes. Clin Exp Ophthalmol. 2017;45:779e789. 23. Department of Statistics Singapore. Singapore census of population 2010, statistical release 1: demographic characteristics, education, language and religion. https://www.singstat.gov.sg/ publications/cop2010/census10_stat_release1; 2011. Accessed 15.06.18. 24. Kelsey JL, Whittemore AS, Evans AS, Thompson WD. Methods in Observational Epidemiology. 2nd ed. New York: Oxford University Press; 1996. 25. Huang OS, Tay WT, Ong PG, et al. Prevalence and determinants of undiagnosed diabetic retinopathy and visionthreatening retinopathy in a multiethnic Asian cohort: the Singapore Epidemiology of Eye Diseases (SEED) study. Br J Ophthalmol. 2015;99:1614e1621.
26. Saw SM, Chan YH, Wong WL, et al. Prevalence and risk factors for refractive errors in the Singapore Malay Eye Survey. Ophthalmology. 2008;115:1713e1719. 27. Pan CW, Wong TY, Lavanya R, et al. Prevalence and risk factors for refractive errors in Indians: the Singapore Indian Eye Study (SINDI). Invest Ophthalmol Vis Sci. 2011;52: 3166e3173. 28. Pan CW, Zheng YF, Anuar AR, et al. Prevalence of refractive errors in a multiethnic Asian population: the Singapore Epidemiology of Eye Disease Study. Invest Ophthalmol Vis Sci. 2013;54:2590e2598. 29. Pan CW, Dirani M, Cheng CY, et al. The age-specific prevalence of myopia in Asia: a meta-analysis. Optom Vis Sci. 2015;92:258e266. 30. Erie JC. Rising cataract surgery rates: demand and supply. Ophthalmology. 2014;121:2e4. 31. Ti SE, Yang YN, Lang SS, Chee SP. A 5-year audit of cataract surgery outcomes after posterior capsule rupture and risk factors affecting visual acuity. Am J Ophthalmol. 2014;157: 180e185. 32. Zheng Y, Cheng CY, Lamoureux EL, et al. How much eye care services do Asian populations need? Projection from the Singapore Epidemiology of Eye Disease (SEED) Study. Invest Ophthalmol Vis Sci. 2013;54:2171e2177. 33. Wong TY, Klein BE, Klein R, et al. Refractive errors and incident cataracts: the Beaver Dam Eye Study. Invest Ophthalmol Vis Sci. 2001;42:1449e1454. 34. Panchapakesan J, Rochtchina E, Mitchell P. Myopic refractive shift caused by incident cataract: the Blue Mountains Eye Study. Ophthalmic Epidemiol. 2003;10:241e247. 35. Klein BE, Klein RE, Lee KE. Incident cataract after a five-year interval and lifestyle factors: the Beaver Dam Eye Study. Ophthalmic Epidemiol. 1999;6:247e255. 36. Younan C, Mitchell P, Cumming RG, et al. Myopia and incident cataract and cataract surgery: the Blue Mountains Eye Study. Invest Ophthalmol Vis Sci. 2002;43: 3625e3632. 37. Wong TY, Foster PJ, Hee J, et al. Prevalence and risk factors for refractive errors in adult Chinese in Singapore. Invest Ophthalmol Vis Sci. 2000;41:2486e2494. 38. Yeo KK, Tai BC, Heng D, et al. Ethnicity modifies the association between diabetes mellitus and ischaemic heart disease in Chinese, Malays and Asian Indians living in Singapore. Diabetologia. 2006;49:2866e2873. 39. Xu L, Xie X, Wang S, et al. Prevalence of diabetes mellitus in China. Exp Clin Endocrinol Diabetes. 2008;116:69e70. 40. Gujral UP, Narayan KM, Pradeepa RG, et al. Comparing type 2 diabetes, prediabetes, and their associated risk factors in Asian Indians in India and in the U.S.: the CARRS and MASALA Studies. Diabetes Care. 2015;38: 1312e1318. 41. Phan TP, Alkema L, Tai ES, et al. Forecasting the burden of type 2 diabetes in Singapore using a demographic epidemiological model of Singapore. BMJ Open Diabetes Res Care. 2014;2:e000012. 42. Ishikawa T, Desapriya E, Puri M, et al. Evaluating the benefits of second-eye cataract surgery among the elderly. J Cataract Refract Surg. 2013;39:1593e1603. 43. Ministry of Health Singapore. Caring for Our People: 50 Years of Healthcare in Singapore. Singapore: MOH Holdings Pte Ltd for the Ministry of Health; 2015.
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Ophthalmology Volume -, Number -, Month 2018 Footnotes and Financial Disclosures Originally received: April 7, 2018. Final revision: July 25, 2018. Accepted: July 27, 2018. Available online: ---.
from the Australian National Health & Medical Research Council, Canberra, Australia. The funding organizations had no role in the design or conduct of this research. Manuscript no. 2018-673.
1
Centre for Vision Research, Department of Ophthalmology, The Westmead Institute for Medical Research, The University of Sydney, Westmead Hospital, Westmead, Australia.
2
Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Republic of Singapore.
3
Ophthalmology and Visual Sciences Academic Clinical Program, DukeNUS Medical School, Singapore, Republic of Singapore.
4
Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Republic of Singapore.
5
School of Public Health, The University of Sydney, Sydney, Australia.
6
Health Services and Systems Research, Duke-NUS Medical School, Singapore, Republic of Singapore. *Both authors contributed equally. Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article. The Singapore Epidemiology of Eye Disease Study is funded by the National Medical Research Council, Singapore, Republic of Singapore (grant nos.: 0796/2003, IRG07nov013, IRG09-nov014, STaR/0003/2008, CG/SERI/2010, 1249/2010, STaR/0016/2013, CIRG/1371/2013, and CIRG/1417/2015); and the Biomedical Research Council, Singapore, Republic of Singapore (grant nos.: 08/1/35/19/550 and 09/1/35/19/616). Ms. Tan is supported by a postgraduate research scholarship (GNT1094094)
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HUMAN SUBJECTS: Human subjects were included in this study. The human ethics committees at the Singapore Eye Research Institute approved the study. All research adhered to the tenets of the Declaration of Helsinki. All participants provided informed consent. No animal subjects were included in this study. Author Contributions: Conception and design: A.G.Tan, Kifley, T.Y.Wong, Cheng Analysis and interpretation: A.G.Tan, Kifley, Tham, Shi, Chee, N.Y.Q.Tan, Wong, Mitchell, Cumming, T.Y.Wong, Wang, Cheng Data collection: Shi, Chee, Sabanayagam, T.Y.Wong, Wang, Cheng Obtained funding: T.Y.Wong, Cheng, Sabanayagam Overall responsibility: A.G.Tan, Kifley, Tham, Sabanayagam, N.Y.Q.Tan, Wong, Mitchell, Cumming, T.Y.Wong, Wang, Cheng Abbreviations and Acronyms: BCVA ¼ best-corrected visual acuity; CI ¼ confidence interval; D ¼ diopter; OR ¼ odds ratio; PAR ¼ population attributable risk; PSC ¼ posterior subcapsular; PVA ¼ presenting visual acuity; SE ¼ spherical equivalent; SEED ¼ Singapore Epidemiology of Eye Diseases; SES ¼ socioeconomic status. Correspondence: Jie Jin Wang, MMed, PhD, Duke-NUS Medical School, 20 College Road, The Academia, Level 6, Room 053, Singapore 169856, Republic of Singapore. E-mail: [email protected].
Age-related cataract remains the leading causes of blindness (35%) and visual impairment (25%) among older people globally.1 Cataract surgery currently is the only effective treatment for cataract.2 In addition to improved visual function, cataract surgery is associated with benefits on other health and social outcomes, including emotional well being, quality of life, economic benefits and productivity, and improved survival of elderly who are visually impaired because of cataract.3e7 However, cataract surgery requires significant investment in terms of the number of ophthalmologists needed and the ª 2018 by the American Academy of Ophthalmology Published by Elsevier Inc.
set-up of clinic and operating theater resources. To plan for such health care and ophthalmic care resources, longitudinal data are needed to determine the number of new cataract surgery cases needed in the population and to identify persons at risk of cataract surgery. Although the incidence of cataract surgery is well documented in Western countries,8e13 there are fewer reports from Asian populations14e17 (Table S1, available at www.aaojournal.org). The use of incidence rates from other countries may provide an estimate; however, it may limit the ability of policy makers and governments to plan adequately for https://doi.org/10.1016/j.ophtha.2018.07.026 ISSN 0161-6420/18
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Ophthalmology Volume -, Number -, Month 2018
The SEED Study is a population-based cohort study of common eye diseases in residents of Singapore 40 years of age and older among 3 major ethnic groups: Malay, Indian, and Chinese. The baseline examinations for each ethnic group were as follows: 3280 (78.7% of eligible) Malay participants were recruited from 2004 through 2006, 3400 (75.6% of eligible) Indian participants were recruited from 2007 through 2009, and 3353 (72.8% of eligible) Chinese participants were recruited from 2009 through 2011. Overall response rate at baseline for the SEED Study was 75.6%. For the 6-year follow-up visits, we re-examined 1901 (72.1% of eligible) Malay participants from 2011 through 2013, 2200 (75.5% of eligible) Indians from 2013 through 2015, and 2661 (87.7% of eligible) Chinese from 2015 through 2017. The study adhered to the principles of the Declaration of Helsinki. Ethics approval was obtained from the Singapore Eye Research Institute Institutional Review Board. Written informed consent was obtained from each participant.
participants with an intact lens in both eyes at baseline were considered at risk. For eye-specific analysis, any eye with an intact lens at baseline was considered at risk of incident cataract surgery. In addition, incident unilateral and bilateral cataract surgery were defined as cataract surgery performed in one eye only and in both eyes, respectively, during the 6-year follow-up period. Interviews were conducted in participants’ choice of English, Chinese, Malay, or Tamil. Information collected from intervieweradministered questionnaires included socioeconomic status (such as education level and income levels), occupation, medical history, medication use, and smoking status. Participants also were asked whether they used any glasses and, if so, how often they visited optometrists, opticians, or ophthalmologists to have their glasses checked. Blood pressure was measured after the participant was seated and rested for 5 minutes using a digital sphygmomanometer (Dinamap model Pro Series DP110X-RW, 100V2; GE Medical Systems Information Technologies, Inc., Milwaukee, WI). Hypertension was defined as systolic blood pressure of 140 mmHg or more, diastolic blood pressure of 90 mmHg or more, physiciandiagnosed hypertension, or self-reported history of hypertension. Smoking status was defined as current and noncurrent smoking. Low socioeconomic status (SES) was defined as having primary or lower education, individual monthly income less than SG$2000, and a 1- to 2-room Housing and Development Board flat. Nonfasting blood samples were collected and processed the same day at the Singapore General Hospital Laboratory. Serum glucose levels were assessed on the Beckman Coulter Unicel DxC 800 analyzer using the oxygen rate method. Diabetes was defined as random glucose level of 11.1 mmol/l or more, use of diabetic medication, or self-reported history of diabetes. Presenting visual acuity (PVA) and best-corrected visual acuity (BCVA) were measured for each eye using a logarithm of the minimum angle of resolution number chart (Lighthouse International, New York) at 4 m. PVA was measured with walk-in optical correction (glasses or contact lenses), if any. BCVA was measured as the best possible correction obtained with subjective refraction conducted by study optometrists. Myopia was defined as spherical equivalent (SE) refraction of less than 0.5 diopters (D). High myopia was defined as less than e5.0 D. Axial length was measured using a noncontact partial coherence laser interferometer (IOLMaster version 3.01; Carl Zeiss, Meditec AG Jena, Germany).
Examination Procedures and Definitions
Statistical Analysis
Similar examination procedures were followed for all ethnic groups for both the baseline and follow-up examinations. Details of the methodology have been reported previously.19e22 Briefly, each participant underwent a detailed eye examination, including slitlamp biomicroscopy (model BQ-900; Haag-Streit, Switzerland) and slit-lamp photography of the lens using digital slit-lamp (Topcon model DC-1 with FD-21 flash attachment; Topcon, Tokyo, Japan) and retroillumination (Nidek EAS-1000; Nidek, Tokyo, Japan) cameras. Cataract was graded from baseline photographs using the Wisconsin Cataract Grading system. Nuclear cataract was defined as grade 4 or more, cortical cataract was defined as 5% or more of the total lens area with cortical opacity involved, and posterior subcapsular (PSC) cataract was defined as any such opacity present. Any cataract refers to the presence of cataract in either eye. Cataract surgery status was defined as the presence of an intraocular lens implant (pseudophakia) or the absence of the natural lens (aphakia), determined from the slit-lamp biomicroscopy examination during the study visit, from the grading of lens photographs, or both. Incidence of cataract surgery was defined as pseudophakia or aphakia at follow-up among participants with an intact lens at baseline. For person-specific analysis,
All analyses were performed using SAS version 9.3 (SAS Institute, Inc., Cary, NC). Findings from each ethnic group were presented separately as well as in combination as the SEED Study population. Differences in baseline characteristics were tested using an independent t test for continuous variables and Pearson’s chisquare test for categorical variables. Age-adjusted incidence for the 3 ethnic groups and the combined SEED Study population was calculated using direct age standardization to the 2010 Singapore Population Census.23 Logistic regression models (person-specific analysis) and generalized estimating equations logistic regression models (eyespecific analysis) were used to determine factors associated with incident cataract surgery after adjusting for baseline age, gender, ethnicity, smoking status, hypertension, diabetes, SES, and myopia. In the person-specific analysis, for the continuous variables PVA, BCVA, and axial length, we used PVA and BCVA from the worse eye (eye with poorer visual acuity) and the mean axial length of the right and left eyes for each person. For the eyespecific analyses, we used variables specific to each eye. We also compared the mean ages at follow-up among those who had incident cataract surgery by the presence versus absence of diabetes and myopia. We determined the proportion of incident
sufficient eye care resources in Asia. Providing geographicand ethnic-specific incidence rates for cataract surgery will aid in planning and allocating resources more accurately. Singapore is a small city-state but has a multiethnic Asian population comprising 3 major ethnic groups: Chinese, Malays, and Indians. Cataract surgical rates among Malay, Indian, and Chinese Singaporeans were evaluated previously almost 2 decades ago based on health expenditure data from the Medisave scheme, a governmentadministered medical savings scheme in Singapore.18 This database does not have factors associated with cataract surgery, nor does it cover private insurance, which is increasingly used to pay for cataract surgery.18 Hence, we investigated the 6-year incidence rates and associated factors of cataract surgery in Singapore’s multiethnic Asian population using recent data from the Singapore Epidemiology of Eye Diseases (SEED) Study.
Methods Study Populations
2
Table 1. Baseline Characteristics of Participants and Nonparticipants in 6-Year Follow-up Examinations from the Singapore Epidemiology of Eye Diseases Study Ethnic Groups: Malays, Indians, and Chinese
Baseline Characteristics
Participants
Nonparticipants P Value
2200 <0.001 56.5 (9.2) <0.001 1113 (50.6) <0.001 293 (13.3) <0.001 1168 (53.2) <0.001 671 (31.6) <0.001 62 (2.9) <0.001 0.3 (0.4) <0.001 0.1 (0.3) <0.001 1741 (79.2) 0.56 393 (22.7) <0.001 202 (10.9) <0.001 409 (20.5) <0.001 157 (7.8) <0.001 253 (11.5) <0.001 96 (4.4) <0.001 157 (7.1) 0.005 696 (32.8) 0.04 83 (3.9) <0.001 23.4 (1.1)
Nonparticipants P Value 1200 60.1 (11.1) 581 (48.4) 206 (17.2) 761 (63.6) 458 (40.2) 70 (6.0) 0.4 (0.4) 0.2 (0.4) 857 (71.5) 192 (22.5) 197 (21.0) 300 (30.1) 143 (14.5) 232 (19.5) 80 (6.7) 152 (12.7) 395 (35.5) 50 (4.6) 23.3 (1.1)
<0.001 0.23 0.003 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.91 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.11 0.38 0.08
Participants 2661 58.4 (11.2) 1365 (51.3) 333 (12.5) 1481 (55.7) 345 (13.5) 35 (1.36) 0.3 (0.4) 0.2 (0.3) 2279 (85.7) 340 (15.0) 299 (12.9) 560 (23.0) 219 (9.1) 278 (10.5) 110 (4.1) 168 (6.3) 1248 (48.1) 246 (9.6) 24.0 (1.4)
Nonparticipants P Value 692 64.5 (9.2) 326 (47.1) 109 (15.8) 501 (72.4) 142 (22.1) 23 (3.44) 0.5 (0.4) 0.3 (0.4) 531 (76.7) 78 (14.9) 155 (29.4) 187 (33.5) 119 (22.0) 168 (24.4) 69 (10.0) 99 (14.3) 325 (49.5) 47 (7.4) 23.8 (1.4)
<0.001 0.05 0.02 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.96 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.52 0.09 <0.001
Participants 6762 57.4 (9.5) 3515 (52.0) 972 (14.4) 3876 (57.5) 1414 (21.7) 294 (4.5) 0.3 (0.4) 0.1 (0.3) 5369 (79.5) 922 (17.3) 778 (13.2) 1478 (23.6) 581 (9.4) 658 (9.8) 266 (3.9) 392 (5.8) 2504 (38.0) 419 (6.4) 23.7 (1.3)
Non-participants P Value 3271 62.0 (11.4) 1575 (48.2) 631 (19.4) 2291 (70.3) 971 (31.3) 334 (10.4) 0.5 (0.5) 0.3 (0.4) 2257 (69.3) 383 (17.3) 740 (28.0) 977 (34.3) 534 (19.0) 557 (17.2) 219 (6.7) 338 (10.3) 1179 (38.1) 140 (4.6) 23.5 (1.1)
<0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.94 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.93 <0.001 <0.001
AL ¼ axial length; BCVA ¼ best-corrected visual acuity (logarithm of the minimum angle of resolution); PSC ¼ posterior subcapsular; PVA ¼ presenting visual acuity (logarithm of the minimum angle of resolution); SES ¼ socioeconomic status (low ¼ primary or lower education, individual monthly income <$2000 [Singapore], and 1e2 room Housing and Development Board flat). Boldface values are statistically significant. Data presented as mean (standard deviation) or number (percentage) accordingly. *Cataract presence is in unoperated eyes at baseline.
Cataract Surgery Incidence in Singapore
1379 62.3 (11.5) 668 (48.4) 316 (23.1) 1029 (75.0) 371 (28.1) 241 (17.7) 0.5 (0.5) 0.3 (0.4) 869 (63.7) 113 (13.4) 388 (33.0) 490 (37.8) 272 (21.2) 157 (11.5) 70 (5.1) 87 (6.3) 459 (34.6) 43 (3.3) 23.5 (1.0)
Participants
Combined Singapore Epidemiology of Eye Diseases Study (n [ 10 033)
Chinese (n [ 3353)
Total no. 1901 Age (yrs), mean (SD) 56.9 (10.1) Female, n (%) 1037 (54.6) Current smokers, n (%) 346 (18.2) Hypertension, n (%) 1227 (64.9) Diabetes, n (%) 398 (21.8) SES (low), n (%) 197 (10.5) PVA, mean (SD) 0.3 (0.4) BCVA, mean (SD) 0.1 (0.3) Wears glasses, n (%) 1349 (71.3) Annual glasses check, n (%) 189 (14.3) Nuclear cataract,* n (%) 277 (16.11) Cortical cataract,* n (%) 509 (27.7) PSC cataract,* n (%) 205 (11.2) Any previous cataract surgery, n (%) 127 (6.7) Unilateral surgery, n (%) 60 (3.2) Bilateral surgery, n (%) 67 (3.5) Myopia, n (%) 560 (29.9) High myopia, n (%) 90 (4.8) AL (mm), mean (SD) 23.6 (1.1)
Indians (n [ 3400)
Tan et al
Malays (n [ 3280)
3
Ophthalmology Volume -, Number -, Month 2018 Table 2. Incident Cataract Surgery Stratified by Age Groups in the Singapore Epidemiology of Eye Diseases Study Ethnic Groups: Malays, Indians, and Chinese Malays Baseline Variable
No./Total*
Incidence (%)
Age group (yrs) 40e49 9/536 50e59 37/651 60e69 73/380 70 55/198 y P value (for trend) Crude 174/1765 9.5 Age-adjusted (95% CI)z
Indians No./Total*
Chinese
Incidence (%)
1.7 15/662 5.7 57/724 19.2 99/451 27.8 42/103 <0.001 9.9 213/1940 (8.1e10.9)x 12.6
No./Total*
Incidence (%)
2.3 13/602 2.2 7.9 40/933 4.3 22.0 116/604 19.2 40.8 100/239 41.8 <0.001 <0.001 11.0 269/2378 11.3 (10.9e14.3)x 11.1 (9.8e12.5)x
Combined Singapore Epidemiology of Eye Diseases Study No./Total*
Incidence (%)
37/1800 134/2308 288/1435 197/540
2.1 5.8 20.1 36.5 <0.001 10.8 11.0 (10.2e11.8)
656/6083
CI ¼ confidence interval. Boldface values are statistically significance. *Number of cases/number at risk. y CochrandArmitage trend test. z Standardized to 2010 Singapore population census. x P values for age-adjusted incidence between the 3 ethnic groups are: Malays vs. Indians, P < 0.001; Indians vs. Chinese, P < 0.001; Malays vs. Chinese, P ¼ 0.002.
cataract surgery cases in the population attributable to modifiable risk exposures (or population attributable risk [PAR]) using the following equation24: ðPrevalence of exposure in the populationÞ ðRisk ratio 1Þ : 1 þ ðPrevalence of exposure in the populationÞ ðRisk ratio 1Þ The adjusted odds ratios (ORs) determined from the logistic regression models and the published prevalence of diabetes and myopia in the SEED Study25e29 were used to calculate the 2 PARs. To determine whether there were factors particularly contributing to risk of bilateral surgery, additional analyses limiting to unilateral versus bilateral incident cataract surgery as outcomes were conducted using logistic regression models. Odds ratios and 95% confidence intervals (CI) are presented. In all statistical analyses, a P value of less than 0.05 was considered statistically significant.
Results A total of 6762 (78.7% of eligible) SEED Study participants were re-examined at the 6-year follow-up visit. Table 1 compares baseline characteristics of participants and nonparticipants at the 6-year follow-up examinations for each ethnic group in the SEED Study. Overall, compared with those who participated, nonparticipants were older, more likely to be men, more likely to be current smokers, and more likely to have hypertension, diabetes, cataract, previous cataract surgery, low SES, and poorer PVA and BCVA and were less likely to have glasses (Table 1). Of the 1901, 2200, and 2661 re-examined Malay, Indian, and Chinese participants, respectively, we excluded 415 participants who had undergone cataract surgery in both eyes before baseline (n ¼ 392) or who had missing baseline (n ¼ 15) or follow-up (n ¼ 8) lens status for one or both eyes. Thus, there were 1765 Malay participants (92.8%), 1940 Indian participants (88.1%), and 2378 Chinese participants (89.4%) with 2 phakic eyes at baseline who were at risk of incident cataract surgery in either eye (i.e., both eyes were at risk). For the entire SEED Study, there were 6083 participants (90.0%) with 2 phakic eyes at baseline who were at risk of incident cataract surgery in either eye. In addition, there were 59 Malay participants (3.1%), 95 Indian participants (4.3%), and 110
4
Chinese (4.1%; 264 participants [3.9%] in the SEED Study) who had undergone cataract surgery in 1 eye before baseline and were at risk of incident cataract surgery in the second eye. The overall 6-year incidence of cataract surgery in the SEED Study was 10.8% (Malay, 9.9%; Indian, 11.0%; and Chinese, 11.3%). Age-adjusted incidence for the SEED Study was 11.0% (95% CI, 10.2%e11.8%; Table 2). The age-adjusted incidences for Malay, Indian, and Chinese participants were 9.5% (95% CI, 8.1%e10.9%), 12.6% (95% CI, 10.9%e14.3%), and 11.1% (95% CI, 9.8%e12.5%), respectively (Table 2). The incidence rate in Malays was the lowest and was significantly different from that in Indians (P < 0.001) and Chinese (P ¼ 0.002; Table 2). The incidence of cataract surgery increased with increasing age in the SEED Study from 2.1% among those 40 to 49 years of age, 5.8% for those 50 to 59 years of age, 20.1% for those 60 to 69 years of age, and 36.5% for those 70 years of age or older (P < 0.001 for trend), with a similar trend for each ethnic group (Table 2). Of the 264 participants with previous unilateral cataract surgery, 148 (56.1%) underwent incident cataract surgery in the second eye (26 eyes in the Malay group, 57 in the Indian group, and 65 in the Chinese group, respectively). Table 3 presents the crude incidence of cataract surgery by baseline characteristics. In the SEED Study sample (combined 3 ethnic groups), there was a significantly higher incidence of cataract surgery among those with diabetes, myopia, high myopia, and cataract at baseline and in those who had their glasses checked annually (Table 3). Baseline factors associated with increased cataract surgery incidence were similar across the 3 ethnic groups, except for hypertension being significant among Chinese participants, but diabetes was not, and an annual glasses check was not significant among Malays and Chinese (Table 3). In a person-specific model including baseline age, gender, ethnicity, smoking status, hypertension, diabetes, SES, and myopia, baseline factors that were associated significantly with increased likelihood of cataract surgery were age, diabetes, visual acuity (PVA or BCVA), yearly glasses check, myopia, high myopia, axial length, and the presence of nuclear, cortical, or PSC cataract at baseline (Table 4). These baseline factors and the magnitude of their associations with incident cataract surgery were similar across the 3 samples, with the exception of the Malay sample, in which yearly glasses check was not a risk
Tan et al
Cataract Surgery Incidence in Singapore
Table 3. Incident Cataract Surgery by Baseline Characteristics in the Singapore Epidemiology of Eye Diseases Study Ethnic Groups: Malays, Indians, and Chinese Malays (n [ 174/1765)* Baseline Characteristics Age (yrs), mean (SD) Gender (%) Male Female Smoking status (%) Nonsmoker Current smoker Hypertension (%) Absent Present Diabetes (%) Absent Present Socioeconomic status (%) High Low PVA, mean (SD) BCVA, mean (SD) Wears glasses (%) No Yes Annual glasses check (%) No Yes Any nuclear (%) No Yes Any cortical (%) No Yes Any PSC (%) No Yes Myopia (%)z Absent Present High myopia (%)x Absent Present AL (mm), mean (SD)
Indians (n [ 213/1940)*
Chinese (n [ 269/2378)*
% with Incident % with Incident % with Incident Surgery P Valuey Surgery P Valuey Surgery P Valuey 64.6 (8.4)
62.8 (8.3)
65.9 (8.0)
Combined Singapore Epidemiology of Eye Diseases Study (n [ 656/6083)* % with Incident Surgery
P Valuey
64.6 (8.3)
8.8 10.7
0.06
11.7 10.3
0.98
11.6 11.0
0.49
10.9 10.7
0.23
10.3 8.0
0.77
11.5 8.2
0.82
11.6 9.2
0.83
11.2 8.5
0.89
5.9 12.2
0.90
7.6 14.5
0.68
5.7 16.3
0.01
6.4 14.4
0.09
8.0 17.0
<0.001
7.3 18.8
<0.001
10.3 18.3
0.06
8.8 18.1
<0.001
9.6 12.2 0.6 (0.5) 0.4 (0.5)
0.60
11.0 21.3 0.5 (0.4) 0.3 (0.4)
0.95
11.3 21.4 0.6 (0.4) 0.3 (0.4)
0.94
10.7 14.9 0.6 (0.4) 0.4 (0.4)
0.35
8.8 10.3
0.73
10.9 11.0
0.24
10.0 11.5
0.47
9.8 11.0
0.22
10.0 11.2
0.14
10.4 13.2
0.02
11.2 13.7
0.20
10.6 13.0
<0.001
5.3 32.7
<0.001
6.2 49.7
<0.001
6.1 46.7
<0.001
5.9 42.4
<0.001
4.9 23.3
<0.001
6.4 29.3
<0.001
6.1 30.8
<0.001
5.9 27.8
<0.001
6.4 40.6
<0.001
7.4 57.3
<0.001
8.6 44.0
<0.001
7.6 46.2
<0.001
7.8 13.2
<0.001
8.8 13.7
<0.001
9.3 12.4
<0.001
8.7 12.9
<0.001
8.9 17.4 23.7 (1.3)
<0.001
9.8 20.8 23.5 (1.4)
<0.001
10.1 12.8 24.0 (1.5)
<0.001
9.6 15.4 23.7 (1.2)
<0.001
AL ¼ axial length; BCVA ¼ best-corrected visual acuity (logarithm of the minimum angle of resolution); PSC ¼ posterior subcapsular cataract; PVA ¼ presenting visual acuity (logarithm of the minimum angle of resolution); SD ¼ standard deviation. Boldface values are statistically significant. *Number of incident cataract surgery cases/total number in population. y Age-adjusted P value. z Myopia defined as spherical equivalent refraction <0.5 diopter. x High myopia defined as spherical equivalent
factor, and the Chinese sample, in which hypertension was a significant risk factor, but diabetes and a yearly glasses check were not (Table 4). Eye-specific analysis showed similar associations between baseline ocular characteristics and incident cataract surgery in the same eye (Table 5). The 2 significant modifiable risk factors of incident cataract surgery were diabetes and myopia. Among participants who had incident cataract surgery, the mean ages at follow-up were significantly younger among those with diabetes than those without
among Malays (mean age, 69.4 years vs. 73.2 years; P ¼ 0.005) and among those with myopia than those without among Indians and Chinese or among the SEED Study population (Indians: 67.6 years vs. 70.0 years [P ¼ 0.04]; Chinese: 69.9 years vs. 74.0 years [P < 0.001]; SEED: 69.4 years vs. 72.0 years [P < 0.001]). The proportion of the risk of having cataract surgery in the SEED Study population attributable to diabetes (i.e., PAR) was 17.6% (21.6%, 24.0%, and 5.7% for Malay, Indian, and Chinese groups, respectively). The PAR for myopia was 19.1% (15.8%,
5
Ophthalmology Volume -, Number -, Month 2018 Table 4. Association between Baseline Demographic, Systemic, and Ocular Factors with Incident Cataract Surgery (in Either Eye) Using Person-Specific Analysis in the Multiethnic Singapore Epidemiology of Eye Diseases Study
Baseline Characteristics Age, per year Gender Male Female Smoking status Nonsmoker Current smoker Hypertension Absent Present Diabetes Absent Present Socioeconomic status High Low PVA, per 0.1 unit BCVA, per 0.1 unit Wears glasses No Yes Annual glasses check No Yes Cataract typey Any nuclear Any cortical Any PSC Myopiaz Absent Present High myopiaz Absent Present AL per mmz
Malays (n [ 1765), Multivariate Adjusted Odds Ratio (95% Confidence Interval)
Indians (n [ 1940), Multivariate Adjusted Odds Ratio (95% Confidence Interval)
Chinese (n [ 2378), Multivariate Adjusted Odds Ratio (95% Confidence Interval)
Combined Singapore Epidemiology of Eye Diseases Study (n [ 6083), Multivariate Adjusted* Odds Ratio (95% Confidence Interval)
1.11 (1.09e1.14)
1.12 (1.10e1.15)
1.15 (1.13e1.17)
1.13 (1.11e1.14)
1.00 (ref) 1.48 (0.98e2.22)
1.00 (ref) 0.96 (0.67e1.36)
1.00 (ref) 1.26 (0.92e1.73)
1.00 (ref) 1.18 (0.96e1.44)
1.00 (ref) 1.42 (0.80e2.50)
1.00 (ref) 0.90 (0.50e1.60)
1.00 (ref) 1.13 (0.68e1.87)
1.00 (ref) 1.12 (0.82e1.52)
1.00 (ref) 0.97 (0.62e1.52)
1.00 (ref) 0.95 (0.66e1.38)
1.00 (ref) 1.45 (1.02e2.05)
1.00 (ref) 1.13 (0.91e1.40)
1.00 (ref) 2.13 (1.46e3.11)
1.00 (ref) 1.92 (1.36e2.71)
1.00 (ref) 1.40 (0.94e2.08)
1.00 (ref) 1.90 (1.54e2.33)
1.00 0.76 1.08 1.19
1.00 1.08 1.19 1.29
1.00 1.34 1.20 1.32
1.00 0.84 1.16 1.26
(ref) (0.43e1.32) (1.02e1.14) (1.10e1.28)
(ref) (0.45e2.56) (1.13e1.26) (1.20e1.39)
(ref) (0.43e4.22) (1.15e1.26) (1.22e1.42)
(ref) (0.55e1.29) (1.12e1.19) (1.21e1.31)
1.00 (ref) 1.30 (0.84e2.01)
1.00 (ref) 0.95 (0.61e1.48)
1.00 (ref) 1.34 (0.83e2.18)
1.00 (ref) 1.18 (0.91e1.53)
1.00 (ref) 1.36 (0.75e2.44)
1.00 (ref) 1.60 (1.05e2.44)
1.00 (ref) 1.17 (0.74e1.83)
1.00 (ref) 1.39 (1.06e1.82)
2.93 (1.75e4.88) 3.14 (2.11e4.67) 4.78 (3.13e7.31)
5.66 (3.55e9.02) 2.77 (1.89e4.04) 11.24 (6.98e18.09)
3.47 (2.33e5.17) 3.25 (2.35e4.49) 3.29 (2.17e4.99)
3.78 (2.91e4.89) 3.01 (2.45e3.71) 5.00 (3.91e6.41)
1.00 (ref) 1.76 (1.17e2.64)
1.00 (ref) 1.82 (1.24e2.67)
1.00 (ref) 1.98 (1.42e2.76)
1.00 (ref) 1.78 (1.44e2.20)
1.00 (ref) 2.25 (1.07e4.72) 1.30 (1.10e1.54)
1.00 (ref) 3.85 (1.90e7.80) 1.26 (1.09e1.46)
1.00 (ref) 2.36 (1.41e3.97) 1.18 (1.04e1.33)
1.00 (ref) 2.44 (1.71e3.49) 1.20 (1.10e1.30)
AL ¼ axial length; BCVA ¼ best corrected visual acuity (logarithm of the minimum angle of resolution); PSC ¼ posterior subcapsular cataract; PVA ¼ presenting visual acuity (logarithm of the minimum angle of resolution). Boldface values are statistically significant. Models adjusting for age, gender, current smoking, hypertension, diabetes, socioeconomic status, and myopia unless otherwise indicated. *Model additionally adjusted for ethnicity. y Each individual cataract type was assessed separately in each model (e.g., analysis for nuclear cataract only had that type of cataract with full model adjustment). z Model adjusted for age, gender, current smoking, hypertension, diabetes, socioeconomic status, and nuclear cataract.
17.6%, and 27.9% for Malay, Indian, and Chinese groups, respectively). Of the 656 incident cataract surgery cases, 368 (56.1%) underwent bilateral incident cataract surgery (85 Malays, 131 Indians, and 152 Chinese). Participants with bilateral cataract surgery were slightly older than those who undergone unilateral surgery in all 3 cohorts. Risk factors for bilateral cataract surgery differed among the 3 ethnic groups (Table S2, available at www.aaojournal.org). Overall in the SEED Study samples combined, compared with unilateral cataract surgery cases, age, female gender, nuclear and PSC cataract, and high myopia were associated with an increased risk of bilateral cataract surgery, whereas low SES was associated with decreased risk of bilateral surgery.
6
Discussion In this population-based cohort study of 3 major ethnic groups in Singapore, we report an overall (person-specific) age-adjusted 6-year incidence of cataract surgery of 11.0% in the SEED Study. Incidence of cataract surgery increased with age in all cohorts from 2.1% among those 40 to 49 years of age up to 36.5% among those 70 years of age or older. Aside from age and presence of cataract at baseline, diabetes and myopia were 2 significant and potentially modifiable risk factors for incident cataract surgery. Among
Tan et al
Cataract Surgery Incidence in Singapore
Table 5. Association between Baseline Ocular Factors with Incident Cataract Surgery Using Eye-Specific Analysis in the Multiethnic Singapore Epidemiology of Eye Diseases Study
Baseline Characteristics PVA, per 0.1 unit BCVA, per 0.1 unit Cataract typey Any nuclear Any cortical Any PSC Myopiaz High myopiaz Axial length, per mmz
Malays (n [ 3589), Multivariate Adjusted Odds Ratio (95% Confidence Interval)
Indians (n [ 3975), Multivariate Adjusted Odds Ratio (95% Confidence Interval)
Chinese (n [ 4866), Multivariate Adjusted Odds Ratio (95% Confidence Interval)
Combined Epidemiology of Eye Diseases Study (n [ 12 430), Multivariate Adjusted* Odds Ratio (95% Confidence Interval)
1.07 (1.00e1.14) 1.19 (1.11e1.28)
1.16 (1.10e1.21) 1.22 (1.13e1.33)
1.21 (1.16e1.26) 1.30 (1.18e1.44)
1.44 (1.11e1.18) 1.23 (1.17e1.29)
1.94 2.40 5.52 1.70 2.52 1.31
3.04 2.43 6.42 1.81 3.51 1.24
2.87 2.16 3.68 1.69 3.12 1.24
2.55 2.25 4.77 1.67 2.84 1.21
(1.29e2.91) (1.68e3.43) (3.82e7.97) (1.21e2.38) (1.30e4.88) (1.12e1.52)
(2.03e4.56) (1.81e3.25) (4.27e9.66) (1.32e2.48) (2.00e6.17) (1.07e1.43)
(2.06e4.02) (1.69e2.76) (2.63e5.16) (1.29e2.22) (2.08e4.67) (1.11e1.38)
(2.05e3.16) (1.91e2.66) (3.86e5.88) (1.40e1.98) (2.13e3.81) (1.12e1.30)
BCVA ¼ best-corrected visual acuity (logarithm of the minimum angle of resolution, per 0.1-unit increase); PSC ¼ posterior subcapsular cataract; PVA ¼ presenting visual acuity (logarithm of the minimum angle of resolution, per 0.1-unit increase). Boldface values are statistically significant. Models adjusted for age, gender, current smoking, hypertension, diabetes, socioeconomic status, and myopia unless otherwise indicated. *Model additionally adjusted for ethnicity. y Each individual cataract type was assessed separately in each model (e.g., analysis for nuclear cataract only had that type of cataract with full model adjustment). z Model adjusting for age, gender, current smoking, hypertension, diabetes, socioeconomic status, and nuclear cataract.
Malays and Indians, diabetes was a more important determinant of incident cataract surgery; in contrast, among Chinese, myopia was a more important determinant of cataract surgery. Female gender was associated with greater risk of bilateral cataract surgery, whereas low SES was associated with less likelihood of bilateral cataract surgery, when compared with incident unilateral cataract surgery. Although direct comparison between studies is difficult because of differing age ranges, durations of follow-up, and periods when previous studies were conducted, the overall incidence of cataract surgery observed in our Singapore cohorts (11.0%) is comparable and within the higher end of the ranges reported by previous studies of similar age groups (40þ years; Table S1). Previously reported cataract surgery incidence rates varied from a 4-year incidence of 1.5% in the Los Angeles Latino Eye Study13 of Latinos 40 years of age or older to a 7-year incidence of 14.7% in the Shihpai Eye Study15 of Taiwanese persons 65 years of age or older (Table S1). In a previous study conducted in Singapore using data from Medisave,18 the average annual rate of cataract surgery for all ages from 1991 through 1996 was 356.4 per 100 000 persons. Because of different study designs and different age ranges of the 2 samples, we cannot compare our findings from this population-based cohort with that from the previous Medisave data. Nevertheless, differences in cataract surgery incidence between our cohort and other population-based cohorts of similar age range may be explained by the advances in cataract surgical technologies and techniques over the past decades, leading to substantial improvements in patient safety and surgical outcomes30 and to lowering visual impairment thresholds for surgery.30 Age is a consistent risk factor for cataract surgery among the 3 cohorts of the SEED, in keeping with findings from
other populations.9e12,14,17 We observed an increasing trend of incident cataract surgery with age from 2.1% among those 40 to 49 years of age up to 36.5% among those 70 years of age or older. This equates to roughly 12 782 persons 40 to 49 years of age and up to 81 708 persons 70 years of age or older, for a total of 186 000 undergoing cataract surgery over 6 years (approximately 30 000 per year) for persons 40 years of age or older, when extrapolating to the Singapore population using numbers from the last census. This is consistent with the reported 48 000 surgeries from 2006 through 2010 (approximately 12 000 per year) performed in the Singapore National Eye Centre, where 40% of the total volume of cataract surgeries in Singapore were performed.31 As expected, of the factors that determine the need for cataract surgery, the presence of cataract at baseline was a major factor. Of the types of cataract, the risk magnitude was highest for PSC cataract, followed by nuclear and cortical cataract. This is consistent with findings from the Beaver Dam Eye Study and the Blue Mountains Eye Study, where the presence of PSC cataract at baseline was the most important ocular risk factor for incident cataract surgery.9,10 This is consistent with the impact of PSC cataract on central vision. Our reported incidence of cataract surgery for Malays, Indians, and Chinese (9.5%, 12.6%, and 11.1%, respectively) was higher than the proportions of SEED Study participants with an unmet need for cataract surgery services at baseline, based on presence of visually significant cataract (7.2%, 4.9%, and 5.8%, respectively).32 However, the higher incidence of cataract surgery reported is consistent with an expected increase in the need for cataract surgery services over time because of factors that affect cataract formation such as age and diabetes.
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Ophthalmology Volume -, Number -, Month 2018 The impact of diabetes and myopia on incident cataract surgery in the SEED Study is considerable, estimated at 17.6% and 19.1% of incident cataract surgery cases attributable to diabetes and myopia, respectively. Diabetes is a well-established risk factor for cataract. Myopia has been documented consistently to be associated with cataract33,34 and cataract surgery.10,33,35,36 In addition, persons with diabetes or myopia may make more frequent visits to doctors and so be more likely to have cataract detected earlier compared with persons without these conditions. Our finding of increased incidence of cataract surgery among those who undergo a yearly glasses check supports this. The burden of these 2 diseases is substantial; in the SEED Study, the overall prevalences of diabetes and myopia were 23.7%25 and 38.9%,28 respectively, with comparable prevalences reported in similar ethnic populations living in37,38 and outside of29,39,40 Singapore. With an increasing prevalence of diabetes41 and myopia28 in Singapore, ensuring adequate resources allocated and patient access to eye care services is needed. We also found significant ethnic differences. Among Malays and Indians, diabetes was a more important determinant of incident cataract surgery (accounting for 21.6% and 24%, respectively, of cataract surgery). In contrast, myopia was a more important determinant of cataract surgery among Chinese, accounting for 27.9% of incident cataract surgery. Strategies to mitigate increasing prevalence of diabetes and myopia in these ethnic groups may help to reduce eye health care burden resulting from early onset of agerelated cataract associated with these 2 common conditions. We observed an increased likelihood of undergoing bilateral cataract surgery among women overall in the SEED Study compared with men, and this seems to be driven by an increased risk of bilateral surgery among Indian women compared with Indian men. This is in keeping with findings of a previous study that, in Singapore, the highest rate of cataract surgery was observed among Indian women.18 Low SES was associated with lower likelihood of having bilateral cataract surgery compared with unilateral surgery overall in the SEED Study, which also seemed to be driven by an association seen in Indians. We speculate that persons who are less comfortable financially delay having secondeye surgery as long as possible. High myopia was associated with a 2-fold increased risk of bilateral cataract surgery compared with unilateral surgery. This may be the result of patients wanting to minimize postoperative anisometropia after unilateral cataract surgery,42 which would be marked in those with high myopia (
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to have a history of hypertension or diabetes, more likely to have cataract at baseline, and had lower SES at baseline, each of which could have led to an underestimation of incident cataract surgery in our study population. Lack of association found between current smoking and incident cataract surgery may be confounded by lower participation rates among current smokers at follow-up. Although the 3 substudies of the SEED Study were conducted in different periods over a span of 7 years, the eye health care practice pattern and the overall health care provision system in Singapore has not changed during this period.43 Therefore, we do not anticipate that there would be apparent cohort effect on cataract surgery incidence rates of the 3 ethnic populations. In conclusion, our study documented that in an urban city-state Asian setting, 1 in 10 Malay, Indian, and Chinese Singaporeans 40 years of age or older had undergone incident cataract surgery in at least 1 eye over 6 years. Apart from age and the presence of cataract at baseline, diabetes and myopia were significant and potentially modifiable risk factors for incident cataract surgery. Our findings provide greater insights on the trends of cataract surgery uptake over time and will inform planning of future provision of eye care services to target at-risk sectors of the Singapore population. Furthermore, our incident cataract surgery rates are substantially higher than those reported from less developed Asian communities, and thus provide further evidence of the need to improve access to cataract surgery in large parts of Asia, home to more than 3 billion people.
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26. Saw SM, Chan YH, Wong WL, et al. Prevalence and risk factors for refractive errors in the Singapore Malay Eye Survey. Ophthalmology. 2008;115:1713e1719. 27. Pan CW, Wong TY, Lavanya R, et al. Prevalence and risk factors for refractive errors in Indians: the Singapore Indian Eye Study (SINDI). Invest Ophthalmol Vis Sci. 2011;52: 3166e3173. 28. Pan CW, Zheng YF, Anuar AR, et al. Prevalence of refractive errors in a multiethnic Asian population: the Singapore Epidemiology of Eye Disease Study. Invest Ophthalmol Vis Sci. 2013;54:2590e2598. 29. Pan CW, Dirani M, Cheng CY, et al. The age-specific prevalence of myopia in Asia: a meta-analysis. Optom Vis Sci. 2015;92:258e266. 30. Erie JC. Rising cataract surgery rates: demand and supply. Ophthalmology. 2014;121:2e4. 31. Ti SE, Yang YN, Lang SS, Chee SP. A 5-year audit of cataract surgery outcomes after posterior capsule rupture and risk factors affecting visual acuity. Am J Ophthalmol. 2014;157: 180e185. 32. Zheng Y, Cheng CY, Lamoureux EL, et al. How much eye care services do Asian populations need? Projection from the Singapore Epidemiology of Eye Disease (SEED) Study. Invest Ophthalmol Vis Sci. 2013;54:2171e2177. 33. Wong TY, Klein BE, Klein R, et al. Refractive errors and incident cataracts: the Beaver Dam Eye Study. Invest Ophthalmol Vis Sci. 2001;42:1449e1454. 34. Panchapakesan J, Rochtchina E, Mitchell P. Myopic refractive shift caused by incident cataract: the Blue Mountains Eye Study. Ophthalmic Epidemiol. 2003;10:241e247. 35. Klein BE, Klein RE, Lee KE. Incident cataract after a five-year interval and lifestyle factors: the Beaver Dam Eye Study. Ophthalmic Epidemiol. 1999;6:247e255. 36. Younan C, Mitchell P, Cumming RG, et al. Myopia and incident cataract and cataract surgery: the Blue Mountains Eye Study. Invest Ophthalmol Vis Sci. 2002;43: 3625e3632. 37. Wong TY, Foster PJ, Hee J, et al. Prevalence and risk factors for refractive errors in adult Chinese in Singapore. Invest Ophthalmol Vis Sci. 2000;41:2486e2494. 38. Yeo KK, Tai BC, Heng D, et al. Ethnicity modifies the association between diabetes mellitus and ischaemic heart disease in Chinese, Malays and Asian Indians living in Singapore. Diabetologia. 2006;49:2866e2873. 39. Xu L, Xie X, Wang S, et al. Prevalence of diabetes mellitus in China. Exp Clin Endocrinol Diabetes. 2008;116:69e70. 40. Gujral UP, Narayan KM, Pradeepa RG, et al. Comparing type 2 diabetes, prediabetes, and their associated risk factors in Asian Indians in India and in the U.S.: the CARRS and MASALA Studies. Diabetes Care. 2015;38: 1312e1318. 41. Phan TP, Alkema L, Tai ES, et al. Forecasting the burden of type 2 diabetes in Singapore using a demographic epidemiological model of Singapore. BMJ Open Diabetes Res Care. 2014;2:e000012. 42. Ishikawa T, Desapriya E, Puri M, et al. Evaluating the benefits of second-eye cataract surgery among the elderly. J Cataract Refract Surg. 2013;39:1593e1603. 43. Ministry of Health Singapore. Caring for Our People: 50 Years of Healthcare in Singapore. Singapore: MOH Holdings Pte Ltd for the Ministry of Health; 2015.
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Ophthalmology Volume -, Number -, Month 2018 Footnotes and Financial Disclosures Originally received: April 7, 2018. Final revision: July 25, 2018. Accepted: July 27, 2018. Available online: ---.
from the Australian National Health & Medical Research Council, Canberra, Australia. The funding organizations had no role in the design or conduct of this research. Manuscript no. 2018-673.
1
Centre for Vision Research, Department of Ophthalmology, The Westmead Institute for Medical Research, The University of Sydney, Westmead Hospital, Westmead, Australia.
2
Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Republic of Singapore.
3
Ophthalmology and Visual Sciences Academic Clinical Program, DukeNUS Medical School, Singapore, Republic of Singapore.
4
Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Republic of Singapore.
5
School of Public Health, The University of Sydney, Sydney, Australia.
6
Health Services and Systems Research, Duke-NUS Medical School, Singapore, Republic of Singapore. *Both authors contributed equally. Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article. The Singapore Epidemiology of Eye Disease Study is funded by the National Medical Research Council, Singapore, Republic of Singapore (grant nos.: 0796/2003, IRG07nov013, IRG09-nov014, STaR/0003/2008, CG/SERI/2010, 1249/2010, STaR/0016/2013, CIRG/1371/2013, and CIRG/1417/2015); and the Biomedical Research Council, Singapore, Republic of Singapore (grant nos.: 08/1/35/19/550 and 09/1/35/19/616). Ms. Tan is supported by a postgraduate research scholarship (GNT1094094)
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HUMAN SUBJECTS: Human subjects were included in this study. The human ethics committees at the Singapore Eye Research Institute approved the study. All research adhered to the tenets of the Declaration of Helsinki. All participants provided informed consent. No animal subjects were included in this study. Author Contributions: Conception and design: A.G.Tan, Kifley, T.Y.Wong, Cheng Analysis and interpretation: A.G.Tan, Kifley, Tham, Shi, Chee, N.Y.Q.Tan, Wong, Mitchell, Cumming, T.Y.Wong, Wang, Cheng Data collection: Shi, Chee, Sabanayagam, T.Y.Wong, Wang, Cheng Obtained funding: T.Y.Wong, Cheng, Sabanayagam Overall responsibility: A.G.Tan, Kifley, Tham, Sabanayagam, N.Y.Q.Tan, Wong, Mitchell, Cumming, T.Y.Wong, Wang, Cheng Abbreviations and Acronyms: BCVA ¼ best-corrected visual acuity; CI ¼ confidence interval; D ¼ diopter; OR ¼ odds ratio; PAR ¼ population attributable risk; PSC ¼ posterior subcapsular; PVA ¼ presenting visual acuity; SE ¼ spherical equivalent; SEED ¼ Singapore Epidemiology of Eye Diseases; SES ¼ socioeconomic status. Correspondence: Jie Jin Wang, MMed, PhD, Duke-NUS Medical School, 20 College Road, The Academia, Level 6, Room 053, Singapore 169856, Republic of Singapore. E-mail: [email protected].