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Risk Factors for Cataracts Treated Surgically in Postmenopausal Women

Open AccessPublished:June 07, 2016DOI:https://doi.org/10.1016/j.ophtha.2016.04.037

      Purpose

      To identify risk factors for cataracts treated surgically in postmenopausal women.

      Design

      Population-based, prospective cohort study.

      Participants

      A total of 1 312 051 postmenopausal women in the UK Million Women Study, aged 56 years on average (standard deviation [SD], 4.8), without previous cataract surgery, hospital admission with cataracts, or cancer at baseline, were followed for cataracts treated surgically.

      Methods

      Cox regression was used to calculate adjusted relative risks (RRs) for cataract surgery by lifestyle factors, treatment for diabetes, reproductive history, and use of hormonal therapies.

      Main Outcome Measures

      Cataract surgery identified by linkage to central National Health Service (NHS) records for inpatient and day-patient admissions (Hospital Episode Statistics for England and Scottish Morbidity Records in Scotland).

      Results

      Overall, 89 343 women underwent cataract surgery during an average of 11 (SD, 3) years of follow-up. Women with diabetes were at greatest risk (diabetes vs. no diabetes RR, 2.90; 95% confidence interval [CI], 2.82–2.97). Other factors associated with an increased risk of cataract surgery were current smoking (current smokers of ≥15 cigarettes/day vs. never smokers RR, 1.26; 95% CI, 1.23–1.30) and obesity (body mass index [BMI] ≥30 vs. <25 kg/m2; RR, 1.12; 95% CI, 1.10–1.14).

      Conclusions

      Diabetes, smoking, and obesity were risk factors for cataract surgery. Alcohol use, physical activity, reproductive history, and use of hormonal therapies had little, if any, association with cataract surgery risk.

      Abbreviations and Acronyms:

      BMI (body mass index), CI (confidence interval), HT (hormone therapy), NHS (National Health Service), OPCS-4 (Office of Population Censuses and Survey's classification of surgical operations and procedures, fourth revision), RR (relative risk), SD (standard deviation), UV (ultraviolet)
      Cataract is the second leading cause of partial sight and blindness in the United Kingdom, exceeded only by age-related macular degeneration.

      Access Economics Pty Limited. Future sight loss UK (1): the economic impact of partial sight and blindness in the UK adult population: full report. Available at: https://www.rnib.org.uk/sites/default/files/FSUK_Report.pdf: RNIB, 2009. Accessed November 24, 2015.

      Identifying potential risk factors for cataract is important given that the only treatment for cataract is the surgical removal of the lens. The most important risk factor for cataract formation is age.
      • Asbell P.A.
      • Dualan I.
      • Mindel J.
      • et al.
      Age-related cataract.
      Other risk factors that have been identified are diabetes, smoking, ultraviolet (UV) light, and steroid use,
      • Asbell P.A.
      • Dualan I.
      • Mindel J.
      • et al.
      Age-related cataract.
      • Pollreisz A.
      • Schmidt-Erfurth U.
      Diabetic cataract–pathogenesis, epidemiology and treatment.
      • Abraham A.G.
      • Condon N.G.
      • West Gower E.
      The new epidemiology of cataract.
      • Yam J.C.
      • Kwok A.K.
      Ultraviolet light and ocular diseases.
      • Urban Jr., R.C.
      • Cotlier E.
      Corticosteroid-induced cataracts.
      • Wang J.J.
      • Rochtchina E.
      • Tan A.G.
      • et al.
      Use of inhaled and oral corticosteroids and the long-term risk of cataract.
      but there is less evidence on the role of factors such as body mass index (BMI), physical activity, reproductive history, use of hormonal therapies, and alcohol consumption.
      • Abraham A.G.
      • Condon N.G.
      • West Gower E.
      The new epidemiology of cataract.
      • Weintraub J.M.
      • Willett W.C.
      • Rosner B.
      • et al.
      A prospective study of the relationship between body mass index and cataract extraction among US women and men.
      • Hiller R.
      • Podgor M.J.
      • Sperduto R.D.
      • et al.
      A longitudinal study of body mass index and lens opacities. The Framingham Studies.
      • Reeves G.K.
      • Balkwill A.
      • Cairns B.J.
      • et al.
      Hospital admissions in relation to body mass index in UK women: a prospective cohort study.
      • Keenan T.
      • Rosen P.
      • Yeates D.
      • Goldacre M.
      Time trends and geographical variation in cataract surgery rates in England: study of surgical workload.
      Cataract surgery is the most common surgical procedure in the National Health Service (NHS) in England, with more than 340 000 operations carried out in 2013 and 2014.

      Health and Social Care Information Centre. Hospital Episode Statistics, Admitted Patient Care, England—2013–14: Diagnosis. Available at: www.hscic.gov.uk. Accessed May 28, 2015.

      Rates of cataract surgery in England have increased rapidly since 1990 because of the widespread uptake of phacoemulsification and day case surgery.
      • Keenan T.
      • Rosen P.
      • Yeates D.
      • Goldacre M.
      Time trends and geographical variation in cataract surgery rates in England: study of surgical workload.
      For people aged more than 60 years, rates are higher for women compared with men.
      • Keenan T.
      • Rosen P.
      • Yeates D.
      • Goldacre M.
      Time trends and geographical variation in cataract surgery rates in England: study of surgical workload.
      It has been proposed that this higher rate of surgery results from higher incidence of cataracts in postmenopausal women compared with men of a similar age because of hormonal differences between men and women.
      • Klein B.E.
      • Klein R.
      • Lee K.E.
      Incidence of age-related cataract: the Beaver Dam Eye Study.
      • Leske M.C.
      • Wu S.Y.
      • Nemesure B.
      • et al.
      Incidence and progression of lens opacities in the Barbados Eye Studies.
      • Worzala K.
      • Hiller R.
      • Sperduto R.D.
      • et al.
      Postmenopausal estrogen use, type of menopause, and lens opacities: the Framingham studies.
      However, epidemiologic evidence on the relationship between cataracts and reproductive and hormonal factors, including use of hormone therapy (HT) for menopause, is limited and inconsistent.
      • Abraham A.G.
      • Condon N.G.
      • West Gower E.
      The new epidemiology of cataract.
      • Lai K.
      • Cui J.
      • Ni S.
      • et al.
      The effects of postmenopausal hormone use on cataract: a meta-analysis.
      • Lindblad B.E.
      • Hakansson N.
      • Philipson B.
      • Wolk A.
      Hormone replacement therapy in relation to risk of cataract extraction: a prospective study of women.
      In a large cohort of postmenopausal women from the United Kingdom, with virtually complete long-term follow-up for surgical procedures through linkage to hospital records, we have examined potential risk factors for cataracts treated surgically, including treatment for diabetes, lifestyle, and reproductive and hormonal factors.

      Methods

       Data Collection and Definitions

      The Million Women Study is a population-based prospective study of women in the United Kingdom. Details of the design and methods of the study have been described.
      Million Women Study Collaborators
      Breast cancer and hormone-replacement therapy in the Million Women Study.
      Briefly, 1.3 million women aged 50 to 64 years were invited for breast cancer screening at NHS clinics in England and Scotland and were recruited to the study between 1996 and 2001 by completing a questionnaire, which included questions on various socioeconomic, lifestyle, reproductive, and hormonal factors. The respondents gave written consent to participate and for follow-up though their NHS medical records; ethical approval was provided by the Oxford and Anglia Multi-Centre Research Ethics Committee. Study questionnaires and details of the study data and access policies can be viewed on the website (www.millionwomenstudy.org).

       Follow-up

      Individuals in the study are linked by their unique NHS identification number to NHS Central Registers, through which they are followed for emigration, death, and cancer registration, and to NHS hospital admissions databases: Hospital Episode Statistics for England and Scottish Morbidity Records for Scotland. The databases include information on both inpatient stays and day-case admissions (e.g., for surgical procedures). Follow-up is 99% complete; only 18 970 women (1%) have been lost to follow-up in the entire cohort, and they have been included in analyses up to the date of loss to follow-up. Information on the date and type of procedures associated with each hospital admission is provided, coded to the Office of Population Censuses and Survey's classification of surgical operations and procedures, fourth revision (OPCS-4). Linked data for England are provided to the cohort through the Health and Social Care Information Centre and the Office for National Statistics, and for Scotland by the NHS Information Services Division.

       Statistical Analysis

      Analyses were restricted to postmenopausal women. Those who reported at recruitment that they had experienced natural menopause (49%) or who had undergone a bilateral oophorectomy (6%) were defined as postmenopausal and included in follow-up from recruitment. Women who were premenopausal, perimenopausal, or of unknown menopausal status at recruitment were assumed to be postmenopausal after they reached the age of 55 years and were included in follow-up from age 55 years, because 96% of women in this cohort with a known age at natural menopause were postmenopausal by that age.
      • Armstrong M.E.G.
      • Cairns B.J.
      • Banks E.
      • et al.
      Different effects of age, adiposity and physical activity on the risk of ankle, wrist and hip fractures in postmenopausal women.
      Women were excluded from the analysis if their linked hospital records showed that they had previous cataract surgery or were admitted to a hospital with cataracts before recruitment, or if the cancer registration records showed that they had preexisting cancer, with the exception of nonmelanoma skin cancer. For these analyses, cases were defined as the first hospital record (day-case or overnight admission) of cataract surgery (OPCS-4:C71–C75) occurring after recruitment into the study. Women were followed until the date of first cataract surgery, date of death, or the end of the hospital admissions follow-up period (March 2011 for England and December 2008 for Scotland).
      Cox proportional hazards models were used to estimate relative risks (RRs) and 95% confidence intervals (CIs) for cataracts treated surgically according to area deprivation (quintiles, based on the Townsend index, a score incorporating census area data for employment, car ownership, home ownership, and household overcrowding
      • Townsend P.
      • Beattie A.
      • Phillimore P.
      Health and Deprivation: Inequality and the North.
      ), educational qualifications (“tertiary” [college or university], “secondary” [A levels or O levels, usually obtained at age 18 and 16 years respectively], “technical” [nursing, teaching, clerical, or commercial], “no qualifications”), smoking status (never, past, current <15 cigarettes per day, current ≥15 cigarettes per day), BMI (<25, 25–29, ≥30 kg/m2), alcohol intake (<2, 2–14, ≥15 units per week [unit ∼10 g alcohol]), strenuous physical activity (rarely/never, some), self-reported treatment for diabetes (yes, no), age at menarche (≤12, 13, 14, ≥15 years), parity (nulliparous, parous), number of children (1, 2, 3, ≥4), duration of oral contraceptive use (<5, ≥5 years), and use of HT for menopause (never, ever). All variables were as reported at recruitment. The underlying time variable was attained age, and all analyses were routinely stratified for the recruitment region (10 geographic regions). For RRs reported as multiply adjusted, analyses were mutually adjusted for all other potential risk factors using the categories described (except for parity, which was adjusted for using 2 categories: parous/nulliparous). Missing values of adjustment factors (<6% for all variables) were included as a separate category.
      In an additional analysis, we investigated the association between cataracts treated surgically and the 2 main types of HT: estrogen-only or estrogen-progestogen. Women reporting current use were classified according to most recent type reported, and analyses accounted for changes in use during follow-up. Women were initially classified using information provided at recruitment, and those who provided updated information on HT use on the second study questionnaire (on average 3 years after recruitment) were then reclassified using this updated information. For all women, the period of follow-up was censored at 48 months after last report of HT use. All analyses used Stata 14.1 (StataCorp LP, College Station, TX).

      Results

      After excluding 4150 women with a hospital record of cataract surgery before recruitment, 166 women with a previous hospital admission diagnosis of cataract, and 44 781 women with preexisting cancer, these analyses included prospective data on cataract surgery in 1 312 051 postmenopausal women. Over a mean follow-up period of 10.7 years (standard deviation [SD], 2.6 years) per woman, 89 343 women (6.8%) underwent cataract surgery, corresponding to an incidence rate of 6.38 (95% CI, 6.33–6.41) per 1000 person-years.
      Table 1 shows the characteristics of the study population at baseline. Mean age at recruitment was 56.1 years (SD, 4.8 years); 21% reported that they were current smokers; mean BMI was 26.2 kg/m2 (SD, 4.7); 59% reported ever using oral contraceptives; and 34% were currently using HT.
      Table 1Baseline Characteristics of Women Who Subsequently Underwent Cataract Surgery and of All Women Included in the Analysis
      Characteristics at BaselineWomen Who Underwent Cataract Surgery during Follow-upAll Women
      No. of women89 3431 312 051
      Mean age at recruitment, yrs (SD)59.5 (5.1)56.1 (4.8)
      Percentage in most deprived quintile (n)23.3 (20 654)19.9 (258 798)
      Percentage with no qualifications (n)50.5 (43 657)43.9 (561 001)
      Percentage current smokers (n)19.4 (16 177)20.5 (253 411)
      Mean BMI, kg/m2 (SD)26.7 (4.9)26.2 (4.7)
      Mean alcohol intake, units/wk (SD)3.5 (5.0)4.1 (5.3)
      Percentage rarely/never strenuously active (n)55.2 (46 960)48.7 (614 944)
      Percentage treated for diabetes (n)7.5 (6671)2.4 (31 612)
      Mean parity (SD)2.2 (1.4)2.1 (1.2)
      Mean age at menarche, yrs (SD)13.1 (1.6)13.0 (1.6)
      Percentage ever used oral contraceptives (n)47.7 (41 916)59.3 (769 595)
      Percentage current user of HT (n)29.5 (25 934)33.5 (434 135)
      BMI = body mass index; HT = hormone therapy; SD = standard deviation.
      Table 2 shows the RR of cataracts treated surgically by various categories of socioeconomic and lifestyle factors, as well as treatment for diabetes. Overall, 2% (31 612) of the women in the study population reported being treated for diabetes, and this was the strongest risk factor for cataracts treated surgically (multiply adjusted RR for diabetes vs. no diabetes, 2.90, 95% CI, 2.82–2.97). Both past and current smoking at recruitment were associated with increased risk of cataracts treated surgically, with multiply adjusted RRs compared with never smokers of 1.10 (95% CI, 1.08–1.12) in past smokers, 1.12 (95% CI, 1.09–1.14) in current smokers of less than 15 cigarettes per day, and 1.26 (95% CI, 1.23–1.30) in current smokers of 15 or more cigarettes per day. Obesity was associated with a small increase in risk of cataracts treated surgically; this association was stronger in the minimally adjusted analysis (adjusted for age and region only) but remained significant after adjustment for other factors, including treatment for diabetes (multiply adjusted RR, 1.12; 95% CI, 1.10–1.14 for women with BMI ≥30 kg/m2 compared with <25 kg/m2). In analyses restricted to those not reporting treatment for diabetes, the association was similar (multiply adjusted RR, 1.15; 95% CI, 1.12–1.17 for women with BMI ≥30 kg/m2 compared with <25 kg/m2).
      Table 2Relative Risk of Cataracts Treated Surgically Associated with Various Socioeconomic Factors, Lifestyle Factors, and Diabetes
      Population at RiskCasesRR (95% CI)

      Minimally Adjusted
      Estimates of RR are adjusted by age and region of residence.
      RR (95% CI)

      Multiply Adjusted
      Estimates of RR are adjusted by age and region of residence plus deprivation, educational attainment, smoking, BMI, alcohol intake, strenuous physical activity, treatment for diabetes, age at menarche, parity, duration of oral contraceptive use, and HT use as appropriate.
      Area deprivation
       1: least deprived262 31615 3881.001.00
       2261 51516 7511.04 (1.02–1.07)1.03 (1.00–1.05)
       3259 78917 4511.10 (1.08–1.13)1.07 (1.04–1.09)
       4260 09318 4471.18 (1.16–1.21)1.11 (1.09–1.13)
       5: most deprived258 79820 6541.38 (1.35–1.41)1.22 (1.22–1.25)
      Educational qualifications
       Tertiary167 90494811.001.00
       Secondary333 44519 2991.01 (0.98–1.03)0.98 (0.96–1.01)
       Technical215 69213 9831.04 (1.01–1.07)0.99 (0.96–1.02)
       No qualifications561 00143 6571.17 (1.14–1.19)1.02 (0.99–1.04)
      Smoking
       Never630 93942 0071.001.00
       Past350 56925 2111.13 (1.11–1.14)1.10 (1.08–1.12)
       Current <15129 96183181.15 (1.13–1.18)1.12 (1.09–1.14)
       Current 15+123 45078591.35 (1.32–1.39)1.26 (1.23–1.30)
      BMI
       <25 kg/m2575 28235 5891.001.00
       25–29 kg/m2445 12130 8211.06 (1.05–1.08)1.02 (1.01–1.04)
       30+ kg/m2223 06517 6451.30 (1.27–1.32)1.12 (1.10–1.14)
      Alcohol (units per week)
       <2557 04543 4471.001.00
       2–14679 38941 3310.86 (0.85–0.87)0.93 (0.91–0.94)
       15+65 31436130.87 (0.83–0.89)0.92 (0.89–0.96)
      Strenuous physical activity
       Rarely/never614 94446 9601.001.00
       Some647 87238 1770.83 (0.82–0.84)0.90 (0.88–0.91)
      Treatment for diabetes
       No1 279 66082 5891.001.00
       Yes31 61266713.15 (3.07–3.23)2.90 (2.82–2.97)
      BMI = body mass index; CI = confidence interval; RR = relative risk.
      Estimates of RR are adjusted by age and region of residence.
      Estimates of RR are adjusted by age and region of residence plus deprivation, educational attainment, smoking, BMI, alcohol intake, strenuous physical activity, treatment for diabetes, age at menarche, parity, duration of oral contraceptive use, and HT use as appropriate.
      Women who reported doing some strenuous physical activity every week had a slightly lower risk of cataracts treated surgically compared with women who reported rarely or never engaging in strenuous physical activity (multiply adjusted RR, 0.90; 95% CI, 0.88–0.91). Alcohol consumption of 2 units or more per week was weakly associated after adjustment, with a slightly lower risk of cataracts treated surgically compared with consumption of less than 2 units per week, but there was no suggestion of a trend by amount of alcohol.
      In minimally adjusted analyses (adjusted for age and region only) both deprivation and lack of educational qualifications were associated with higher risks of cataracts treated surgically. However, after adjustment for other factors, there was no association with education, and the association with deprivation was attenuated.
      Table 3 shows the RR of cataracts treated surgically by reproductive history and use of hormonal therapies. There were no major differences in the risk of cataracts treated surgically according to age at menarche or use of oral contraceptives. Parous women seemed to be slightly less likely to undergo cataract surgery than nulliparous women, but there was no evidence for a trend in risk by number of children among parous women. Ever users of HT at recruitment were slightly more likely than never users to undergo surgery for cataract (multiply adjusted RR, 1.07; 95% CI, 1.06–1.09). In analyses looking at risk in relation to HT type (in 1228856 women; 6444986 total follow-up years), current users of estrogen-only HT had an RR of 1.08 (95% CI, 1.04–1.13) for cataracts treated surgically, and current users of estrogen-progestogen HT had an RR of 1.02 (95% CI, 0.98–1.07).
      Table 3Relative Risk of Cataracts Treated Surgically Associated with Reproductive History and Use of Hormonal Therapies
      Population at RiskCasesRR (95% CI)

      Minimally Adjusted
      Estimates of RR are adjusted by age and region of residence.
      RR (95% CI)

      Multiply Adjusted
      Estimates of RR are adjusted by age and region of residence plus deprivation, educational attainment, smoking, BMI, alcohol, strenuous physical activity, treatment for diabetes, age at menarche, parity, duration of oral contraceptive use, and HT use as appropriate.
      Age at menarche
       ≤12 yrs489 91632 1901.00
       13 yrs312 59620 3540.93 (0.92–0.95)0.96 (0.95–0.98)
       14 yrs264 09318 1890.94 (0.93–0.96)0.96 (0.94–0.98)
       15+ yrs218 44416 6340.99 (0.97–1.01)0.99 (0.97–1.01)
      Parity
       Nulliparous141 53810 2911.001.00
       Parous1 168 26578 8380.94 (0.92–0.96)0.92 (0.90–0.94)
      No. of children
      In 1 168 265 women who had had at least 1 child.
       1185 57113 1781.001.00
       2550 54333 6140.92 (0.90–0.94)0.96 (0.94–0.98)
       3282 72819 3410.95 (0.93–0.97)0.95 (0.93–0.97)
       4+149 42312 7051.06 (1.03–1.08)0.98 (0.95–1.00)
      Duration of oral contraceptive use
       Never527 76745 9561.001.00
       <5 yrs308 82117 2071.01 (0.99–1.02)1.03 (1.01–1.05)
       5+ yrs428 71222 3500.98 (0.96–0.99)1.00 (0.99–1.02)
      HT use
       Never643 48446 7991.001.00
       Ever652 76841 0531.04 (1.02–1.05)1.07 (1.06–1.09)
      CI = confidence interval; HT = hormone therapy; RR = relative risk.
      Estimates of RR are adjusted by age and region of residence.
      Estimates of RR are adjusted by age and region of residence plus deprivation, educational attainment, smoking, BMI, alcohol, strenuous physical activity, treatment for diabetes, age at menarche, parity, duration of oral contraceptive use, and HT use as appropriate.
      In 1 168 265 women who had had at least 1 child.

      Discussion

      In this large prospective study of postmenopausal women, previously reported associations between both diabetes and smoking and an increased risk of cataracts were confirmed. There was also evidence of an increased risk for obese women. Physical activity, alcohol intake, reproductive factors, and hormonal factors had little, if any, association with cataracts treated surgically: the RRs were small in magnitude, and the effect of residual confounding cannot be ruled out.

       Diabetes and Lifestyle Factors and Risk of Cataracts Treated Surgically

      Previous research has shown that cataracts develop at an earlier age in people with diabetes.
      • Pollreisz A.
      • Schmidt-Erfurth U.
      Diabetic cataract–pathogenesis, epidemiology and treatment.
      • Klein B.E.
      • Klein R.
      • Lee K.E.
      Diabetes, cardiovascular disease, selected cardiovascular disease risk factors, and the 5-year incidence of age-related cataract and progression of lens opacities: the Beaver Dam Eye Study.
      • Klein B.E.
      • Klein R.
      • Wang Q.
      • Moss S.E.
      Older-onset diabetes and lens opacities. The Beaver Dam Eye Study.
      The pathogenesis of cataracts in diabetic individuals is not fully understood.
      • Pollreisz A.
      • Schmidt-Erfurth U.
      Diabetic cataract–pathogenesis, epidemiology and treatment.
      • Obrosova I.G.
      • Chung S.S.
      • Kador P.F.
      Diabetic cataracts: mechanisms and management.
      Lifestyle factors that have been identified as risk factors for cataracts are smoking and UV light exposure, both of which are thought to affect cataract formation through oxidation.
      • Abraham A.G.
      • Condon N.G.
      • West Gower E.
      The new epidemiology of cataract.
      • Yam J.C.
      • Kwok A.K.
      Ultraviolet light and ocular diseases.
      • Christen W.G.
      • Glynn R.J.
      • Ajani U.A.
      • et al.
      Smoking cessation and risk of age-related cataract in men.
      • Hankinson S.E.
      • Willett W.C.
      • Colditz G.A.
      • et al.
      A prospective study of cigarette smoking and risk of cataract surgery in women.
      • Hiller R.
      • Sperduto R.D.
      • Podgor M.J.
      • et al.
      Cigarette smoking and the risk of development of lens opacities. The Framingham studies.
      In addition, the use of corticosteroids, both systemic and inhaled, has been identified as a risk factor for cataract formation.
      • Asbell P.A.
      • Dualan I.
      • Mindel J.
      • et al.
      Age-related cataract.
      • Urban Jr., R.C.
      • Cotlier E.
      Corticosteroid-induced cataracts.
      • Wang J.J.
      • Rochtchina E.
      • Tan A.G.
      • et al.
      Use of inhaled and oral corticosteroids and the long-term risk of cataract.
      This study did not have information on UV light exposure or use of corticosteroids at baseline, but our results for smoking confirm the higher risks found in other studies.
      • Christen W.G.
      • Glynn R.J.
      • Ajani U.A.
      • et al.
      Smoking cessation and risk of age-related cataract in men.
      • Hankinson S.E.
      • Willett W.C.
      • Colditz G.A.
      • et al.
      A prospective study of cigarette smoking and risk of cataract surgery in women.
      • Hiller R.
      • Sperduto R.D.
      • Podgor M.J.
      • et al.
      Cigarette smoking and the risk of development of lens opacities. The Framingham studies.
      Our results also provide further confirmatory evidence that there is an increased risk of cataracts in past smokers as well as in current smokers.
      • Christen W.G.
      • Glynn R.J.
      • Ajani U.A.
      • et al.
      Smoking cessation and risk of age-related cataract in men.
      Two recent meta-analyses have examined the relationship between alcohol intake and the risk of cataract or cataracts treated surgically.
      • Gong Y.
      • Feng K.
      • Yan N.
      • et al.
      Different amounts of alcohol consumption and cataract: a meta-analysis.
      • Wang W.
      • Zhang X.
      Alcohol intake and the risk of age-related cataracts: a meta-analysis of prospective cohort studies.
      The first meta-analysis in 2014 of 7 prospective cohort studies did not find alcohol to be a statistically significant risk factor for cataract surgery or cataracts.
      • Wang W.
      • Zhang X.
      Alcohol intake and the risk of age-related cataracts: a meta-analysis of prospective cohort studies.
      The second meta-analysis in 2015 of 5 prospective studies and 5 case-control studies reported a borderline increased risk of cataracts for heavy alcohol consumption (classified as >14 units per week), but confounding by smoking was seen.
      • Gong Y.
      • Feng K.
      • Yan N.
      • et al.
      Different amounts of alcohol consumption and cataract: a meta-analysis.
      We did not find a clearly increased risk of cataracts treated surgically related to heavy alcohol consumption, but there are few heavy alcohol drinkers in this cohort. The slight decreased risk in our study for moderate alcohol consumption is consistent with the previous evidence of a lack of association.
      • Gong Y.
      • Feng K.
      • Yan N.
      • et al.
      Different amounts of alcohol consumption and cataract: a meta-analysis.
      • Wang W.
      • Zhang X.
      Alcohol intake and the risk of age-related cataracts: a meta-analysis of prospective cohort studies.
      We found evidence that obesity (BMI ≥30 kg/m2) may weakly increase the risk of cataracts treated surgically, but there was no increased risk related to overweight (25–29 kg/m2). This is in line with the results of a meta-analysis of 6 prospective studies that showed that the development of all types of cataract (nuclear, cortical, or posterior subcapsular) was associated with obesity.
      • Pan C.W.
      • Lin Y.
      Overweight, obesity, and age-related cataract: a meta-analysis.
      It is unclear how much of the association with obesity is due to clinical or subclinical diabetes.
      • Abraham A.G.
      • Condon N.G.
      • West Gower E.
      The new epidemiology of cataract.
      • Weintraub J.M.
      • Willett W.C.
      • Rosner B.
      • et al.
      A prospective study of the relationship between body mass index and cataract extraction among US women and men.
      • Hiller R.
      • Podgor M.J.
      • Sperduto R.D.
      • et al.
      A longitudinal study of body mass index and lens opacities. The Framingham Studies.
      • Reeves G.K.
      • Balkwill A.
      • Cairns B.J.
      • et al.
      Hospital admissions in relation to body mass index in UK women: a prospective cohort study.
      • Pan C.W.
      • Lin Y.
      Overweight, obesity, and age-related cataract: a meta-analysis.
      However, when women who reported treatment for diabetes were excluded, the association we found between BMI and cataracts treated surgically did not change, which suggests that obesity may be an independent risk factor.
      Previous evidence on the potential effect of physical activity is sparse, with only 3 prospective studies having been carried out,
      • Williams P.T.
      Prospective epidemiological cohort study of reduced risk for incident cataract with vigorous physical activity and cardiorespiratory fitness during a 7-year follow-up.
      • Williams P.T.
      Walking and running are associated with similar reductions in cataract risk.
      and only 1 in the general population.
      • Zheng Selin J.
      • Orsini N.
      • Ejdervik Lindblad B.
      • Wolk A.
      Long-term physical activity and risk of age-related cataract: a population-based prospective study of male and female cohorts.
      The evidence from our study of a slightly lower risk associated with doing some strenuous physical activity agrees with previous evidence. However, this lower risk associated with physical activity could be due to reverse causation bias, because women with cataracts might be less likely to participate in strenuous physical activity because of visual impairment.

       Hormonal and Reproductive Factors and Risk of Cataracts Treated Surgically

      A recent meta-analysis of 4 prospective cohort studies concluded that use of HT for menopause was associated with a decreased risk of diagnosed cataract for ever users (pooled OR, 0.83; 95% CI, 0.71–0.97 compared with never users).
      • Lai K.
      • Cui J.
      • Ni S.
      • et al.
      The effects of postmenopausal hormone use on cataract: a meta-analysis.
      In contrast, a prospective study from Sweden, with more than 30 000 women and 4324 cataract surgery cases, not included in the meta-analysis, found that HT use was associated with an increase in risk of cataracts treated surgically (RR, 1.14; 95% CI, 1.07–1.21 for ever users compared with never users).
      • Lindblad B.E.
      • Hakansson N.
      • Philipson B.
      • Wolk A.
      Hormone replacement therapy in relation to risk of cataract extraction: a prospective study of women.
      In our multiply adjusted analyses, ever users of HT at recruitment were slightly more likely than never users to undergo surgery for cataract (RR, 1.07; 95% CI, 1.06–1.09), with no material difference in risk between users of estrogen-only and estrogen-progestogen HT. These findings should be interpreted with caution because such small increases (or decreases) in RR may well reflect residual confounding. The present results suggest that a strong relationship between HT use and cataracts is unlikely.
      Few other studies have investigated the association of reproductive factors with cataracts, and these have had mixed results.
      • Kanthan G.L.
      • Wang J.J.
      • Burlutsky G.
      • et al.
      Exogenous oestrogen exposure, female reproductive factors and the long-term incidence of cataract: the Blue Mountains Eye Study.
      • Klein B.E.
      • Klein R.
      • Lee K.E.
      Reproductive exposures, incident age-related cataracts, and age-related maculopathy in women: the Beaver Dam Eye Study.
      • Minassian D.C.
      • Mehra V.
      • Reidy A.
      Childbearing and risk of cataract in young women: an epidemiological study in central India.
      We found no evidence to support a role of the reproductive factors studied (age at menarche and parity) in relation to risk of cataracts treated surgically; while a statistically significant reduction in risk was found for parous compared with nulliparous women, there was no evidence for a trend in risk by number of children among parous women, and, again, residual confounding could well explain a small apparent association.

       Study Strengths and Limitations

      The strengths of this study are the large sample size and the long average follow-up period of 11 years. This is the largest single study examining risk factors for cataracts treated surgically. With approximately one quarter of eligible women in the United Kingdom participating in the Million Women Study and the power to examine risk factors across a full range of population values, the study can be considered representative of the UK population of middle-aged women. The incidence rates of cataract surgery (6.38 per 1000) are similar to those reported for the whole UK population in 2004
      • Keenan T.
      • Rosen P.
      • Yeates D.
      • Goldacre M.
      Time trends and geographical variation in cataract surgery rates in England: study of surgical workload.
      (6.37 per 1000). The inclusion of socioeconomic, lifestyle, reproductive, and hormonal factors, as well as treatment for diabetes, enabled us to adjust for many risk factors at the same time. The use of linked routinely collected health records of cataract surgery as the end point of interest is both a strength—allowing near-complete, unbiased, long-term, cost-effective follow-up in a large cohort—and a limitation, in that hospital records provide limited information on clinical details such as type of cataract and extent of visual loss.
      In general, the majority of surgeries in the United Kingdom are performed within the NHS,
      • Williams B.
      • Whatmough P.
      • McGill J.
      • Rushton L.
      Private funding of elective hospital treatment in England and Wales, 1997-8: national survey.
      but some women in the cohort may have undergone privately funded cataract surgery outside the NHS and therefore would not be identified by the record linkage to NHS data. In 1997 and 1998, an estimated 14% of lens operations in England and Wales were privately funded and carried out in private hospitals.
      • Williams B.
      • Whatmough P.
      • McGill J.
      • Rushton L.
      Private funding of elective hospital treatment in England and Wales, 1997-8: national survey.
      This estimate predates follow-up for this study, but we are not aware of more recent estimates. Misclassification of cases is unlikely to have had a substantial effect on power to detect risk factor associations, but, together with residual confounding, this could account for the association between deprivation and cataracts treated surgically.
      The risk factor associations identified in the current article in relation to surgery for cataracts may not be identical to those related to the development of cataract; although minimally invasive surgery for cataract is widely available in the United Kingdom, comorbidities that may be related to the risk factors studied are likely to affect uptake of surgery. For example, cataract surgery can be performed to assist the management of other eye conditions, such as diabetic retinopathy.

      The Royal College of Ophthalmologists. Commissioning Guide: Cataract Surgery - February 2015. Available at: https://www.rcophth.ac.uk/2015/03/cataract-commissioning-guidance. Accessed November 20, 2015.

      However, our findings for diabetes and smoking are consistent with previous studies of both cataract
      • Klein B.E.
      • Klein R.
      • Lee K.E.
      Diabetes, cardiovascular disease, selected cardiovascular disease risk factors, and the 5-year incidence of age-related cataract and progression of lens opacities: the Beaver Dam Eye Study.
      • Christen W.G.
      • Glynn R.J.
      • Ajani U.A.
      • et al.
      Smoking cessation and risk of age-related cataract in men.
      • Kelly S.P.
      • Thornton J.
      • Edwards R.
      • et al.
      Smoking and cataract: review of causal association.
      and surgery for cataract.
      • Klein B.E.
      • Klein R.
      • Wang Q.
      • Moss S.E.
      Older-onset diabetes and lens opacities. The Beaver Dam Eye Study.
      • Christen W.G.
      • Glynn R.J.
      • Ajani U.A.
      • et al.
      Smoking cessation and risk of age-related cataract in men.
      • Hankinson S.E.
      • Willett W.C.
      • Colditz G.A.
      • et al.
      A prospective study of cigarette smoking and risk of cataract surgery in women.
      In conclusion, cataracts are the second leading cause of partial sight and blindness in the United Kingdom, and cataract surgery is the most common operation performed in the United Kingdom. Therefore, it is important to identify any risk factors that may be modifiable. For the women in this large prospective cohort study in the United Kingdom, diabetes and smoking were associated with a higher risk of undergoing cataract surgery. There was also evidence of a small increase in risk for obese women. Alcohol use, physical activity, reproductive history, and use of hormonal therapies had little, if any, association with cataract surgery risk.

      Acknowledgments

      The authors thank the women who participated in the Million Women Study and the staff from the participating NHS breast cancer screening centers; the NHS Information Centre for Health and Social Care in England and the Information Services Division in Scotland for the hospital admission data; and Angela Balkwill for statistical support. The Advisory Committee members are Emily Banks, Valerie Beral, Lucy Carpenter, Carol Dezateux, Jane Green, Julietta Patnick, Richard Peto, and Cathie Sudlow. The coordinating staff for the Million Women Study are Hayley Abbiss, Simon Abbott, Miranda Armstrong, Krys Baker, Angela Balkwill, Isobel Barnes, Valerie Beral, Judith Black, Kathryn Bradbury, Anna Brown, Benjamin Cairns, Dexter Canoy, Andrew Chadwick, Dave Ewart, Sarah Ewart, Lee Fletcher, Sarah Floud, Toral Gathani, Laura Gerrard, Adrian Goodill, Jane Green, Lynden Guiver, Alicia Heath, Michal Hozak, Carol Herman, Isobel Lingard, Sau Wan Kan, Nicky Langston, Kath Moser, Kirstin Pirie, Gillian Reeves, Keith Shaw, Emma Sherman, Helena Strange, Sian Sweetland, Sarah Tipper, Clare Wotton, Lucy Wright, Owen Yang, and Heather Young. The following NHS breast screening centers took part in the recruitment and breast screening follow-up for the Million Women Study: Avon, Aylesbury, Barnsley, Basingstoke, Bedfordshire & Hertfordshire, Cambridge & Huntingdon, Chelmsford & Colchester, Chester, Cornwall, Crewe, Cumbria, Doncaster, Dorset, East Berkshire, East Cheshire, East Devon, East of Scotland, East Suffolk, East Sussex, Gateshead, Gloucestershire, Great Yarmouth, Hereford & Worcester, Kent (Canterbury, Rochester, Maidstone), Kings Lynn, Leicestershire, Liverpool, Manchester, Milton Keynes, Newcastle, North Birmingham, North East Scotland, North Lancashire, North Middlesex, North Nottingham, North of Scotland, North Tees, North Yorkshire, Nottingham, Oxford, Portsmouth, Rotherham, Sheffield, Shropshire, Somerset, South Birmingham, South East Scotland, South East Staffordshire, South Derbyshire, South Essex, South Lancashire, South West Scotland, Surrey, Warrington Halton St Helens & Knowsley, Warwickshire Solihull & Coventry, West Berkshire, West Devon, West London, West Suffolk, West Sussex, Wiltshire, Winchester, Wirral, and Wycombe.

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      Linked Article

      • Re: Floud et al.: Risk factors for cataracts treated surgically in postmenopausal women (Ophthalmology. 2016;123:1704-1710)
        OphthalmologyVol. 124Issue 4
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          We read with interest the recent article by Floud et al1 identifying the risk factors for cataracts treated surgically in postmenopausal women. However, there are certain points we wish to highlight. First, in a study by Leuschen et al,2 6972 pairs of statin users and nonusers were compared. The risk for cataract was higher among statin users in comparison with nonusers in the propensity score-matched cohort (odds ratio, 1.09; 95% confidence interval, 1.02–1.17). Hence, history of intake of certain drugs like statins which increase the risk of acquiring cataracts which might require surgery2 in postmenopausal women should be elucidated.
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