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Ten-Year Incidence of Age-Related Cataract and Cataract Surgery in an Older Australian Population
Ten-Year Incidence of Age-Related Cataract and Cataract Surgery in an Older Australian Population The Blue Mountains Eye Study Gowri L. Kanthan, MBBS, MOphthSc, Jie Jin Wang, MMed, PhD, Elena Rochtchina, BSc, MAppStat, Ava Grace Tan, BSc(Hons), MAIT, Anne Lee, MBBS, PhD, Ee-Mun Chia, MBBS, Paul Mitchell, PhD, FRANZCO Purpose: To estimate the 10-year incidence of cataract and cataract surgery in an older Australian population. Design: Prospective population-based study. Participants: Persons at least 49 years old living in 2 postcode areas west of Sydney, Australia. Methods: Eye examinations were performed at baseline and at 5- and 10-year follow-up visits. Lens photographs were taken and graded by masked graders using the Wisconsin Cataract Grading System. Main Outcome Measures: Incidences of nuclear cataract, cortical cataract, posterior subcapsular cataract (PSC), and cataract surgery. Results: Ten-year person-specific incidences were 36.0% for nuclear cataract, 28.0% for cortical cataract, 9.1% for PSC, and 17.8% for cataract surgery. Corresponding rates were 31.7%, 24.4%, 8.2%, and 14.4%, respectively, in men and 39.3%, 30.8%, 9.8%, and 20.1%, respectively, in women. The incidence for each type of cataract and cataract surgery was positively associated with age (P⬍0.0001). Women had a significantly higher incidence than men for nuclear cataract (P ⫽ 0.04), cortical cataract (P ⫽ 0.007), any cataract (P ⫽ 0.0006), and cataract surgery (P ⫽ 0.03) after adjusting for age. There was no significant gender difference for PSC. The mean age at cataract surgery was 75.8 years, and there was no significant gender difference (P ⫽ 0.9). Among persons who developed any cataract, 22% had more than one type and 1.3% had all 3 types present. Nuclear cataract and PSC were significantly associated with visual impairment (visual acuity worse than 20/40). Conclusion: Age- and gender-specific cataract incidences in this study were similar to those reported from the U.S. Beaver Dam Eye Study. In this study, 72% of the participants were affected by cataract or had had cataract surgery over the 10-year follow-up period. Ophthalmology 2008;115:808 – 814 © 2008 by the American Academy of Ophthalmology.
Cataract remains the leading cause of world blindness.1 In Australia, cataract is the second most frequent cause of unilateral blindness (visual acuity [VA] of 20/200 or worse),2 and the most frequent cause of mild to moderate visual impairment (corresponding to VA levels 20/40 –20/ 160).2 Cataract prevalence increases steadily with age.3 With population aging, the prevalence and burden of visual impairment from cataract are expected to rise further. Cataract extraction and intraocular lens implant surgery is Originally received: November 26, 2006. Final revision: July 3, 2007. Accepted: July 5, 2007. Available online: September 27, 2007. Manuscript no. 2006-1347. From University of Sydney Department of Ophthalmology, Center for Vision Research, Westmead Millennium Institute, Westmead Hospital, Sydney, Australia.
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© 2008 by the American Academy of Ophthalmology Published by Elsevier Inc.
the most commonly performed ophthalmic surgical procedure in Western countries.4 Despite recent advances in the technology and safety of this procedure, its economic cost is relatively high.5 Population-based data on incidence of cataract and cataract surgery are important in projecting demand and planning for eye health care and cataract surgical services. The prevalence of cataract has been reported from various populations,3,6 –13 and a few studies have examined the incidence of cataract.14 –21 Of these, to date, only the Beaver Dam Eye Study (BDES) has reported the 10-year incidence Supported by the Australian National Health and Medical Research Council, Canberra, Australia (grant nos. 974159, 211069). Correspondence to Paul Mitchell, PhD, FRANZCO, Center for Vision Research, Westmead Hospital, Hawkesbury Road, Westmead, Sydney, Australia 2145. E-mail: [email protected]. ISSN 0161-6420/08/$–see front matter doi:10.1016/j.ophtha.2007.07.008
Kanthan et al 䡠 10-Year Incidence of Age-Related Cataract in Australia of cataract.14,22 The Barbados Eye Study has reported 9-year incidence of cataract in a predominantly black population.21 In this study, we aim to report the 10-year incidence of cataract and cataract surgery in the Australian Blue Mountains Eye Study (BMES) population.
Materials and Methods Study Population Details of the BMES population and methods are reported elsewhere.2 In brief, the BMES is a population-based cohort study of vision and common eye diseases in an urban older population comprising 2 postcode areas in the Blue Mountains region, west of Sydney, Australia. This geographically well-defined area has a stable population that is reasonably representative of Australia in socioeconomic status and other measures. All residents of these 2 postcode areas who were 49 years or older were eligible and invited to participate in the survey. At baseline examination (1992–1994), 4433 residents were identified as eligible to participate, of whom 3654 (82.4%) were interviewed and examined. The difference between participants and nonparticipants at baseline has been reported previously.3 All surviving participants were invited for follow-up eye examinations after 5 (1997–1999) and 10 years (2002–2004). Participants who did not return to the 5-year follow-up were also invited to attend the 10-year examinations. There were 2335 participants (63.9% of the original cohort or 75.1% of survivors) examined after 5 years and 1952 (53.4% of the original cohort or 75.6% of survivors) examined after 10 years. Thus, a total of 2564 participants were examined at least once after the baseline examination.
Procedures The study was approved by the Western Sydney Area Health Service Human Research Ethics Committee. Written informed consent was obtained from all participants. At baseline, detailed demographic and medical histories were taken. Questions regarding previous diagnosis of cataract and details of cataract surgery were included. All participants underwent detailed eye examinations. Slit-lamp lens photographs were taken from each eye using Ektachrome 200 color film (Kodak, Rochester, NY) and an SL-7E photograph slit-lamp camera (Topcon, Tokyo, Japan) to assess presence of nuclear cataract. Retroillumination lens photographs were taken using a CT-R cataract camera (Neitz Instruments, Tokyo, Japan) to assess presence of cortical cataract and posterior subcapsular cataract (PSC). At the 5- and 10-year follow-up visits, similar questionnaires were used to collect updated demographic and medical history data for the past 5 years. Participants were examined in approximately the same order as at baseline, using the same procedures and equipment.
Lens Grading The Wisconsin Cataract Grading System, first developed in 1990 for use in the BDES, was used to perform masked grading of the lens photographs. Details of this method have been previously reported, and it was shown to have good reproducibility in the study.23,24 A 5-point scale was used to assess the presence and severity of nuclear cataract. This was done by comparing participant photographs with 4 standards of increasing opacity. Nuclear cataract was defined as nuclear opacity worse than standard 3. The presence and severity of cortical cataract and PSC were graded from Neitz photographs using a circular grid divided into 8 equal
wedges and a central circle. Graders estimated the percentage area in each of the 9 segments that was involved by cataract. The percentage of opacities in each segment was then summated to give a score for the whole lens area. Cortical cataract was considered present when at least 25% of the lens area was involved. Posterior subcapsular cataract was defined if present.
Reproducibility Intergrader and intragrader reproducibilities of lens grading were assessed using quadratic weighted statistics.25,26 A single grader assessed baseline cortical cataract and PSC, with adjudication provided by a senior ophthalmologist (PM). Repeated masked grading of a random sample of 183 eyes by this grader gave weighted s of 0.85 for cortical cataract and 0.92 for PSC. Two graders performed nuclear cataract grading of both the baseline and 5-year follow-up lens photographs. Weighted s for intraobserver reliability were 0.73 and 0.79, respectively, for the 2 graders. Intergrader reproducibilities were 0.79 for nuclear cataract, 0.78 for cortical cataract, and 0.57 for PSC. After excluding 2 eyes that also had very dense nuclear cataract, weighted for PSC improved to 0.65. These values represent acceptable reproducibility.26 The 10-year follow-up photographs were graded by one examiner (GLK) for all 3 types of cataract, with all positive cortical cataract cases also graded by another senior grader (AGT) and nuclear cataract and PSC cases also graded by a senior researcher (JJW). Repeated masked grading of 90 random eyes by the same examiner (GLK) gave weighted s of 0.81 for nuclear cataract, 0.92 for cortical cataract, and 0.89 for PSC. The same examiner graded a random sample of baseline photographs to compare intergrader reproducibilities. This gave weighted values of 0.52 for nuclear cataract, 0.72 for cortical cataract, and 0.79 for PSC. Nuclear cataract cases detected at all 3 examinations were either graded or regraded by one senior researcher (JJW), who had an intragrader reliability of 0.79.
Statistical Analysis Statistical analysis was performed using SAS software (SAS, Cary, NC). Ten-year cumulative incidence was calculated using the Kaplan–Meier (product-limit) method. Participants who did not have a particular type of cataract or cataract surgery in either eye at baseline were considered at risk of developing that type of cataract in the follow-up period. Those who did not have a particular cataract type at the 5-year follow-up examination and did not present for the 10-year follow-up were censored to the 5-year examination date. Participants were divided into 4 age groups (⬍55, 55– 64, 65–74, ⱖ74 years) to study the effect of age on cataract incidence. A discrete logistic model was used to determine the effect of age and gender as 2 explanatory variables. We also measured the effect of incident cataract on visual function by calculating the VA of affected individuals at the time of censoring. Visual acuity was defined as the number of letters on the Early Treatment Diabetic Retinopathy Study chart read correctly by participants. For each cataract type, the proportion of patients with significant visual impairment was calculated. Visual impairment was defined as best-corrected VA worse than 20/40. Finally, we also calculated the incidence of cataract surgery by cataract type and the mean age at which cataract surgery was performed.
Results A comparison of participants and nonparticipants at each follow-up examination is summarized in Table 1 (available at http://aaojournal.
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Ophthalmology Volume 115, Number 5, May 2008 Table 2. Age- and Gender-Specific Incidence of Cataract by Subtype in Either Eye in the Blue Mountains Eye Study (BMES) and Comparison with Beaver Dam Eye Study (BDES) Findings Incidence Incident Cases/ Persons at Risk
BMES 5 Year (%)
BDES 10 Year (%)
10 Year (%)
11.6 25.5 54.2 78.7 ⬍0.0001
6.2 24.6 53.3 72.7 ⬍0.0001
Nuclear cataract Age ⬍55 55–64 65–74 ⬎74 P for trend Gender Female Male P value (age adjusted) Total Age ⬍55 55–64 65–74 ⬎74 P for trend Gender Female Male P value (age adjusted) Total Age ⬍55 55–64 65–74 ⬎74 P for trend Gender Female Male P value (age adjusted) Total
20/206 116/547 186/407 69/99
5.8 12.6 35.1 61.6
239/714 152/545
23.7 21.3
391/1259
22.6 Cortical cataract
47/329 161/759 142/563 42/146
5.5 10.4 14.6 21.2
17.1 26.4 33.9 50.8 ⬍0.0001
245/1005 153/792
13.2 9.7
30.8 24.4 0.007 28.1
398/1797 11.7 Posterior subcapsular cataract
26.7 20.3 0.0005 23.7
9.7 27.7 36.9 48.2 ⬍0.0001 22.8 20.8 0.26 21.8
8/328 51/809 62/679 18/214
0.6 2.4 4.9 6.1
3.0 7.9 12.9 15.1 ⬍0.0001
3.4 8.9 12.9 14 ⬍0.0001
84/1173 55/857
3.3 3.3
139/2030
3.3
9.8 8.2 0.49 9.1
7.8 7.8 0.81 7.8
org). Nonparticipants were significantly younger (P⬍0.0001), more likely to be smokers (P⬍0.0001) and to have diabetes (P ⫽ 0.049). They were also more likely to report lower health related quality of life (P ⫽ 0.041) and were less likely to live in their own home (P ⫽ 0.0006) than those who participated in follow-up examinations. Of the 2564 participants who were observed, we excluded 100 who had cataract surgery performed on one or both eyes at baseline and thus were not considered at risk of cataract or cataract surgery in the first eye. After excluding participants who had nuclear cataract present at baseline and patients with missing or ungradable photographs, 1259 were considered at risk of developing nuclear cataract. The corresponding numbers at risk for cortical and PSC cataract were 1797 and 2030, respectively, with 1057 at risk of any type of cataract and 2448 at risk of cataract surgery (Fig 1 [available at http://aaojournal.org]). Age- and gender-specific incidences of each type of cataract are presented in Table 2, with 10-year incidence rates reported by the BDES shown for comparison. Five-year incidences were 22.6% for nuclear cataract, 11.7% for cortical cataract, and 3.3% for PSC, whereas 10-year incidences were 36.0% for nuclear cataract, 27.9% for cortical cataract, and 9.1% for PSC. The 10-year inci-
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39.3 31.7 0.04 36.0
dence of each cataract type increased significantly with age (P for trend ⬍ 0.0001). After adjusting for age, the 10-year incidence was significantly higher in women than in men for nuclear cataract (P ⫽ 0.04) and cortical cataract (P ⫽ 0.007). There was no significant gender difference in the incidence of PSC cataract (P ⫽ 0.49). Age- and gender-specific incidences of any cataract and cataract surgery are presented in Table 3. Incidences of any type of cataract were 29.1% after 5 years and 53.7% after 10 years; they increased significantly with age (P for trend ⬍ 0.0001) and were significantly higher in women than in men (59.1% vs. 47.3%, P ⫽ 0.0006), after adjusting for age. Of the 567 participants who developed at least one type of cataract during the 10-year follow-up period, 22% developed more than one type of cataract (Fig 2); 13.4% developed both nuclear and cortical opacities, 4.8% developed both nuclear and posterior subcapsular opacities, 2.6% developed both cortical and posterior subcapsular opacities, and 1.3% had developed all 3 types of lens opacities. Of the remaining 78% who developed a single type of cataract, 45.3% developed nuclear cataract only, 27.4% developed only cortical cataract, and 5.3% developed only PSC. The proportion of participants undergoing cataract surgery over
Kanthan et al 䡠 10-Year Incidence of Age-Related Cataract in Australia Table 3. Age- and Gender-Specific Incidence of Any Cataract or Cataract Surgery in Either Eye in the Blue Mountains Eye Study (BMES) and Comparison with Beaver Dam Eye Study (BDES) Findings Incidence BMES
Incident Cases/ Persons at Risk
5 Year (%)
BDES 10 Year (%)
10 Year (%)
16.4 46.8 75.1 87.7 ⬍0.0001
Any cataract Age ⬍55 55–64 65–74 ⬎74 P value (trend) Gender Female Male P value (age adjusted) Total Age ⬍55 55–64 65–74 ⬎74 P value (trend) Gender Female Male P value (age adjusted) Total
39/197 191/487 201/310 49/63
10.7 20.5 46.4 68.2
24.0 47.7 77.0 87.3 ⬍0.0001
285/577 195/480
31.4 26.5
59.1 47.3 0.0006 53.7
480/1057
29.1 Cataract surgery
12/377 74/928 193/847 86/296
0.5 1.5 7.3 16.6
242/1418 123/1030
5.5 4.8
365/2448
5.2
the period was 5.2% after 5 years and increased to 17.8% after 10 years (Table 3). The 10-year incidence of cataract surgery was strongly age related (P for trend ⬍ 0.0001) and was significantly greater in women than in men (20.2% vs. 14.4%) after adjusting for age (P ⫽ 0.03). The effect of incident cataract on visual function at the time of censoring is shown in Table 4. Among participants without any cataract, 4.6% were noted to have visual impairment, compared with 21.2% among participants with incident PSC (odds ratio [OR], 3.8; 95% confidence interval [CI], 2.0 –7.0) and 13.2% among those with incident nuclear cataract (OR, 1.8; 95% CI, 1.1–2.9). The corresponding proportion among participants with incident cortical cataract was 10.0% (OR, 1.5; 95% CI, 0.9 –2.5). Similarly, those without any incident cataract had mean VA of 52.3 letters, compared with 48.7 letters among those with incident
3.6 9.1 28.0 45.4 ⬍0.0001 20.2 14.4 0.03 17.8
40.4 35.3 0.01 38.0
2.7 11.2 26.4 29.8 ⬍0.0001 15.2 10.0 0.0007 13.0
cortical cataract (P ⫽ 0.005), 46.8 letters among those with incident nuclear cataract (P ⫽ 0.0006), and 42.9 letters among those with incident PSC (P⬍0.0001). Table 5 shows the association between cataract subtype and the incidence of cataract surgery. Of participants with nuclear cataract, cortical cataract, or PSC in the right eye at baseline, 32.5%, 26.8%, and 40.9%, respectively, underwent cataract surgery in that eye during the following 10-year period. In our study population, mean age at cataract surgery in the first eye was 75.8 years (median, 76; range, 53–92). It was 75.8 years for women and 75.9 years for men (P ⫽ 0.9). Mean age at surgery in the second eye was 76.2 years, indicating that, for most cases, surgery of the second eye followed soon after surgery for the first eye. Among participants who had surgery in their first eye within the 10-year follow up period, 49% had this surgery between the ages of 70 and 79.
Discussion
Figure 2. Frequency of pure lens opacities and multiple cataract types.
Several classification and grading methods have been developed to measure the presence and extent of cataract including the Oxford,27 Wilmer,28 Lens Opacities Classification System,29 –31 and Wisconsin.23 The Wisconsin Cataract Grading System was first developed in 1990 for use in the BDES. It was shown to have good reproducibility when applied to the BMES population.24 Studies that have examined cataract incidence are summarized in Table 6. These studies differ from each other in terms of their study samples, years of follow-up, and grading method used. The present study is only the second population-based one to report 10-year incidence of cata-
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Ophthalmology Volume 115, Number 5, May 2008 Table 4. Prevalence of Visual Impairment and Mean Best-Corrected Logarithm of the Minimum Angle of Resolution (logMAR) Visual Acuity in the Right Eyes of Participants at the Time of Censoring by Cataract Type
Cataract Type
Subjects with Visual Impairment* [% (n)]
Age†- and Gender-Adjusted Odds Ratio for Visual Impairment (95% CI)
logMAR Visual Acuity [Mean‡ (SD)]
Age†- and GenderAdjusted P Value
None Cortical§ Nuclear§ Posterior subcapsular§
4.6 (35) 10.0 (31) 13.2 (44) 21.2 (21)
1 (referent) 1.5 (0.9–2.5) 1.8 (1.1–2.9)) 3.8 (2.0–7.0)
52.3 (10.0) 48.7 (12.5) 46.8 (15.8) 42.9 (11.3)
Referent 0.005 0.0006 ⬍0.0001
CI ⫽ confidence interval; SD ⫽ standard deviation. *Best-corrected vision worse than 20/40. † At the time of censoring. ‡ Mean no. of letters correctly read on the logMAR visual acuity chart. § Alone or in combination with other types of cataract.
ract, after the BDES.14 We used the same protocol as that used in the BDES to assess cataract and have documented very similar age- and gender-specific incidence rates from our study population compared with those reported by this earlier landmark study. Both studies show that nuclear cataract is the most frequently developing lens opacity type (10-year incidence, 24%–36%). This is closely followed by cortical cataract (10-year incidence, 22%–28%). According to the BDES, women had a significantly higher incidence of both nuclear cataract and cataract surgery, but there was no significant gender difference in the incidence of cortical cataract and PSC. In our study, women had a significantly higher incidence of nuclear cataract, cortical cataract, and cataract surgery. An explanation for this gender difference in cataract incidence is not clear, but it may be related to hormonal factors.32–35 Despite the significantly higher incidence of cataract surgery in women, there was no significant gender difference (P ⫽ 0.9) between men and women in the mean age at which cataract surgery was performed in our study. As shown in Tables 2 and 3, both the BMES and BDES report similar 10-year age-specific incidence rates for each cataract subtype and for cataract surgery for all age groups except the under 55 group, for which there was a difference in eligible age for participation. The overall incidence for each cataract subtype and for cataract surgery, however, is higher in the BMES than in the BDES population, probably due to the BMES population being older (range, 49 –97) than the BDES population (range, 43– 84). To compare the crude incidence rates from both studies more accurately, we Table 5. Ten-Year Incidence of Cataract Surgery by Type of Cataract at Baseline Cataract Type Nuclear Cortical Posterior subcapsular
10-Year Incidence of Odds Ratio* for Cataract Cataract Surgery Surgery (95% CI) 32.5% 26.8% 40.9%
3.0 (2.0–4.5) 2.1 (1.4–3.0) 5.3 (2.9–9.6)
CI ⫽ confidence interval. *Reference group is persons without any cataract at baseline.
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excluded the under 55 age group from both samples and standardized the incidence rates observed in the BMES to the age distribution of the BDES population (Table 7). This analysis demonstrated that 10-year incidences reported by both studies were very similar for each cataract subtype and for cataract surgery. Interestingly, the incidence of nuclear cataract in the first 5 years of follow-up was slightly higher than that observed during the second 5-year period. In an assessment using the different numbers of participants at risk of incident cataract at these different time points, nuclear cataract incidences were 20.4% (95% CI, 17.5%–23.6%) during the first 5-year period and 16.7% (95% CI, 13.6%–19.9%) during the second 5-year period (P⬎0.05). The corresponding proportions who had undergone cataract surgery were 4.5% (95% CI, 3.5%–5.6%) and 12.5% (95% CI, 10.9%–14.2%), respectively, for the 2 periods. We believe, therefore, the slightly lower incidence of nuclear cataract in the second 5-year period was likely caused by the greater proportion having cataract surgery. There is also likely to have been a higher mortality during the second 5-year period, resulting in survival bias, as the survivors were relatively younger in terms of biological aging, of which nuclear cataract is a marker. Strengths of our study include its population-based sample and long-term follow-up with reasonable surveillance rates (75% of survivors participated at each follow-up) and high consistency of the methods used in both the examinations and cataract grading. Limitations of our study should be noted. Nonparticipants in the follow-up examinations differed significantly from participants in age, smoking status, diabetes, and socioeconomic characteristics. As age, cigarette smoking,36 –38 diabetes,39 – 41 and socioeconomic status42 are all known risk factors for cataract, these differences between participants and nonparticipants could have led to an underestimation of cataract and cataract surgery incidence. Of the 2464 eligible participants, 1009 had missing or ungradable slit lamp (Topcon) photographs and, hence, were not included in the analysis for the incidence of nuclear cataract. This was due, however, to a random malfunction of the photograph slit lamp at the baseline examination, so that any difference, if present, was nondifferential3 and was unlikely to bias the study estimates of cataract incidence. Another limitation was the relatively high vari-
Kanthan et al 䡠 10-Year Incidence of Age-Related Cataract in Australia Table 6. Studies That Have Reported Cataract Incidence Study
Population
Age Range (yrs)
Follow-up (yrs)
Barbados Eye Study21 Italian-American Cataract Study Group17† Melbourne Visual Impairment Project16† Longitudinal Study of Cataract18,19† Italian (Priverno) Study20
Population based Clinic based
40–84 45–79
9 5
ⱖ40
14†
Beaver Dam Eye Study Blue Mountains Eye Study†
Nuclear
Cortical
Posterior Subcapsular
LOCS II LOCS II
42.0* 11.5‡
33.8* 28.2‡
6.3* 9.6‡
5
Wilmer
16.4
7.7
7
Median ⫽ 65
5
LOCS III
8
7.7
4.3
Population based
45–69
7
Population based Population based
43–86 ⱖ49
10 10
Any opacity and visual Not provided Not provided Not provided acuity ⬍ 0.2 logMAR Wisconsin 23.7 21.8 7.8 Wisconsin 36.0 28.0 9.1
Cluster random sample Clinic based
Grading Method
LOCS ⫽ Lens Opacities Classification System; logMAR ⫽ logarithm of the minimum angle of resolution. *For black participants. † Photographs were used to assess lens opacity. ‡ For the 65- to 74-yr age group only.
ability in PSC grading between graders. Due to this variability, the incidence could have been either slightly overestimated or underestimated. In our study population, 54% of participants developed unoperated cataract and a further 18% underwent cataract surgery, representing a total of 72% affected by incident cataract over the 10-year follow-up period. As the population is aging, the proportion with cataract can be expected to increase further. The Australian population over 49 years is currently 6.3 million persons, and is expected to increase to 8.7 million by the year 2021.43 Projecting the incidence rates based on our findings shows that 4.5 million Australians will develop significant cataract in the next 10 years, and this will increase to 6.3 million Australians during the period 2021 to 2031. Similarly, if the incidence of cataract surgery remained unchanged, 1.1 million Australians would undergo cataract surgery over the next 10 years, and this would increase to 1.6 million for the period 2021 to 2031. We previously showed that the prevalence of cataract surgery is increasing,44 so the actual incidence of cataract surgery is likely to be higher than this conservative estimate. Our data thus confirm that age-related cataract represents a significant public health burden in Australia. The BMES is only the second population-based study to report the 10-year incidence of cataract in an older populaTable 7. Ten-Year Incidence of Cataract and Cataract Surgery in People over 54 Years Old: Age-Standardized Comparison between the Blue Mountains Eye Study (BMES) and Beaver Dam Eye Study (BDES)
Nuclear cataract Cortical cataract PSC Any cataract Cataract surgery
BMES* (95% CI)
BDES
39.7 (37.2–42.1) 31.2 (29.3–33.0) 10.6 (9.6–11.6) 59.6 (56.1–63.1) 21.8 (20.6–22.9)
38.4 32.8 11.0 58.4 19.9
CI ⫽ confidence interval; PSC ⫽ posterior subcapsular cataract. *Rates standardized to the BDES population.
tion. We found age-and gender-specific incidence rates for cataract remarkably similar to those previously reported by the BDES. Among persons 49 years or older, 7 of 10 would be expected to develop significant cataract over the next 10 years, whereas around 2 of 10 will need surgery. All 3 cataract subtypes were found to have a significant impact in reducing VA, though this was most marked for PSC and least for cortical cataract. Cataract and cataract surgery clearly represent a significant public health burden in the context of an aging population.
References 1. Thylefors B, Negrel AD, Pararajasegaram R, Dadzie KY. Global data on blindness. Bull World Health Organ 1995;73: 115–21. 2. Attebo K, Mitchell P, Smith W. Visual acuity and the causes of visual loss in Australia: the Blue Mountains Eye Study. Ophthalmology 1996;103:357– 64. 3. Mitchell P, Cumming RG, Attebo K, Panchapakesan J. Prevalence of cataract in Australia: the Blue Mountains Eye Study. Ophthalmology 1997;104:581– 8. 4. Keeffe JE, Taylor HR. Cataract surgery in Australia 1985–94. Aust N Z J Ophthalmol 1996;24:313–7. 5. Steinberg EP, Javitt JC, Sharkey PD, et al. The content and cost of cataract surgery. Arch Ophthalmol 1993;111:1041–9. 6. Klein BE, Klein R, Linton KL. Prevalence of age-related lens opacities in a population: the Beaver Dam Eye Study. Ophthalmology 1992;99:546 –52. 7. Sperduto RD, Hiller R. The prevalence of nuclear, cortical, and posterior subcapsular lens opacities in a general population sample. Ophthalmology 1984;91:815– 8. 8. Maraini G, Pasquini P, Sperduto RD, et al. Distribution of lens opacities in the Italian-American Case-Control Study of AgeRelated Cataract. Ophthalmology 1990;97:752– 6. 9. Giuffre G, Giammanco R, Di Pace F, Fonte F. Casteldaccia Eye Study: prevalence of cataract in the adult and elderly population of a Mediterranean town. Int Ophthalmol 1995;18: 363–71. 10. McCarty CA, Nanjan MB, Taylor HR. Operated and unoperated cataract in Australia. Clin Experiment Ophthalmol 2000; 28:77– 82.
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Ophthalmology Volume 115, Number 5, May 2008 11. Leske MC, Connell AM, Wu SY, et al. Prevalence of lens opacities in the Barbados Eye Study. Arch Ophthalmol 1997; 115:105–11. 12. Gupta SK. Prevalence and risk factors of cataract in India: a review. Dev Ophthalmol 1997;27:1–5. 13. Vassileva P, Gieser S, West S, et al. Prevalence of blindness and visual impairment due to cataract—Sofia Eye Survey. Dev Ophthalmol 1997;27:19 –24. 14. Klein BE, Klein R, Lee KE. Incidence of age-related cataract over a 10-year interval: the Beaver Dam Eye Study. Ophthalmology 2002;109:2052–7. 15. Leske MC, Wu SY, Nemesure B, et al. Incidence and progression of lens opacities in the Barbados Eye Studies. Ophthalmology 2000;107:1267–73. 16. McCarty CA, Mukesh BN, Dimitrov PN, Taylor HR. Incidence and progression of cataract in the Melbourne Visual Impairment Project. Am J Ophthalmol 2003;136:10 –7. 17. Italian-American Cataract Study Group. Incidence and progression of cortical, nuclear, and posterior subcapsular cataracts. Am J Ophthalmol 1994;118:623–31. 18. Leske MC, Chylack LT Jr, Wu SY, et al. Incidence and progression of nuclear opacities in the Longitudinal Study of Cataract. Ophthalmology 1996;103:705–12. 19. Leske MC, Chylack LT Jr, He Q, LSC Group. Incidence and progression of cortical and posterior subcapsular opacities: the Longitudinal Study of Cataract. Ophthalmology 1997;104:1987–93. 20. Cedrone C, Culasso F, Cesareo M, et al. Prevalence and incidence of age-related cataract in a population sample from Priverno, Italy. Ophthalmic Epidemiol 1999;6:95–103. 21. Leske MC, Wu SY, Nemesure B, et al. Nine-year incidence of lens opacities in the Barbados Eye Studies. Ophthalmology 2004;111:483–90. 22. Klein R, Klein BE, Linton KL, De Mets DL. The Beaver Dam Eye Study: visual acuity. Ophthalmology 1991;98:1310 –5. 23. Klein BE, Klein R, Linton KL, et al. Assessment of cataracts from photographs in the Beaver Dam Eye Study. Ophthalmology 1990;97:1428 –33. 24. Panchapakesan J, Cumming RG, Mitchell P. Reproducibility of the Wisconsin Cataract Grading System in the Blue Mountains Eye Study. Ophthalmic Epidemiol 1997;4:119 –26. 25. Steiner DL, Norman GR. Health Measurement Scales: A Practical Guide to Their Development and Use. Oxford, United Kingdom: Oxford University Press; 1989:94 – 6. 26. Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977;33:159 –74. 27. Sparrow JM, Bron AJ, Brown NA, et al. The Oxford Clinical Cataract Classification and Grading System. Int Ophthalmol 1986;9:207–25. 28. Taylor HR, West SK. The clinical grading of lens opacities. Aust N Z J Ophthalmol 1989;17:81– 6. 29. Chylack LT Jr, Leske MC, Sperduto R, et al. Lens Opacities Classification System. Arch Ophthalmol 1988;106:330 – 4.
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30. Chylack LT Jr, Leske MC, McCarthy D, et al. Lens Opacities Classification System II (LOCS II). Arch Ophthalmol 1989; 107:991–7. 31. Chylack LT Jr, Wolfe JK, Singer DM, et al. The Lens Opacities Classification System III. Arch Ophthalmol 1993;111: 831– 6. 32. Klein BE, Klein R, Ritter LL. Is there evidence of an estrogen effect on age-related lens opacities? The Beaver Dam Eye Study. Arch Ophthalmol 1994;112:85–91. 33. Younan C, Mitchell P, Cumming RG, et al. Hormone replacement therapy, reproductive factors, and the incidence of cataract and cataract surgery: the Blue Mountains Eye Study. Am J Epidemiol 2002;155:997–1006. 34. Hales AM, Chamberlain CG, Murphy CR, McAvoy JW. Estrogen protects lenses against cataract induced by transforming growth factor-beta (TGFbeta). J Exp Med 1997;185: 273– 80. 35. Bigsby RM, Cardenas H, Caperell-Grant A, Grubbs CJ. Protective effects of estrogen in a rat model of age-related cataracts. Proc Natl Acad Sci U S A 1999;96:9328 –32. 36. Klein BE, Klein R, Linton KL, Franke T. Cigarette smoking and lens opacities: the Beaver Dam Eye Study. Am J Prev Med 1993;9:27–30. 37. Klein BE, Klein RE, Lee KE. Incident cataract after a fiveyear interval and lifestyle factors: the Beaver Dam Eye Study. Ophthalmic Epidemiol 1999;6:247–55. 38. Cumming RG, Mitchell P. Alcohol, smoking and cataracts: the Blue Mountains Eye Study. Arch Ophthalmol 1997;115: 1296 –303. 39. Saxena S, Mitchell P, Rochtchina E. Five-year incidence of cataract in older persons with diabetes and pre-diabetes. Ophthalmic Epidemiol 2004;11:271–7. 40. Klein BE, Klein R, Lee KE. 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. Am J Ophthalmol 1998; 126:782–90. 41. Klein BE, Klein R, Wang Q, Moss SE. Older-onset diabetes and lens opacities: the Beaver Dam Eye Study. Ophthalmic Epidemiol 1995;2:49 –55. 42. Klein BE, Klein R, Lee KE, Meuer SM. Socioeconomic and lifestyle factors and the 10-year incidence of age-related cataracts. Am J Ophthalmol 2003;136:506 –12. 43. Australian Bureau of Statistics. Population projections, Australia, 1999 –2101. 2000:71–3. ABS catalogue no. 3222.0. Available at: http://www.abs.gov.au/AUSSTATS/[email protected]/DetailsPage/3222. 01999%20to%202101?OpenDocument. Accessed May 19, 2007. 44. Tan AG, Wang JJ, Rochtchina E, et al. Increase in cataract surgery prevalence from 1992–1994 to 1997–2002: analysis of two population cross-sections. Clin Experiment Ophthalmol 2004;32:284 – 8.
Kanthan et al 䡠 10-Year Incidence of Age-Related Cataract in Australia Table 1. Differences between Participants and Nonparticipants at Follow-up
Age (yrs) (mean) Gender (% female) Health status Current smokers (%) Ex-smokers (%) Hypertension (%) Diabetes (%) Inhaled steroid use (%) Health-related QOL (%) Socioeconomic status Own home (%) Higher job prestige (%)
Participants
Nonparticipants
P Value
64.3 58
62.2 62
⬍0.0001 0.16
13 36 43 6 11 58
22 35 47 9 11 52
⬍0.0001 0.92 0.25 0.049 0.90 0.041
91 64
85 60
0.0006 0.17
QOL ⫽ quality of life.
Figure 1. Participants included in the analysis. PSC ⫽ posterior subcapsular cataract.
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Cataract remains the leading cause of world blindness.1 In Australia, cataract is the second most frequent cause of unilateral blindness (visual acuity [VA] of 20/200 or worse),2 and the most frequent cause of mild to moderate visual impairment (corresponding to VA levels 20/40 –20/ 160).2 Cataract prevalence increases steadily with age.3 With population aging, the prevalence and burden of visual impairment from cataract are expected to rise further. Cataract extraction and intraocular lens implant surgery is Originally received: November 26, 2006. Final revision: July 3, 2007. Accepted: July 5, 2007. Available online: September 27, 2007. Manuscript no. 2006-1347. From University of Sydney Department of Ophthalmology, Center for Vision Research, Westmead Millennium Institute, Westmead Hospital, Sydney, Australia.
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© 2008 by the American Academy of Ophthalmology Published by Elsevier Inc.
the most commonly performed ophthalmic surgical procedure in Western countries.4 Despite recent advances in the technology and safety of this procedure, its economic cost is relatively high.5 Population-based data on incidence of cataract and cataract surgery are important in projecting demand and planning for eye health care and cataract surgical services. The prevalence of cataract has been reported from various populations,3,6 –13 and a few studies have examined the incidence of cataract.14 –21 Of these, to date, only the Beaver Dam Eye Study (BDES) has reported the 10-year incidence Supported by the Australian National Health and Medical Research Council, Canberra, Australia (grant nos. 974159, 211069). Correspondence to Paul Mitchell, PhD, FRANZCO, Center for Vision Research, Westmead Hospital, Hawkesbury Road, Westmead, Sydney, Australia 2145. E-mail: [email protected]. ISSN 0161-6420/08/$–see front matter doi:10.1016/j.ophtha.2007.07.008
Kanthan et al 䡠 10-Year Incidence of Age-Related Cataract in Australia of cataract.14,22 The Barbados Eye Study has reported 9-year incidence of cataract in a predominantly black population.21 In this study, we aim to report the 10-year incidence of cataract and cataract surgery in the Australian Blue Mountains Eye Study (BMES) population.
Materials and Methods Study Population Details of the BMES population and methods are reported elsewhere.2 In brief, the BMES is a population-based cohort study of vision and common eye diseases in an urban older population comprising 2 postcode areas in the Blue Mountains region, west of Sydney, Australia. This geographically well-defined area has a stable population that is reasonably representative of Australia in socioeconomic status and other measures. All residents of these 2 postcode areas who were 49 years or older were eligible and invited to participate in the survey. At baseline examination (1992–1994), 4433 residents were identified as eligible to participate, of whom 3654 (82.4%) were interviewed and examined. The difference between participants and nonparticipants at baseline has been reported previously.3 All surviving participants were invited for follow-up eye examinations after 5 (1997–1999) and 10 years (2002–2004). Participants who did not return to the 5-year follow-up were also invited to attend the 10-year examinations. There were 2335 participants (63.9% of the original cohort or 75.1% of survivors) examined after 5 years and 1952 (53.4% of the original cohort or 75.6% of survivors) examined after 10 years. Thus, a total of 2564 participants were examined at least once after the baseline examination.
Procedures The study was approved by the Western Sydney Area Health Service Human Research Ethics Committee. Written informed consent was obtained from all participants. At baseline, detailed demographic and medical histories were taken. Questions regarding previous diagnosis of cataract and details of cataract surgery were included. All participants underwent detailed eye examinations. Slit-lamp lens photographs were taken from each eye using Ektachrome 200 color film (Kodak, Rochester, NY) and an SL-7E photograph slit-lamp camera (Topcon, Tokyo, Japan) to assess presence of nuclear cataract. Retroillumination lens photographs were taken using a CT-R cataract camera (Neitz Instruments, Tokyo, Japan) to assess presence of cortical cataract and posterior subcapsular cataract (PSC). At the 5- and 10-year follow-up visits, similar questionnaires were used to collect updated demographic and medical history data for the past 5 years. Participants were examined in approximately the same order as at baseline, using the same procedures and equipment.
Lens Grading The Wisconsin Cataract Grading System, first developed in 1990 for use in the BDES, was used to perform masked grading of the lens photographs. Details of this method have been previously reported, and it was shown to have good reproducibility in the study.23,24 A 5-point scale was used to assess the presence and severity of nuclear cataract. This was done by comparing participant photographs with 4 standards of increasing opacity. Nuclear cataract was defined as nuclear opacity worse than standard 3. The presence and severity of cortical cataract and PSC were graded from Neitz photographs using a circular grid divided into 8 equal
wedges and a central circle. Graders estimated the percentage area in each of the 9 segments that was involved by cataract. The percentage of opacities in each segment was then summated to give a score for the whole lens area. Cortical cataract was considered present when at least 25% of the lens area was involved. Posterior subcapsular cataract was defined if present.
Reproducibility Intergrader and intragrader reproducibilities of lens grading were assessed using quadratic weighted statistics.25,26 A single grader assessed baseline cortical cataract and PSC, with adjudication provided by a senior ophthalmologist (PM). Repeated masked grading of a random sample of 183 eyes by this grader gave weighted s of 0.85 for cortical cataract and 0.92 for PSC. Two graders performed nuclear cataract grading of both the baseline and 5-year follow-up lens photographs. Weighted s for intraobserver reliability were 0.73 and 0.79, respectively, for the 2 graders. Intergrader reproducibilities were 0.79 for nuclear cataract, 0.78 for cortical cataract, and 0.57 for PSC. After excluding 2 eyes that also had very dense nuclear cataract, weighted for PSC improved to 0.65. These values represent acceptable reproducibility.26 The 10-year follow-up photographs were graded by one examiner (GLK) for all 3 types of cataract, with all positive cortical cataract cases also graded by another senior grader (AGT) and nuclear cataract and PSC cases also graded by a senior researcher (JJW). Repeated masked grading of 90 random eyes by the same examiner (GLK) gave weighted s of 0.81 for nuclear cataract, 0.92 for cortical cataract, and 0.89 for PSC. The same examiner graded a random sample of baseline photographs to compare intergrader reproducibilities. This gave weighted values of 0.52 for nuclear cataract, 0.72 for cortical cataract, and 0.79 for PSC. Nuclear cataract cases detected at all 3 examinations were either graded or regraded by one senior researcher (JJW), who had an intragrader reliability of 0.79.
Statistical Analysis Statistical analysis was performed using SAS software (SAS, Cary, NC). Ten-year cumulative incidence was calculated using the Kaplan–Meier (product-limit) method. Participants who did not have a particular type of cataract or cataract surgery in either eye at baseline were considered at risk of developing that type of cataract in the follow-up period. Those who did not have a particular cataract type at the 5-year follow-up examination and did not present for the 10-year follow-up were censored to the 5-year examination date. Participants were divided into 4 age groups (⬍55, 55– 64, 65–74, ⱖ74 years) to study the effect of age on cataract incidence. A discrete logistic model was used to determine the effect of age and gender as 2 explanatory variables. We also measured the effect of incident cataract on visual function by calculating the VA of affected individuals at the time of censoring. Visual acuity was defined as the number of letters on the Early Treatment Diabetic Retinopathy Study chart read correctly by participants. For each cataract type, the proportion of patients with significant visual impairment was calculated. Visual impairment was defined as best-corrected VA worse than 20/40. Finally, we also calculated the incidence of cataract surgery by cataract type and the mean age at which cataract surgery was performed.
Results A comparison of participants and nonparticipants at each follow-up examination is summarized in Table 1 (available at http://aaojournal.
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Ophthalmology Volume 115, Number 5, May 2008 Table 2. Age- and Gender-Specific Incidence of Cataract by Subtype in Either Eye in the Blue Mountains Eye Study (BMES) and Comparison with Beaver Dam Eye Study (BDES) Findings Incidence Incident Cases/ Persons at Risk
BMES 5 Year (%)
BDES 10 Year (%)
10 Year (%)
11.6 25.5 54.2 78.7 ⬍0.0001
6.2 24.6 53.3 72.7 ⬍0.0001
Nuclear cataract Age ⬍55 55–64 65–74 ⬎74 P for trend Gender Female Male P value (age adjusted) Total Age ⬍55 55–64 65–74 ⬎74 P for trend Gender Female Male P value (age adjusted) Total Age ⬍55 55–64 65–74 ⬎74 P for trend Gender Female Male P value (age adjusted) Total
20/206 116/547 186/407 69/99
5.8 12.6 35.1 61.6
239/714 152/545
23.7 21.3
391/1259
22.6 Cortical cataract
47/329 161/759 142/563 42/146
5.5 10.4 14.6 21.2
17.1 26.4 33.9 50.8 ⬍0.0001
245/1005 153/792
13.2 9.7
30.8 24.4 0.007 28.1
398/1797 11.7 Posterior subcapsular cataract
26.7 20.3 0.0005 23.7
9.7 27.7 36.9 48.2 ⬍0.0001 22.8 20.8 0.26 21.8
8/328 51/809 62/679 18/214
0.6 2.4 4.9 6.1
3.0 7.9 12.9 15.1 ⬍0.0001
3.4 8.9 12.9 14 ⬍0.0001
84/1173 55/857
3.3 3.3
139/2030
3.3
9.8 8.2 0.49 9.1
7.8 7.8 0.81 7.8
org). Nonparticipants were significantly younger (P⬍0.0001), more likely to be smokers (P⬍0.0001) and to have diabetes (P ⫽ 0.049). They were also more likely to report lower health related quality of life (P ⫽ 0.041) and were less likely to live in their own home (P ⫽ 0.0006) than those who participated in follow-up examinations. Of the 2564 participants who were observed, we excluded 100 who had cataract surgery performed on one or both eyes at baseline and thus were not considered at risk of cataract or cataract surgery in the first eye. After excluding participants who had nuclear cataract present at baseline and patients with missing or ungradable photographs, 1259 were considered at risk of developing nuclear cataract. The corresponding numbers at risk for cortical and PSC cataract were 1797 and 2030, respectively, with 1057 at risk of any type of cataract and 2448 at risk of cataract surgery (Fig 1 [available at http://aaojournal.org]). Age- and gender-specific incidences of each type of cataract are presented in Table 2, with 10-year incidence rates reported by the BDES shown for comparison. Five-year incidences were 22.6% for nuclear cataract, 11.7% for cortical cataract, and 3.3% for PSC, whereas 10-year incidences were 36.0% for nuclear cataract, 27.9% for cortical cataract, and 9.1% for PSC. The 10-year inci-
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39.3 31.7 0.04 36.0
dence of each cataract type increased significantly with age (P for trend ⬍ 0.0001). After adjusting for age, the 10-year incidence was significantly higher in women than in men for nuclear cataract (P ⫽ 0.04) and cortical cataract (P ⫽ 0.007). There was no significant gender difference in the incidence of PSC cataract (P ⫽ 0.49). Age- and gender-specific incidences of any cataract and cataract surgery are presented in Table 3. Incidences of any type of cataract were 29.1% after 5 years and 53.7% after 10 years; they increased significantly with age (P for trend ⬍ 0.0001) and were significantly higher in women than in men (59.1% vs. 47.3%, P ⫽ 0.0006), after adjusting for age. Of the 567 participants who developed at least one type of cataract during the 10-year follow-up period, 22% developed more than one type of cataract (Fig 2); 13.4% developed both nuclear and cortical opacities, 4.8% developed both nuclear and posterior subcapsular opacities, 2.6% developed both cortical and posterior subcapsular opacities, and 1.3% had developed all 3 types of lens opacities. Of the remaining 78% who developed a single type of cataract, 45.3% developed nuclear cataract only, 27.4% developed only cortical cataract, and 5.3% developed only PSC. The proportion of participants undergoing cataract surgery over
Kanthan et al 䡠 10-Year Incidence of Age-Related Cataract in Australia Table 3. Age- and Gender-Specific Incidence of Any Cataract or Cataract Surgery in Either Eye in the Blue Mountains Eye Study (BMES) and Comparison with Beaver Dam Eye Study (BDES) Findings Incidence BMES
Incident Cases/ Persons at Risk
5 Year (%)
BDES 10 Year (%)
10 Year (%)
16.4 46.8 75.1 87.7 ⬍0.0001
Any cataract Age ⬍55 55–64 65–74 ⬎74 P value (trend) Gender Female Male P value (age adjusted) Total Age ⬍55 55–64 65–74 ⬎74 P value (trend) Gender Female Male P value (age adjusted) Total
39/197 191/487 201/310 49/63
10.7 20.5 46.4 68.2
24.0 47.7 77.0 87.3 ⬍0.0001
285/577 195/480
31.4 26.5
59.1 47.3 0.0006 53.7
480/1057
29.1 Cataract surgery
12/377 74/928 193/847 86/296
0.5 1.5 7.3 16.6
242/1418 123/1030
5.5 4.8
365/2448
5.2
the period was 5.2% after 5 years and increased to 17.8% after 10 years (Table 3). The 10-year incidence of cataract surgery was strongly age related (P for trend ⬍ 0.0001) and was significantly greater in women than in men (20.2% vs. 14.4%) after adjusting for age (P ⫽ 0.03). The effect of incident cataract on visual function at the time of censoring is shown in Table 4. Among participants without any cataract, 4.6% were noted to have visual impairment, compared with 21.2% among participants with incident PSC (odds ratio [OR], 3.8; 95% confidence interval [CI], 2.0 –7.0) and 13.2% among those with incident nuclear cataract (OR, 1.8; 95% CI, 1.1–2.9). The corresponding proportion among participants with incident cortical cataract was 10.0% (OR, 1.5; 95% CI, 0.9 –2.5). Similarly, those without any incident cataract had mean VA of 52.3 letters, compared with 48.7 letters among those with incident
3.6 9.1 28.0 45.4 ⬍0.0001 20.2 14.4 0.03 17.8
40.4 35.3 0.01 38.0
2.7 11.2 26.4 29.8 ⬍0.0001 15.2 10.0 0.0007 13.0
cortical cataract (P ⫽ 0.005), 46.8 letters among those with incident nuclear cataract (P ⫽ 0.0006), and 42.9 letters among those with incident PSC (P⬍0.0001). Table 5 shows the association between cataract subtype and the incidence of cataract surgery. Of participants with nuclear cataract, cortical cataract, or PSC in the right eye at baseline, 32.5%, 26.8%, and 40.9%, respectively, underwent cataract surgery in that eye during the following 10-year period. In our study population, mean age at cataract surgery in the first eye was 75.8 years (median, 76; range, 53–92). It was 75.8 years for women and 75.9 years for men (P ⫽ 0.9). Mean age at surgery in the second eye was 76.2 years, indicating that, for most cases, surgery of the second eye followed soon after surgery for the first eye. Among participants who had surgery in their first eye within the 10-year follow up period, 49% had this surgery between the ages of 70 and 79.
Discussion
Figure 2. Frequency of pure lens opacities and multiple cataract types.
Several classification and grading methods have been developed to measure the presence and extent of cataract including the Oxford,27 Wilmer,28 Lens Opacities Classification System,29 –31 and Wisconsin.23 The Wisconsin Cataract Grading System was first developed in 1990 for use in the BDES. It was shown to have good reproducibility when applied to the BMES population.24 Studies that have examined cataract incidence are summarized in Table 6. These studies differ from each other in terms of their study samples, years of follow-up, and grading method used. The present study is only the second population-based one to report 10-year incidence of cata-
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Ophthalmology Volume 115, Number 5, May 2008 Table 4. Prevalence of Visual Impairment and Mean Best-Corrected Logarithm of the Minimum Angle of Resolution (logMAR) Visual Acuity in the Right Eyes of Participants at the Time of Censoring by Cataract Type
Cataract Type
Subjects with Visual Impairment* [% (n)]
Age†- and Gender-Adjusted Odds Ratio for Visual Impairment (95% CI)
logMAR Visual Acuity [Mean‡ (SD)]
Age†- and GenderAdjusted P Value
None Cortical§ Nuclear§ Posterior subcapsular§
4.6 (35) 10.0 (31) 13.2 (44) 21.2 (21)
1 (referent) 1.5 (0.9–2.5) 1.8 (1.1–2.9)) 3.8 (2.0–7.0)
52.3 (10.0) 48.7 (12.5) 46.8 (15.8) 42.9 (11.3)
Referent 0.005 0.0006 ⬍0.0001
CI ⫽ confidence interval; SD ⫽ standard deviation. *Best-corrected vision worse than 20/40. † At the time of censoring. ‡ Mean no. of letters correctly read on the logMAR visual acuity chart. § Alone or in combination with other types of cataract.
ract, after the BDES.14 We used the same protocol as that used in the BDES to assess cataract and have documented very similar age- and gender-specific incidence rates from our study population compared with those reported by this earlier landmark study. Both studies show that nuclear cataract is the most frequently developing lens opacity type (10-year incidence, 24%–36%). This is closely followed by cortical cataract (10-year incidence, 22%–28%). According to the BDES, women had a significantly higher incidence of both nuclear cataract and cataract surgery, but there was no significant gender difference in the incidence of cortical cataract and PSC. In our study, women had a significantly higher incidence of nuclear cataract, cortical cataract, and cataract surgery. An explanation for this gender difference in cataract incidence is not clear, but it may be related to hormonal factors.32–35 Despite the significantly higher incidence of cataract surgery in women, there was no significant gender difference (P ⫽ 0.9) between men and women in the mean age at which cataract surgery was performed in our study. As shown in Tables 2 and 3, both the BMES and BDES report similar 10-year age-specific incidence rates for each cataract subtype and for cataract surgery for all age groups except the under 55 group, for which there was a difference in eligible age for participation. The overall incidence for each cataract subtype and for cataract surgery, however, is higher in the BMES than in the BDES population, probably due to the BMES population being older (range, 49 –97) than the BDES population (range, 43– 84). To compare the crude incidence rates from both studies more accurately, we Table 5. Ten-Year Incidence of Cataract Surgery by Type of Cataract at Baseline Cataract Type Nuclear Cortical Posterior subcapsular
10-Year Incidence of Odds Ratio* for Cataract Cataract Surgery Surgery (95% CI) 32.5% 26.8% 40.9%
3.0 (2.0–4.5) 2.1 (1.4–3.0) 5.3 (2.9–9.6)
CI ⫽ confidence interval. *Reference group is persons without any cataract at baseline.
812
excluded the under 55 age group from both samples and standardized the incidence rates observed in the BMES to the age distribution of the BDES population (Table 7). This analysis demonstrated that 10-year incidences reported by both studies were very similar for each cataract subtype and for cataract surgery. Interestingly, the incidence of nuclear cataract in the first 5 years of follow-up was slightly higher than that observed during the second 5-year period. In an assessment using the different numbers of participants at risk of incident cataract at these different time points, nuclear cataract incidences were 20.4% (95% CI, 17.5%–23.6%) during the first 5-year period and 16.7% (95% CI, 13.6%–19.9%) during the second 5-year period (P⬎0.05). The corresponding proportions who had undergone cataract surgery were 4.5% (95% CI, 3.5%–5.6%) and 12.5% (95% CI, 10.9%–14.2%), respectively, for the 2 periods. We believe, therefore, the slightly lower incidence of nuclear cataract in the second 5-year period was likely caused by the greater proportion having cataract surgery. There is also likely to have been a higher mortality during the second 5-year period, resulting in survival bias, as the survivors were relatively younger in terms of biological aging, of which nuclear cataract is a marker. Strengths of our study include its population-based sample and long-term follow-up with reasonable surveillance rates (75% of survivors participated at each follow-up) and high consistency of the methods used in both the examinations and cataract grading. Limitations of our study should be noted. Nonparticipants in the follow-up examinations differed significantly from participants in age, smoking status, diabetes, and socioeconomic characteristics. As age, cigarette smoking,36 –38 diabetes,39 – 41 and socioeconomic status42 are all known risk factors for cataract, these differences between participants and nonparticipants could have led to an underestimation of cataract and cataract surgery incidence. Of the 2464 eligible participants, 1009 had missing or ungradable slit lamp (Topcon) photographs and, hence, were not included in the analysis for the incidence of nuclear cataract. This was due, however, to a random malfunction of the photograph slit lamp at the baseline examination, so that any difference, if present, was nondifferential3 and was unlikely to bias the study estimates of cataract incidence. Another limitation was the relatively high vari-
Kanthan et al 䡠 10-Year Incidence of Age-Related Cataract in Australia Table 6. Studies That Have Reported Cataract Incidence Study
Population
Age Range (yrs)
Follow-up (yrs)
Barbados Eye Study21 Italian-American Cataract Study Group17† Melbourne Visual Impairment Project16† Longitudinal Study of Cataract18,19† Italian (Priverno) Study20
Population based Clinic based
40–84 45–79
9 5
ⱖ40
14†
Beaver Dam Eye Study Blue Mountains Eye Study†
Nuclear
Cortical
Posterior Subcapsular
LOCS II LOCS II
42.0* 11.5‡
33.8* 28.2‡
6.3* 9.6‡
5
Wilmer
16.4
7.7
7
Median ⫽ 65
5
LOCS III
8
7.7
4.3
Population based
45–69
7
Population based Population based
43–86 ⱖ49
10 10
Any opacity and visual Not provided Not provided Not provided acuity ⬍ 0.2 logMAR Wisconsin 23.7 21.8 7.8 Wisconsin 36.0 28.0 9.1
Cluster random sample Clinic based
Grading Method
LOCS ⫽ Lens Opacities Classification System; logMAR ⫽ logarithm of the minimum angle of resolution. *For black participants. † Photographs were used to assess lens opacity. ‡ For the 65- to 74-yr age group only.
ability in PSC grading between graders. Due to this variability, the incidence could have been either slightly overestimated or underestimated. In our study population, 54% of participants developed unoperated cataract and a further 18% underwent cataract surgery, representing a total of 72% affected by incident cataract over the 10-year follow-up period. As the population is aging, the proportion with cataract can be expected to increase further. The Australian population over 49 years is currently 6.3 million persons, and is expected to increase to 8.7 million by the year 2021.43 Projecting the incidence rates based on our findings shows that 4.5 million Australians will develop significant cataract in the next 10 years, and this will increase to 6.3 million Australians during the period 2021 to 2031. Similarly, if the incidence of cataract surgery remained unchanged, 1.1 million Australians would undergo cataract surgery over the next 10 years, and this would increase to 1.6 million for the period 2021 to 2031. We previously showed that the prevalence of cataract surgery is increasing,44 so the actual incidence of cataract surgery is likely to be higher than this conservative estimate. Our data thus confirm that age-related cataract represents a significant public health burden in Australia. The BMES is only the second population-based study to report the 10-year incidence of cataract in an older populaTable 7. Ten-Year Incidence of Cataract and Cataract Surgery in People over 54 Years Old: Age-Standardized Comparison between the Blue Mountains Eye Study (BMES) and Beaver Dam Eye Study (BDES)
Nuclear cataract Cortical cataract PSC Any cataract Cataract surgery
BMES* (95% CI)
BDES
39.7 (37.2–42.1) 31.2 (29.3–33.0) 10.6 (9.6–11.6) 59.6 (56.1–63.1) 21.8 (20.6–22.9)
38.4 32.8 11.0 58.4 19.9
CI ⫽ confidence interval; PSC ⫽ posterior subcapsular cataract. *Rates standardized to the BDES population.
tion. We found age-and gender-specific incidence rates for cataract remarkably similar to those previously reported by the BDES. Among persons 49 years or older, 7 of 10 would be expected to develop significant cataract over the next 10 years, whereas around 2 of 10 will need surgery. All 3 cataract subtypes were found to have a significant impact in reducing VA, though this was most marked for PSC and least for cortical cataract. Cataract and cataract surgery clearly represent a significant public health burden in the context of an aging population.
References 1. Thylefors B, Negrel AD, Pararajasegaram R, Dadzie KY. Global data on blindness. Bull World Health Organ 1995;73: 115–21. 2. Attebo K, Mitchell P, Smith W. Visual acuity and the causes of visual loss in Australia: the Blue Mountains Eye Study. Ophthalmology 1996;103:357– 64. 3. Mitchell P, Cumming RG, Attebo K, Panchapakesan J. Prevalence of cataract in Australia: the Blue Mountains Eye Study. Ophthalmology 1997;104:581– 8. 4. Keeffe JE, Taylor HR. Cataract surgery in Australia 1985–94. Aust N Z J Ophthalmol 1996;24:313–7. 5. Steinberg EP, Javitt JC, Sharkey PD, et al. The content and cost of cataract surgery. Arch Ophthalmol 1993;111:1041–9. 6. Klein BE, Klein R, Linton KL. Prevalence of age-related lens opacities in a population: the Beaver Dam Eye Study. Ophthalmology 1992;99:546 –52. 7. Sperduto RD, Hiller R. The prevalence of nuclear, cortical, and posterior subcapsular lens opacities in a general population sample. Ophthalmology 1984;91:815– 8. 8. Maraini G, Pasquini P, Sperduto RD, et al. Distribution of lens opacities in the Italian-American Case-Control Study of AgeRelated Cataract. Ophthalmology 1990;97:752– 6. 9. Giuffre G, Giammanco R, Di Pace F, Fonte F. Casteldaccia Eye Study: prevalence of cataract in the adult and elderly population of a Mediterranean town. Int Ophthalmol 1995;18: 363–71. 10. McCarty CA, Nanjan MB, Taylor HR. Operated and unoperated cataract in Australia. Clin Experiment Ophthalmol 2000; 28:77– 82.
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Ophthalmology Volume 115, Number 5, May 2008 11. Leske MC, Connell AM, Wu SY, et al. Prevalence of lens opacities in the Barbados Eye Study. Arch Ophthalmol 1997; 115:105–11. 12. Gupta SK. Prevalence and risk factors of cataract in India: a review. Dev Ophthalmol 1997;27:1–5. 13. Vassileva P, Gieser S, West S, et al. Prevalence of blindness and visual impairment due to cataract—Sofia Eye Survey. Dev Ophthalmol 1997;27:19 –24. 14. Klein BE, Klein R, Lee KE. Incidence of age-related cataract over a 10-year interval: the Beaver Dam Eye Study. Ophthalmology 2002;109:2052–7. 15. Leske MC, Wu SY, Nemesure B, et al. Incidence and progression of lens opacities in the Barbados Eye Studies. Ophthalmology 2000;107:1267–73. 16. McCarty CA, Mukesh BN, Dimitrov PN, Taylor HR. Incidence and progression of cataract in the Melbourne Visual Impairment Project. Am J Ophthalmol 2003;136:10 –7. 17. Italian-American Cataract Study Group. Incidence and progression of cortical, nuclear, and posterior subcapsular cataracts. Am J Ophthalmol 1994;118:623–31. 18. Leske MC, Chylack LT Jr, Wu SY, et al. Incidence and progression of nuclear opacities in the Longitudinal Study of Cataract. Ophthalmology 1996;103:705–12. 19. Leske MC, Chylack LT Jr, He Q, LSC Group. Incidence and progression of cortical and posterior subcapsular opacities: the Longitudinal Study of Cataract. Ophthalmology 1997;104:1987–93. 20. Cedrone C, Culasso F, Cesareo M, et al. Prevalence and incidence of age-related cataract in a population sample from Priverno, Italy. Ophthalmic Epidemiol 1999;6:95–103. 21. Leske MC, Wu SY, Nemesure B, et al. Nine-year incidence of lens opacities in the Barbados Eye Studies. Ophthalmology 2004;111:483–90. 22. Klein R, Klein BE, Linton KL, De Mets DL. The Beaver Dam Eye Study: visual acuity. Ophthalmology 1991;98:1310 –5. 23. Klein BE, Klein R, Linton KL, et al. Assessment of cataracts from photographs in the Beaver Dam Eye Study. Ophthalmology 1990;97:1428 –33. 24. Panchapakesan J, Cumming RG, Mitchell P. Reproducibility of the Wisconsin Cataract Grading System in the Blue Mountains Eye Study. Ophthalmic Epidemiol 1997;4:119 –26. 25. Steiner DL, Norman GR. Health Measurement Scales: A Practical Guide to Their Development and Use. Oxford, United Kingdom: Oxford University Press; 1989:94 – 6. 26. Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977;33:159 –74. 27. Sparrow JM, Bron AJ, Brown NA, et al. The Oxford Clinical Cataract Classification and Grading System. Int Ophthalmol 1986;9:207–25. 28. Taylor HR, West SK. The clinical grading of lens opacities. Aust N Z J Ophthalmol 1989;17:81– 6. 29. Chylack LT Jr, Leske MC, Sperduto R, et al. Lens Opacities Classification System. Arch Ophthalmol 1988;106:330 – 4.
814
30. Chylack LT Jr, Leske MC, McCarthy D, et al. Lens Opacities Classification System II (LOCS II). Arch Ophthalmol 1989; 107:991–7. 31. Chylack LT Jr, Wolfe JK, Singer DM, et al. The Lens Opacities Classification System III. Arch Ophthalmol 1993;111: 831– 6. 32. Klein BE, Klein R, Ritter LL. Is there evidence of an estrogen effect on age-related lens opacities? The Beaver Dam Eye Study. Arch Ophthalmol 1994;112:85–91. 33. Younan C, Mitchell P, Cumming RG, et al. Hormone replacement therapy, reproductive factors, and the incidence of cataract and cataract surgery: the Blue Mountains Eye Study. Am J Epidemiol 2002;155:997–1006. 34. Hales AM, Chamberlain CG, Murphy CR, McAvoy JW. Estrogen protects lenses against cataract induced by transforming growth factor-beta (TGFbeta). J Exp Med 1997;185: 273– 80. 35. Bigsby RM, Cardenas H, Caperell-Grant A, Grubbs CJ. Protective effects of estrogen in a rat model of age-related cataracts. Proc Natl Acad Sci U S A 1999;96:9328 –32. 36. Klein BE, Klein R, Linton KL, Franke T. Cigarette smoking and lens opacities: the Beaver Dam Eye Study. Am J Prev Med 1993;9:27–30. 37. Klein BE, Klein RE, Lee KE. Incident cataract after a fiveyear interval and lifestyle factors: the Beaver Dam Eye Study. Ophthalmic Epidemiol 1999;6:247–55. 38. Cumming RG, Mitchell P. Alcohol, smoking and cataracts: the Blue Mountains Eye Study. Arch Ophthalmol 1997;115: 1296 –303. 39. Saxena S, Mitchell P, Rochtchina E. Five-year incidence of cataract in older persons with diabetes and pre-diabetes. Ophthalmic Epidemiol 2004;11:271–7. 40. Klein BE, Klein R, Lee KE. 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. Am J Ophthalmol 1998; 126:782–90. 41. Klein BE, Klein R, Wang Q, Moss SE. Older-onset diabetes and lens opacities: the Beaver Dam Eye Study. Ophthalmic Epidemiol 1995;2:49 –55. 42. Klein BE, Klein R, Lee KE, Meuer SM. Socioeconomic and lifestyle factors and the 10-year incidence of age-related cataracts. Am J Ophthalmol 2003;136:506 –12. 43. Australian Bureau of Statistics. Population projections, Australia, 1999 –2101. 2000:71–3. ABS catalogue no. 3222.0. Available at: http://www.abs.gov.au/AUSSTATS/[email protected]/DetailsPage/3222. 01999%20to%202101?OpenDocument. Accessed May 19, 2007. 44. Tan AG, Wang JJ, Rochtchina E, et al. Increase in cataract surgery prevalence from 1992–1994 to 1997–2002: analysis of two population cross-sections. Clin Experiment Ophthalmol 2004;32:284 – 8.
Kanthan et al 䡠 10-Year Incidence of Age-Related Cataract in Australia Table 1. Differences between Participants and Nonparticipants at Follow-up
Age (yrs) (mean) Gender (% female) Health status Current smokers (%) Ex-smokers (%) Hypertension (%) Diabetes (%) Inhaled steroid use (%) Health-related QOL (%) Socioeconomic status Own home (%) Higher job prestige (%)
Participants
Nonparticipants
P Value
64.3 58
62.2 62
⬍0.0001 0.16
13 36 43 6 11 58
22 35 47 9 11 52
⬍0.0001 0.92 0.25 0.049 0.90 0.041
91 64
85 60
0.0006 0.17
QOL ⫽ quality of life.
Figure 1. Participants included in the analysis. PSC ⫽ posterior subcapsular cataract.
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