The Association of Outdoor Activity and Age-Related Cataract in a Rural Population of Taizhou Eye Study: Phase 1 Report
The Association of Outdoor Activity and Age-Related Cataract in a Rural Population of Taizhou Eye Study: Phase 1 Report
Yating Tang 0 1 2
Yinghong Ji 0 1 2
Xiaofang Ye 0 1 2
Xiaofeng Wang 0 1 2
Lei Cai 0 1 2
Jianming Xu 0 1 2
Yi Lu 0 1 2
0 1 Department of Ophthalmology, Eye and ENT Hospital of Fudan University , 83 Fenyang Road, Xuhui District, Shanghai , China , 2 Myopia Key Laboratory of the Health Ministry & Visual Impairment and Reconstruction Key Laboratory of Shanghai , Shanghai , China , 3 Fudan University and Shanghai Key Laboratory of Meteorology and Health, Pudong Meteorological Service , Shanghai , China , 4 State Key Laboratory of Genetic Engineering and MOE Key Laboratory of Contemporary Anthropology, Collaborative Innovation Center for Genetics and Development, School of Life Sciences and Institutes of Biomedical Sciences, Fudan University , Shanghai , China , 5 Fudan-Taizhou Institute of Health Sciences , 1 Yaocheng Road, Taizhou, Jiangsu Province , China , 6 Shanghai Key Laboratory of Meteorology and Health, Pudong Meteorological Service , Shanghai , China
1 Funding: The work was supported by grants for Natural Science Foundation of China (NSFC81270989 and 81300745), Shanghai Science and Technology Commission (11231200602), Key Projects in the National Science & Technology Pillar Program (2011BAI09B00), New One Hundred People's Plan of Shanghai Health Bureau (XBR2011056) and Visual Impairment and Reconstruction Key Laboratory of Shanghai (12DZ2260500). The funders had no role in study
2 Editor: Haotian Lin, Sun Yat-sen University , CHINA
To study the relationship between outdoor activity and risk of age-related cataract (ARC) in
a rural population of Taizhou Eye Study (phrase 1 report).
A population-based, cross-sectional study of 2006 eligible rural adults ( 45 years old) from
Taizhou Eye Study was conducted from Jul. to Sep. 2012. Participants underwent detailed
ophthalmologic examinations including uncorrected visual acuity (UCVA), best corrected
visual acuity (BCVA), intraocular pressure (IOP), slit lamp and fundus examinations as well
as questionnaires about previous outdoor activity and sunlight protection methods. ARC
was recorded by LOCSⅢ classification system. The prevalence of cortical, nuclear and
posterior subcapsular cataract were assessed separately for the risk factors and its association
Of all 2006 eligible participants, 883 (44.0%) adults were diagnosed with ARC. The
prevalence rates of cortical, nuclear and posterior subcapsular cataract per person were 41.4%,
30.4% and 1.5%, respectively. Women had a higher tendency of nuclear and cortical
catarespectively). Adults with high myopia had a higher prevalence of nuclear cataract than
design, data collection and analysis, decision to
publish, or preparation of the manuscript.
Competing Interests: The authors have declared
that no competing interests exist.
revealed that age was risk factor of nuclear (OR = 1.190, 95% CI 1.167–1.213) and cortical
(OR = 1.203, 95% CI 1.181–1.226) cataract; eyes with fundus diseases was risk factor of
posterior subcapsular cataract (OR = 6.529, 95% CI 2.512–16.970). Outdoor activity was
an independent risk factor of cortical cataract (OR = 1.043, 95% CI 1.004–1.083). The risk
of cortical cataract increased 4.3% (95% CI 0.4%-8.3%) when outdoor activity time
increased every one hour. Furthermore, the risk of cortical cataract increased 1.1% (95% CI
0.1%-2.0%) when cumulative UV-B exposure time increased every one year.
Outdoor activity was an independent risk factor for cortical cataract, but was not risk factor
for nuclear and posterior subcapsular cataract. The risk of cortical cataract increased 4.3%
when outdoor activity time increased every one hour. In addition, the risk of cortical cataract
increased 1.1% (95% CI 0.1%-2.0%) when cumulative UV-B exposure time increased
every one year.
Age-related cataract (ARC) remains the predominant cause of blindness all over the world,
especially in China, home to 1/5 of the world’s population[1,2]. The Beijing Eye Study showed
that the prevalence of cataract was 53.1% in adults 40 years old in China. Cataract surgery
is the only effective treatment of cataract and still expensive in developing countries at present.
With the increasing aging population, the morbidity and burden of ARC is expected to
increase[4,5], which means heavier load to public health care. Therefore, it is very important to
study the risk factors and mechanisms of cataract and to carry out some prevention work by
epidemiologic method. However, so far in mainland China, most of the epidemiologic studies
stress more on the prevalence of ARC and cataract surgery[3,6,7,8,9,10]. Population-based
epidemiologic studies focusing on risk factors of ARC in China are still rare when compared to
Unite States[11,12,13], Australia, Singapore[15,16] and Europe[17,18].
Although age is the most important risk factor of ARC, there are some other potential risk
factors that may influence the development of ARC including gender, smoking, sunlight
exposure, diabetes and drug intake. However, the risk factors vary from different countries and
living environment. For example, sunlight exposure was proved to be significantly related to
cataract in some European studies[20,21], but no correlation was found in Beaver Dam Eye
Study. Furthermore, the relationship between sunlight exposure and risk factor of cataract
has been seldom studied in mainland China. Therefore, we studied the association of outdoor
activity with risk factor of cortical, nuclear and posterior subcapsular cataract in a rural
population of Taizhou Eye Study, China. This report is an exploration of the relationship between
outdoor activity as well as some other risk factors and ARC development.
The population and data for this study were derived from the Taizhou Eye Study. The details
of the population and methods of Taizhou Eye Study have been previously described. In
brief, Taizhou Eye Study is part of a large scaled prospective study called Taizhou Longitudinal
Study carried out from 2007. For Taizhou Eye Study, it is an ongoing large-scale
population based on prospective cohort study carried out from April 2012 in Taizhou City,
Jiangsu Province, middle-east part of China. Taizhou Eyes Study focuses primarily on the
prevalence, incidence and risk factors of ARC and other age-related eye diseases. The total
population of this study was about 10,000 adults aged 45 years old. In this report, we randomly
selected 4 villages with a rural population of 2600 adults aged 45 years old. Of these
individuals, 2006 eligible participants (77.2% response rate) finished the total procedure from Jul. to
Sep. 2012. Within one week prior to the baseline survey, related advertisement material were
distributed to every household of the aimed community by the study group. All participants
were self-identified Han Chinese (at least four generations were Han Chinese) and local
residents for at least 10 years. This study adhered to the Declaration of Helsinki and was approved
by the Human Ethics Committee of School of Life Science of Fudan University. Consents in
written form were also obtained from all participants prior to participation.
Interview and Clinical Examination Procedure
At each examination site, participants were brought to the nearby village clinics or village
offices for general physical, detailed ophthalmic examinations and questionnaires on
prescheduled examination days. Those who failed to come to the examination site were revisited. Those
physically disabled and those who still failed to come to the examination site after second visit
were conducted an ocular examinations (using portable equipment) in their home at the end of
the work in every examination site.
The detailed examination procedure has been reported. In brief, after registering of name,
ID, gender and age and some general examination (including heart rate, blood pressure, body mass
index, etc.), vein blood was collected for serological and genetic analysis in the future. Presenting
visual acuity (PVA, wearing present correction if any) was measured using a retro-illuminated
logarithm E chart with the minimum angle of resolution at a distance of 4 meters and at 1 meter for
those who failed to read the top line figures (20/200), as Zhao et al. used in the Nine-Province
Eye Survey. When PVA was 20/40 in either eye, the best corrected visual acuity (BCVA) was
determined by subjective refraction without cycloplegia. Intraocular pressure was measurement by
Icare rebound tonometry (Icare TAO1i, Helsinki, Finland). A-scan (AL-3000, TOMEY, Tokyo,
Japan) was performed to measure the axial length (AL), central anterior chamber depth (ACD)
and lens thickness of all participates under topical anesthesia. The examinations were repeated if
the ophthalmologist considered the results unreliable. All of these ocular examinations were carried
out by 4 experienced technicians from Taizhou Eye Study Team. All of the eye technicians were
required to complete standardized ophthalmologic training and had certification to conduct the
eye examinations. The examination consistency was over 95% between different examiners.
Lens and ocular anterior segment examination were evaluated using a slit-lamp (Topcon
SL-8Z; Topcon, Inc., Tokyo, Japan) after dilation of the pupil to give the lens opacification
records of all residents. Fundus examination was carried out by +90 diopter (D) lens at X16
magnification or direct ophthalmoscopy. Those who were under high risk of angle closure
glaucoma were examined only under small pupil situation. The lens and fundus examination
were carried out by one experienced ophthalmologist (Dr. Yating Tang) to make sure the
consistence of the results. Individuals with typical fundus diseases were taken fundus photos after
dilation of the pupil using Canon retinal camera system (CX1, Canon, Inc., Tokyo, Japan) by
one experienced ophthalmologist.
The face-to-face questionnaires interviews concerning economic situation, education level,
life habit, tobacco, alcohol and tea intake, activity hours outdoors, drug intake history and
disease history and so on were administered by the study clerks using computers. Average daily
outdoor activity hours and some sunlight protection methods (sunglass, sun hat, sun umbrella
or without any protection) were recorded to evaluated the sunlight exposure condition. For
quality control, the method of sampling, questionnaire design, training, physical examination,
laboratory examinations, and data management have been centralized and standardized.
General examinations and interviewer staff were required to complete standardized training
and to get certifications to conduct specific survey. All of the interviews were tape-recorded,
and about 5% of the tapes were used for interviewing quality evaluation. All examination and
questionnaires data were put into computer database on examination day. Computers were
used to check the reasonable responses throughout the whole examination process to identify
contradictory responses. Phase summary and statistical analysis was made to make sure the
data was accurate, consistent and standardized.
Grading of Cataract and Lens Opacities
Cataract were recorded using lens opacities classification system Ⅲ (LOCSⅢ). According
to LOCSⅢ, nuclear lens opacities were classified into 6 grades (NO1 NC1-NO6 NC6), cortical
lens opacities were classified into 5 grades (C1-C5) and posterior subcapsular cataract (PSC)
5 grades (P1-P5). A person with cataract was defined as any LOCS III grading of 2 in either eye
and lens opacities degree was compatible with visual impairment. Cortical cataract was defined
as LOCSⅢ 2 for cortical opacities, nuclear cataract as 2 for nuclear opacities or 2 for nuclear
color and subcapsular cataract as 2 for subcapsular opacities. Any cataract was defined as
cortical, nuclear or posterior subcapsular cataract or had cataract surgery in either eye. If one eye has
two or three types of cataract, for example, combined cortical and nuclear cataract, it will be
classified into cortical and nuclear cataract, respectively. One individual could be classified into
different groups of cataract types. Phakic status (phakic, pseudophakic or aphakic) of each eye
was recorded, respectively. In eyes where lens assessement was not available, reasons were also
recorded. If a participant had unilateral lens extraction, we used the LOCS III grading from the
contralateral phakic eye defined the lens opacity types per person. If a participant had bilateral
lens extraction (bilateral pseudophakic or aphakic eyes), we excluded him/her in specific types of
cataract prevalence analysis as it was difficult to evaluate that.
Eye Disease Diagnosis
The eye diseased diagnosis criteria have been described in our previous report. Briefly, we
defined myopic macular degeneration in subjects with a refractive error exceeding -6.0
dipoters, axial length of 26 mm or more, and typical degenerative myopic fundus changes. We
defined AMD according to the Wisconsin Age-related Maculopathy Grading System and
glaucoma according to the International Society for Epidemiological Ophthalmology
classification. Additionally, the diagnoses of diabetic retinopathy, corneal opacity, retinal
detachment, pterygium, uveitis, and others diseases followed the clinical standard.
Cumulative UV-B Exposure Years
For cumulative UV-B exposure years calculation, we used a modified and simplified formula
that was derived from the Melbourne visual impairment project model. The formula was
E ¼ Ec þ Ea ¼ <
E = cumulative UV-B exposure years (y).
Ec = UV-B exposure years during children period.
Ea = UV-B exposure years during adult period.
Yearsc = years of children period, that is, 18 years in total in our study.
Hc = average outdoor exposure hours during children period. For the period was school
period, we defined 2 hours per day for outdoor exposure hours during this period.
H = maximum 11 hours (8:00–18:00) of outdoor exposure per day in Taizhou Eye Study.
Age = age of participant in Taizhou Eye Study.
Ha = average outdoor activity hours during adult period, we recorded the “Ha” using the
Statistical analysis was performed using SPSS Statistics 17.0 (IBM SPSS Inc., Chicago IL, USA).
The risk factors for each type of lens opacity were calculated separately. The data are shown as
mean±standard deviation form. Univariate logistic regression was used to assess the univariate
association of each risk factor with cataract (cortical, nuclear and PSC vs. no cataract). Stepwise
multivariable logistic regression was conducted to evaluate the independent associations for
each risk indicator. The candidate risk factors include age, gender, outdoor activity time,
cumulative UV-B exposure years, sunlight protection, glaucoma, age-related macular degeneration
(AMD), other fundus disease (including diabetic retinopathy, macular hole, retinal
detachment, branch retinal vessel occlusion, etc.). Odds ratios (OR) value and 95% confidence
intervals (CI) were presented. P<0.05 was regarded as statistically significant.
Of all the 2006 eligible participants, the mean age was 60.1±9.5 years old (age range 45–100
years old). The percentage of female: male was 1189:817 (1.46:1). The mean time of ourdoor
activity was 5.7±3.2 hours (time range 0–16.0 hours) and the ratio of adults who have sunlight
protection measures vs those have no sunlight protection measures was 1007:994 (1.01:1).
We examined the lens conditions in 3995 eyes (right eye 1998 and left eye 1997) of 2006
people, 17 eyes (right eye 8 and left eye 9) were excluded because it was unable to evaluate the
lens opacification condition with the reasons of ocular atrophy or prosthetic eye, corneal
opacities, etc. In specific cataract calculation, 11 people had bilateral cataract surgery and therefore,
1995 individuals were included in the specific cataract per person analysis.
Table 1 showed the prevalence of cataract and cataract surgery per eye and per person in
this study. There were in total 1627 eyes (40.7%, 95% CI 39.2%-42.3%) had cataract or
underwent cataract surgery. 883 people (44.0%, 95% CI 41.8%-46.2%) were diagnosed with cataract
including 744 adults (37.1%, 95% CI 35.0%-39.2%) with binocular cataract and 139 adults
(6.9%, 95% CI 5.9%-8.1%) with monocular cataract. 37 people (1.84%, 95% CI 1.3%-2.5%)
underwent cataract surgery. The mean age of people took cataract surgery was 69±10.8 years
old, higher than those who did not (59.9 ±9.4 years old). The prevalence of cortical, nuclear
and PSC per person were 827 (41.4%, 95% CI 39.3–43.7), 607 (30.4%, 95% CI 28.4%-32.5%)
and 29 (1.5%, 95% CI 1.0%-2.1%), respectively. The prevalence of cortical, nuclear and any
cataract per person increased with age (Fig 1).
Table 2 showed the univariate and multivariable regression of risk factors for nuclear
cataract. Using univariate analysis, age, shorter outdoor activity, longer cumulative UV-B exposure
years, eyes with high myopia, eyes with AMD and other fundus diseases were risk factors of
nuclear cataract. Using multivariable regression model, age (OR = 1.19, P<0.001), gender
PSC: posterior subcapsular cataract.
Right Eye (%, 95% CI)
1173 (58.7, 56.5–60.9)
Left Eye (%, 95% CI)
1195 (59.9, 57.7–62.0)
Number of People (%, 95% CI)
883 (44.0, 41.8–46.2)
827 (41.4, 39.3–43.7)
607 (30.4, 28.4–32.5)
1086 (54.1, 51.9–56.3)
(OR = 1.56, P = 0.001) and high myopia (OR = 2.53, P = 0.038) were three independent risk
factors of nuclear cataract.
Table 3 showed the univariate and multivariable analysis of risk factors for cortical cataract.
Using univariate regression, age, gender, shorter outdoor activity, longer cumulative UV-B
exposure years, eye protection, AMD and other fundus diseases were risk factors of cortical
cataract. Using multivariable regression model, age (OR = 1.2, P<0.001), gender (OR = 1.86,
P<0.001), outdoor activity (OR = 1.043, P = 0.03), cumulative UV-B exposure years
(OR = 1.011, OR = 0.035) and other fundus diseases (OR = 2.04, P = 0.013) were independent
risk factors of cortical cataract. The risk of cortical cataract increased 4.3% (95% CI 0.4%-8.3%)
when outdoor activity time increased every one hour. Moreover, the risk of cortical cataract
increased 1.1% (95% CI 0.1%-2.0%) when cumulative UV-B exposure time increased every one
Fig 1. Prevalence of cortical, nuclear and any cataract per person in each age group. Ages were
classified into eight continuous groups (45–49, 50–54, 55–59, 60–64, 65–69, 70–74, 75–79 and 80 years
old). For cortical cataract, the prevalence at different age groups were 2.8%, 13.1%, 28.5%, 50.5%, 72.2%,
75.8%, 89.5% and 93.6%. For nuclear cataract, the prevalence were 2.2%, 7.6%, 13.9%, 33.2%, 57.5%,
62.9%, 78.9% and 87.2%. For posterior subcapsular cataract (PSC), the prevalence were 0.3%, 1.1%, 0.7%,
2.1%, 2.8%, 3.0%, 0.0% and 1.4%. For any cataract, the prevalence were 5.2%, 16.7%, 30.5%, 53.5%,
74.2%, 77.4%, 90.0% and 96.2%.
Outdoor activity (hours)
Cumulative UV-B exposure years (y)
Table 4 showed the univariate and multivariable regression of risk factors for PSC. Using
univariate analysis, age, outdoor activity and other fundus diseases were risk factors of PSC.
Using multivariable regression model, only other fundus diseases (OR = 6.53, P<0.001) was
independent risk factor of PSC.
This study population was phrase 1 part summary of Taizhou Eye Study. Our study provided
new population-based data on the association of outdoor activity and risk of cataract in rural
residents aging 45 years old. We found that outdoor activity was risk factor for cortical
cataract, but was not for nuclear and posterior subcapsular cataract. Furthermore, our study
regarded outdoor activity density as a continuous variable and evaluated that the risk of cortical
cataract increased 4.3% when outdoor activity time increased every one hour. Moreover, the
risk of cortical cataract increased 1.1% (95% CI 0.1%-2.0%) when cumulative UV-B exposure
time increased every one year.
Our study confirmed the cross-sectional association between outdoor activity and cortical
cataract in Chinese population. Our result was consistence with some previous studies
[20,21,31,32,33]. Epidemiology studies have showed that the prevalence rate of cataract in
areas with low latitude and longer sunlight exposure is higher than areas with higher latitude
Outdoor activity (hours)
Cumulative UV-B exposure years (y)
and shorter sunlight exposure. In the U.S., the probability of cataract surgery increases 3% for
every 1 degree decrease in latitude. Latitude is directly associated with the UV-B degree
of sunlight. UV-B is risk factor of cortical and nuclear cataract; ocular UV-B exposure may
explain about 10% of the cortical cataract in the population. The mechanisms of UV-B
inducing cataract likely involve the apoptosis of human lens epithelium cells (HLECs). UV-B
irradiation-initiated HLECs apoptosis may involve complicated mechanisms including
mitochondrial dysfunction and caspase-3 activation. The main dysfunction of mitochondrial
was related to oxidative stress. Reduction of sunlight exposure is in many ways an effective
means of preventing cataract related visual disability. In our study, longer outdoor activity
was also correlated with higher risk of cortical cataract (OR = 1.043, P = 0.03). Furthermore,
the risk of cortical cataract increased 1.1% (95% CI 0.1%-2.0%) when cumulative UV-B
exposure time increased every one year. Using the cumulative UV-B exposure year, it’s not
surprising that some older individuals with few outdoor activity may have a higher risk of cortical
cataract than the younger patient with more outside hours because the older individuals may
have higher cumulative UV-B exposure years. However, we did not find the correlation of
outdoor activity with nuclear cataract in our study, which might implicate different risk factors
and prevention methods of different types of cataract in Chinese people.
Outdoor activity (hours)
Cumulative UV-B exposure years (y)
Previous studies have showed that ARC occurs more common in female than male
[3,37,38,39,40]. In our present study, female gender was also found as independent risk factors
for cortical and nuclear cataract. The Blue Mountains Eye Study reported that the hormone
replacement therapy could reduce the rate of cortical cataract and thus played a protective
effect, the result was also proved in Salisbury Eye Evaluation. However, contrary result
was found in some other studies[43,44]. In a meta-analysis by Lai K. et al, Hormone
therapy could significantly decrease the risk of nuclear cataract (OR = 0.72, 95% CI 0.61–0.85).
Hormone replace therapy was not specifically studied in our study. However, prospective
studies will be carried out in our future study about the association between hormone therapy and
cataracts considering the limited numbers of studies in the meta-analysis.
High myopia has been proved as an independent risk factor of nuclear cataract in many
epidemiologic studies[38,46,47]. In Beijing Eye Study, the age-adjusted nuclear cataract rate
was significantly correlated with myopia. In the Beaver Dam Eye Study, the Los Angeles
Latino Eye Study and the Blue Mountains Eye Study, high myopia was also found to
be associated with increased incidence of nuclear cataract. In our study, we also found high
myopia (OR = 2.53, P = 0.038) as independent risk factor of nuclear cataract, which was
consistent with previous studies. The potential mechanisms that high myopia leads to nuclear
cataract are still unknown, but some researchers have hypothesized that axial myopia is a reason of
a longer vitreous cavity that may cause decreased nutrition diffusion to the posterior lens and
thus inhibits the oxidative defense mechanisms. The hypothesis is supported by the fact
that the hyperbaric oxygen treatment could result in a rapid nuclear cataract formation and
that nuclear cataract occurs more common after vitrectomy surgeries, whereby the lens were
exposed to a higher level of intraocular oxygen [48,49]. Prospective data from our study
population may help to evaluate the direct role of myopia in the progression of nuclear cataract in
our future work.
The potential risk factors of PSC include steroid usage, diabetic retinopathy, myopia and
female gender in previous studies[11,19]. In our study, we only found the fundus diseases as a
single strong independent risk factor for PSC (OR = 6.529, 95% CI 2.51–16.97). As the
prevalence of PSC was very low (29 people, rate 1.4%) and the population was still limited in this
study, we did not study the effect of diabetic retinopathy on PSC but put all of the other fundus
diseases except AMD and glaucoma together. In our study, the effect of other fundus diseases
on PSC was very strong, which implicated the significant role of fundus diseases on the
development of PSC in Chinese population. However, specific fundus diseases will be studied in
details of their effect on PSC in our further reports.
There were also some shortcomings of our manuscript; for example, we just evaluated the
sunlight protection yes or no, instead of the accurate protection time. However, in this
population-based epidemiologic study on the association of outdoor activity and different types of
cataract in a Chinese rural population, we found that the outdoor activity was significantly
associated with cortical cataract, but was not for nuclear and posterior subcapsular cataract. In
conclusion, the risk of cortical cataract increased 4.3% when outdoor activity time increased
every one hour. Furthermore, the risk of cortical cataract increased 1.1% when cumulative
UV-B exposure time increased every one year. Our study gave an accurate quantitative
evidence of the outdoor activity time effect on cortical cataract mechanisms and cataract
The authors thank the Epidemiologic Disease Control Center of Taizhou City, the members of
the Taizhou Eye Study team for their contribution to this study. The work was supported by
grants for Natural Science Foundation of China (NSFC81270989 and 81300745), Shanghai
Science and Technology Commission (11231200602), Key Projects in the National Science &
Technology Pillar Program (2011BAI09B00), New One Hundred People’s Plan of Shanghai
Health Bureau (XBR2011056) and Visual Impairment and Reconstruction Key Laboratory of
Conceived and designed the experiments: YT YJ XW YL. Performed the experiments: YT XW
LC YL. Analyzed the data: XY YT JX. Contributed reagents/materials/analysis tools: YT XY.
Wrote the paper: YT YJ.
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