Prevalence of visual impairment and outcomes of cataract surgery in Chaonan, South China
Prevalence of visual impairment and outcomes of cataract surgery in Chaonan, South China
Xiujuan Zhang 0 1
Emmy Y. Li 0 1 2
Christopher Kai-Shun Leung 0 1
David C. Musch 0
Xin Tang 0
Chongren Zheng 0
Mingguang He 0
David F. Chang 0
Dennis Shun- Chiu Lam 0 1
0 Editor: James Fielding Hejtmancik, National Eye Institute , UNITED STATES
1 Department of Ophthalmology and Visual Sciences, the Chinese University of Hong Kong , Hong Kong , China , 2 Tianjin Eye Hospital , Tianjin , China , 3 Project Vision Charitable Foundation , Hong Kong , China
2 Hong Kong Eye Hospital , Kowloon, Hong Kong , China , 5 Department of Ophthalmology and Visual Sciences, University of Michigan Medical School , Ann Arbor , Michigan, United States of America, 6 State Key Laboratory of Ophthalmology, Sun Yat-Sen University , Guangzhou , China , 7 The University of California , San Francisco, California , United States of America
impairment (VI) were defined by the World Health Organization criteria. Participants with
visual acuity (VA) < 6/18 in either eye were examined by ophthalmologists. The primary
causes of blindness and VI were reported with reference to the participant's better eye.
Main outcome measures
comes of cataract surgery
Prevalence and main causes of blindness, severe visual impairment (SVI), VI and the out
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Funding: Financial support for this research
project: The Project Vision Charity Foundation,
Hong Kong. The funders had no role in study
design, data collection and analysis, decision to
publish, or preparation of the manuscript.
Competing interests: The authors have declared
that no competing interests exist.
To estimate the prevalence and causes of blindness and visual impairment (VI), and report the outcomes of cataract surgery in Chaonan Region, Guangdong Province, southern
Cross-sectional population-based survey
The standardized prevalence rates of blindness, SVI, and VI were 2.4% (95% confidence
interval [CI], 1.9±2.9%), 1.0% (95% CI, 0.7±1.4%), and 6.4% (95% CI, 5.6%± 7.1%),
respectively. The principal cause of blindness and SVI was cataract, accounting for 67.1%
and 67.6% respectively, and the principal cause of VI was refractive error (46.9%). One
hundred and fifty five out of 3484 (4.4%) people (211 eyes) had cataract surgery. Of the 211
eyes that had cataract surgery, 96.7% were pseudophakic. 67.2% of the 211 operated eyes
had a presenting visual acuity (PVA) of 6/18 or better.
The prevalence of blindness, SVI, and VI was high among rural residents in Chaonan. Cataract remained the leading cause of avoidable blindness. Outcomes of cataract surgery performed in rural private clinics were suboptimal. Quality-control initiatives such as hands-on training program should be introduced to improve cataract surgery outcomes.
In 2010, the World Health Organization (WHO) estimated that there were 39 million people
in the world with blindness and 285 million with visual impairment. China had the largest
number with 8 million blind and 75 million visually impaired individuals[
]. Population based
surveys in China have identified cataract as the leading cause of blindness and visual
impairment[2±7]. Cataract surgery is an effective means to reverse cataract blindness.
However, the cataract surgical rate (CSR) in China remains relatively low at about 772 cases per
one million per year,[
] which is much lower than its neighbor India[
]. A major cause of the
low CSR is the lack of experienced surgeons in rural areas. The Chinese Ministry of Health has
reported that 45% of China's 2400 county hospitals do not offer cataract surgery services[
and most rural residents are unable to afford surgery in urban centers. Thus, a large number of
patients with severe cataract have little or no access to affordable surgical services. On this
account, Project Vision, a non-governmental organization, was established to build a
sustainable model to reduce cataract blindness in rural China. Project Vision's first priority is to
develop rural charity eye centers wherein local doctors are trained to provide high quality and
low cost cataract surgery[
Liangying Hospital, located in the Chaonan Region, was the first county hospital designated
to be a local charity eye center in 2004. After 6 months of hands-on training, the local surgeons
were approved to perform cataract surgery independently by at least two experienced senior
ophthalmologists from Project Vision[
]. The number of cataract operations increased
annually in the past seven years. The two surgeons have performed approximately 11,000
cataract operations since the establishment of the Charity eye center in 2004.
Rapid Assessment of Avoidable Blindness (RAAB) aims to provide information on the
prevalence of visual impairment due to avoidable causes of vision loss[
]. RAAB also collects
data on cataract surgical coverage, major barriers to the uptake of cataract surgery, and visual
outcome after surgery for individuals aged 50 years. The aim of this study was to define the
prevalence of blindness and visual impairment among people aged 50 years in Chaonan and
to evaluate the outcomes of cataract surgery performed in the region.
2 / 13
This study was approved by the Ethics Committee of the Chinese University of Hong Kong
and the Disabled Federation of Chaonan Region, and conformed to the tenets of the
Declaration of Helsinki. Subjects aged 50 years, residing in 11 towns and 241 villages in the Chaonan
region were enrolled from April to July in 2012. Persons were considered ineligible if they had
moved out of the village, had not lived there in the past 6 months since we selected the sample
in April 2012. All the study procedures were explained in detail to each subject and the family
by the study investigators with local dialect, in the presence of two to three community heads
of the village. Written informed consent with signature or inked fingerprint was obtained
from all participants before examination.
Cataract surgical facilities in research setting
The study site, Chaonan Region, is a rural plane, situated in eastern Guangdong, approxi
mately 150 km from the provincial capital of Guangzhou City and 36 km from Shantou City.
The Zhongshan Ophthalmic Center (ZOC) and the Joint Shantou International Eye Center
(JSIEC), located in Guangzhou and Shantou, respectively, are two major public hospitals in
China. There were eighteen experienced surgeons providing cataract surgery in ZOC, and six
surgeons in JSIEC. Besides the two public hospitals, there are other facilities that can provide
cataract surgeries in the local area.
1. Charity eye centers: There were three surgeons performing cataract surgeries in two charity
eye centers of this region. As these local surgeons became recognized by residents in the
area, the number of patients receiving cataract surgery in charity centers steadily increased.
2. Private eye clinics: There were three private eye clinics with four surgeons providing cataract surgery services in the region.
Sample size calculation
According to the 2010 Chaonan Region Census, the population size of Chaonan Region was
1,288,165, and the target population aged 50 years was 214,425. According to the report
from the China Nine-province Survey in 2008, the expected prevalence of blindness in adults
aged 50 or above was estimated to be 2.68% in Guangdong Province[
]. With a confidence
interval of 95%, a precision of 25%, and a design effect set at 1.5, the minimum sample size was
3,295. Assuming a 90% response rate; the sample size was estimated to be 3,662. We therefore selected 74 clusters, each with 50 participants.
Selecting the sample
A two stage sample selection was adopted[
]. A cluster random sampling with probability
proportional to population size, as proposed by Wu et al, was performed to select 74
clusters. In brief, names of the enumeration area and the corresponding cumulative population
were listed to create a sampling frame. The sampling interval was calculated as the total
population divided by the number of clusters required (i.e., 74). The starting point was first
determined by multiplying a computer-generated random number between 0 and 1 with the
sampling interval. The starting point was then tracked in the cumulative column and the
corresponding enumeration area was selected as the first cluster. The second cluster was identified
by adding the sampling interval to the starting point number and the same procedures were
repeated until 74 enumeration areas were selected. An enumeration area is either a large village
3 / 13
with a population of more than 1000 or a suburb residence at administrative level composed
by a number of small natural villages, each with around 150±200 residents, defined by
geographical boundaries. The natural villages were considered as segments in the enumeration
area and numbered. For each selected enumeration area, all the segment numbers were written
on small pieces of paper and one was randomly picked.
In each segment, the random walk method was used to enroll the first 50 people aged 50
years and above. A random direction was chosen prior to the survey. After starting from a
randomly selected household, the next nearest household in the direction chosen was visited until
50 subjects aged 50 or above were identified[
]. Those available and willing were examined
on-site. If there were households who were known to be residents aged 50 or above, but
unavailable at the time of the first visit, the survey team would revisit on another day to examine them.
When all the households in a selected segment were visited and there were less than 50 eligible subjects, the next nearest segment in the enumeration area were visited to complete the cluster.
A 7-day workshop was held under the supervision of two expert ophthalmologists who had
conducted RAAB surveys prior to commencement of this survey. Two research teams
including ophthalmologists, optometrists, computer operators and local research assistants
conducted the surveys. Training and inter-observer variation test were performed 3 weeks before
the commencement of the survey. Each team examined the same group of subjects during a
pre-study pilot according to the protocol described in the RAAB manual. These subjects were
examined by 3 ophthalmologists and the examination findings were compared to the most
experienced examiner in the team, Dr ZXJ, to calculate the inter-observer agreement. The
assessment included examination of visual acuity, lens status, and tests to determine the main
cause of visual loss. Kappa for agreement between teams on examination findings was
calculated during the pre-study pilot, and a kappa of at least 0.80 was required before the survey
commenced. During the first 2 weeks, the two research teams worked together to examine 50
people in the same cluster under supervision to minimize discrepancy between different
examiners. After that, a field supervisor (ZXJ) accompanied the teams at least once a week during
the study to check the reliability and validity of data collection.
According to the World Health Organization (WHO) definition, blindness was defined as
visual acuity (VA) of <3/60, severe VI (SVI) was defined as VA 3/60 and <6/60 and visual
impairment (VI) was defined as VA 6/60 and <6/18 in the better eye with available spectacle
correction. Refractive error, a cause of visual impairment, was defined as VA<6/18 that
improved to 6/18 with a pinhole. Cataract was defined as visible opacity in the pupil
impairing vision with partial or complete obscuration of red reflex on distant direct ophthalmoscopy.
Operated eyes with cataract surgery were defined as all pseudophakic/aphakic eyes due to
cataract. Cataract surgical coverage (CSC) percentage for persons was calculated as: Number of
persons operated in either eye × 100/Number of persons operated + Number of persons
bilaterally visually impaired by cataract (Pinhole VA<3/60, <6/60 or <6/18). The CSC percentage
for eyes was calculated as follows: Number of operated eyes × 100 /Number of operated eyes
+ Number of operable cataract eyes (Pinhole VA<3/60, <6/60 or <6/18)[
]. The causes of
blindness and visual impairment were classified into 4 groups: curable (cataract, refractive
error, uncorrected aphakia); preventable (surgical complications, trachoma, phthisis, other
corneal scars, onchocerciasis); potentially preventable (diabetic retinopathy, glaucoma); and
other causes (age-related macular degeneration (AMD), posterior segment lesions, central
4 / 13
nervous system defects). The first 2 categories (preventable and curable) were designated as
Visual acuity was measured by a research assistant at the household, using a tumbling ªEº
letter with optotype size 6/18 on one side and 6/60 on the other side at 6 and 3 m. All
measurements were taken in full daylight with available spectacle correction. If the VA with available
correction was <6/18 in either eye, then pinhole vision would be measured following the same
procedure. For assessment of lens status, distant direct ophthalmoscope was used in a shaded
or semi-dark environment without pupillary dilatation. Relative afferent pupillary defect
(RAPD) was checked with a swinging flashlight test and the fundus was examined using a
direct ophthalmoscope by the ophthalmologist in all participants with VA<6/18 in either eye
]. The pupils were dilated with a short-acting 1% tropicamide eye drops to confirm the cause
of visual impairment when the pinhole VA was <6/18. The principal cause of blindness or VI
was recorded by the ophthalmologists. When there were co-existing primary disorders in the
same or different eyes, mark as the principal disorder that which is most readily curable. The
following is a recommended ranking of the disorders with respect to these criteria by RAAB
protocol: refractive error, cataract, uncorrected aphakia, surgery related complications,
preventable corneal opacities and phthisis, glaucoma, and other posterior segment disorders.
A mobile clinic equipped with simple instruments including slit lamp and indirect ophthal
moscope was set up in the same village where the research team conducted the RAAB survey.
Subjects were advised to attend the clinic for further examination if a definitive diagnosis could not be made. Tropicamide 1% eye drops were instilled to check for the posterior segment pathology and to define the cause of visual impairment.
A data entry package, EpiData Entry 3.1(freeware, http://www.epidata.dk), was used for this study, which incorporated range and consistency checks. Data were entered independently by two operators in two separate computers. Consistency checks were performed each afternoon and inconsistencies were adjudicated on the same day.
Prevalence of blindness, SVI and VI were estimated, and the effect of cluster sampling was
taken into account by using the ªproc surveyº commands in SAS statistics software version 9.3
(SAS Institute Inc, Cary, NC) to allow for the cluster sampling approach for calculation of
prevalence, odds ratio (OR) and 95% confidence intervals (CIs)[
]. Age and gender
adjusted prevalence were calculated with reference to the National Population census 2010
data in Chaonan Region. Visual outcome of cataract surgery was reported among all the
pseudophakic or aphakic eyes. Cataract surgery coverage was calculated by eye and person.
Among the 3700 people selected from 74 clusters, 169 (4.6%) could not be reached, 20 (0.5%)
were physically or mentally unable to communicate, and 27 (0.7%) refused to be examined.
Consequently, 3484 persons (response rate 94.2%) with a mean (±standard deviation) age of
64.4±9.8 years were examined. These included 1397 men (40.1%) with an average age of 65.3
±9.6 years and 2087 women (59.9%) with an average age of 63.8±9.8 years. A comparison of
the age and gender distributions between the sampled and total populations is shown in
5 / 13
Prevalence of blindness and visual impairment
As shown in Table 2, the unadjusted prevalence in the better seeing eye of blindness, SVI and
VI in the examined population aged 50 year were 2.4% (95% CI, 1.9%±2.9%), 1.1% (95% CI,
0.7±1.4%), and 7.0% (95% CI, 6.2%±7.8%), respectively. Rates for males were lower than for
females for all three categories of impairment. Age and gender adjusted prevalence was 2.4%
(95% CI, 1.9%± 2.9%), 1.0% (95% CI, 0.7±1.4%), and 6.4% (95% CI, 5.6%± 7.1%), respectively
(Table 2). For persons with PVA (presenting visual acuity)<6/18 in the better eye, the
unadjusted prevalence was 10.5% (95% CI, 9.5±11.5%) and the age and gender adjusted prevalence
was 9.8% (95% CI, 8.8±10.8%), respectively. The prevalence of blindness based on pin-hole
VA decreased to 2.2% (77 people, 95%CI, 1.7±2.7).
Risk factors for blindness and visual impairment
Of 3484 subjects, 134 subjects refused to give us the information about their literacy and
marital status (S1 Table). Consequently, 3350 persons were interviewed for risk factors of blindness
and visual impairment. Gender, literacy and marital status-adjusted logistic regression
analyses (Table 3) revealed that the prevalence of blindness increased significantly, with subjects in
the 80+ year age group carrying 15.6-fold (95% CI, 6.7±36.2) higher odds of blindness than
subjects aged 50 to 59 years. The odds of blindness was lower among those who were literate
(OR, 0.6; 95% CI, 0.4±1.1) with adjusted by other factors. Participants who were widowed or
unmarried had more than twice the odds of blindness compared with the married (OR, 2.4;
95% CI, 1.4±4.0). Similar patterns were observed for SVI, and VI (Table 3).
6 / 13
VI: Visual Impairment, was defined as presenting visual acuity <6/18 and 6/60; SVI: Severe Visual Impairment, defined as presenting visual acuity <6/60
and 3/60; OR: Odds Ratio; CI: Confidence Interval;
+: Adjusted by gender, education and marital status;
*: Adjusted by age, education and marital status;
#: Adjusted by age, gender and marital status;
^: Adjusted by age, gender and education
Causes of blindness and visual impairment
Totally, 11 subjects were advised to attend the clinic for further examination when definitive
diagnosis could not be made at their houses. Table 4 shows the percentages of major causes of
visual loss. Cataract was the leading cause of blindness (67.1%), followed by posterior segment
disorders (11.8%), and then refractive error (7.1%). Overall, cataract was the main cause of any
visual impairment (PVA<6/18) (48.8%), followed by refractive error (33.2%), and then
posterior segment diseases (11.5%). Of all causes of blindness, 83.5% were considered to be
avoidable, of which 75.3% were curable and 8.2% treatable. Similarly, 75.7% of SVI and 88.5% of VI
Outcomes of cataract surgery
In this survey, 155 out of 3484 (4.4%) people (211 eyes) had cataract surgery. Among all the
operated patients, 56 (36.1%) received bilateral surgery. Of the 211 eyes that received cataract
surgery, 96.7% had an intraocular lens (IOL) inserted. Thirty-five (16.6%) eyes had poor
outcome with a PVA of worse than 6/60. The proportion decreased to 13.8% with pin-hole vision.
Causes for post-operative VA <6/18 included surgery complications in 19 eyes (27.5%),
comorbidities in 29 eyes (42.0%), long-term complications (subsequent vision loss due to
postoperative capsule opacification or retinal detachment) in 4 eyes (5.8%), and un-corrected
refractive error in 17 eyes (24.6%). Table 5 compares the outcomes of surgery from different
surgical locations. Cataract operations performed in the charity centers resulted in a higher
rate of IOL insertion, better visual outcomes (VA 6/18) and a lower surgical complication
rate compared with the local clinics.
7 / 13
Cataract surgical coverage
Based on the number of operated eyes, the cataract surgical coverage was 51.1% for pinhole
VA <3/60; 47.5% for pinhole VA<6/60; and 30.9% for pinhole VA<6/18. In terms of cataract
PVA: Presenting visual acuity; VA: Visual impairment; VI: Visual impairment; SVI: Severe visual impairment;
PH: Public Hospitals; CEC: Charity Eye Centers; PC: Private Clinics
surgical coverage by person, the rates increased to 74.9%, 68.9%, and 47.5% for pin-hole VA
<3/60, <6/60 and <6/18 respectively.
The 364 participants with un-operated cataract were interviewed to identify for not having cat
aract surgery. The fact that they did not know their visual impairment was due to cataract was
the main reason (271, 74.5%). Twenty-seven (7.4%) subjects claimed that they did not seek
surgery because of old age. Twenty (5.5%) subjects mentioned that the cost of surgery was not
affordable. A minority of the participants (46, 1.3%) refused to undergo cataract surgery for
other reasons such as fear of surgery, associated medical problems, and so on (S2 Table).
The prevalence of blindness varies in different regions of China, ranging from 0.6% (in
Gaungzhou City) to 4.4% (in Hainan province)[2±5, 16, 22±24]. The reported prevalence of
blindness in Chaonan in 2012(2.4%) was similar to the Nine-Province survey in China (2.3%)
]. The prevalence of blindness in Chaonan (2.4%) was much higher than that in
Guangzhou City (0.6%), the capital of Guangdong Province. This may be primarily related
to lower socioeconomic status, which has been associated with higher prevalence of blindness
], among the sample population. Chaonan's per capita gross domestic product in 2010 was
14,201 RMB (renminbi, Chinese currency unit; approximately USD 2219; 6.4 renminbi = US
$1), which was considerably lower than that of Guangdong Province as a whole (43,596 RMB,
USD6812) and Guangzhou City (83,494 RMB, USD 13045) in the same year. Similar
results were reported in Beijing Eye Study.[
In the current study, the prevalence of blindness was higher in females and those who were
illiterate. These findings were also observed in other regions of China[
] and other countries
] and Sudan[
]. The participants who were widowed or unmarried
were particularly affected by blindness. This might implicate that family support is very
important for patients to seek eye care services. Age was strongly associated with any visual
impairment (PVA<6/18) and the risk increased almost 18 times from age of 50 years to age of
80 years. With the increase in the life expectancy in China due to improved socioeconomic
conditions and better access to health care services, the prevalence of any visual impairment
(PVA<6/18) is likely to increase in the future if no affordable solutions are available.
The large majority (83.5%) of blindness that was detected in this study, was avoidable and
cataract was the leading cause, which was consistent with other studies in China[
4, 5, 22
other developing countries[19, 28, 30±33]. Although more than 60% of China's population lives
in these rural regions, more than 80% of the country's health resources are concentrated in its
]. Strengthening rural cataract services would be the most effective way to reduce
cataract blindness in China. However, most of experienced cataract surgeons in China are
concentrated in the urban public hospitals. The number of qualified cataract surgeons in rural areas
is less than 2 per million population[
]. The lack of sufficient training opportunities for junior
ophthalmologists has adversely limited the manpower for cataract surgery in China. Some rural
ªeye doctorsº without any special training have opened private clinics providing low qualified
cataract surgery. The previous population based studies in Doumen and Shunyi[
documented poor outcomes of cataract surgeries performed in these rural areas of China, with
only 25.0% and 23.7% of the operated eyes having PVA better than 6/18, respectively.
In our study, 46.1% of patients operated in local rural eye clinics had postoperative PVA
that was 6/18 or better, which is similar to that reported in the recent Nine-Province survey in
China (46.5%). But better visual outcomes and less surgical complication rates were
9 / 13
observed among subjects whose cataract surgery was performed in charitable eye centers. The
good surgical outcome (PVA 6/18, 71.7%) is similar to the metropolitan cities with top
medical resources in mainland China. In Beijing[
] and Guangzhou[
], 80% and 62% of
cataractoperated eyes had presenting VA > = 6/18. This may be attributed to the well-established
quality control system and surgical training procedures implemented in the charity centers.
Consultant ophthalmologists from urban centers provided on-site surgical training to local
doctors, and supervised on sutureless large incision manual cataract extraction (SLIMCE)[
]. After 6 months of hands-on training, these local surgeons were able to perform cataract
surgery independently with encouraging outcomes. Recently, experience from Guangdong
] and in Jiangxi[
] have demonstrated that rural trainees were capable of
operating independently and achieved good results after appropriate hands-on training[
the favorable outcomes became recognized by residents in the catchment area, the number of
patients receiving cataract surgery in charity centers steadily increased. In our study, The
prevalence of cataract surgery in Chaonan (4.4%, 95%CI, 3.8%-5.1%) was higher than that reported
in Yangjiang County, a rural county of the Guangdong province(3.07%, 95% CI,
3.70%), overall reported in the China Nine-Province survey (2.09%) and similar to that in
the developed provincial cities including Guangzhou City(4.4%)[
] and Singapore (4.2%)
Currently, the indication for cataract surgery was largely accepted as VA less than 6/18[
]. The cataract surgery coverage was 30.9% for pin-hole VA<6/18. In other words, about
70% of operable cataract did not receive cataract surgery even in this region wherein two
charity eye centers were established and two large public hospitals were within 5-hour driving
distance. Among the barriers to cataract surgery, lack of awareness their VI due to cataract is the
most common reason (74.5%); followed by no perceived need and lack of financial support for
surgery. Grounded on this information, the barriers of cataract surgery in this region might be
improved by an enhanced screening program and public education. Further studies are
needed to identify the most effective measure to promote cataract surgery uptake.
Efficient and effective methods to estimate blindness are vital to policy makers for resource
allocation. One of the strengths of the survey is the high response rate, which is important in
minimizing selection bias. A population-based survey with 94.1% participation highlights the
importance of door-to-door visits, advocacy before the survey and repeated household visits to
seek participation. While the coverage of the sample population was high (94.2%), there was a
slightly lower response rate in younger males (aged 50±59 years), which was similar to most
other population-based surveys[
2, 5, 20, 22
], The younger people who were absent from home
or reluctant to participate might be migrant workers or those with better visual function.
In conclusion, the prevalence of blindness in Chaonan was still high in this region. Cataract
blindness is still and will continue to be a heavy burden for the aging population in China. Our
study showed that there is significant room for improvement in the quality of surgeries
performed in the rural private clinics. The rural cataract surgical services were suboptimal and
should be strengthened. Outcomes of cataract surgery in this survey have demonstrated that
rural trainees are capable of operating independently and achieving good results after
appropriate hands-on training. Appropriate strategies of public awareness programs and patient
education might help to improve uptake of cataract surgery and increase cataract surgical coverage.
S1 Table. The age and gender distribution of 134 participants for refusing to answer
literacy and marital status.
10 / 13
S2 Table. Barriers to uptake of cataract surgery (among subjects with pin-hole VA <6/18
in one or both eyes, with principal cause of as cataract). A participant could make at most
Conceptualization: Dennis Shun-Chiu Lam.
Data curation: Xiujuan Zhang, Chongren Zheng.
Formal analysis: Xiujuan Zhang.
Funding acquisition: Dennis Shun-Chiu Lam.
Investigation: Xiujuan Zhang.
Methodology: Emmy Y. Li, Christopher Kai-Shun Leung, David C. Musch, Xin Tang, Mingguang He, David F. Chang.
Project administration: Chongren Zheng.
Resources: Chongren Zheng, Dennis Shun-Chiu Lam.
Software: Christopher Kai-Shun Leung.
Supervision: Christopher Kai-Shun Leung, Dennis Shun-Chiu Lam.
Validation: Emmy Y. Li, Christopher Kai-Shun Leung, David C. Musch, Xin Tang, Mingguang He, David F. Chang, Dennis Shun-Chiu Lam.
Writing ± original draft: Xiujuan Zhang.
Writing ± review & editing: Emmy Y. Li, Christopher Kai-Shun Leung, David C. Musch, Xin
Tang, Mingguang He.
11 / 13
12 / 13
1. New WHO blindness estimates . http://www.who.int/blindness/en/index.html. Last accessed on 2011 Feb 26 .
2. Liang YB , Friedman DS , Wong TY , Zhan SY , Sun LP , Wang JJ , et al. Prevalence and causes of low vision and blindness in a rural chinese adult population: the Handan Eye Study . Ophthalmology . 2008 ; 115 ( 11 ): 1965 ± 72 . Epub 2008/08/08. https://doi.org/10.1016/j.ophtha. 2008 . 05 .030 PMID: 18684506 .
3. Huang S , Zheng Y , Foster PJ , Huang W , He M. Prevalence and causes of visual impairment in Chinese adults in urban southern China . Arch Ophthalmol . 2009 ; 127 ( 10 ): 1362 ± 7 . Epub 2009/10/14. https://doi. org/10.1001/archophthalmol. 2009 .138 PMID: 19822854 .
4. Xiao B , Kuper H , Guan C , Bailey K , Limburg H . Rapid assessment of avoidable blindness in three counties , Jiangxi Province, China. The British journal of ophthalmology . 2009 ; 94 ( 11 ): 1437 ± 42 . https://doi. org/10.1136/bjo. 2009 .165308 PMID: 20852316 .
5. Wu M , Yip JL , Kuper H . Rapid assessment of avoidable blindness in Kunming, china . Ophthalmology . 2008 ; 115 ( 6 ): 969 ± 74 . https://doi.org/10.1016/j.ophtha. 2007 . 08 .002 PMID: 17953988 .
6. Li S , Xu J , He M , Wu K , Munoz SR , Ellwein LB . A survey of blindness and cataract surgery in Doumen County, China . Ophthalmology. 1999 ; 106 ( 8 ): 1602 ± 8 . Epub 1999/08/12. https://doi.org/10.1016/ S0161- 6420 ( 99 ) 90459 - 1 PMID: 10442910 .
7. Taylor HR . The Global Issue of Vision Loss and What We Can Do About It: Jose Rizal Medal 2015 . Asia-Pacific journal of ophthalmology . 2016 ; 5 ( 2 ): 95 ± 6 . Epub 2016/03/05. https://doi.org/10.1097/APO. 0000000000000188 PMID: 26939111 .
8. Ministry of health of the people's republic of China. China's CSR report in 2009. Annex tables . http:// www.moh.gov.cn/publicfiles///business/cmsresources/mohyzs/cmsrsdocument/doc8347.xls. Accessed Oct 27th , 2009 . [Internet].
9. Dua HS , Said DG , Otri AM . Are we doing too many cataract operations? Cataract surgery: a global perspective . The British journal of ophthalmology . 2009 ; 93 ( 1):1±2 . Epub 2008/12/23. https://doi.org/10. 1136/bjo. 2008 .143685 PMID: 19098039 .
10. Lin Y . Comparative study on preventing avoidable blindness in China and in Nepal . Chin Med J (Engl) . 2007 ; 120 ( 4 ): 280 ± 3 . Epub 2007/03/22. PMID: 17374277 .
11. Lam DS , Li EY , Chang DF , Zhang MZ , Zhan HK , Pang CP . Project vision: a new and sustainable model for eliminating cataract blindness in China . Clin Experiment Ophthalmol . 2009 ; 37 ( 5 ): 427 ± 30 . Epub 2009/07/25. https://doi.org/10.1111/j.1442- 9071 . 2009 . 02084 .x PMID: 19624336 .
12. Lam DS , Congdon NG , Rao SK , Fan H , Liu Y , Zhang L , et al. Visual outcomes and astigmatism after sutureless, manual cataract extraction in rural China: study of cataract outcomes and up-take of services (SCOUTS) in the caring is hip project, report 1 . Arch Ophthalmol . 2007 ; 125 ( 11 ): 1539 ± 44 . Epub 2007/10/24. https://doi.org/10.1001/archopht.125.11.eeb70013 PMID: 17954509 .
13. Liu Y , Congdon NG , Fan H , Zhao X , Choi K , Lam DS . Ocular comorbidities among cataract-operated patients in rural China: the caring is hip Study of Cataract Outcomes and Uptake of Services (SCOUTS) , report No. 3 . Ophthalmology . 2007 ; 114 ( 11 ):e47± 52 . Epub 2007/11/06. https://doi.org/10. 1016/j.ophtha. 2007 . 07 .013 PMID: 17980740 .
14. Kuper H , Polack S , Limburg H . Rapid assessment of avoidable blindness . Community eye health / International Centre for Eye Health . 2006 ; 19 ( 60 ): 68 ± 9 . PMID: 17515970 .
15. The sixth National Population Census, Chaonan Region . In: Bureau CS, editor. Chaonan Region, Guangdong Province2010.
16. Zhao J , Ellwein LB , Cui H , Ge J , Guan H , Lv J , et al. Prevalence of vision impairment in older adults in rural China: the China Nine-Province Survey . Ophthalmology . 2010 ; 117 ( 3 ): 409 ± 16 , 16 e1 . Epub 2010/ 01/19. https://doi.org/10.1016/j.ophtha. 2009 . 11 .023 PMID: 20079923 .
17. Turner AG , Magnani RJ , Shuaib M. A not quite as quick but much cleaner alternative to the Expanded Programme on Immunization (EPI) Cluster Survey design . International journal of epidemiology . 1996 ; 25 ( 1 ): 198 ± 203 . PMID: 8666490 .
18. RAAB instruction manual . Version 4 .02 for Windows ® . http://www.cehjournal.org/files/raab-5.html. Acessed at August 2007 . 2007 .
19. Rajavi Z , Katibeh M , Ziaei H , Fardesmaeilpour N , Sehat M , Ahmadieh H , et al. Rapid assessment of avoidable blindness in Iran . Ophthalmology. 2011 ; 118 ( 9 ): 1812 ± 8 . Epub 2011/05/17. https://doi.org/10. 1016/j.ophtha. 2011 . 01 .049 PMID: 21571371 .
20. Mathenge W , Bastawrous A , Foster A , Kuper H. The Nakuru posterior segment eye disease study: methods and prevalence of blindness and visual impairment in Nakuru, Kenya . Ophthalmology. 2012 ; 119 ( 10 ): 2033 ± 9 . Epub 2012/06/23. https://doi.org/10.1016/j.ophtha. 2012 . 04 .019 PMID: 22721919 .
21. The Big Four: Analyzing Complex Sample Survey Data Using SAS®, SPSS®, STATA®, and SUDAAN ®. Paper presented at: Thirty-First SAS Users Group International conference (SUGI); March 27 , 2006 ; San Francisco, CA. http://www2.sas.com/proceedings/sugi31/ 172 - 31 .pdf. Accessed October 30 , 2008 . [Internet].
22. Li E , Liu Y , Zhang H , Liang Y , Zhang X , Zheng C , et al. Prevalence of Blindness and Outcomes of Cataract Surgery in Hainan Province in South China . Ophthalmology. in pressed.
23. Xu L , Cui T , Yang H , Hu A , Ma K , Zheng Y , et al. Prevalence of visual impairment among adults in China: the Beijing Eye Study . Am J Ophthalmol . 2006 ; 141 ( 3 ): 591 ± 3 . Epub 2006/02/24. https://doi.org/ 10.1016/j.ajo. 2005 . 10 .018 PMID: 16490524 .
24. Li Z , Cui H , Liu P , Zhang L , Yang H . Prevalence and causes of blindness and visual impairment among the elderly in rural southern Harbin, China . Ophthalmic epidemiology. 2008 ; 15 ( 5 ): 334 ± 8 . Epub 2008/ 10/14. https://doi.org/10.1080/09286580802227386 PMID: 18850470 .
25. Kuper H , Polack S , Eusebio C , Mathenge W , Wadud Z , Foster A. A case-control study to assess the relationship between poverty and visual impairment from cataract in Kenya, the Philippines, and Bangladesh . PLoS medicine . 2008 ; 5 ( 12 ): e244 . Epub 2008 /12/19. https://doi.org/10.1371/journal.pmed. 0050244 PMID: 19090614 ;
26. Guangdong Year Book in 2011 [Internet].
27. Xu L , Wang Y , Li Y , Cui T , Li J , Jonas JB . Causes of blindness and visual impairment in urban and rural areas in Beijing: the Beijing Eye Study . Ophthalmology . 2006 ; 113 ( 7 ): 1134 e1± 11 . Epub 2006/05/02. https://doi.org/10.1016/j.ophtha. 2006 . 01 .035 PMID: 16647133 .
28. Dineen B , Bourne RR , Jadoon Z , Shah SP , Khan MA , Foster A , et al. Causes of blindness and visual impairment in Pakistan. The Pakistan national blindness and visual impairment survey . The British journal of ophthalmology . 2007 ; 91 ( 8 ): 1005 ± 10 . Epub 2007/01/19. https://doi.org/10.1136/bjo. 2006 .108035 PMID: 17229806 ;.
29. Ngondi J , Ole-Sempele F , Onsarigo A , Matende I , Baba S , Reacher M , et al. Prevalence and causes of blindness and low vision in southern Sudan . PLoS medicine . 2006 ; 3 ( 12 ): e477 . Epub 2006 /12/21. https://doi.org/10.1371/journal.pmed.0030477 PMID: 17177596 ;
30. Polack S , Yorston D , Lopez-Ramos A , Lepe-Orta S , Baia RM , Alves L , et al. Rapid assessment of avoidable blindness and diabetic retinopathy in Chiapas, Mexico . Ophthalmology. 2012 ; 119 ( 5 ): 1033 ± 40 . https://doi.org/10.1016/j.ophtha. 2011 . 11 .002 PMID: 22342012 .
31. Kandeke L , Mathenge W , Giramahoro C , Undendere FP , Ruhagaze P , Habiyakare C , et al. Rapid Assessment of Avoidable Blindness in Two Northern Provinces of Burundi without Eye Services . Ophthalmic epidemiology . 2012 ; 19 ( 4 ): 211 ±5. https://doi.org/10.3109/09286586. 2012 .690493 PMID: 22775276 .
32. Morchen M , Langdon T , Ormsby GM , Meng N , Seiha D , Piseth K , et al. Prevalence of blindness and cataract surgical outcomes in Takeo Province, Cambodia . Asia Pac J Ophthalmol (Phila) . 2015 ; 4 ( 1 ): 25 ± 31 . Epub 2015/06/13. https://doi.org/10.1097/APO.0000000000000061 PMID: 26068610 .
33. Morchen M , Mao N , Ang C , Bonn TS . Outcome and Monitoring of Cataract Surgical Services at Takeo Province, Cambodia. Asia-Pacific journal of ophthalmology . 2012 ; 1 ( 6 ): 340 ± 4 . Epub 2012/11/01. https://doi.org/10.1097/APO.0b013e3182710eff PMID: 26107726 .
34. He M , Xu J , Li S , Wu K , Munoz SR , Ellwein LB . Visual acuity and quality of life in patients with cataract in Doumen County, China . Ophthalmology. 1999 ; 106 ( 8 ): 1609 ± 15 . Epub 1999/08/12. https://doi.org/ 10.1016/S0161- 6420 ( 99 ) 90460 - 8 PMID: 10442911 .
35. Zhao J , Sui R , Jia L , Fletcher AE , Ellwein LB . Visual acuity and quality of life outcomes in patients with cataract in Shunyi County, China . Am J Ophthalmol . 1998 ; 126 ( 4 ): 515 ± 23 . Epub 1998/10/21. PMID: 9780096 .
36. Zhao J , Ellwein LB , Cui H , Ge J , Guan H , Lv J , et al. Prevalence and outcomes of cataract surgery in rural China the China nine-province survey . Ophthalmology . 2010 ; 117 ( 11 ): 2120 ± 8 . Epub 2010/07/29. https://doi.org/10.1016/j.ophtha. 2010 . 03 .005 PMID: 20663565 .
37. Liu B , Xu L , Wang YX , Jonas JB . Prevalence of cataract surgery and postoperative visual outcome in Greater Beijing: the Beijing Eye Study . Ophthalmology . 2009 ; 116 ( 7 ): 1322 ± 31 . Epub 2009/06/09. https://doi.org/10.1016/j.ophtha. 2009 . 01 .030 PMID: 19500855 .
38. Huang W , Huang G , Wang D , Yin Q , Foster PJ , He M. Outcomes of cataract surgery in urban southern China: the Liwan Eye Study . Invest Ophthalmol Vis Sci . 2011 ; 52 ( 1 ): 16 ± 20 . Epub 2010/08/07. https:// doi.org/10.1167/iovs.10-5382 PMID: 20688728 ;.
39. Huang G , Crooms R , Chen Q , Congdon N , He M. Compliance with follow-up after cataract surgery in rural China . Ophthalmic epidemiology . 2012 ; 19 ( 2 ): 67 ± 73 . Epub 2012/03/28. https://doi.org/10.3109/ 09286586. 2011 .628777 PMID: 22448612 .
40. Yan X , Congdon N , He M . Prevention of Cataract Blindness in Rural China . Asia Pac J Ophthalmol (Phila) . 2012 ; 1 ( 2 ): 69 ± 71 . Epub 2012/03/01. https://doi.org/10.1097/APO.0b013e31824a4383 PMID: 26107125 .
41. Huang W , Ye R , Liu B , Chen Q , Huang G , Liu Y , et al. Visual outcomes of cataract surgery performed by supervised novice surgeons during training in rural China . Clin Experiment Ophthalmol . 2012 . Epub 2012/10/20. https://doi.org/10.1111/ceo.12021 PMID: 23078185 .
42. Lavanya R , Wong TY , Aung T , Tan DT , Saw SM , Tay WT , et al. Prevalence of cataract surgery and post-surgical visual outcomes in an urban Asian population: the Singapore Malay Eye Study . The British journal of ophthalmology . 2009 ; 93 ( 3 ): 299 ± 304 . Epub 2008/10/18. https://doi.org/10.1136/bjo. 2008 . 148650 PMID: 18927226 .
43. Zhang XJ , Liang YB , Liu YP , Jhanji V , Musch DC , Peng Y , et al. Implementation of a free cataract surgery program in rural China: a community-based randomized interventional study . Ophthalmology . 2013 ; 120 ( 2 ): 260 ± 5 . Epub 2012/10/31. https://doi.org/10.1016/j.ophtha. 2012 . 07 .087 PMID: 23107580 .