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Visual Disability, Visual Function, and Myopia among
Rural Chinese Secondary School Children: The Xichang
Pediatric Refractive Error Study (X-PRES)—Report 1
Nathan Congdon,
1,2
Yunfei Wang,
1
Yue Song,
1
Kai Choi,
3
Mingzhi Zhang,
1
Zhongxia Zhou,
1
Zhenling Xie,
1
Liping Li,
4
Xueyu Liu,
4
Abhishek Sharma,
2,5
Bin Wu,
6
and Dennis S. C. Lam
1,2
PURPOSE. To evaluate visual acuity, visual function, and preva-
lence of refractive error among Chinese secondary-school chil-
dren in a cross-sectional school-based study.
M
ETHODS. Uncorrected, presenting, and best corrected visual
acuity, cycloplegic autorefraction with refinement, and self-
reported visual function were assessed in a random, cluster
sample of rural secondary school students in Xichang, China.
R
ESULTS. Among the 1892 subjects (97.3% of the consenting
children, 84.7% of the total sample), mean age was 14.7 ⫾ 0.8
years, 51.2% were female, and 26.4% were wearing glasses.
The proportion of children with uncorrected, presenting, and
corrected visual disability (ⱕ6/12 in the better eye) was 41.2%,
19.3%, and 0.5%, respectively. Myopia ⬍⫺0.5, ⬍⫺2.0, and
⬍⫺6.0 D in both eyes was present in 62.3%, 31.1%, and 1.9%
of the subjects, respectively. Among the children with visual
disability when tested without correction, 98.7% was due to
refractive error, while only 53.8% (414/770) of these children
had appropriate correction. The girls had significantly (P ⬍
0.001) more presenting visual disability and myopia ⬍⫺2.0 D
than did the boys. More myopic refractive error was associated
with worse self-reported visual function (ANOVA trend test,
P ⬍ 0.001).
C
ONCLUSIONS. Visual disability in this population was common,
highly correctable, and frequently uncorrected. The impact of
refractive error on self-reported visual function was significant.
Strategies and studies to understand and remove barriers to
spectacle wear are needed. (Invest Ophthalmol Vis Sci. 2008;
49:2888–2894) DOI:10.1167/iovs.07-1160
U
ncorrected refractive error is the leading cause of visual
disability among school-aged children in the world today,
a fact that has been documented among children of Asian,
1–4
Hispanic,
5
and European descent.
6
Among secondary-school
students in China, 43% to 78% of 15-year-old children suffer
from refractive error, which accounts for over 95% of visual
disability when tested without correction.
3,7,8
Between 60%
and 70% of refractive error was uncorrected by spectacles in
population-based studies in Chile
5
and China,
7
while even in
Australia, one of four children needing glasses did not have
them.
9
The fact that a large number of children are without sight-
improving glasses is particularly concerning in view of recent
studies demonstrating significant improvement in self-reported
visual function associated with spectacle wear among children
with only moderate levels of myopia.
10
The provision of spec
-
tacles is a noninvasive and inexpensive intervention potentially
capable of improving the visual function of a large number of
school-aged children; however, the full impact of this interven-
tion has not been achieved in many populations.
The reasons for not wearing the spectacles are poorly un-
derstood and are likely to differ among populations. Although
lack of access to services may play an important role in many
areas, a recent report from rural Mexico indicates that, among
children provided free spectacles, fewer than one in six were
wearing them at an unannounced follow-up, and fewer than
half had the glasses with them at all.
11
In addition to outright failure to wear the spectacles, the
provision of inaccurate or poorly fitting glasses may add to the
burden of visual disability associated with refractive error in
many populations. Although few reports on the accuracy of
habitually worn spectacles exist in the developing world, a
population-based study in Australia found that fully a third of
children wearing spectacles had no measurable refractive er-
ror.
9
Few if any population-based studies have been conducted
to quantify the impact of prevalent refractive error on self-
reported visual function among school-aged children. The full
visual burden of uncorrected and inadequately corrected re-
fractive error cannot be quantified without adequate measures
of the impact on visual function in at-risk populations.
The Xichang Pediatric Refractive Error Study (X-PRES) is a
school-based evaluation of refractive error prevalence, patterns
of spectacle wear, self-reported visual function, attitudes to-
ward and use of refractive services, and factors determining
refractive error and glasses wear among 1900 children in junior
middle school years 1 and 2 (ages, 13–17 years) in rural China.
Because of compulsory education in this age range, the sample
is probably representative of the population at large. The
current report provides data on (1) the prevalence of refractive
error and visual disability and (2) the association between
refractive error and self-reported visual function.
From the
1
Joint Shantou International Eye Center, Shantou Uni
-
versity and Chinese University of Hong Kong, Shantou, Peoples Repub-
lic of China; the
2
Department of Ophthalmology and Visual Science,
Chinese University of Hong Kong, Hong Kong SAR, Peoples Republic
of China; the
3
Centre for Epidemiology and Biostatistics, Chinese
University of Hong Kong School of Public Health, Hong Kong SAR,
Peoples Republic of China; the
4
Shantou University School of Public
Health, Shantou, Peoples Republic of China;
5
Department of Public
Health, Oxford University, Oxford, United Kingdom; and the
6
Xichang
Eye Center, Xichang, Peoples Republic of China.
Supported by the Li Ka Shing Foundation, the Chinese University
of Hong Kong, and the Joint Shantou International Eye Center.
Submitted for publication September 8, 2007; revised December
10, 2007, and January 3 and 31, and February 27, 2008; accepted May
7, 2008.
Disclosure: N. Congdon, None; Y. Wang, None; Y. Song, None;
K. Choi, None; M. Zhang, None; Z. Zhou, None; Z. Xie, None; L. Li,
None; X. Liu, None; A. Sharma, None; B. Wu, None; D.S.C. Lam,
None
The publication costs of this article were defrayed in part by page
charge payment. This article must therefore be marked “advertise-
ment” in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Corresponding author: Nathan Congdon, Joint Shantou Interna-
tional Eye Center, Dongxia North Road, Shantou, Guangdong, PRC;
ncongdon@cuhk.edu.hk.
Investigative Ophthalmology & Visual Science, July 2008, Vol. 49, No. 7
2888
Copyright © Association for Research in Vision and Ophthalmology
METHODS
Xichang is a rural village located within 2 hours of the town of Shantou
in eastern Guangdong province. Eye services are provided principally
through a free-standing eye clinic run in cooperation between the
government-run village-level medical clinic and the Caring is Hip eye
care program, supported by the Li Kai Shing Foundation. Basic refrac-
tive services and spectacles are available at the eye clinic and also at a
small number of privately run optical shops in Xichang. The popula-
tion of Xichang was 109,673 in 2002.
12
In April to July 2007, we performed a school-based survey on a
cluster-based random sample, selected by class (class size was approx-
imately 60 students) among children in junior middle school years 1
and 2 at all three middle schools in Xichang. Compulsory education in
China extends through the age of 16 years (third year of junior middle
school), and so the sample is likely representative of the population in
this age-range. The purpose of the survey was to determine the prev-
alence and predictors of visual disability, refractive error, spectacle
wear, and uptake of refractive services among Chinese rural-dwelling
children. The protocol was approved by the Ethics Committee at the
Joint Shantou International Eye Center in Shantou, the parent hospital
for the Xichang Eye Clinic. Informed consent was obtained from one or
more parents of all participating children, and the Declaration of
Helsinki was adhered to throughout.
Participants
The parents of all children in randomly selected junior middle school
year 1 and 2 classes at the three middle schools in Xichang Village were
sent letters of invitation explaining the purpose and methods of the
study. The parents were asked to check a box indicating whether they
were willing for their child to participate in the study, and to return the
form to school with the child. There were 2235 children in the sample.
Among 2197 (98.2%) returned forms, permission was granted for 1945
children (88.5% of returned forms, 87.0% of the sample), and 1892 of
these (97.3% of children with consenting parents, 84.7% of the sample)
were examined (Fig. 1).
Assessment of Vision
Teachers observed vision measurement and then performed measure-
ments with monitoring by study ophthalmologists in a total of 10
subjects of the same age range as those participating in the study.
Teachers then performed vision screening for all children in their class
(approximately 60 subjects), unobserved by study personnel. All teach-
ers gave written informed consent and answered a brief questionnaire
regarding their age, sex, teaching history, glasses wear, and beliefs
about the importance and impact of glasses wear on children’s school
performance.
All subjects then underwent assessment of vision a second time in
a separate room by study personnel, all of whom were trained vision
professionals (optometrists and ophthalmologists). Data included in
the current report are based solely on measurements by study per-
sonnel.
Both teachers and study personnel measured uncorrected visual
acuity and visual acuity in the children who were wearing habitual
refraction if available, in well-lighted areas during daylight hours, at a
FIGURE 1. Flowchart detailing re-
cruitment and examination of sub-
jects for the Xichang Pediatric Re-
fractive Error Study (X-PRES).
IOVS, July 2008, Vol. 49, No. 7 Visual Function and Myopia in Rural Chinese Children 2889
distance of 6 m, separately for each eye of each child. Children who did
not have their spectacles at school were asked to bring them for vision
assessment on a separate day. Identical illuminated Snellen tumbling E
vision chart (Shantou City Medical Equipment Ltd., Shantou, China)
were used for all testing. The nontested eye was covered by the subject
with a handheld occluder, with proper occlusion and neutral head
position monitored by the examiner. The right eye was tested first. A
single optotype of each size was presented first, starting at 6/30. If the
child failed to read a letter, testing began two lines above, with the
child being asked to read all optotypes on the line sequentially. A
subject had to identify correctly more than half of the letters on a given
line (e.g., three of five) to be considered to have achieved that level of
acuity.
Basic Questionnaire
All study subjects (n ⫽ 1892; Fig. 1) were administered a basic ques-
tionnaire by study personnel before being told the results of their
vision assessments. The basic questionnaire included questions on age,
sex, parental education, history of glasses wear, reasons for not wear-
ing the glasses, and time spent in a variety of near-work activities
including reading, video games, and computer use and in outdoor
activities.
The basic questionnaire included a Chinese translation of an instru-
ment developed originally by Fletcher et al.,
13
to assess self-reported
visual function (VF) in rural Asia. All questions were administered in
mandarin or the local dialect (Chaoshanhua) by one of six native
speakers after a period of training and standardization. This instrument
has been validated for use in Chinese,
14,15
and is described elsewhere
in detail.
13
Briefly, the VF questionnaire assesses overall vision, visual percep-
tion, limitation in daily activities, peripheral vision, near vision, sensory
adaptation, light–dark adaptation, visual search, color discrimination,
glare disability, and depth perception. The questionnaire could be
administered in 5 to 10 minutes. Each of 13 responses was scored from
one (no problems) through four (maximum problems), with scales in
each of the areas calibrated between 100 (the best possible score) and
0 (the worst score). The overall VF scale score was calculated by
averaging the scores for the different areas, thus giving a summary
score of 0 to 100.
13
Although the questionnaire was originally devel
-
oped for use in adults, none of the questions describe adult-specific
situations or activities. Thus, the questionnaire was not modified from
its original format for use in children, nor were any questions omitted.
Detailed Examination
All subjects with uncorrected vision of 6/12 or worse in either eye, and
a 25% random sample of subjects with vision of ⬎6/12 in both eyes
(n ⫽ 1233, Fig. 1), underwent a detailed examination consisting of the
following elements:
Cycloplegia with cyclopentolate 1% and tropicamide 1%: one drop
of each every 5 minutes for a total of three drops of each medica-
tion, followed by autorefraction (model RK-F1 Refractometer/Ker-
atometer; Canon, Inc., Tochigi, Japan) with refinement in each eye
by an ophthalmologist.
Slitlamp (YZ5F1; Suzhou Liuliu, Suzhou, China) examination of the
anterior and poster segment by an ophthalmologist.
Measurement of intraocular pressure, corneal hysteresis, and cor-
neal resistance factor (Ocular Response Analyzer; Reichert Instru-
ments, Depew, NY).
Measurement by ultrasound A-scan (ODM 2200; Tianjin Maida Med-
ical Technology Co., Ltd., Tianjin, China) of axial length, anterior
chamber depth, and lens thickness.
Ultrasound measurement of central corneal thickness (IOP
AC
Ad
-
vanced; Heidelberg Engineering and Starfish, Victoria, British Co-
lumbia, Canada).
Referral for Spectacles and Detailed Questionnaire
Recommendation was made for new spectacles for the following
children:
All subjects with presenting VA ⱕ6/12 in either eye (with or
without spectacles), and whose vision could be improved by two
or more lines in either eye with refraction.
Children with spectacles improving the vision to ⬎6/12, but whose
vision could be improved by ⱖ2 lines with refraction.
All such children (n ⫽ 674, Fig. 1), received a card with a map
depicting the location of the Xichang eye clinic, their refraction and a
message indicating that glasses were recommended. The parents of
these children received a telephone call from the child’s teacher
explaining the need to obtain new or corrected spectacles and the
potential benefit in classroom performance. These children and their
teachers also were given a brief lecture in Mandarin on refractive error
and the benefit of spectacles.
Statistical Methods
Raw data were presented as mean (SD) or frequency (%), as appropri-
ate. Average presenting vision of the two eyes (minimum angle of
resolution, MAR) was minus log-transformed to correct its skewness
before statistical analyses, though the untransformed numbers are
presented in tables for the sake of clarity.
The data for astigmatism, hyperopia, and myopia prevalence (with
cutoffs of ⫺0.5 and ⫺2.0 D) include estimates for refractive error
prevalence among unrefracted children with vision ⬎6/12 in both
eyes. These estimates were based on the 248 children with normal
vision who were randomly chosen for full examination and refraction,
who had a range of refractions from ⫺2.25 to ⫹5.0 D (mean between
the two eyes). Among children with normal vision, only one had
refractive error ⬎⫹2.0 in both eyes, two had myopia ⬍⫺2.0 D in both
eyes, and none had ⬍⫺6.0 D in both eyes. The 95% confidence interval
for the prevalence was estimated using the Clopper-Pearson method.
16
All univariate comparisons were made using the t-test, Pearson
2
test or the Fisher exact test. The ANOVA trend test was used to assess
the linear trend of visual function score across the different spherical
equivalent groups. Multiple comparisons on visual function scores
between the reference spherical equivalent group (SE ⱖ ⫺0.5) and
each of the other groups were analyzed with the Dunnett test. Univar-
iate analyses of the association between visual function and its poten-
tial predictors were assessed with the bivariate correlation coefficient
or t-test. Multivariate analysis was performed with multiple regression.
All statistical analyses were performed with commercial software (SPSS
14.0; SPSS Inc., Chicago, IL). All statistical tests were two sided, and
P ⬍ 0.05 was considered statistically significant.
RESULTS
The mean age of the 1892 children examined was 14.7 ⫾ 0.8
years (range, 11.4 – 17.1 years), 969 (51.2%) were female, and
26.4% were wearing glasses at the time of examination. Less
than a third of the children indicated that their more-educated
parent had completed high school. The girls were significantly
more likely to have failed vision screening (uncorrected vision
in either eye ⱕ6/12) than were the boys (P ⬍ 0.001). The
mean self-reported visual function of children failing screening
(67.8 ⫾ 15.9) was significantly worse than for children with
normal vision (84.7 ⫾ 11.3, P ⬍ 0.001; Table 1).
Among the 1892 children examined, 780 (41.2%) had un-
corrected vision ⱕ6/12 in the better-seeing eye. The number
was 365 (19.3%) for presenting vision ⱕ6/12 in the better-
seeing eye (our study definition of visual disability), which was
measured with glasses if available. Only 10 children (0.5%) had
best-corrected vision ⱕ6/12 in the better-seeing eye. The girls
2890 Congdon et al. IOVS, July 2008, Vol. 49, No. 7
had significantly worse uncorrected, presenting, and best-cor-
rected vision than did the boys (Table 2).
A large majority (98.7%, 770/780) of bilateral uncorrected
vision ⱕ6/12 was due to refractive error and was correctable
(Table 2). However, only 53.8% (414/770) of these children
with uncorrected vision ⱕ6/12 due to refractive error had
appropriate correction (data not shown). Causes of uncorrect-
able bilateral vision ⱕ6/12 in this population included ambly-
opia (n ⫽ 6), hypoplastic optic nerve (n ⫽ 2), myopic retinop-
athy (n ⫽ 1), and cataract (n ⫽ 1).
When cutoffs of ⬍⫺0.5, ⬍⫺2.0, and ⬍⫺6.0 D in both
eyes were used to define myopia prevalence among the 1892
examined children, the figures were 62.3% (1178/1892), 31.1%
(588/1892), and 1.9% (35/1892), respectively. Astigmatism of
⬎⫹0.75 D in both eyes was present in 1.7% (33/1892) of the
subjects, and hyperopia ⱖ ⫹2.0 D was even more uncommon
(Table 2). The girls had significantly more myopia ⬍⫺2 D and
more astigmatism than did the boys (Table 2).
Among the 1233 children undergoing refraction, a more
myopic refractive error was significantly associated with worse
TABLE 1. Basic Demographic, Glasses Wear, and Visual Function Characteristics of 1892 Middle School Children in Rural China who Passed or
Failed Initial Vision Screening
All (n ⴝ 1892)
Failed Screening (Uncorrected VA
<6/12 in Either Eye; n ⴝ 985)
Passed Screening (Uncorrected VA
>6/12 in Both Eyes; n ⴝ 907) P
Age (y)* 14.7 (0.8) 14.7 (0.8) 14.7 (0.8) 0.252
Sex
Male 923 (48.8%) 401 (40.7%) 522 (57.6%) ⬍0.001
Female 969 (51.2%) 584 (59.3%) 385 (42.4%)
Wearing glasses
No 1392 (73.6%) 494 (50.2%) 898 (99.0%) ⬍0.001
Yes 500 (26.4%) 491 (49.8%) 9 (1.0%)
Parent’s education
Primary or below 413 (21.8%) 226 (22.9%) 187 (20.6%) 0.542
Junior school 880 (46.5%) 444 (45.1%) 436 (48.1%)
High school 576 (30.4%) 303 (30.8%) 273 (30.1%)
College or above 23 (1.2%) 12 (1.2%) 11 (1.2%)
Visual function score* 75.8 (16.3) 67.8 (15.9) 84.7 (11.3) ⬍0.001
* Mean (SD); all the others are n (%).
TABLE 2. Visual and Refractive Information on 1892 Middle School Children in Rural China
All (n ⴝ 1892)* Boys (n ⴝ 923) Girls (n ⴝ 969)* P†
Uncorrected vision in the better eye
ⱕ6/60 26 (1.4%) 11 (1.2%) 15 (1.5%) ⬍0.001
⬎6/60–ⱕ6/12 754 (39.9%) 302 (32.7%) 452 (46.6%)
⬎6/12–⬍1.0 275 (14.5%) 142 (15.4%) 133 (13.7%)
ⱖ1.0 837 (44.2%) 468 (50.7%) 369 (38.1%)
Presenting vision in the better eye
ⱕ6/60 1 (0.1%) 0 1 (0.1%) 0.020
⬎6/60–ⱕ6/12 364 (19.2%) 169 (18.3%) 195 (20.1%)
⬎6/12–⬍1.0 419 (22.1%) 184 (19.9%) 235 (24.3%)
ⱖ1.0 1108 (58.6%) 570 (61.8%) 538 (55.5%)
Best corrected vision in the better eye
ⱕ6/60 0 0 0 0.928
⬎6/60–ⱕ6/12 10 (0.5%) 5 (0.5%) 5 (0.5%)
⬎6/12–⬍1.0 119 (6.3%) 56 (6.1%) 63 (6.5%)
ⱖ1.0 1763 (93.2%) 862 (93.4%) 901 (93.0%)
Myopia
⬍⫺0.5 D in both eyes 1178 (62.3%)‡ 535 (58.0%)‡ 643 (66.4%)‡ ⬍0.001
Prevalence (95% CI) 62.3% (60.1%–64.5%) 58.0% (54.7%–61.2%) 66.4% (63.4%–69.4%)
Myopia
⬍⫺2.0 D in both eyes 588 (31.1%)‡ 239 (25.9%)‡ 349 (36.1%)‡ ⬍0.001
Prevalence (95% CI) 31.1% (29.0%–33.2%) 25.9% (23.1%–28.9%) 36.1% (33.0%–39.2%)
Myopia
⬍⫺6.0 D in both eyes 35 (1.9%)‡ 17 (1.8%)‡ 18 (1.9%)‡ 0.977
Prevalence (95% CI) 1.9% (1.3%–2.6%) 1.8% (1.1%–2.9%) 1.9% (1.1%–2.9%)
Astigmatism
⬎⫹0.75 D in both eyes 33 (1.7%) 9 (1.0%)‡ 23 (2.4%)‡ 0.018
Prevalence (95% CI) 1.7% (1.2%–2.4%) 1.0% (0.4%–1.8%) 2.4% (1.5%–3.5%)
Hyperopia
ⱖ ⫹2.0 D in both eyes 4 (0.2%)‡ 1 (0.1%)‡ 3 (0.3%)‡ 0.340
Prevalence (95% CI) 0.2% (0.06%–0.5%) 0.1% (0.0%–0.6%) 0.3% (0.06%–0.9%)
* One subject with visual disability (uncorrected VA ⱕ0.5 in either eye) was missing data for spherical equivalent refraction.
† Probability for comparison between boys and girls.
‡ The numbers and percentages were estimated using projections from the 248 children with normal vision that were randomly chosen for
full examination, in addition to the data for children with visual disability. Among the 248 normal children, 1 had refractive error ⬎⫹2D in both
eyes, 2 had ⬍⫺2D in both eyes, and none had ⬍⫺6 D in both eyes.
IOVS, July 2008, Vol. 49, No. 7 Visual Function and Myopia in Rural Chinese Children 2891
self-reported visual function (ANOVA test for trend, P ⬍ 0.001;
Table 3). Children with refractive error ⱖ ⫺0.5D(n ⫽ 185)
had a mean self-reported visual function of 82.6 ⫾ 13.9, which
declined monotonically to 57.6 ⫾ 15.5 for children with my-
opia ⬍⫺5.5D (n ⫽ 59; Table 3). Spherical equivalent was
more strongly associated with visual function than was pre-
senting vision (average between the two eyes) in multivariate
models (Table 4).
DISCUSSION
Visual disability in this rural Chinese middle school population
was common, highly correctable, and frequently uncorrected.
Nearly one in five children had presenting vision of ⱕ6/12 in
both eyes, whereas ⬎98% of visual disability as measured
without correction in this cohort could be further improved
with spectacles. However, due to a combination of spectacle
nonownership, nonwear, and inaccurate prescriptions, only
slightly more than half of children whose vision could be
corrected bilaterally to better than 6/12 with refraction actually
wore glasses that could improve their vision to this level, even
after repeated examinations were performed to accommodate
children who had not brought their glasses to school. Given
the likely lower rates of glasses wear under actual day-to-day
conditions, the proportion of children regularly benefiting
from spectacle correction is probably even lower. These re-
sults are consistent with other reports of low rate of spectacle
ownership and wear in rural China
7
and of low utilization in
other regions of spectacles made available through free distri-
bution programs aimed at school-aged children.
11
Of note, a
relatively high rate of spectacle wear among children with
refractive error (74%) has been reported for urban China.
17
Presenting vision of ⱕ6/12 in both eyes (visual disability)
was observed in ⬎19% of children in this cohort. The defini-
tion of presenting visual disability used in the present report
was identical with that in a series of population-based studies
of refractive error, the Refractive Error Study in Children
(RESC).
18
Direct comparison of data is difficult because of
different age compositions of the samples and the higher prev-
alence of myopia among older children. Nonetheless, the prev-
alence of presenting visual disability in the current report is
higher than that for any of the RESC samples, with the next-
highest figure of 16.6% being for the RESC study from rural
China.
7
Based on the results of the present study, it appears
that a high prevalence of myopia and relatively low rates of
spectacle wear to a large extent explain the heavy burden of
visual disability present among rural Chinese secondary school
children.
It has recently been estimated that when uncorrected re-
fractive error is included as a cause of visual disability, the
TABLE 3. Association between Average Spherical Equivalent and Visual Function Score among 1233 Chinese Middle School Children
Undergoing Cycloplegic Autorefraction with Subjective Refinement by an Ophthalmologist
n (%) VF Mean (SD) P (Trend)* P (Dunnett)†
Average Spherical Equivalent of the Two Eyes (D) ⬍0.001
ⱖ ⫺0.5‡ 185 (15.0%) 82.6 (13.9)
ⱖ ⫺1.5 to ⬍⫺0.5 224 (18.2%) 78.5 (11.7) 0.022
ⱖ ⫺2.5 to ⬍⫺1.5 290 (23.5%) 71.7 (15.1) ⬍0.001
ⱖ ⫺3.5 to ⬍⫺2.5 246 (20.0%) 66.4 (14.5) ⬍0.001
ⱖ ⫺4.5 to ⬍⫺3.5 142 (11.5%) 62.9 (15.2) ⬍0.001
ⱖ ⫺5.5 to ⬍⫺4.5 86 (7.0%) 58.1 (18.0) ⬍0.001
⬍⫺5.5 59 (4.8%) 57.6 (15.5) ⬍0.001
All 1232§ 75.8 (16.3)
* One way ANOVA trend test on visual function across the seven spherical equivalent groups.
† Dunnett test adjusts for multiple comparisons between the reference group (ⱖ ⫺0.5) and each of the other groups.
‡ Reference group for comparisons.
§ One subject missing data for spherical equivalent.
TABLE 4. Potential Predictors of Self-Reported Visual Function among 1233 Chinese Middle School Children Undergoing Cycloplegic
Autorefraction with Subjective Refinement by an Ophthalmologist
Independent Variables
Univariate Analysis Multivariate Analysis
Correlation*/
Mean (SD)† P

Standard
Error P
Sex
Male‡ 71.3 (16.2)
Female 70.5 (16.7) 0.407 ⫺0.071 0.848 0.933
Age ⫺0.02 0.555 0.077 0.520 0.882
Parental education (Highest level attended)
Primary or below‡ 68.1 (16.1)
Junior school 71.4 (16.2) 0.006 3.511 1.087 0.001
High school 72.2 (17.1) 0.002 3.788 1.160 0.001
College or above 68.5 (13.1) 0.911 4.204 3.913 0.283
Average presenting vision§ ⫺0.19 ⬍0.001 ⫺1.945 1.889 0.303
Average spherical equivalent 0.46 ⬍0.001 3.763 0.234 ⬍0.001
* Pearson’s correlation coefficient between visual function and continuous variables (age, presenting vision, spherical equivalent).
† Mean (SD) of visual function for each level of categorical variables (sex, parental education).
‡ Reference group for analyses involving categorical variables.
§ Log of the minimum angle of resolution (logMAR).
2892 Congdon et al. IOVS, July 2008, Vol. 49, No. 7
estimated number of persons worldwide with visual impair-
ment is increased by 61%.
19
Although such data have led to a
renewed appreciation of uncorrected refractive error as a
cause of disability, the impact of refractive error on self-re-
ported visual function has not, to the best of our knowledge,
been described for a school-aged population. In this cohort of
middle school children, myopia was significantly and mono-
tonically associated with worse self-reported visual function
(Table 3). Myopic refractive error was more strongly associated
with self-reported visual function than was presenting vision.
This finding may suggest that myopia is associated with visual
disabilities not completely captured by Snellen acuity measure-
ments, potentially including micropsia and deficits of periph-
eral vision among children wearing spectacle correction.
To place these results into perspective, the difference in
self-reported visual function between children with the least
amount of refractive error (ⱖ ⫺0.5 D) and those with 0.5 to
1.5 D of myopia was 4.1 points, which exceeded the 3.2-point
benefit accruing from second-eye cataract surgery, as measured
using the identical instrument among adults in the same re-
gion.
20
The decrement in visual function reported by children
with ⱖ ⫺3.5 to ⬍⫺2.5 D of myopia compared with those
with refractive error ⱖ ⫺0.5 D was 16.2 points, which exceeds
the difference in self-reported visual function between persons
with postoperative vision above and below 6/60 in the surgical
eye in the above-cited study. This very significant impact of
refractive error on self-reported visual function is consistent
with our recent report of significant improvement in visual
function with provision of spectacles among school-aged chil-
dren having modest levels of refractive error in rural Mexico.
10
More than 60% of these teen-aged rural Chinese children
had myopia (spherical equivalent ⬍⫺0.5 D in both eyes),
whereas more significant near-sightedness (⬍⫺2.00 D in both
eyes) was present in nearly a third. The reported prevalence of
myopia in Chinese children is among the highest in the
world.
2–4,7,8
Population-based studies of school-aged children
in Asia have generally reported a higher prevalence of myopia
among urban groups
2,8
as opposed to rural-dwellers.
1,7
Our
finding of a high prevalence of refractive error in this rural
Chinese population is nonetheless consistent with the report
of He at al.,
7
who found myopia (spherical equivalent ⱕ ⫺0.5
D in either eye) in 33% of Chinese 13- to 17-year-olds at rural
schools in Yangxi County, Guangdong. That myopia and asso-
ciated poor vision should be so common among rural Chinese
school-children is of particular importance to public health
policy-makers: access to vision care and health services gener-
ally is an increasingly recognized problem for Chinese rural-
dwellers.
21
Our finding of a higher prevalence of visual disability and
refractive error among girls as opposed to boys in this popu-
lation is consistent with results reported for rural China by He
et al.,
7
where girls had a myopia prevalence of 51% versus 34%
for boys. A similar preponderance of myopia among school-age
girls versus boys has been reported for populations in urban
China,
17
rural India,
1
and Malaysia.
22
However, population
studies using a protocol identical with that used in some of the
articles just described
17,22
failed to report a tendency toward
higher myopia prevalence among school-aged girls in South
Africa,
23
urban India (where girls were actually more hyper
-
opic),
24
Chile,
25
or Nepal (again, with a tendency toward more
hyperopia in girls).
26
Given these variable results, it may be
that the sex distribution of myopia among school-aged children
in different societies reflects a complex of behavioral and
biological factors. However, the tendency toward higher my-
opia prevalence among girls in China appears to be consistent
across studies involving rural and urban populations.
7,18
The limitations of the X-PRES study must be acknowledged.
Although we were able to examine a large proportion of the
children of consenting parents (1892/1945 ⫽ 97%), consent
could not be obtained for 290 potential subjects. We were not
able to obtain demographic information on these children
without parental consent; though approximately 85% of sub-
jects in our sample were examined, we cannot exclude the
possibility that those children for whom we could not obtain
parental consent differed in important ways from examined
children.
Although our results are in many ways similar to those from
another published study of myopia prevalence among school-
aged children in rural China,
7
application of our results to the
population of rural China as a whole may only be made out
with caution. Our sample was school based, rather than pop-
ulation based. There is some evidence to suggest that children
engaged in larger amounts of near work may be at greater risk
for myopia.
27
If so, our sample may overrepresent the preva
-
lence of myopia in the population as a whole. However, school
attendance is compulsory for children in the age range in-
cluded in our study, and secondary school enrollment rates of
greater than 91% have been reported for nearby areas of rural
Guangdong.
28
Thus, our sample is likely to be fairly represen
-
tative of the population as a whole.
Finally, estimates of myopia prevalence at the ⬍⫺0.5-D
level for this population depended on projections among chil-
dren with vision ⬎6/12 in both eyes based on 248 children
with normal vision (a 25% random sample) who underwent
refraction. The confidence interval around this statistic is thus
wider than it would otherwise be if all subjects had been
refracted.
Nonetheless, the X-PRES study is the first of which we are
aware to report the population impact of refractive error on
self-reported visual function among school-aged children. This
study documents significant visual disability associated with
refractive error in this rural Chinese population, a result with
potential significance for vision program planners because of
the very large number of children affected. Subsequent reports
from X-PRES will discuss determinants of spectacle wear in this
population and will outline and describe the impact of inter-
ventions to increase uptake of refractive services.
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