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Study on the refractive errors of school going children of Pokhara city in Nepal

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Refractive errors are the one of the most common visual disorders found worldwide in school going children and also it is one of the causes of blindness. It can easily be prevented, if timely proper measures are taken. In Kathmandu valley and Mechi Zone of Nepal, the distribution of refractive errors was found to be very high. No records are available from the Western part of Nepal. Considering the importance of the refractive errors the present study had been undertaken in Pokhara city. 964 subjects (474 boys, 490 girls) were selected between age groups 10 to 19 years from 6 schools representing different region of Pokhara. After Preliminary examination: on acuity of vision with Snellen's and Jaeger's charts, the subjects were referred to the Manipal Teaching Hospital, Pokhara for confirmation of the refractive errors. Sixty two schools children (6.43%), out of 964 had refractive errors. The myopia was found to be most common (4.05%). The refractive errors were found more in Private school children (9.29%) than Government school children (4.23%), which is statistically significant (P < 0.05). More boys (7.59%) were found to have suffered from refractive errors than girls (5.31%). Further, children with vegetarian diet (10.52%) had greater number of refractive errors than non-vegetarian diet children (6.17%). In the present study, percentage distribution of myopia was found to be higher (4.05%) than the hyperopia (1.24%) and astigmatism (1.14%). Interestingly, in the present study the refractive errors were found significantly higher in Private schools children than Government schools because the children who read in Private schools have higher socioeconomic status; spend more time in home work, watching Television and Computer as compared to government schools children. These near activities of the eyes causes stress on eyes of the children and might be one of the causes of developing myopia.
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67
Kathmandu University Medical Journal (2009), Vol. 7, No. 1, Issue 25, 67-72
Original Article
Correspondence
Mr. Dilli Ram Niroula
Lecturer
Nobel Medical College & Teaching Hospital
Biratnagar- 2, Nepal
E-mail: dilliram_manipal@hotmail.com
Study on the refractive errors of school going children of Pokhara city
in Nepal
Niroula DR1, Saha CG2
1Lecturer, Nobel Medical College & Teaching Hospital, Biratnagar, Nepal, 2Professor and Head, Department of
Physiology, Manipal College of Medical Sciences, Pokhara, Nepal
Abstract
Objectives: Refractive errors are the one of the most common visual disorders found worldwide in school going
children and it is also one of the causes of blindness. It can easily be prevented, if timely proper measures are taken. In
Kathmandu valley and Mechi Zone of Nepal, the distribution of refractive errors was found to be very high. No records
are available from the Western part of Nepal. Considering the importance of the refractive errors the present study had
been undertaken in Pokhara city.
Materials and methods: Nine hundred and sixty four subjects (474 boys, 490 girls) were selected between age groups
10 to 19 years from six schools representing different region of Pokhara. After Preliminary examination: on acuity of
vision with Snellen’s and Jaeger’s charts, the subjects were referred to the Manipal Teaching Hospital, Pokhara for
con rmation of the refractive errors.
Results: Sixty two schools children (6.43%), out of 964 had refractive errors. Myopia was found to be most common
(4.05%). The refractive errors were found more in Private school children (9.29%) than Government school children
(4.23%), which is statistically signi cant (P < 0.05). More boys (7.59%) were found to have suffered from refractive
errors than girls (5.31%). Further, children with vegetarian diet (10.52%) had greater number of refractive errors than
non-vegetarian diet children (6.17%).
Conclusion: In the present study, percentage distribution of myopia was found to be higher (4.05%) than the hyperopia
(1.24%) and astigmatism (1.14%). Interestingly, in the present study the refractive errors were found signi cantly higher
in Private schools children than Government schools because the children who read in Private schools have higher
socioeconomic status; spend more time in home work, watching Television and Computer as compared to government
schools children. These near activities of the eyes causes stress on eyes of the children and might be one of the causes
of developing myopia.
Key words: Refractive errors, Nepal, Myopia, Hyperopia
Visual impairment is one of the important health
hazards among the school going children1.
Visual disorders are caused by various physiological,
environmental and pathological conditions, and have
been reported to be associated with higher rate of
morbidity and mortality; in particular, uncorrected
refractive errors increase morbidity2.
The prevalence of refractive errors of the children
varies worldwide. Refractive errors are one of the most
common visual impairment in the world3. The worldwide
study of distribution of refractive errors showed that
800 millions to 2.3 billions people have suffered from
refractive errors4. Blindness due to refractive errors
in any population, suggests that eye care services in
that population are inadequate. Since the treatment of
refractive errors is perhaps the simplest and effective
forms of eye care, it can easily be prevented.
Nepal is a developing country and many people are
living under poverty line. One of the most common eye
disorders of school going children in Nepal is refractive
errors. Many of them are not aware of the eye problems
and some of them even do not go for the treatment until
vision is badly affected5.
There is no nationwide research about the refractive
errors in Nepal. Some surveys were done in Kathmandu
valley6,7 and some in Eastern part at Mechi Zone8. So
far no studies on refractive errors have been done in
Pokhara city, and Western part of Nepal. Considering
68
the importance of refractive errors, the present survey
had been undertaken in Pokhara city.
Material and methods
In the present study, six secondary schools were selected
randomly out of 130 schools keeping in mind that all
areas of Pokhara city are represented. The total number
of schools children were 964 (474 boys and 490 girls)
from grade six to grade ten with age between 10 to 19
years. Among 24,819 numbers of school children in
Pokhara9; 1000 school children were randomly selected
for Primary examination. But 36 school children
were excluded due to incomplete examination. The
study had been done from March to June 2006. The
Preliminary examination of school children was done
at the respective schools. During Primary selection, all
subjects were interviewed thoroughly to know their
medical history, food habit, economic status etc. Before
the examination, the purpose of the study was explained
to all the subjects and consent was obtained from the
proper authority.
The visual acuity was tested by Snellen’s chart for
far vision keeping it at six meters distance from the
subjects, and near vision was tested with the help of
Jaeger’s chart keeping the distance of 25-30cm from
the eyes of the subjects. Other ocular problems were
also tested with the help of Torch Light, Ishihara chart
etc. The refractive errors were screened; in the schools,
by using Pin-hole method. The subjects who had visual
acuity equal or less than 6/12 were referred to Manipal
Teaching Hospital, Pokhara for further con rmatory
examinations. The following examinations were
done in Ophthalmology Department: Retinoscopy
with Dry and Cycloplegic refraction (Cyclopentolate,
1%), Ophthalmoscopy and Slit lamp Biomicroscopy.
The refractive errors were con rmed with the help of
above examinations. Data was analyzed by using SPSS
(Statistical Package for Social Science).
The types of refractive errors were separated by
following criteria: if refractive error was recorded as “–
0.5 dioptre” or more spherical power, it was considered
as myopia; if refractive error was recorded “+0.5
dioptre” or more spherical power, it was considered as
hyperopia (hypermetropia) and if refractive error was
found “+ 0.5 dioptre” or more cylindrical power, it was
considered as astigmatism.
Results
The age of the subjects ranged from 10 years to 19 years
with mean age 14.09 +1.65 years. Among 964 school
children 474 (49.2%) were boys and 490 (50.8%) were
girls from grade six to grade ten.
All the results of the refractive errors observed are
summarized in the tables- 1,2,3 and  gures-1, 2.
In table 1 the refractive errors are presented in both
sexes. The prevalence of all the varieties of refractive
errors was found more in male than female. However,
among them myopia seems to be more than hyperopia
and astigmatism, but the differences were not statistically
signi cant. In both the sexes’ the percentage distribution
of myopia was more than other groups.
Table 2 shows the distribution of refractive errors,
(all the refractive errors combined) in different age
groups from age 10 to 19 years. Very little difference
of refractive errors could be observed between different
age groups except in the age group of 16 years, where
it was slightly more (8.33%). In the age groups 10,
18 & 19, the numbers of subjects were very little, so
the results are inconclusive. However, the percentage
distributions of refractive errors were slightly more in
16 and 17 years.
The prevalence of the refractive errors in private
schools was found to be higher (9.29%) as compared to
the government schools (4.23%), which is statistically
signi cant (P< 0.05).
Figure 1 represents the percentage distribution of
various types of refractive errors between government
and private schools children. When compared among
different varieties of refractive errors between private &
government schools, myopia was found to be the most
and astigmatism the least.
The refractive errors among different ethnic groups are
presented in Table 3. The numbers of the subjects are
not equal in all the groups, and the numbers were very
low in Newar, Darji, Tamang & Thakali respectively
(47, 33, 20 and 45). The percentage distribution of
refractive errors were found to be more in: Brahmin
(8.03%), Chhetri (9.45%), Newar (8.51%) and Thakali
(8.89%).
Out of 964 school students 907 were non-vegetarian
and only 57 were vegetarians (Figure 2). Though
the difference in numbers were great, we found the
percentage distribution of refractive errors was more
in vegetarian (10.52%) than that in the non-vegetarian
(6.17%). But the difference was found statistically
insigni cant.
69
0
2
4
6
8
10
12
Non - vegetarian Vegetarian
Table 1: Distribution of the Refractive Errors of the subjects in two Sexes.
Refractive errors Boys
(n = 474) %Girls
(n = 490) %Total
(n = 964) %
Myopia 22 4.64 17 3.47 39 4.05
Hyperopia 7 1.48 5 1.02 12 1.24
Astigmatism 7 1.47 4 0.81 11 1.14
Total 36 7.59 26 5.30 62 6.43
Table 2: Distribution of the Refractive Errors in different Age group.
Age Total Subjects (n = 964) No. of the subjects
with refractive errors
%
of corresponding age
10600
11 49 3 6.12
12 118 6 5.08
13 193 13 6.73
14 205 13 6.34
15 184 11 6.04
16 144 12 8.33
17 57 4 7.02
18700
19100
Table 3: Distribution of Refractive Errors of the subjects in different Ethnic groups.
Ethnic Groups Total Subjects No. of Subjects with
Refractive error % of corresponding caste
Brahmin 137 11 8.03
Chhetri 127 12 9.45
Magar 225 12 5.33
Gurung 267 13 4.87
Newar 47 4 8.51
Darji 33 2 6.06
Tamang 20 1 5.00
Thakali 45 4 8.89
0
1
2
3
4
5
6
Myopia Hyperopia Astigmatism
Percenta
g
e
% of corresponding habit
Fig 1: Distribution of refractive errors between Private
and government Schools children (p<0.05).
Fig 2: Distribution of Refractive errors between
vegetarian and non-vegetarian Subjects (p values
were not statistically signi cant).
Private School Government Sc hool
70
Discussion
In our present study, the prevalence of refractive errors
among Nine hundred sixty four (964) school going
children between 10-19 years old age in Pokhara,
Nepal was found to be 6.43% which is less than the
studies of Nepal et al6, 8.1% in 5-17 years age groups
and Shrestha et al7, in 5-16 years of age group children
in Kathmandu valley. In another study8, out of 5067
children from 5-15 years of age in Mechi, Nepal; only
2.9% children suffered from the refractive errors. These
variations of percentage distribution of refractive errors
of different authors are likely to be due to difference in
study samples, methodology and de nition of refractive
errors adopted in their study.
However, the percentage distribution of refractive errors
in our present study is higher than the refractive errors
recorded by Naidoo et al10, (4.7%) in South Africa, and
Schimiti et al11, (4.55%) in Brazil. On the other hand,
the percentage distribution of refractive errors found in
India12 was 25.32%, in Chile13 17.05% and in Zaire14
16%. These studies indicate that the prevalence of
refractive errors is much higher than our results. The
wide variations of percentage distribution of refractive
errors observed by different authors are naturally
likely to be due to: sample size, different geographical
situation, ethnic variation, nutritional status and
different criteria adopted by different authors. It seems
that the refractive errors especially in growing children
are one of the major health problems in both developed
and developing countries.
In our present study, the percentage of refractive errors
in the boys is found more (7.59%) than in the girl’s
counterpart (5.31%). This result is different from other
studies, where the percentage of refractive errors in girls
was found higher as compared to boys15, 16. However,
some studies in Nepal8, Chile13 did not found gender
difference in refractive errors.
It is interesting to note that in our present study, among
the refractive errors, percentage distribution of myopia
was found to be higher than that in hyperopia and
astigmatism. During the growing period of children
(10-19 years age), they are subjected to various stresses
and strains on eyes: near vision for reading and writing,
watching Television and Computers for more hours etc.
Such strains are likely to be the cause of developing
myopia12. The relationship between near work and
myopia had been observed by Saw et al17 in Singapore,
Mutti et al18 in Orinda & Colorado and Wong et al19 in
Hong Kong. In longitudinal study by Mutti et al18, they
showed that heredity is most important factor associated
with Juvenile myopia, but the weakness of our study
was that parental status of refractive errors were not
taken during the study.
The refractive errors in private school children were
found higher (9.29%) than the government school
children (4.23%), which is statistically signi cant. The
present study agrees well with other studies done in
Nepal. The similar results were observed by shrestha
et al7 in Kathmandu Valley. He found in Private school
children, 21 percent children had refractive errors
whereas Nepal et al6 observed 8.1 percent in Government
school children.
The high prevalence of myopia among the refractive
errors seems to be associated with increased near works
load in the private school children. Children do more
homework in private schools as compared to government
schools. In the present study socioeconomic status of
the children in private schools are comparatively better
than government schools. The time spent in Television
and Computer is also found more in private schools
children, which may be the reasons for development
of the refractive errors. This inference is drawn on the
basis of direct interview taken on children on their daily
habit.
In our present study, Brahmin, Chhetri, Newar and
Thakali children showed more refractive errors (Table
3). The literacy rate among these ethnic groups is higher
as compared to other ethnic groups which also indicate
the reason of high refractive errors in them. One study
from Kathmandu20 also found that the refractive errors
were more common in Newar community. Crawford &
Hammer4 also found that the racial and ethnic difference,
affects the prevalence of refractive errors.
In the present study, we found that 10.52% of vegetarian
and 6.17% of non-vegetarian school children had
refractive errors. The higher rate is though statistically
not signi cant. The nutritional factor may be one of the
important factors in causing the refractive errors in the
children.
Conclusion
In many parts of the world, refractive errors seem to
be the second largest cause of treatable blindness
after cataract. Blindness due to refractive errors is a
substantial public health problem in many parts of
the world. Since the treatment of refractive errors is
probably the simplest and most effective of eye care
interventions3, its presence implies inadequate eye
care service in the population concerned. Uncorrected
refractive errors are not only considered as a serious
issue in developing countries but also in developed
countries like Australia21. So it is desirable to start a
worldwide program for elimination of blindness due to
refractive errors.
71
In the present study, it showed that 6.43% of schools
going children in Pokhara city are suffering from
refractive errors. The school going children are the
backbone of a Nation. Unless there is a nationwide
program for corrective measures of refractive errors,
blindness due to unattended refractive errors may
cause a great burden on the nation. The percentage
distribution of refractive errors found in our studies and
studies done by Nepal et al.6 and Shrestha et al.7 indicate
the importance of the problem in Nepal. So the vision
screening of school children in developing countries
could be very useful in detecting correctable causes
of decreased vision especially refractive errors and the
corrective measures could be easily taken.
Acknowledgements
We would like to offer our heartiest thanks to Dr.
T.C. Saikia, the Professor and Head, Dr. Soumitra
Mukhopadhyay, Professor, Department of Physiology,
Nobel Medical College, Biratnagar, Dr. P. S. Debray,
and other faculty members of Physiology and
Ophthalmology Departments of Manipal College of
Medical Sciences, Pokhara. We are also grateful to all
the teaching staffs and students of various schools, who
helped in data collection and for their participation as
subjects in this study.
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... School based studies done in Nepal showed prevalence ranging from 2.4-21.9%. [8][9][10][11] In India, they reported prevalence of refractive error between 2.6% to 8.8%. 12 A study done in Pokhara reported the prevalence of myopia 4.05% which was twofold less than this study. ...
... 12 A study done in Pokhara reported the prevalence of myopia 4.05% which was twofold less than this study. 11 In rural India, the prevalence of myopia has increased from 4.6% (1980-2008) to 6.8% (2009-2019) compared to urban children from 7.9% to 8.9% during the same period. 13 Myopia has been found to be the commonest form of refractive error in various studies. ...
... 13 Myopia has been found to be the commonest form of refractive error in various studies. 3,9,11 The increased trend of myopia is a public health problem worldwide. It is estimated that the myopia and high myopia will affect five billion people and one billion people respectively by 2050 globally. ...
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Background: Ocular morbidity is common among school going children. The uncorrected refractive error is an important cause of childhood blindness and visual impairment. School based eye screening programs help to identify the ocular abnormalities so that early intervention can be done and prevent children from permanent visual disability. Objectives: This research was done to find the prevalence of ocular morbidity and their pattern among primary school children of Pokhara Valley, Nepal. Methods: A descriptive cross-sectional study was conducted among children of three primary schools of Pokhara Valley from January to March 2021. Children who needed further evaluation were referred to ophthalmology department, Gandaki Medical College. After the ethical clearance from the institutional review committee, 1034 children were taken by convenient sampling method. Visual acuity, objective and subjective refraction, extraocular motility, cover test, anterior and posterior segment findings were documented in predesigned proforma. Point estimate at 95% confidence interval along with frequency and proportion were calculated. SPSS 20.0 was used for data analysis. Results: A total 1034 children between 5-16 years were examined. Ocular morbidity was observed in 181 (17.5%) at 95% confidence interval (15.4-18.6). The mean age of children with ocular morbidity was 12.33 ± 2.39 years with male to female ratio of 1.18:1. The common type of ocular morbidity was refractive error 107 (10.35%), conjunctivital diseases 35 (3.38%) and eyelid diseases 26 (2.5%). Myopia 83 (8.02%) was the most common type of refractive error. Conclusion: Refractive error was the commonest form of ocular morbidity among school children.
... There are two types of schools in Dhangadhi in terms of ownership i.e., public, and private. Public schools receive government funding, and the schooling is not strict whereas private schools run with funding from parents so have strict schooling with lot of educational pressure.Though studies have found that refractive error prevalence is higher among private school in comparison to public school children, few studies have compared refractive error prevalence in public and private school children[14,16,17]. The higher prevalence of refractive error among children going to private school in comparison to those going to public schools could be related to rigorous schooling in private schools. ...
... Contrary to this, study in Jhapa district among school children found slightly higher prevalence of refractive error among male (9.8%) in comparison to female children (7.5%)[14].Caste/ethnicity wise distribution of refractive error found that highest prevalence was among Brahmin/Chhetry group (public school 3.5% and private schools 5.2%) whereas lowest prevalence was among Janajati group (public school 1.9% and private schools 2.9%) accounting for almost half of the children with refractive error. A study done in western Nepal found that Chhetry had the highest prevalence of refractive error whereas lowest prevalence was among Gururng caste/ethnic group[17]. Unlike in eastern Nepal, in our study population the proportion of Mangoloid group was low. Disadvantage non dalit were fewer in number in public (n=7) and private school (n=1), so meaningful comparisons could not be made. ...
... Myopia was reported in 15, 61,66-80 hypermetropia in seven 57,61,66-69 and astigmatism in ten studies. 57,61,[66][67][68][69][70]72,73,76 The pooled prevalences for myopia, hypermetropia and astigmatism from these studies were 7.1% (95% CI: 3.7 to 11.4), 1.0% (95% CI: 0.7 to 1.3) and 2.2% (95% CI: 0.9 to 3.9) respectively. In individual studies, the prevalence of myopia ranged from 0.6% 72 to 27.1%, 75 hypermetropia from 0.3% 68 to 1.4% 67 and astigmatism from 0.6% 75 to 9.0%. ...
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... (23) While the prevalence of myopia is much lower in the underdeveloped regions of the world, this rate is increasing with urbanization. (24) The correlation between close work and myopia is not completely clear. As a result of some epidemiological studies; Extreme close studies, high level of education and less outdoor activity have been shown as risk factors for myopia development. ...
... Whereas, a study from North India reported no signicant difference in the overall prevalence of ocular morbidity in government and private 7 schools. The signicantly higher prevalence of refractive errors among the private schools (19.94%) as compared to government school (14.91%) in this study is similar to a cross-sectional study from western Nepal where a signicantly higher refractive error was reported in private schools as compared to government school children and this has been attributed to the higher educational load in private 14 schools. ...
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Background Refractive error is an important preventable cause of visual impairment and blindness worldwide. In adult life, reduced vision can potentially affect the academic performance, choice of occupation and socio-economic status. This study aimed to assess the prevalence of refractive errors and related visual impairment among undergraduate male students in Prince Sattam bin Abdulaziz University in Al-Kharj, Saudi Arabia. Methods A descriptive cross-sectional study was employed in the current work. After obtaining an informed consent; each eligible student was asked to fill a self-constructed survey and have screened in the college premises for visual acuity and refractive error. Candidates detected with defective vision have been referred for further examination at well-equipped ophthalmology clinic in the University Hospital. Results A total of 420 undergraduate students, with age ranged from 18 to 30 years, have participated in the current study. About 25.0% of the participants have used spectacles at the time of examination. Positive family history of spectacles use was found in 71.4%. Our study showed that visual acuity in the better eye was low in 34.76% of the participants. Seventy-eight students (18.6%) of the total participants reported defective vision and have fulfilled refractometric examination. Of the examined students 83.3% were found to have refractive errors. Astigmatism, 52.6%, was the most frequently encountered refractive error among the participants; followed by myopia, 26.9%; and hypermetropia 2.6%. Conclusion The current study confirms that refractive error is an important preventable cause of visual impairment. Significant portion of the examined participants were found to have refractive errors recommending further work to improve visual status in undergraduate students.
... [12,13] The prevalence is much lower in underdeveloped areas of the world such as Sherpa in Nepal. [14] ...
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To assess the prevalence of refractive errors and vision impairment in school-age children in a suburban area (La Florida) of Santiago, Chile. Random selection of geographically defined clusters was used to identify a representative sample of children 5 to 15 years of age. Children in the 26 selected clusters were enumerated through a door-to-door survey and invited to report to a community health clinic for examination. Visual acuity measurements, cycloplegic retinoscopy, cycloplegic autorefraction, ocular motility evaluation, and examination of the external eye, anterior segment, media, and fundus were done from April through August 1998. Independent replicate examinations of all children with reduced vision and a sample of those with normal vision were done for quality assurance monitoring in six clusters. A total of 6,998 children from 3,830 households were enumerated, and 5,303 children (75.8%) were examined. The prevalence of uncorrected, presenting, and best visual acuity 0.50 (20/40) or worse in at least one eye was 15.8%, 14.7%, and 7.4%, respectively; 3.3% had best visual acuity 0.50 or worse in both eyes. Refractive error was the cause in 56.3% of the 1,285 eyes with reduced vision, amblyopia in 6.5%, other causes in 4.3%, with unexplained causes in the remaining 32.9%. Myopia -0.50 diopter or less in either eye was present in 3.4% of 5-year-old children, increasing to 19.4% in males and 14.7% in females by age 15. Over this same age range, hyperopia 2.00 diopters or greater decreased from 22.7% to 7.1% in males and from 26.3% to 8.9% in females. Females had a significantly higher risk of hyperopia than males. Refractive error, associated primarily with myopia, is a major cause of reduced vision in school-age children in La Florida. More than 7% of children could benefit from the provision of proper spectacles. Efforts are needed to make existing programs that provide free spectacles for school children more effective. Further studies are needed to determine whether the upward trend in myopia continues far beyond 15 years of age.
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A nationwide survey was performed in 2000 to determine the prevalence and severity of myopia among schoolchildren in Taiwan and to compare these findings with the results of the last survey performed in 1995. We first divided the whole island into regions according to developmental grade scores and then sampled with the probability proportional to the size of the population within each stratum. A total of 10,889 students were enrolled, including 5,664 boys and 5,225 girls, with ages ranging from 7 to 18 years. The refractive status and corneal radius of each student were measured with an autorefractometer under cycloplegia and checked with retinoscopy. Axial length was measured using biometric ultrasound. The myopia rate increased from 20% at 7 years, to 61% at 12 years, and 81% at 15 years. A myopic rate of 84% was found for schoolchildren aged 16 years through 18 years. The mean refractive index reached myopic status at the age of 8, and increased to -4.12 D in girls and -3.15 D in boys at the age of 18 years. The prevalence of high myopia (> -6.0 D) at the age of 18 years was 24% in girls and 18% in boys. The increase in axial length corresponded with the progression of myopia. The anterior chamber depth was slightly deeper from 7 years to 13 years and then remained stable. The lens thickness decreased from 7 years to 11 years. After age 15, further thickening of the lens was correlated with both age and severity of myopia. However, the corneal curvature was not related to age or severity of myopia. Girls had a higher prevalence and more severe degree of myopia than boys. Children in urban areas had a higher prevalence and more severe degree of myopia than children in rural areas. The prevalence and severity of myopia in schoolchildren in Taiwan in 2000 increased compared to 1995, with the most severe increases occurring in younger age groups. Thus, preventing schoolchildren developing myopia at a young age may slow down the increase in severity of myopia in Taiwan.
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To estimate the cause-specific prevalence and distribution of blindness and low vision in the United States by age, race/ethnicity, and gender, and to estimate the change in these prevalence figures over the next 20 years. Summary prevalence estimates of blindness (both according to the US definition of < or =6/60 [< or =20/200] best-corrected visual acuity in the better-seeing eye and the World Health Organization standard of < 6/120 [< 20/400]) and low vision (< 6/12 [< 20/40] best-corrected vision in the better-seeing eye) were prepared separately for black, Hispanic, and white persons in 5-year age intervals starting at 40 years. The estimated prevalences were based on recent population-based studies in the United States, Australia, and Europe. These estimates were applied to 2000 US Census data, and to projected US population figures for 2020, to estimate the number of Americans with visual impairment. Cause-specific prevalences of blindness and low vision were also estimated for the different racial/ethnic groups. Based on demographics from the 2000 US Census, an estimated 937 000 (0.78%) Americans older than 40 years were blind (US definition). An additional 2.4 million Americans (1.98%) had low vision. The leading cause of blindness among white persons was age-related macular degeneration (54.4% of the cases), while among black persons, cataract and glaucoma accounted for more than 60% of blindness. Cataract was the leading cause of low vision, responsible for approximately 50% of bilateral vision worse than 6/12 (20/40) among white, black, and Hispanic persons. The number of blind persons in the US is projected to increase by 70% to 1.6 million by 2020, with a similar rise projected for low vision. Blindness or low vision affects approximately 1 in 28 Americans older than 40 years. The specific causes of visual impairment, and especially blindness, vary greatly by race/ethnicity. The prevalence of visual disabilities will increase markedly during the next 20 years, owing largely to the aging of the US population.