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1 From the Public Health Ophthalmology Service, L. V. Prasad Eye Institute, Hyderabad, India; and the 2 Centre for Eye Research Australia, Department of Ophthalmology, University of Melbourne, Australia.
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Abstract |
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METHODS. Two thousand five hundred twenty-two subjects of all ages,
representative of the Hyderabad population, were examined in the
population-based Andhra Pradesh Eye Disease Study. Objective and
subjective refraction was attempted on subjects >15 years of age with
presenting distance and/or near visual acuity worse than 20/20 in
either eye. Refraction under cycloplegia was attempted on all subjects
15 years of age. Spherical equivalent >0.50 D in the worse eye was
considered as refractive error. Data on objective refraction under
cycloplegia were analyzed for subjects 15 years and on subjective
refraction were analyzed for subjects >15 years of age.
RESULTS. Data on refractive error were available for 2,321 (92.0%) subjects. In
subjects 15 years of age, age-gender–adjusted prevalence of myopia
was 4.44% (95% confidence interval [CI], 2.14%–6.75%), which was
higher in those 10 to 15 years of age (odds ratio, 2.75; 95% CI,
1.25–6.02), of hyperopia 59.37% (95% CI, 44.65%–74.09%), and of
astigmatism 6.93% (95% CI, 4.90%–8.97%). In subjects >15 years of
age, age-gender–adjusted prevalence of myopia was 19.39% (95% CI,
16.54%–22.24%), of hyperopia 9.83% (95% CI, 6.21%–13.45%), and
of astigmatism 12.94% (95% CI, 10.80%–15.07%). With multivariate
analysis, myopia was significantly higher in subjects with Lens Opacity
Classification System III nuclear cataract grade 
3.5 (odds ratio,
9.10; 95% CI, 5.15–16.09), and in subjects with education of
class 11 or higher (odds ratio, 1.80; 95% CI, 1.18–2.74); hyperopia
was significantly higher in subjects 30 years of age compared with
those 16 to 29 years of age (odds ratio, 37.26; 95% CI,
11.84–117.19), in females (odds ratio, 1.86; 95% CI, 1.33–2.61), and
in subjects belonging to middle and upper socioeconomic strata (odds
ratio, 2.10; 95% CI, 1.09–4.03); and astigmatism was significantly
higher in subjects 40 years of age (odds ratio, 3.00; 95% CI,
2.23–4.03) and in those with education of college level or higher
(odds ratio, 1.73; 95% CI, 1.07–2.81).
CONCLUSIONS. These population-based data on distribution and demographic associations of refractive error could enable planning of eye-care services to reduce visual impairment caused by refractive error. If these data are extrapolated to the 255 million urban population of India, among those >15 years of age an estimated 30 million people would have myopia, 15.2 million hyperopia, and 4.1 million astigmatism not concurrent with myopia or hyperopia; in addition, based on refraction under cycloplegia, 4.4 million children would have myopia and 2.5 million astigmatism not concurrent with myopia or hyperopia.
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Introduction |
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Little is known about the prevalence, distribution, and demographic associations of refractive error in India.10 There are no population-based estimates of the prevalence, distribution, and demographic associations of refractive error on which the need for refractive correction can be based. We report these data for the urban population of Hyderabad in southern India, obtained as part of the population-based Andhra Pradesh Eye Disease Study. These data are expected to help in better planning of eye-care services, because refractive errors were responsible for a significant proportion of blindness and moderate visual impairment in this population.11 12
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Methods |
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Clinical Examination
Subjects were brought to a clinic set up for this study. Informed
consent was obtained before the examination. For subjects 15 years of
age, this consent was obtained from the parent or the guardian. The
clinical examination included measurement of distance and near visual
acuity with logMAR charts, refraction, and a detailed examination of
anterior segment, gonioscopy, dilatation, a detailed examination of
lens, vitreous and posterior segment, and visual fields based on
uniform predefined criteria.11
12
13
Nuclear cataract was
graded using Lens Opacity Classification System (LOCS)
III.15
Those subjects who were physically debilitated and
unable to come to the clinic were examined at home with portable
equipment.13
For subjects >15 years of age, refraction was attempted on all those who presented with distance and/or near visual acuity worse than 20/20 in either eye. Objective refraction was performed by an optometrist using a streak retinoscope, which was further refined by subjective refraction. For subjects with distance and near visual acuity of 20/20 or better with current refractive correction, this correction was considered as the refractive error. Subjects who were not using optical correction and had distance and near visual acuity of 20/20 or better were considered as not having refractive error.
Objective refraction under cycloplegia (cyclopentolate 1% and
tropicamide 1%) was attempted on all subjects 15 years of
age.13
Statistical Analyses
Data were analyzed separately for subjects 15 years of age,
because objective refraction under cycloplegia was considered for
analyses for this age group. For subjects >15 years of age, subjective
refraction was considered for analysis. Data were analyzed for the
worse eye (eye with higher refractive error). Spherical equivalent (SE)
was used to analyze data for myopia and hyperopia. Spherical equivalent
was calculated by adding half of the cylindrical value to the spherical
value of the refractive error. Subjects with SE higher than -0.50 D
were considered as having myopia and those with SE higher than +0.50 D
were considered as having hyperopia. In subjects with antimetropia
(myopia in one eye and hyperopia in the other eye) the eye with the
higher refractive error (in terms of magnitude) was classified as the
worse eye. Astigmatism higher than 0.50 D was considered for analysis.
Astigmatism was analyzed on the basis of the type of astigmatism,
against-the-rule astigmatism, with-the-rule astigmatism, and oblique
astigmatism.
Analysis for myopia and hyperopia was also done for SE higher than or equal to 0.75 D and for SE higher than or equal to 1.00 D; for astigmatism, analysis was also done for magnitudes higher than or equal to 0.75 D and for magnitudes higher than or equal to 1.00 D.
The demographic associations of refractive error were assessed with
age, gender, education, socioeconomic status, and religion. Association
of myopia was also assessed with nuclear cataract and self-reported
diabetes for subjects >15 years of age. Education was not considered
in the multivariate model for subjects 15 years of age.
These associations were assessed by univariate analyses followed by multiple logistic regression. The effect of each category of a multicategorical variable was assessed by keeping the first or the last category as the reference. Analyses were done using the SPSS software (SPSS for Windows, Rel.7.0.0.1995; SPSS, Chicago, IL). Adjustment of the estimates for the age and gender distributions of the Hyderabad population was done.16 Based on the rates in each cluster, the design effect of the sampling strategy was calculated for the prevalence estimates,17 and the 95% CIs adjusted accordingly.
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Results |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Subjects 15 Years of Age
Of the 2,321 subjects, 663 (28.6%) were 15 years of age. Data
on objective refraction under cycloplegia were available for 599
(90.3%) subjects. Of these 599 subjects, 352 (58.8%) were between 0
and 9 years, and 295 (49.2%) were females.
Myopia in the worse eye was present in 30 subjects, an
age-gender–adjusted prevalence of 4.44% (95% CI, 2.14%–6.75%). On
applying multiple logistic regression, myopia was significantly more
frequent in subjects 10 to 15 years of age (odds ratio, 2.75; 95% CI,
1.25–6.02). Hyperopia in the worse eye was present in 350 subjects, an
age-gender–adjusted prevalence of 59.37% (95% CI, 44.65%–74.09%).
The distributions of myopia and hyperopia for 15 years of age are
shown in Figure 1 . Astigmatism in the worse eye was present in 44 subjects, an
age-gender–adjusted prevalence of 6.93% (95% CI, 4.90%–8.97%). No
significant associations of hyperopia and astigmatism with age, gender,
socioeconomic status, and religion were found on applying multiple
logistic regression.
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0.75 D were
almost the same as those with >0.50 D. The results of multiple
logistic regression for demographic associations for myopia, hyperopia,
and astigmatism 1.00 D were essentially similar to those for >0.50
D.
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Subjects >15 Years of Age
Of the 2,321 subjects, 1,722 (74.2%) were >15 years of age. Of
these 1,722 subjects, 1,264 (73.4%) were 30 years of age, 959
(55.7%) were females, and 1,091 (63.3%) were Hindus.
Myopia in the worse eye was present in 362 subjects with an
age-gender–adjusted prevalence of 19.39% (95% CI, 16.54%–22.24%).
When multiple logistic regression was applied (Table 2)
, myopia was significantly higher in subjects with LOCS III nuclear
cataract grade 3.5 (odds ratio, 9.10; 95% CI, 5.15–16.09) and in
subjects with education of class 11 or higher (odds ratio, 1.80; 95%
CI, 1.18–2.74). Although univariate analysis showed that myopia
increased with increase in age (P < 0.0001), it was not
significant in multivariate logistic regression. This was due to a
significant interaction between age and nuclear cataract (data not
reported). There was no significant interaction between education and
socioeconomic status and no significant association of myopia with
gender, socioeconomic status, religion, or self-reported diabetes.
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30
years of age (odds ratio, 37.26; 95% CI, 11.84–117.19), in females
(odds ratio, 1.86; 95% CI, 1.33–2.61), and in subjects belonging to
middle and upper socioeconomic strata (odds ratio, 2.10; 95% CI,
1.09–4.03). Although the odds of having hyperopia for subjects with
any level of education were higher than for those with no education,
they were of borderline statistical significance (odds ratio, 1.41;
95% CI, 1.00–1.97). There was no significant interaction between
education and socioeconomic status for hyperopia and no significant
association of hyperopia with religion. Figure 2 shows the age-gender–adjusted prevalence of the various magnitudes of myopia and hyperopia. The gender-adjusted prevalences of the various magnitudes of myopia in the different age groups are shown in Figure 3 , and of hyperopia in Figure 4 .
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40 years of age
(odds ratio, 3.00; 95% CI, 2.23–4.03) and with education of college
level or higher (odds ratio, 1.73; 95% CI, 1.07–2.81). There was no
significant interaction between education and socioeconomic status for
astigmatism and no significant association of astigmatism with gender,
socioeconomic status, or religion. The distribution of astigmatism
based on type and magnitude is shown in Figure 5 .
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0.75 D were almost the same as with >0.50 D.
The results of multiple logistic regression for demographic
associations for myopia, hyperopia, and astigmatism with definition
1.00 D compared with those for >0.50 D were mostly similar; the
minor difference was that the associations with education became
weaker: myopia with education of class 11 or higher (odds ratio, 1.40;
95% CI, 0.96–2.02), hyperopia with any education (odds ratio, 1.32;
95% CI, 0.92–1.90), and astigmatism with education of college or
higher (odds ratio, 1.45; 95% CI, 0.94–2.24). Astigmatism showed higher concurrence with myopia than hyperopia. Fifty-one percent of subjects with against-the-rule astigmatism also had myopia, and 27.5% had hyperopia; 52.3% of subjects with with-the-rule astigmatism also had myopia, and 21.5% had hyperopia; and 61.5% of subjects with oblique astigmatism had myopia, and 23.1% had hyperopia.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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We have reported refractive error under cycloplegia for subjects 15
years of age. Myopia prevalence in this age group was 4.44%, and it
increased with age from 10 years onward. Other studies that have
included younger age groups have shown that prevalence of myopia
increases with age.18
19
As expected, in refraction under
cycloplegia, hyperopia dominated in those 15 years of age, with a
prevalence of 59.37%. Our estimates of the prevalence of myopia and
hyperopia in those 3 years of age could be biased because it is
difficult to perform refraction on subjects in this age group. In our
data, 47 subjects (31.8%) in this age group were excluded from
analyses because refraction could not be performed on these subjects.
There was a similar prevalence of against-the-rule and with-the-rule
astigmatism under cycloplegia in those 15 years of age.
Subjective refraction has been reported by us for subjects >15 years of age. We found a prevalence of 19.39% for myopia in our population >15 years of age. Univariate analysis revealed that prevalence of myopia increased with age, but this was not significant in the multivariate model, which included nuclear cataract. Our data show a significant increase in myopia with nuclear cataract. Because nuclear cataract is an age-related change in the lens, a significant interaction between age and nuclear cataract is responsible for this finding. Myopic shift in the very old age group has been associated with age-related changes in the lens in a recent study in Melbourne.9
We found a significant but weak association of myopia with higher levels of education in our study compared with the associations reported in some previous studies.2 8 9 Educational status has been shown to be closely related to near-work, and association between near-work activities and myopia has been reported previously,7 which has also been used in support of the use-abuse theory of myopia.18
Prevalence of hyperopia in our population >15 years of age was 9.83%.
There was an increase in prevalence of hyperopia beyond 30 years of
age. The odds of having hyperopia are quite high for subjects 30
years of age in the multivariate model, possibly because of lower
prevalence of hyperopia in the age group used as reference in the
model. The increase in hyperopia beyond 30 years of age seen in our
population is unlikely to be explained by residual accommodation. This
hyperopic shift could be explained by a decrease in the power of the
aging lens, either a decrease in the curvature of its surface as it
grows throughout life or an increase in the density of the cortex that
makes the lens more uniformly refractive.20
We found a significantly higher prevalence of hyperopia in females than in males. It could possibly be explained by the fact that females have smaller eyes than males as shown in studies on normal eyes21 22 and, hence, have a higher chance of being hyperopic. We found an association of hyperopia with education, which had borderline statistical significance. However, previous studies have shown a link between hyperopia and academic underachievement.23 24 25 We also found a significant association of hyperopia with middle and higher socioeconomic strata. We are not aware of any other study that has revealed these associations, and these findings need to be understood further.
Refraction was not performed on subjects >15 years of age who had distance and near visual acuity of 20/20 or better and who were not using optical correction because they were considered as not having refractive error. This approach in our study should not have affected the prevalence of myopia but may have underestimated the prevalence of hyperopia.
The prevalence of astigmatism in our population >15 years of age was 12.94%. This prevalence of astigmatism included those who had either myopia or hyperopia concurrent with astigmatism. Age-gender–adjusted prevalence of "pure" astigmatism not concurrent with myopia or hyperopia in this population was 2.67% (95% CI, 1.91%–3.43%). Few distribution curves for astigmatism have been published.26 27 28 29 The most common astigmatism in our population was against-the-rule astigmatism. However, with-the-rule astigmatism has been reported to be the most common astigmatism in other populations.26 27 28 29 The trend toward against-the-rule astigmatism beyond the age of 40 years has been shown previously.29 In our population, against-the-rule astigmatism was dominant in all age groups, and the shift toward against-the-rule astigmatism increased from 40 years of age onward. The hypothesis that eyelid tension is responsible for with-the-rule astigmatism by steepening the vertical corneal meridian and flattening the horizontal meridian30 explains the changes associated with age. As lid tension reduces with age, so does the with-the-rule astigmatism. Such a high proportion of against-the-rule astigmatism as in our population has not been documented previously. It could be speculated that the lid tension may be less in our population to begin with, which reduces further with age. However, there could be other unidentified reasons for our finding. Our data also show a mild association of astigmatism with higher education. Astigmatism showed a higher concurrence with myopia than with hyperopia, and myopia was associated with a higher education level in our population. This could be a reason why astigmatism was associated with higher education.
Extrapolating the age-gender–adjusted prevalence of myopia, hyperopia,
and astigmatism, defined as >0.50 D, in our study to the urban
population of India >15 years of age, 155 million in
1997,14
30 (95% CI, 24.3–35.6) million people would have
myopia, 15.2 (95% CI, 8.5–21.7) million have hyperopia, and 4.1 (95%
CI, 3.0–5.3) million have astigmatism without concurrent myopia or
hyperopia. Therefore, a total of 49.3 million people is estimated to
have refractive error in the urban population of India >15 years of
age. If our data on refraction under cycloplegia were extrapolated to
the 100 million children in urban India,14
4.4 (95% CI,
2.1–6.8) million children would have myopia, and 2.5 (95% CI,
1.3–3.8) million would have astigmatism without concurrent myopia or
hyperopia. With the stricter definitions of refractive errors, these
projections would not change substantially for 0.75 D and would be
reduced modestly for 1.00 D.
Data about the distribution and demographic associations of refractive errors reported in this article can help in estimating the need for refractive correction and in planning of effective eye-care services in India to reduce the visual impairment due to refractive errors.
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Acknowledgements |
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Footnotes |
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Submitted for publication March 3, 1999; revised June 8, 1999; accepted June 28, 1999.
Commercial relationships policy: N.
Corresponding author: Rakhi Dandona, ICARE, L. V. Prasad Eye Institute, L.V. Prasad Marg, Banjara Hills, Hyderabad–500 034, India. E-mail: rakhi{at}lvpeye.stph.net
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