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1 From the International Centre for Advancement of Rural Eye Care, L.V. Prasad Eye Institute, Hyderabad, India; and the 2 Centre for Eye Research Australia, University of Melbourne, Australia.
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Abstract |
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METHODS. A population-based epidemiology study, using a stratified, random, cluster, systematic sampling strategy, was conducted in the state of Andhra Pradesh in India. Participants of all ages (n = 10,293), 87.3% of the 11,786 eligible, from 94 clusters in one urban and three rural areas representative of the population of Andhra Pradesh, underwent interview and a detailed dilated ocular evaluation by trained professionals. Blindness was defined as presenting distance visual acuity < 6/60 or central visual field < 20o in the better eye.
RESULTS. Two hundred seventy-five participants were blind, a prevalence of 1.84% (95% confidence interval, 1.49%–2.19%) when adjusted for the age, sex, and urban–rural distribution of the population in 2000. The causes of this blindness were easily treatable in 60.3% (cataract, 44%; refractive error, 16.3%). Preventable corneal disease, glaucoma, complications of cataract surgery, and amblyopia caused another 19% of the blindness. Blindness was more likely with increasing age and decreasing socioeconomic status, and in female subjects and in rural areas. Among the 76 million population of Andhra Pradesh, 714,400 are estimated to have cataract-related blindness (615,600 cataract, 53,200 cataract surgery-related complications, 45,600 aphakia), and 228,000 refractive error-related blindness (159,600 myopia, 22,800 hyperopia, 45,600 refractive error-related amblyopia). If 95% of the cataract and refractive error blindness in Andhra Pradesh had been treated effectively, 3.4 and 7.4 million blind-person-years, respectively, could have been prevented. If 90% of the blindness due to preventable corneal disease and glaucoma had been prevented, another 2.7 million blind-person-years could have been prevented.
CONCLUSIONS. The prevalence of blindness in this Indian state has increased from 1.5% in the late 1980s to 1.84% currently, as against the target of the National Program for Control of Blindness to reduce the prevalence to 0.3% by 2000. The number of people with cataract-related blindness has not reduced even with the eye care policy focus on cataract. Reduction of blindness in India will require strategies that are more effective than those that have been pursued so far.
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionReferences |
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To have the appropriate plan to eliminate avoidable blindness in India, current population-based data on the magnitude and causes of blindness in all age groups are a prerequisite. A national survey done during 1986–1989 reported that 1.5% of the population in India was blind, with presenting visual acuity < 6/60 in the better eye, and that 80% of this blindness was caused by cataract.4 Consequently, in the 1990s the focus of the National Program for the Control of Blindness was almost exclusively on reducing cataract blindness,5 6 which included large funding under a World Bank cataract project.5 The original target of the National Program was to reduce the prevalence of blindness to 0.3% by 2000, though it was acknowledged by the mid-1990s that achievement of this target was unlikely.5 The current prevalence of blindness in the entire age range of the population is not known for India.
Andhra Pradesh is a state in the southern part of India with a population of 76 million in 2000.7 The prevalence of blindness in Andhra Pradesh was reported as 1.5% in the 1986–1989 survey.4 From October 1996 to February 2000 we conducted the population-based Andhra Pradesh Eye Disease Study (APEDS) in one urban and three rural areas, representative of the population of Andhra Pradesh, to assess the prevalence and causes of blindness and other levels of visual impairment, risk factors for various eye diseases, effect of visual impairment on quality of life, and barriers to access to eye care services.8 We reported earlier from the urban component of this study that the previous national survey likely overestimated the proportion of blindness attributed to cataract because detailed dilated eye examination was not done.9 In this article, we report the combined results from the three rural and one urban components of APEDS to estimate the current prevalence and causes of blindness in Andhra Pradesh.
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Methods |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionReferences |
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Study Sample
We calculated a sample size of 10,000 persons, 5000 each below
and above 30 years of age. This was based on the assumption that a
0.5% prevalence of an eye disease in either of these age groups may be
of public health significance. The planned sample would estimate this
prevalence as 0.3% to 0.8% at the 95% confidence
level.8
A multistage sampling procedure was used to select
the study sample. One urban and three rural areas from different parts
of the southern Indian state of Andhra Pradesh were selected, with the
aim of including approximately 2500 participants in each area, such
that these would roughly reflect the urban–rural and socioeconomic
distribution of the population of this state. These four areas were
located in Hyderabad (urban), West Godavari district (well-off rural),
and Adilabad and Mahabubnagar districts (poor rural; Fig. 1
). APEDS was conducted from October 1996 to June 1997 in Hyderabad, July
1997 to May 1998 in West Godavari, June 1998 to March 1999 in Adilabad,
and April 1999 to February 2000 in Mahabubnagar.
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30 years of age eligible for the study. This was done to obtain
a similar number of participants in the <30- and 30-years age
groups.8
Without this approach the desired approximately
equal sample in these two age groups would not have been achieved
because the population structure of India is pyramidal.10
This oversampling of the 30-years age group was later adjusted in the
calculations to obtain estimates of blindness for the entire
population. The sampling of the urban sample in Hyderabad has been described previously.9 The major difference between the urban and rural sampling was that the former was selected from blocks stratified by socioeconomic status and religion, whereas the latter were selected from villages stratified by caste. Approximately 2950 persons were sampled in each of the four study areas such that at least 2500 participants would be recruited for each study area by aiming for a participation rate of at least 85%. Trained investigators interviewed the participants in the study, including information about income from all sources.8
Examination
The participants were brought for examination in a van to
clinics specially set up for this study in Hyderabad and West Godavari,
and to our rural eye center in Adilabad and Mahabubnagar where an area
was assigned separately for the study. Written informed consent was
obtained from the participants before examination. For participants
15 years of age, consent was obtained from the parent or accompanying
guardian. The illiterate participants gave thumbprint as consent after
the content of the consent form was explained to them. The examinations
were done by four ophthalmologists and four optometrists who had
received special training in the procedures of this study for
standardization of the documentation of the findings. Distance and near
visual acuity, both presenting and best corrected after refraction,
were measured for each eye separately using logMAR (logarithm of
minimum angle of resolution) charts.12
Presenting visual
acuity was measured with currently used refractive correction, or no
correction if none was being used by the participant. English alphabet
logMAR chart was used for those who could read the English alphabet,
and E-type logMAR chart for those who could not read the English
alphabet. Distance visual acuity was measured in a standardized manner
using illumination of at least 200 lux,8
which was checked
with a photometer. Initially, the distance acuity was measured at a
distance of 3.8 m. The logMAR equivalent of the number of letters
read correctly was recorded as the visual acuity. If no letter was read
at this distance, indicating acuity worse than 1.0 logMAR units or
6/60, the distance was reduced to 1.9 m and the logMAR scale
adjusted accordingly. If no letter was read even at this distance,
indicating acuity worse than 1.3 logMAR units or 3/60, finger counting
at 1 m, hand motion close to face, projection of light, and
perception of light, were assessed in that order. If presenting visual
acuity was worse than 6/6 (0.0 logMAR units), objective refraction was
performed with a streak retinoscope, followed by subjective acceptance
with which the best-corrected acuity was measured and recorded.
External eye and anterior segment examination were done with slitlamp biomicroscope. Intraocular pressure was measured with Goldmann applanation tonometer. Gonioscopy was attempted on all participants with NMR-K two-mirror goniolens (Ocular Instruments Inc., Bellevue, WA) and the angle was graded as open, occludable, or occluded based on the classification of Scheie.13 If the participant could not cooperate with gonioscopy, the angle was graded with the slitlamp using van Herick technique.14 All participants had their pupils dilated unless contraindicated because of risk of angle closure. After dilatation, the lens was examined with the slitlamp and nuclear cataract was graded according to the Lens Opacities Classification System III,15 and cortical and posterior subcapsular cataracts were graded using the Wilmer classification.16 If the crystalline (natural) lens was not present, the absence of any lens (aphakia) or the presence of intraocular lens (pseudophakia) was documented. Stereoscopic fundus examination, including assessment of the vitreous, retina, and optic disc, was done at the slitlamp using 78 diopter lens and with the indirect ophthalmoscope using 20 diopter lens.
Automated visual fields were done with the Humphrey visual field analyzer17 using the central 24-2 threshold strategy in those participants assessed to have any suspicion of glaucoma or other optic nerve pathology or higher visual pathway lesion, and in those with significant macular/retinal pathology (such as retinitis pigmentosa), according to uniform predefined criteria. If the visual field was abnormal or unreliable, it was repeated on another day. Anterior segment pathology was photographed with Nikon photograph-slitlamp (Nikon Corporation, Tokyo, Japan), and optic disc, macular or other retinal pathology with a Zeiss fundus camera (Carl Zeiss, Jena, Germany).
Those participants who were physically debilitated and unable to come to the clinic were examined at home with portable equipment. This examination was similar to the one at the clinic except that gonioscopy, examination with 78 diopter lens, automated visual fields, and photography could not be done.
Definition of Blindness
Various definitions of blindness are used worldwide. We assessed
blindness with two definitions: (1) presenting distance visual acuity
< 6/60 or central visual field <
20o in the better eye, and (2) presenting
distance visual acuity < 3/60 or central visual field <
10o in the better eye. Definition one is similar
to the definition of economic blindness used previously in
India.4
9
Definition two is similar to that recommended by
WHO,18
except that instead of best-corrected visual acuity
in the WHO definition we used presenting visual acuity so that
blindness due to refractive error would not be missed.9
A
uniform method of scoring visual field constriction with automated
perimetry was used.19
Cause of Blindness
The cause of blindness in each eye was initially documented by
the ophthalmologist examining the participant. This was later discussed
with the principal investigator (LD) and coinvestigator (RD), along
with the visual fields and photographs obtained according to the study
protocol, and the final decision on the cause of blindness was made. If
the information available to make this decision for a particular
participant was thought to be unsatisfactory, that participant was
reexamined by the principal investigator.
If cataract and a posterior-segment lesion of the optic nerve or retina coexisted, and removal of cataract would not restore vision, the cause of blindness was considered to be the posterior-segment lesion. If dense cataract was present that prevented any view of the posterior segment, and if no signs suggestive of any other cause of visual loss were present, the cause of blindness was considered to be cataract. If index myopia was present due to cataract, and even if the vision improved with refraction, the cause of blindness was considered cataract and not refractive error because the former was the underlying cause. If the two eyes of a subject were blind from two different causes, both were given 50% weight, rather than arbitrarily choosing one or the other as the cause for that participant.
Cataract and refractive error were considered easily treatable causes of blindness because their treatment is relatively simple in most cases. The majority of blindness due to corneal disease encountered in this study, primary angle-closure glaucoma, complications of cataract surgery, and refractive error–related amblyopia, and half of that due to primary open-angle glaucoma, were considered preventable with the currently available knowledge. It was then assumed that with effective provision of eye care services, 95% of the cataract-related and refractive error–related blindness, 90% of the corneal blindness, and 90% of the preventable glaucoma blindness, might be prevented.
To calculate the number of blind-person-years20 from treatable and preventable causes of blindness, the age of onset of blindness from the different causes was estimated from the history obtained from each participant. Because past examination data were not available for most participants, the estimation of the age of onset of blindness had to be based on the best interpretation of the history of poor vision. Based on this, the average number of years lived with blindness over a lifetime from the different causes, after accounting for the reduced life expectancy due to blindness,21 were estimated as follows: 5 for cataract, primary glaucoma, aphakia, and complications of cataract surgery; 32 for myopia; 40 for hyperopia and amblyopia; 43 for childhood corneal opacity,21 and 10 for other corneal disease.
Data Management
Data were initially documented on the APEDS data collection
forms by the clinical examiners and the field
investigators.8
This data collection was monitored by the
principal investigator and coinvestigator of the study and discussed
with the clinical and field teams at regular intervals. The data were
entered in a FoxPro database at the study headquarters in Hyderabad,
and consistency checks were performed for these data.8
Statistical Analysis
The age- and sex-specific rates of blindness in the 15, 16 to
29, 30 to 39, 40 to 49, 50 to 59, 60 to 69, and 70 years age groups
in each of the four study areas were used to standardize the estimates
of blindness to the estimated age and sex distribution of the
population of India in mid-2000.10
To obtain the composite
estimate of blindness in Andhra Pradesh, the age- and sex-adjusted
rates from the four study areas were combined by giving 0.284 weight to
the urban rates and 0.239 weight to each of the three rural rates,
because 28.4% of the population in India was estimated to be urban in
2000.22
The variations of blindness rates among the different clusters were
used to calculate the design effect of the cluster sampling strategy
with the method described by Bennett et al.23
A
multiplication factor equal to the square root of the design effect was
used to calculate the 95% confidence intervals (CIs) for the estimates
of blindness to avoid erroneously narrow CIs.23
Poisson
distribution24
was assumed for prevalence < 1%, and
normal approximation of binomial distribution for prevalence 1%. The
association of blindness with age, sex, socioeconomic status, and
urban–rural residence was evaluated with univariate and multivariate
analyses.24
The software SPSS for Windows (SPSS Inc.,
Chicago, IL) was used for statistical analysis.
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Results |
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A total of 275 participants were blind by definition one. After adjustment for the age, sex, and urban–rural distribution of the population in 2000, the prevalence of blindness was 1.84% (95% CI, 1.49%–2.19% [design effect 1.84]). Table 1 shows the prevalence of blindness for the four study areas and the causes of blindness. Of this blindness, 9.8% was due to visual field constriction, the causes of which included retinitis pigmentosa, glaucoma, and optic atrophy. The prevalence of blindness in the three rural areas combined was 2.03% (95% CI, 1.64%–2.42% [design effect 1.58]).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionReferences |
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Cataract-related Blindness
The survey of 1986–1989 reported that 80% of the 1.5%
prevalence of blindness in Andhra Pradesh was due to
cataract.4
This proportion of blindness attributed to
cataract was an overestimate because detailed dilated eye examination
was not done in that survey which would have misclassified blindness
due to glaucoma, optic atrophy, and retinal causes as cataract
blindness.9
We estimated that the real proportion of
blindness due to cataract would have been <55%.9
This
and the 4.7% aphakic blindness reported in the previous
survey4
would suggest that a decade ago approximately 60%
of the 1.5% blindness in Andhra Pradesh was cataract related, which
amounts to a 0.9% prevalence or 585,000 persons among the 65 million
population then. The data reported in this article suggest that
currently the prevalence of cataract-related blindness in Andhra
Pradesh is 0.94% or 714,400 persons. During the past decade, the
population of Andhra Pradesh has increased by 11 million, and the life
expectancy by 4 years, which would result in a larger number of persons
developing cataract. However, the lack of reduction in cataract-related
blindness is disturbing given the background of the stated emphasis of
the National Program for Control of Blindness to reduce cataract
blindness.5
6
The World Bank sanctioned a loan for a US$
135 million project to reduce cataract blindness in seven states of
India, including Andhra Pradesh, from 1994 to 2001.5
The
annual number of cataract surgeries in India has increased rapidly over
this period, with about half still without intraocular lens
implantation.25
Even with this increase there is no
evidence of reduction in cataract-related blindness, which may be due
to a combination of poor outcome of cataract surgery and a low number
of surgeries on blind persons. The poor outcome of cataract surgery is
evident from our finding that for every six persons blind from cataract
there is one person blind from cataract surgery complications or
aphakia. As part of APEDS, we found that among the eyes operated for
cataract in the population of Hyderabad, 21.4% were blind after
surgery, the majority due to surgery complications or
aphakia.26
In the populations of West Godavari, Adilabad,
and Mahabubnagar, blindness after cataract surgery was present in
36.4%, 34%, and 43% of the eyes, respectively. Such poor results of
cataract surgery in the community at large are likely discouraging many
from seeking treatment. Poor quality cataract surgery seems to be a
widespread phenomenon in the developing world because poor outcomes
have also been reported recently from other parts of
India27
28
29
as well as other countries.30
31
32
Better outcome of cataract surgery in India has to be achieved by
improving the quality of surgical training and improving the eye care
infrastructure to provide reasonable follow-up care. Some new models of
providing good quality and sustainable eye care in rural India are
showing reasonable results.33
Similar experiments are
needed on a larger scale. Another reason for the continuing high rate
of cataract blindness may be that the increase in the number of
cataract surgeries includes a large number of surgeries on persons who
are not blind in both eyes.
An interesting finding was that the total potential cataract blindness in the well-off rural West Godavari was more than twice that in the poor rural Mahabubnagar. The reasons for this are not clear yet, but may include a possibly higher life expectancy in West Godavari or other demographic, environmental, or biological variables, which need to be explored further. However, this finding suggests that the risk of developing cataract blindness can vary considerably between different areas of the same state. Another finding that needs to be understood further is that the total potential cataract blindness in rural female subjects was more than in the male subjects, which may be related to the higher life expectancy of women,10 or to other biological or nutritional variables.
Refractive Error-related Blindness
Refractive error–related blindness in Andhra Pradesh accounts for
more than twice the number of blind-person-years compared with cataract
over the lifetime of those currently blind because blindness due to
refractive error manifests at a young age. Of this burden 65.2% was
due to high myopia and 11.6% due to high hyperopia, which are easily
correctable. The remaining 23.2% of this burden due to amblyopia
caused by uncorrected high refractive error during childhood is
preventable if adequate refractive services are available. Only 17.9%
of the total potential refractive error blindness had been prevented in
rural areas, compared with 81.7% in urban Hyderabad. This prevented
blindness was particularly low for rural women at 2.7%. Because of the
large burden on society due to the easily treatable refractive error
blindness, it is necessary to develop simple and effective community
screening programs in India. Knowledge about the distribution of
refractive errors in the population34
and the pattern of
utilization of eye care services35
would assist in
developing these programs. Screening of school children has been
suggested for detecting refractive error.36
This has the
advantage of having a concentrated target population, but misses out a
large proportion of the children in rural India who do not attend
school. In addition to detection of refractive error blindness, two
other major issues have to be addressed to reduce this burden in India.
One is the need to have many more ophthalmic technicians in underserved
areas who are trained adequately to do a reasonable refraction. The
other is the need to develop systems through which the poor can obtain
spectacles at an affordable price. Some success is reported with a
program which addresses these various issues,33
but this
is an isolated example that needs to be developed further and applied
widely.
Corneal Blindness
Corneal blindness also causes a large number of blind-person-years
in Andhra Pradesh as a large proportion is due to corneal opacity after
childhood fever, which could possibly be vitamin A deficiency
precipitated by measles or debilitation, and is preventable. Control of
vitamin A deficiency is covered under the Reproductive and Child Health
Program in India. The coverage of prophylactic vitamin A administration
along with immunization in India has been reported to be
poor.37
This has to be improved through better primary
health care, along with efforts to improve awareness about and intake
of vitamin A rich foods. The other major causes of corneal blindness in
our study, keratitis scar and use of harmful traditional eye medicine,
can be prevented with behavioral change brought about with better
awareness. It is interesting that the prevalence of corneal blindness
was high in urban Hyderabad, the reason for which was that many of
these persons had migrated previously from rural areas to beg in
Hyderabad because corneal opacity is clearly visible to others and
makes it easier to arouse sympathy in others. Both, improvements in
primary health care and behavioral change, which could lead to
prevention of the majority of the corneal blindness, are slow processes
and can be brought about only with sustained strategies.
Glaucoma Blindness
Blindness due to primary angle-closure glaucoma is potentially
avoidable if this condition is detected early and peripheral iridotomy
or iridectomy is done. This requires detection of occludable angles,
which lead to primary angle-closure glaucoma, using slitlamp
examination and gonioscopy. Blindness due to primary open-angle
glaucoma is more difficult to prevent,38
and therefore, we
made a conservative assumption that 50% of this may be preventable if
this condition is detected early with good optic disc examination and
applanation tonometry. Because the examination techniques required to
detect glaucoma early are not practiced commonly in India, better
training of eye care providers in India has to be initiated if
blindness due to glaucoma has to be prevented.38
39
Because the strategies required to reduce the preventable blindness due to corneal disease and glaucoma are likely to become effective only over a long time, it would seem prudent to initiate these now so that their benefits start manifesting in a decade or so.
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Conclusion |
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Acknowledgements |
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Footnotes |
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Submitted for publication September 18, 2000; revised December 4, 2000; accepted December 15, 2000.
Commercial relationships policy: N.
Corresponding author: Lalit Dandona, International Centre for Advancement of Rural Eye Care, L.V. Prasad Eye Institute, Banjara Hills, Hyderabad 500 034, India. dandona{at}icare.stph.net
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