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Causes of blindness and visual impairment in Pakistan. The Pakistan National Blindness and Visual Impairment Survey

Authors:
  • Pakistan Institute of Community Ophthalmology PICO

Abstract

To determine the causes of blindness and visual impairment in adults (> or =30 years old) in Pakistan, and to explore socio-demographic variations in cause. A multi-stage, stratified, cluster random sampling survey was used to select a nationally representative sample of adults. Each subject was interviewed, had their visual acuity measured and underwent autorefraction and fundus/optic disc examination. Those with a visual acuity of <6/12 in either eye underwent a more detailed ophthalmic examination. Causes of visual impairment were classified according to the accepted World Health Organization (WHO) methodology. An exploration of demographic variables was conducted using regression modeling. A sample of 16 507 adults (95.5% of those enumerated) was examined. Cataract was the most common cause of blindness (51.5%; defined as <3/60 in the better eye on presentation) followed by corneal opacity (11.8%), uncorrected aphakia (8.6%) and glaucoma (7.1%). Posterior capsular opacification accounted for 3.6% of blindness. Among the moderately visually impaired (<6/18 to > or =6/60), refractive error was the most common cause (43%), followed by cataract (42%). Refractive error as a cause of severe visual impairment/blindness was significantly higher in rural dwellers than in urban dwellers (odds ratio (OR) 3.5, 95% CI 1.1 to 11.7). Significant provincial differences were also identified. Overall we estimate that 85.5% of causes were avoidable and that 904 000 adults in Pakistan have cataract (<6/60) requiring surgical intervention. This comprehensive survey provides reliable estimates of the causes of blindness and visual impairment in Pakistan. Despite expanded surgical services, cataract still accounts for over half of the cases of blindness in Pakistan. One in eight blind adults has visual loss from sequelae of cataract surgery. Services for refractive errors need to be further expanded and integrated into eye care services, particularly those serving rural populations.
WORLD VIEW
Causes of blindness and visual impairment in Pakistan. The
Pakistan national blindness and visual impairment survey
B Dineen, R R A Bourne, Z Jadoon, S P Shah, M A Khan, A Foster, C E Gilbert, M D Khan, on behalf of
the Pakistan National Eye Survey Study Group
...................................................................................................................................
See end of article for
authors’ affiliations
........................
Correspondence to:
Rupert Bourne, Research
Unit, Department of
Infectious and Tropical
Diseases, London School of
Hygiene and Tropical
Medicine; Rupert.Bourne@
lshtm.ac.uk
Accepted for publication
3 January 2007
Published Online First
17 January 2007
........................
Br J Ophthalmol 2007;91:1005–1010. doi: 10.1136/bjo.2006.108035
Objective: To determine the causes of blindness and visual impairment in adults (>30 years old) in Pakistan,
and to explore socio-demographic variations in cause.
Methods: A multi-stage, stratified, cluster random sampling survey was used to select a nationally
representative sample of adults. Each subject was interviewed, had their visual acuity measured and
underwent autorefraction and fundus/optic disc examination. Those with a visual acuity of ,6/12 in either
eye underwent a more detailed ophthalmic examination. Causes of visual impairment were classified
according to the accepted World Health Organization (WHO) methodology. An exploration of demographic
variables was conducted using regression modeling.
Results: A sample of 16 507 adults (95.5% of those enumerated) was examined. Cataract was the most
common cause of blindness (51.5%; defined as ,3/60 in the better eye on presentation) followed by corneal
opacity (11.8%), uncorrected aphakia (8.6%) and glaucoma (7.1%). Posterior capsular opacification
accounted for 3.6% of blindness. Among the moderately visually impaired (,6/18 to >6/60), refractive
error was the most common cause (43%), followed by cataract (42%). Refractive error as a cause of severe
visual impairment/blindness was significantly higher in rural dwellers than in urban dwellers (odds ratio (OR)
3.5, 95% CI 1.1 to 11.7). Significant provincial differences were also identified. Overall we estimate that
85.5% of causes were avoidable and that 904 000 adults in Pakistan have cataract (,6/60) requiring
surgical intervention.
Conclusions: This comprehensive survey provides reliable estimates of the causes of blindness and visual
impairment in Pakistan. Despite expanded surgical services, cataract still accounts for over half of the cases of
blindness in Pakistan. One in eight blind adults has visual loss from sequelae of cataract surgery. Services for
refractive errors need to be further expanded and integrated into eye care services, particularly those serving
rural populations.
Pakistan, the sixth most populous country in the world,
1
is a
developing country situated in the World Health
Organization’s (WHO) Eastern Mediterranean Region.
The country ranks 135 in the United Nations Human
Development Index,
2
and a recent report has suggested that
the country is facing significant hardship; a declining growth in
gross domestic product (GDP) and a near doubling of the
proportion of the population living below the poverty line
between 1987 and 2003.
3
The geography and climate of
Pakistan are extremely diverse; the eastern and southern parts
are dominated by the Indus River and its tributaries, the
northern parts by the snow-covered Himalayan mountain
range. The country’s four provinces are Punjab, Sindh, North
West Frontier Province (NWFP) and Balochistan.
The evidence base on national blindness and visual impair-
ment in Pakistan prior to this survey is extremely limited. One
study, estimating the main cause of blindness to be cataract
(66.7%),
4
led the National Committee for the Prevention of
Blindness (NCPB) to develop a Five Year National Plan for the
Prevention of Blindness (1994–1999) with a particular focus on
large-scale expansion of cataract surgical services.
The aim of this second national survey (conducted between
2002 and 2004) was to apply more rigorous survey methodol-
ogies to produce accurate data. Details of the prevalence of
blindness among adults (aged >30 years) have been published
5
and we now report on the causes of blindness and visual
impairment, providing estimates of the magnitude of the major
causes and exploring their demographic associations.
SUBJECTS AND METHODS
A detailed description of the methods used in the survey for
sampling and training, and ocular examination protocols has
already been published.
6
A brief summary of the key
methodological details is provided below.
Sample size
Based on an assumed prevalence of blindness of 1.8%, a
random sampling error precision of 0.3%, a design effect of 2.0
and a 10% increase for non-response, the total sample size was
calculated as 16 600.
Sampling strategy
Multi-stage stratified cluster random sampling, with probabil-
ity proportional-to-size (PPS) procedures, was used.
Enumeration, using the random walk method, was undertaken
until the target number of adults was attained in each cluster.
All enumerated individuals were asked to attend the survey
station, set up in their community, for ophthalmic examination
in the following days. Enumerated individuals who were
unable to attend were examined in their home whenever
Abbreviations: BL, blindness; IOL, intraocular lens; logMAR, logarithm of
minimum angle of acuity; MVI, moderate visual impairment; NCPB,
National Committee for the Prevention of Blindness; NWFP, North West
Frontier Province; OR, odds ratio; PCO, posterior capsule opacification;
SVI, severe visual impairment; WHO, World Health Organization; YAG,
yttrium–aluminium–garnet
1005
www.bjophthalmol.com
possible. Three visits were made to homes before marking the
subject as a non-responder.
Ethical and official government approval
Ethical approval was provided by the Pakistan Medical
Research Council (PMRC) in March 2002. This study followed
the tenets of the Declaration of Helsinki.
Definitions used in the ophthalmic examination
Visual impairment
The WHO categories of visual impairment were used in this
study.
7
Blindness (BL) was defined as a presenting visual acuity
(ie, with glasses for distance if normally worn, or unaided) of
,3/60 (,20/400 (logarithm of minimum angle of acuity
(logMAR) .1.30) in the better eye. Severe visual impairment
(SVI) was defined as ,6/60 to >3/60, and moderate visual
impairment (MVI) as ,6/18 to >6/60. A ‘‘near normal’’
category was also included as ,6/12 but >6/18. Any person
with an acuity of ,6/12 in the better eye was regarded as
visually impaired. As visual fields were only assessed on a
subset of the sample, constricted visual fields were not included
in the definition of blindness. The Snellen notation for visual
acuity has been used herein for ease of comparison.
Unilateral SVI/BL
This was defined as a participant presenting with >6/12 in one
eye and ,6/60 in the other eye.
Clinical examination
Distance visual acuities were measured in all subjects using a
reduced logMAR tumbling ‘‘E’’ chart.
8
All study participants
had a basic eye examination and all also underwent auto-
refraction (Nikon Retinomax K-plus II Nikon, Tokyo, Japan).
Individuals with ,6/12 presenting visual acuity in one or both
eyes (‘‘red card holders’’) were subject to a more detailed
examination. All ‘‘red carders’’ had their visual acuity retested
with the autorefraction result in a trial frame and all had a slit-
lamp examination with a dilated posterior segment examina-
tion. All ‘‘red carders’’ presenting with ,6/18 with a treatable
condition were referred to the nearest eye care facility.
Identification of causes of visual loss
The survey ophthalmologist, epidemiologist and the three
clinical ophthalmologists determined the cause(s) of visual
loss, following the principles outlined in the WHO Prevention of
Blindness Proforma (Version III). For each eye, all pathological
findings were recorded at the time of examination. Any degree
of improvement in visual acuity when retested with a refractive
correction was deemed evidence of refractive error present in
that eye. One main cause was then selected for each eye, the
WHO recommendations stipulating that (1) if any pathology is
secondary to another, the primary pathology should be selected
(eg, if the pathology was band keratopathy secondary to uveitis,
uveitis should be selected), and/or (2) conditions amenable to
treatment or (3) which could have been prevented are
preferentially selected over and above unavoidable causes.
Following this, the main cause in the right eye or the main
cause in the left eye was chosen to represent the principal cause
for the individual. If the main causes in the right eye and the
left eye differed, the principal disorder for the individual was
selected as the one most readily treatable or, if not treatable, the
one which was more amenable to prevention (eg, if the main
causes were right eye cataract and left eye optic atrophy,
cataract was selected as the principal cause). Refractive error
was considered more amenable to treatment than cataract.
9
If
refractive error and cataract co-existed in the same eye, cataract
was given as the main cause if refractive error correction did
not improve the visual acuity >6/18.
Statistical analysis
All data were double entered by two trained data processors.
Conditions were subgrouped as preventable or treatable (ie,
avoidable), or unavoidable. Cause-specific proportions of
blindness and visual impairment were determined by age
group, gender, province, location of household (rural/urban)
and level of literacy. Univariate and age/gender-adjusted
logistic regression modelling was used to explore associations
of the major causes (eg, cataract vs all other causes) with
demographic variables. Generalised estimating equations were
used in the models to adjust for dependency in the data due to
clustered sampling. Estimation of the cause-specific magnitude
in Pakistan was calculated from age- and gender-standardised
prevalence data (using the latest population data).
1
Extrapolations for the year 2020 were calculated using
projected population estimates derived from the US census
bureau.
10
RESULTS
Study population
A total of 17 314 adults (>30 years) were enumerated, 16 507
(95.3%) of whom were examined and included in this study. Of
the study sample, 53.1% were women, their mean age being
significantly lower than that of males (45.9 vs 48.9 years,
respectively, p,0.001). The demographics of responders and
non-responders, and details of the prevalence of visual
impairment have been described in detail elsewhere.
5
A total
of 4416 subjects (27%, 95% CI 26.1% to 27.4%) were identified
with a presenting visual acuity ,6/12. Of these, 561 subjects
(crude prevalence 3.4%, 95% CI: 3.1% to 3.7%) presented blind.
Causes of bilateral blindness and visual impairment
Initially, all possible pathologies of a reduced visual acuity in
eyes that presented with ,6/12 vision were recorded by the
examining ophthalmologist (total of 14 881 eyes). Refractive
error and cataract were recorded as causes in 5463 (36.7%) and
5345 (35.9%) eyes, respectively. The next most common cause
was central corneal opacity (912 eyes, 6.1%), uncorrected
aphakia (430 eyes, 2.9%) and macular degeneration (418 eyes,
2.8%).
Data were then analysed using the principal cause as shown
in table 1. Overall, an extremely high proportion of all
categories of visual loss were due to conditions which could
have been treated or prevented. A striking 85.4% of blindness
was due to avoidable causes. Unoperated cataract together with
uncorrected aphakia and posterior capsule opacification (PCO)
accounted for 46.8, 78.1 and 63.7% of MVI, SVI and blindness,
respectively. Under/uncorrected refractive errors accounted for
70.2% of visual loss in individuals with ,6/12, but only 2.7% of
blindness.
Amongst the 47 blind from ‘‘other’’ causes, posterior segment
disorders dominated, including retinitis pigmentosa (11 sub-
jects), vitreous haemorrhage (six subjects) and retinal detach-
ment (two subjects).
Causes of unilateral SVI/BL
The main causes of unilateral reduced vision are presented in
fig 1. Overall, more men were unilaterally blind than women
(238 men, 187 women, p,0.001).
Demographic variation
We have previously reported that the prevalence of blindness
increased almost exponentially with increasing age. The
1006 Dineen,Bourne,Jadoon,etal
www.bjophthalmol.com
prevalence was also associated with female gender, rural
dwelling and illiteracy.
5
Among blind subjects, cataract was the main cause in all age
groups. There were no persons blind as a result of glaucoma or
uncorrected aphakia in the 30–39 year age group; however,
among those aged 70 years and older, glaucoma and
uncorrected aphakia accounted for 9 and 10%, respectively.
PCO was not a cause of blindness in the younger age groups (ie,
30–59 years) but in older subjects it was a prominent treatable
cause (6.3% in 60–69 year olds). In contrast amblyopia was a
more common cause in younger subjects but was not reported
as a cause in subjects >60years. The highest proportion of
phthsis/absent globe as a cause was found in the youngest age
group (7.8%). The distribution in individuals with MVI is
shown in fig 2.
The principal causes of MVI stratified by demographic
variables are presented in table 2. In men, the principal cause
was cataract (45.4%), whereas in women it was refractive error
(45.4%). Provincial differences suggested that refractive error
was a more common problem in NWFP (48.5%). Similarly
refractive error was more common in urban settings (47.5%)
(whereas in rural settings cataract dominated (45.3%)) and in
literate subjects (59.3%). The proportion attributed to corneal
opacity was highest in Balochistan (9.9%).
Association analysis
The age- and gender-adjusted association analyses of the
principal cause in participants with SVI/BL are presented in
table 3. The odds of refractive error as a cause compared with
any other cause steadily decreased with age (p = 0.025),
whereas the odds of cataract and aphakia increased with each
decade (p = 0.023 and p = 0.025, respectively).
Estimate of the number of adults presenting with visual
impairment in Pakistan by cause
If the acuity level of ,6/60 is used to denote ‘‘operable
cataract’’, there are 904 000 (95% CI 736 000 to 1 107 000)
adults requiring surgery. A further 173 000 individuals have
uncorrected aphakia or PCO. A total of 1 390 000 adults have a
presenting visual acuity of ,6/60 in the better eye due to
avoidable causes (table 4). Assuming the prevalence and
patterns of causes remain unchanged, the figures for the year
2020 show that a total of 2 560 000 adults will have avoidable
causes of SVI and blindness. The estimate for ‘‘operable
cataract’’ is predicted to increase to almost 2 million by the
year 2020.
Projections for the year 2020 are shown in table 4. Regarding
adults with MVI (,6/18 to >6/60, better eye), 2 140 000 would
benefit from having their refractive error corrected, this number
increasing to 4 320 000 adults in 2020.
DISCUSSION
The survey reported in this paper used a diagnostically rigorous
methodology, similar to that used in the recent surveys in
Bangladesh and India.
11 12
The response rate was very high
(95.3%), minimising potential non-response bias. The use of
the WHO criteria for coding causes of visual loss allows
comparisons with other similarly coded surveys.
The refractive status of every individual was assessed by
autorefraction, and, furthermore, subjects with a visual acuity
of ,6/12 in either eye had trial lens-corrected visual acuities
measured. This allowed an accurate evaluation of refractive
Table 1 Principal cause, by category, of visual loss in the better eye (presenting visual acuity)
,6/12–6/18 ,6/18–6/60 ,6/60–3/60 ,3/60
n (%) n (%) n (%) n (%)
Treatable*
Refractive error 1047 (70.2) 905 (42.7) 17 (6.9) 15 (2.7)
Cataract 287 (19.2) 883 (41.6) 166 (67.8) 289 (51.5)
Uncorrected aphakia 23 (1.5) 66 (3.1) 13 (5.3) 48 (8.6)
PCO 15 (1.0) 45 (2.1) 11 (4.5) 20 (3.6)
Glaucoma 10 (0.7) 36 (1.7) 6 (2.4) 40 (7.1)
Diabetic retinopathy 4 (0.3) 10 (0.5) 1 (0.4) 1 (0.2)
Total treatable 1386 (93.0) 1945 (91.7) 214 (87.3) 413 (73.6)
Preventable*
Central corneal scar 29 (1.9) 55 (2.6) 8 (3.3) 66 (11.8)
Total avoidable 1415 (94.9) 2000 (94.3) 222 (90.6) 479 (85.4)
Unavoidable
Phthisis/absent globe 1 (0.1) 3 (0.1) 1 (0.4) 15 (2.7)
Macular degeneration 8 (0.5) 21 (1.0) 5 (2.0) 12 (2.1)
Optic atrophy 2 (0.1) 5 (0.2) 1 (0.4) 5 (0.9)
Amblyopia 10 (0.7) 13 (0.6) 2 (0.8) 3 (0.5)
Other 55 (3.7) 79 (3.7) 14 (5.7) 47 (8.4)
Total unavoidable 76 (5.1) 121 (5.7) 23 (9.4) 82 (14.6)
Grand total 1491 (100.0) 2121(100.0) 245 (100.0) 561 (100.0)
*In this analysis, a treatable condition was one in which an intervention existed to restore visual function or an
intervention existed, if administered early, that prevented the consequences of established disease. A preventable cause
was one in which a cost-effective intervention existed that prevented the condition from occurring in the first place.
PCO, posterior capsule opacification.
Posterior capsule opacification
Optic atrophy
Macular degeneration
Refractive error
Glaucoma
Uncorrected aphakia
Amblyopia
Phthisis/absent globe
Central corneal opacity
Cataract
0 5 10 15 20
25 30 35 4
0
Percentage
Figure 1 Main causes of unilateral reduced vision in 427 subjects (,6/60
presenting vision in one eye and 6/12 or better in the fellow eye). The 10
most common causes are presented.
Causes of blindness and visual impairment in Pakistan 1007
www.bjophthalmol.com
error as a cause of visual impairment, these data being
important for planning refractive error services (a priority of
the global initiative to eliminate avoidable blindness, VISION
2020: The Right to Sight
13
). The examination process also
involved a dilated examination of all eyes with a visual acuity
,6/12, allowing the detection of posterior segment disease,
which has often been overlooked in the presence of cataract.
14
For logistical reasons, fields were not performed on all
subjects. Visual fields were only performed on a subset of the
sample for normative data collection and on those who had
optic disc changes that were suggestive of glaucoma, hence the
decision not to use a definition of blindness that involved visual
field construction. As fields were not performed on all subjects,
constricted fields were not included in our definition of
blindness. As the primary cause of a phthisical/absent globe
could not always be determined, it is possible that some
‘‘unavoidable’’ cases could have been treatable or preventable
(misclassification bias).
We found 14 881 eyes with visual acuity ,6/12. When all
pathological findings in each eye were analysed together,
refractive error caused as much visual loss as cataract (36.7 and
35.6%, respectively).
Almost 75% of individuals who were blind had treatable
causes, and .90% of subjects had treatable causes of visual
impairment. The two most important treatable causes of
blindness were unoperated cataract (or uncorrected aphakia,
8.6%; and PCO, 3.6%) and glaucoma (7.1%), others being
refractive error (2.7%) and diabetic retinopathy (0.2%). In the
1990 study,
4
cataract accounted for 66.7% of blindness, whereas
the current survey found unoperated cataract accounting for
51.5%. It is not possible to compare data for cataract between
these studies directly, as different age groups were used, but the
observed reduction almost certainly represents a real reduction,
given the large-scale increase in cataract surgical service
delivery in Pakistan. However, the finding that despite this
increase nearly 1 in 10 adults in Pakistan were visually
impaired (,6/12) due to unoperated cataract highlights the
importance of continued support of the NCPB for extending
cataract surgical services in Pakistan.
In this survey, .12% of blindness was due to the sequelae of
cataract surgery (ie, uncorrected aphakia 8.6% and PCO 3.6%).
A survey conducted in rural NWFP identified uncorrected
aphakia as the second most common cause of blindness.
15
A
hospital-based study in Lahore, Pakistan showed that only 50%
of eyes among individuals returning for follow-up after cataract
surgery had had intraocular lens (IOL) implantation.
16
As low-
cost, high-quality IOLs are now readily available, IOL surgery
should be routine. Visual loss from PCO is certain to increase as
cataract surgical rates increase, and YAG (yttrium–aluminium–
garnet) lasers need to be made available for hospitals delivering
high-volume cataract surgery, with training in their use,
upkeep and repair made a priority.
After cataract and the sequelae of cataract surgery, glaucoma
was the next most important cause of treatable blindness,
accounting for 7.1%. This is lower than the 11% quoted for the
WHO Eastern Mediterranean region, subregion D, which
includes Pakistan,
18
but much higher than in a similarly
designed survey in Bangladesh (1.2%). A survey in India of
adults aged >50 years, which used a blindness definition of ,6/
60, showed that 5.8% of blindness was due to glaucoma.
19
The
earlier study in Pakistan estimated the number of people blind
100
80
60
40
20
030_39 40_49 50_59 60_69 70+
A
g
e
g
rou
p
Percentage
Other Cataract Refractive error
Figure 2 The relative contribution of the most common ocular pathologies
for the moderately visually impaired (presenting ,6/18 to 6/60) subjects
according to age group.
Table 2 Principal cause of visual loss for persons with moderate visual impairment(,6/18 but >6/60 in better eye)
n
Treatable
(%) Preventable (%)
Unavoidable
(%)
RE Cataract PCO UA DR Glaucoma Corneal opacity Optic atrophy MD Other
Gender
Male 935 39.1 45.4 2.1 2.9 0.3 2.1 2.9 0.2 1.2 3.8
Female 1186 45.4 39.8 2.1 3.3 0.6 1.3 2.4 0.3 0.8 4.0
Province
Balochistan 101 38.6 29.7 1.0 3.0 0.0 3.0 9.9 1.0 1.0 12.8
NWFP 342 48.5 36.5 2.3 1.5 0.3 0.9 4.1 0.9 1.2 3.8
Punjab 1159 40.7 43.0 1.2 5.0 0.8 2.1 2.3 0.0 1.0 3.9
Sindh 519 43.9 44.3 4.2 0.0 0.0 1.0 0.8 0.2 0.8 4.8
Location
Urban 729 47.5 34.6 2.5 2.5 1.2 1.5 2.9 0.1 1.8 5.4
Rural 1392 40.2 45.3 1.9 3.4 0.1 1.8 2.4 0.3 0.6 4.0
Literacy
Literate 290 59.3 28.6 1.0 1.7 1.4 1.7 1.4 0.3 0.3 4.3
Illiterate 1831 40.0 43.7 2.3 3.3 0.3 1.7 2.8 0.2 1.1 4.6
DR, diabetic retinopathy; MD, macular degeneration; NWFP, North West Frontier Province; PCO, posterior capsule opacification; RE, refractive error; UA, uncorrected
aphakia.
1008 Dineen,Bourne,Jadoon,etal
www.bjophthalmol.com
from glaucoma to be 80 000,
4
which is similar to the estimate
from the current survey (89 000). As cataract is becoming
increasingly controlled in developing countries, strategies for
the detection and treatment of glaucoma will need to increase
in profile. In this survey, glaucoma blindness was highest in
Balochistan, the most deprived province (89% of the rural
population live in high deprivation districts)
20
with limited
access to eye care services.
Diabetic retinopathy accounted for 0.2% of blindness.
However, this is likely to underestimate the true burden of
retinopathy in the population as diabetic patients are more
likely to have cataract, which would be preferentially recorded
as the cause of their visual loss, and vitreous haemorrhage
(possibly from diabetic neovascularisation) was classified in the
‘other’ category. It is predicted that with rapid urbanisation,
Pakistan will be among the five countries with the highest
prevalence of diabetes by the year 2025.
21
This is likely to alter
the existing pattern of blindness and, in order to prevent a
public health problem, preventive strategies need to be
established.
In the 1990 Pakistan study, refractive error (including
uncorrected aphakia) accounted for 11.4% of blindness,
4
which
is identical to the figure in the current survey, indicating that
there has been minimal progress in addressing this highly
treatable condition. Refractive error was the leading cause of
MVI, particularly among the economically active working age
group. Targeting this group, particularly with ready-made
spectacles, should be made a priority as this would prove to
be extremely cost effective. It must be recognised, however, that
barriers exist—for example, the social implications of spectacle
wear. In addition, many individuals have mild myopia and, as
they have adequate near vision, they may not feel impaired.
Corneal pathology, the main preventable cause, was the
second most common cause of blindness overall (11.8%), again
similar to that found in the 1990 survey.
4
There are many
causes of corneal scarring, trachoma being one. Trachoma is
still endemic in parts of the country, and a recent rapid
assessment found that of 233 villages surveyed, 151 (64.8%)
had individuals requiring trichiasis surgery.
22
Pakistan has set
up a dedicated national task force for trachoma control and is
part of the GET 2020 alliance.
23
Phthisis/absent globe was the most important cause of
unavoidable blindness and the third most important cause of
unilateral SVI/BL. This highlights the importance of ocular
trauma in Pakistan. A previous study on ocular trauma in
NWFP found that 57.7% of cases had a perforating injury and
that men outnumbered women by 5:1.
24
A similar gender
difference in unilateral blindness was noted in our survey.
A comparison of the findings of this survey with others in the
region shows that Pakistan has the lowest proportion of SVI/BL
(57%) due to cataract (India 62.4%,
20
Bangladesh 82%
12
).
Refractive error (including uncorrected aphakia) was lowest
in Bangladesh (7.5%), followed by Pakistan (12%) and India
(19.7%). Corneal opacity, responsible for nearly 1 in 10 cases of
SVI/BL, was particularly prevalent in Pakistan but accounted
for ,1% of SVI/BL in India
20
and Bangladesh.
12
The reason for
this high disparity is unclear but warrants further investigation.
In subjects with ,6/12, cataract and refractive error were of
similar importance in Pakistan; however, this contrasts with
Bangladesh where the main cause was cataract (73.4%), with
refractive error only accounting for 18.9%.
12
Our findings are markedly different from the findings in high
income countries where the primary causes of blindness are
age-related macular degeneration, diabetic retinopathy and
myopic degeneration, one survey in the USA indicating that
these causes accounted for 63% of blindness.
25
Based on the findings from this survey and future population
dynamics, eye care service delivery needs to continue to expand
in Pakistan, focusing principally on high-quality cataract
surgery and aftercare, and on increased capacity for the
correction of refractive errors. This recommendation is con-
sistent with the prioritised areas of action for the region as
outlined by the WHO South-East Asia policy VISION 2020: The
Right to Sight. The more challenging conditions to control,
Table 3 Age- and gender-adjusted association analysis of the principal causes of subjects presenting with severe visual impairment
and blindness (,6/60 in the better eye)
RE Cataract PCO UA Corneal opacity Glaucoma
Age*30–39 1 1 1 1 1 1
Decade increase 0.7 (0.6 to 1.0) 1.2 (1.0 to 1.3) 1.33 (0.91 to 1.96) 1.4 (1.0 to 1.8) 0.93 (0.8 to 1.1) 1.23 (0.9 to 1.7)
GenderWomen 1 1 1 1 1 1
Men 0.8 (0.4 to 1.6) 0.8 (0.6 to 1.1) 0.5 (0.2 to 1.0) 0.8 (0.5 to 1.4) 0.9 (0.8 to 1.1) 0.9 (0.5 to 1.6)
Province NWFP 1 1 1 1 1 1
Balochistan 1.0 (0.3 to 4.2) 0.5 (0.3 to 0.95) 0.6 (0.1 to 3.1) 1.5 (0.3 to 9.4) 3.61 (0.6 to 22.5) 6.2 (1.2 to 32.9)
Punjab 0.6 (0.3 to 1.6) 0.8 (0.5 to 1.2) 0.4 (0.2 to 1.1) 4.3 (1.3 to 14.0) 7.1 (1.7 to 30.0) 4.1 (1.0 to 17.5)
Sindh 0.6 (0.2 to 1.7) 0.91 (0.6 to 1.5) 0.9 (0.3 to 2.3) 1.78 (0.5 to 6.8) 8.0 (1.8 to 34.9) 2.4 (0.5 to 11.5)
Dwelling Urban 1 1 1 1 1 1
Rural 3.5 (1.1 to 11.7) 0.2 (0.7 to 1.3) 0.6 (0.3 to 1.4) 1.06 (0.6 to 1.9) 1.4 (0.8 to 2.6) 1.2 (0.6 to 2.6)
Literacy Illiterate 1 1 1 1 1 1
Literate 1.18 (0.3 to 4.5) 1.20 (0.7 to 2.2) NA`1.0 (0.3 to 3.5) 0.38 (0.1 to 1.3) 0.8 (0.2 to 3.4)
*Gender adjusted; age adjusted; `no literate subjects were found with PCO as their principal cause of severe visual impairment and blindness.
Statistically significant associations are indicated in bold (p,0.05)
PCO, posterior capsule opacification; RE, refractive error; UA, uncorrected aphakia.
Table 4 Estimated number of adults (>30 years) in
Pakistan with severe visual impairment and blindness
(presenting vision ,6/60 in the better eye) by cause (age-/
gender-standardised figures)
Cause 2003 (139 million)*2020 (213
million)
Treatable
Cataract 904 000 1 860 000
Uncorrected aphakia 116 000 238 000
Glaucoma 89 000 185 000
Refractive error 72 000 147 000
Posterior capsule opacification 57 000 119 000
Diabetic retinopathy 3200 6900
Preventable
Central corneal opacity 150 000 308 000
Other
Macular degeneration 35 000 72 000
Optic atrophy 15 000 32 000
Total1 620 000 3 320 000
*Total Pakistan population; estimated total Pakistan population
11
;
`including other causes.
Causes of blindness and visual impairment in Pakistan 1009
www.bjophthalmol.com
namely glaucoma, macular degeneration and diabetic retino-
pathy, are also emerging as priorities.
26 27
ACKNOWLEDGEMENTS
The authors are grateful for the contribution of the ‘‘Pakistan National
Eye Survey Study Group’’ which consisted of the following individuals:
Professor Shad Mohammed, Professor Zia Uddin Sheik, Professor Asad
Aslam, Professor Nasim Panazai, Dr Shabbir Mir Dr Niaz Ali. Mr Pak
Sang Lee (Technical Coordinator, International Centre for Eye Health,
London), Ikram Ullah Khan (Biomedical Engineer, Pakistan Institute of
Community Ophthalmology), Dr Haroon (Sight Savers International),
Dr Rubina Gillani (Fred Hollows Foundation), Dr Babar Qureshi
(Christoffel Blindenmission), Dr Mohammed Shabbir and Dr Falak Naz
(Clinical and Community Ophthalmologists, respectively, North West
Frontier Province team), Dr Abdul Ghafoor and Dr Kiramatullah
(Survey Ophthalmologists, Punjab and Baluchistan Teams), and Dr
Waheed Shaikh and Dr Amjad Shaikh (Survey Ophthalmologists,
Sindh Team). The survey was financially supported by the
‘‘International Blindness Prevention Collaborative Group’’ which
consisted of: The Government of Pakistan, the World Health
Organization East Mediterranean Regional Office and Pakistan Office,
Sight Savers International, Christoffel Blinden Mission, and the Fred
Hollows Foundation. The authors also wish to thank Mr Tauqeer Abbas
and Mr Fakhre-e Alam for data entry, Dr Mahwash Akhtar-Khan,
Yelena Alexander and Rahul Shah for assisting in data cleaning, and Mr
Fazl-Subhan for assisting with financial management. Heidelberg
Engineering (Heidelberg, Germany) kindly lent two HRT-II instru-
ments. Lateef Brothers, Lahore and S. Haji Ameerdin and Sons, both
based in Lahore, Pakistan, were generous in their instrument support.
Ophthalmic medications were generously donated by the NWFP
divisions of the companies Remington and Kobec.
This study was supported financially by the ‘‘International Blindness
Prevention Collaberative Group’’:
The Government of Pakistan, Sight Savers International, Christoffel
Blindenmission, Fred Hollows Foundation, WHO Pakistan Office, The
International Centre for Eye Health, Pakistan Institute of Community
Ophthalmology.
Authors’ affiliations
.......................
B Dineen, R R A Bourne, S P Shah, A Foster, C E Gilbert, International
Centre for Eye Health, Department of Infectious and Tropical Diseases,
London School of Hygiene and Tropical Medicine, London, UK
Z Jadoon, M A Khan, M D Khan, Pakistan Institute of Community
Ophthalmology, Kyber Institute of Ophthalmic Medical Sciences,
Peshawar, Pakistan
Competing interests: None declared.
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This paper presents estimates of the prevalence of visual impairment and its causes in 2002, based on the best available evidence derived from recent studies. Estimates were determined from data on low vision and blindness as defined in the International statistical classification of diseases, injuries and causes of death, 10th revision. The number of people with visual impairment worldwide in 2002 was in excess of 161 million, of whom about 37 million were blind. The burden of visual impairment is not distributed uniformly throughout the world: the least developed regions carry the largest share. Visual impairment is also unequally distributed across age groups, being largely confined to adults 50 years of age and older. A distribution imbalance is also found with regard to gender throughout the world: females have a significantly higher risk of having visual impairment than males. Notwithstanding the progress in surgical intervention that has been made in many countries over the last few decades, cataract remains the leading cause of visual impairment in all regions of the world, except in the most developed countries. Other major causes of visual impairment are, in order of importance, glaucoma, age-related macular degeneration, diabetic retinopathy and trachoma.
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India's National Programme for Control of Blindness focuses almost exclusively on cataract, based on a national survey done in the 1980s which reported that cataract caused 80% of the blindness in India. No current population-based data on the causes of blindness in India are available. We assessed the rate and causes of blindness in an urban population in southern India. We selected 2954 participants by stratified, random, cluster, systematic sampling from Hyderabad city. Eligible participants were interviewed and given a detailed ocular assessment, including visual acuity, refraction, slitlamp biomicroscopy, applanation intraocular pressure, gonioscopy, dilatation, grading of cataract, stereoscopic fundus assessment, and automated-threshold visual fields. 2522 participants, including 1399 aged 30 years or more, were assessed. 49 participants (all aged > or =30 years) were blind (presenting distance visual acuity <6/60 or central visual field <200 in the better eye). The rate of blindness among those aged 30 years or more, adjusted for age and sex, was 3.08% ([95% CI 1.95-4.21]). Causes included cataract (29.7%), retinal disease (17.1%), corneal disease (15.4%), refractive error (12.5%), glaucoma (12.1%), and optic atrophy (11.0%). 15.7% of the blindness caused by visual-field constriction would have been missed without visual-field examination. Also without visual-field and detailed dilated-fundus assessments, blindness attributed to cataract would have been overestimated by up to 75.8%. If the use of cataract surgery in this urban population was half that found in this study, which simulates the situation in rural India, cataract would have caused 51.8% (39.4-64.2) of blindness, significantly less than the 80% accepted by current policy. Much of the blindness in this Indian population was due to non-cataract causes. The previous national survey did not include detailed dilated-fundus assessment and visual-field examination which could have led to overestimation of cataract as a cause of blindness in India. Policy-makers in India should encourage well-designed population-based epidemiological studies from which to develop a comprehensive long-term policy on blindness in addition to dealing with cataract.
Article
Reported rates of posterior capsule opacification (PCO) vary widely and are based on various definitions of PCO, varying lengths and intervals of follow-up, and the use of different surgical techniques, intraocular lens (i.o.l.) designs, and methods of IOL implantation. This study was designed to obtain a more precise overall estimate of the incidence of PCO and to explore factors that might influence the rate of PCO development. A meta-analysis. Published articles were selected for study based on a computerized MEDLINE search of the literature and a manual search of the bibliographies of relevant articles. Articles meeting selected inclusion criteria were reviewed systematically, and the reported data were abstracted and synthesized using the statistical techniques of meta-analysis. Pooled estimates of the proportion of eyes developing PCO at three postoperative timepoints--1 year, 3 years, and 5 years--were measured. There is significant heterogeneity among published rates of PCO. The overall pooled estimates (95% confidence limits) of the incidence of PCO were 11.8% (9.3%-14.3%) at 1 year, 20.7% (16.6%-24.9%) at 3 years, and 28.4% (18.4%-38.4%) at 5 years after surgery. There is no evidence of a significant decline in PCO incidence during the study period. Visually significant PCO develops in more than 25% of patients undergoing standard extracapsular cataract extraction or phacoemulsification with posterior chamber intraocular lens implantation over the first 5 years after surgery. Patient characteristics, surgical techniques, and differences in research design and reporting may account for some of the variability in reported rates. However, no specific factors were identified in the authors' analysis. More precise estimates of incidence and identification of risk factors for PCO will depend on the development of a standardized measurement of PCO and wider adoption of more rigorous study methodology.
Article
To determine the current prevalence and causes of blindness in the Indian state of Andhra Pradesh to assess if blindness has decreased since the last survey of 1986-1989. 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 < 20(o) in the better eye. 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. 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.
Article
To determine the visual outcome and factors influencing visual outcome after cataract surgery in an urban charity hospital in Pakistan. A series of selected outpatients were examined who had undergone cataract surgery in the preceding 24 months. 181 patients aged 45-82 years were examined. The type of cataract operations they had had were extracapsular cataract extraction (ECCE) only in 50% (91), phacoemulsification (phaco) only in 11% (20), ECCE with intraocular lens (IOL) in 17% (31), and phaco with IOL in 22% (39). At presentation, 49.7% (90) had poor functional vision; after refraction 68% (123) had a good visual outcome. Functional vision in eyes undergoing ECCE with IOL was good in 77% (22) and with phaco with IOL in 71.8% (28). After refraction a higher proportion of eyes with IOL surgery (93%) had a good outcome than those with non-IOL surgery (53%). Uncorrected refractive error, present in 75.5% (68), was the commonest cause of poor functional vision. This study demonstrates that it is possible to obtain good results with IOL surgery in the developing world. Increasing cataract surgery with IOL implantation should reduce the number of eyes with poor functional vision after cataract surgery. More attention should be directed towards ensuring that successful outcomes are indeed being realised by continued visual monitoring postoperatively.