Blindness and eye diseases in Tibet: findings from a randomised, population based survey

1443
WORLD VIEW
Blindness and eye diseases in Tibet: findings from a
randomised, population based survey
S Dunzhu, F S Wang, P Courtright, L Liu, C Tenzing, K Noertjojo, A Wilkie, M Santangelo,
K L Bassett
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Br J Ophthalmol 2003;87:1443–1448
Background: Public health officials of the Tibet Autonomous Region (TAR) of China requested a survey of
blindness, eye diseases, and eye care service utilisation to assist the development of a 10 year blindness
prevention and treatment plan. The objective of the survey was to determine the prevalence of blindness
and visual impairment, as well as cataract surgical coverage and surgical outcome in the TAR.
See end of article for
authors’ affiliations
Methods: The Tibet Eye Care Assessment was a cross sectional prevalence study of three of the seven
. . . . . . . . . . . . . . . . . . . . . . .
prefectures (provinces) of the TAR (Lhoka, Nakchu, and Lingzhr) selected to represent its three main
environmental regions. The survey sample was selected using a random multistage cluster method. Two
Correspondence to:
Dr Ken Bassett, Director,
teams conducted the survey in a standardised fashion in each prefecture, Lhoka during May and Nakchu
Centre for Epidemiologic
during June 1999, and Lingzhr during May 2000. Visual acuity, cause of vision loss, trachoma, and
and International
vitamin A deficiency were included in the clinical examination.
Ophthalmology,
Department of
Results: Among the 15 900 people enumerated, 12 644 were examined for an overall response rate of
Ophthalmology, The
79.6%. The crude prevalence of blindness (presenting better eye visual acuity of less than 6/60) was 2.3%;
University of British
age and sex adjusted blindness prevalence was 1.4% (95% CI 1.3 to 1.5). Visual impairment (better eye
Columbia, 429-2194
presenting visual acuity of 6/24 to 6/60) was found in 10.9% (95% CI 10.5 to 11.2) of the population
Health Sciences Mall,
Vancouver BC V6T 1Z3,
(age and sex adjusted). Cataract was the primary cause of blindness (50.7%), followed by macular
Canada;
degeneration (12.7%) and corneal opacity (9.7%).
bassett@chspr.ubc.ca
Conclusion: Blindness is a serious public health problem in Tibet, with prevalence higher than in similar
Accepted for publication
studies in eastern China. As elsewhere in the world, women have an excess burden of blindness compared
17 June 2003
to men. About 75% of blindness in Tibet can be either prevented or treated. Eye care planning for Tibet
. . . . . . . . . . . . . . . . . . . . . . .
must focus on cataract, particularly among women.
The Tibet Autonomous Region (TAR) of the People’s ofblindness,eyediseases(includingtrachomaandvitaminA
Republic of China, with 1.2 million square kilometres,
deficiency), and use of eyecare services be undertaken in
forms one of the highest and harshest human habita-
their region. Their goal was to use the findings in the creation
tions on earth. Approximately 80% of its 2.4 million people
of a 10 year plan aimed at addressing the primary blinding
live in rural settings, either in small farming communities at
conditions of Tibet, a worldwide initiative to eliminate
elevations around 4000 metres or as semi-nomadic herders at
avoidable blindness by the year 2020. In response, the Tibet
higher elevations.
Eye Care Assessment (TECA) protocol was developed to
Following centuries of isolation, Tibetans have faced
measure blindness and visual impairment, trachoma and
several decades of unprecedented exposure to foreign
vitamin A deficiency, as well as cataract surgical coverage and
political and economic influence. At the same time, a growing
surgical outcome in the TAR. Cataract surgical coverage and
percentage of Tibetans have moved to urban areas. An ageing
outcome will be reported separately.
Tibetan population has greatly increased demand for health
care services, particularly services for the ‘‘diseases of ageing’’
METHODS
such as stroke, diabetes, cancer, and cataract.
Study site
The high prevalence of age related cataract blindness
TECA was a cross sectional prevalence study of three of the
among Tibetans is perhaps due to high altitude ultraviolet
seven prefectures (provinces) of the Tibet Autonomous
light exposure. Particular concern about this issue emerged in
Region, selected to represent its three main environmental
1987, following the findings from a population based cataract
regions. Lokha (population 281 738 in the 1990 census) is
survey of Duilong-Deqing County adjacent to Lhasa.1 Hu et al
characterised by a lower elevation (around 3000 metres)
reported a strikingly elevated cataract prevalence of 12–18/
farming communities and plains. Lingzhr (population
1000 (11.8% among people over 40 years of age). The
110 616) is at similar elevation to Lokha but with farming
prevalence of cataract among the Tibetans near Lhasa
communities and forests. Nakchu (population 296 023) is an
(altitude 4000 metres) was 60% higher than an age and sex
area of high elevation, primarily populated by nomadic
matched population concurrently surveyed in a county near
herders. Each prefecture is divided into counties (about
Beijing (altitude 50 metres).
20 000 population); counties are divided into townships
Hu et al raised important questions regarding the pre-
(‘‘xiangs’’); and xiangs are divided into villages.
valence of cataract among Tibetans of a relatively young age.
However, the researchers sampled only a small portion of the
Sampling plan
Tibetan population and studied only cataract prevalence.
The study population was selected using a random multistage
Public health officials in the TAR, who recognise the
cluster sampling method. The first stage of randomisation
significant need for eyecare services, requested that a survey
used a population proportional to size (PPS) method to select
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1444
Dunzhu, Wang, Courtright, et al
Table 1 Prevalence of blindness (visual acuity ,6/60) by prefecture
Age adjusted
Age and sex adjusted
% (95% CI)
Prefecture
Men
Women
% (95% CI)
p Value*
Lokha
0.97 (0.95 to 0.98)
1.53 (1.51 to 1.55)
1.25 (1.23 to 1.26)
0.02
Nakchu
1.44 (1.35 to 1.53)
2.09 (1.91 to 2.21)
1.75 (1.63 to 1.86)
0.13
Lingzhr
0.98 (0.95 to 1.01)
1.18 (1.10 to 1.26)
1.06 (1.01 to 1.11)
0.28
Total
1.11 (1.06 to 1.16)
1.60 (1.49 to 1.71)
1.39 (1.31 to 1.47)
,0.01
*Indicates comparison of men versus women
xiangs: 23/147 xiangs in Lokha, 25/146 in Nakchu, and 24/
Survey teams
177 in Lingzhr. The 23 xiangs selected in Lhoka were spread
Two teams conducted the survey in each prefecture, Lhoka
over nine of 12 counties, the 25 xiangs selected in Nakchu
during May 1999, Nakchu during June 1999, and Lingzhr
were spread over eight of 11 counties, and the 24 xiangs
during May 2000. Each team consisted of two ophthalmol-
selected in Lingzhr were spread over all seven counties.
ogists (one Tibetan trained in ‘‘Western’’ or allopathic
Within each xiang, one village (again using PPS) was
medicine at a medical school in China, and the other
selected. Forty households from each selected village
‘‘foreign’’ trained in Western medicine in India, the United
(randomly sampled from village household lists) were invited
States, or Canada); a ‘‘five senses’’ doctor (the Tibetan
to participate in the survey. With an average number of
equivalent of a specialist in eye, ear, nose, and throat
household members of five, a sample of 5000 people of all
problems) who conducted visual acuity testing; a nurse
ages was anticipated from each prefecture.
who primarily acted in a clerical role; an interviewer; two
enumerators; and two xiang/village assistants. The teams also
Sample size
included an overall team leader in charge of protocol; and
two representatives, one from the prefecture health bureau,
The sample size was calculated in order to estimate the
and one from the Tibet Development Fund who organised
prevalence of blindness (defined as better eye presenting
communication, transportation, and accommodation.
vision of ,6/60) for the adult population over 50 years of
age. The a priori assumption of blindness prevalence was
One of the authors (CT) acted as the lead ophthalmologist,
taken as 5% among people 50 years of age or older, based on
maintaining quality control and conducting clinical exam-
the earlier cataract survey in which the population prevalence
inations during the survey in all three prefectures. The same
of blindness was estimated at 1%, and at least 5% among
Tibetan ophthalmologists, five senses doctors, and enumera-
those 50 years of age and over. Based upon these assump-
tion team leaders performed the survey in all three
tions, 455 people over 50 years of age were needed from each
prefectures. The nurses, interviewers, and some of the
prefecture. Approximately 18% of the TAR population is over
enumerators were different personnel in Lingzhr prefecture
during the second year.
age 50, resulting in a total sample of at least 2528. This
sample size was doubled to 5000 in each prefecture to
compensate for the multistage (as opposed to a simple
Field procedures
random sampling) method. This larger sample size also
Enumeration
improved the assessment of use of eye care services, cataract
Under the protocol, the enumeration team was to precede the
surgical coverage, and outcome of surgery at the prefectural
clinical team by one day. In practice, however, this arrange-
level; and also accommodated anticipated non-response.
ment varied, particularly in the more sparsely populated and
Overall, a total of 15 000 individuals were to be enrolled in
geographically difficult terrain found in Nakchu. Enu-
the TECA.
merators recorded total population, number of households,
Table 2 Prevalence of blindness by age and sex by prefecture
Nakchu
Lingzhr
Lokha
Three prefectures
No (%)
No (%)
No (%)
No (%)
Men
,20 years
1 (0.19)
2 (0.45)
2 (0.35)
5 (0.33)
20–29
0
2 (0.73)
1 (0.43)
3 (0.39)
30–39
1 (0.31)
0
1 (0.40)
2 (0.23)
40–49
2 (1.12)
1 (0.65)
5 (2.46)
8 (1.49)
50–59
4 (2.05)
3 (2.14)
2 (1.11)
9 (1.74)
60–69
9 (6.82)
4 (3.51)
3 (2.07)
16 (4.09)
70+
24 (33.33)
10 (12.05)
11 (18.03)
45 (20.83)
Overall
41 (2.45)
22 (1.48)
25 (1.53)
88 (1.84)
Women
,20 years
0
1 (0.20)
1 (0.16)
2 (0.13)
20–29
0
0
1 (0.27)
1 (0.10)
30–39
1 (0.34)
0
2 (0.52)
3 (0.29)
40–49
2 (1.17)
2 (0.87)
3 (1.10)
7 (1.04)
50–59
7 (4.43)
4 (1.99)
6 (2.72)
17 (2.93)
60 to 69
9 (6.08)
4 (3.36)
12 (6.35)
25 (5.48)
70+
36 (33.33)
25 (21.37)
33 (27.73)
94 (27.32)
Overall
55 (3.33)
36 (1.98)
58 (2.68)
149 (2.64)
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Blindness and eye diseases in Tibet
1445
Table 3 Prevalence of visual impairment (visual acuity 6/24 to 6/60) by prefecture
Age adjusted
Age and sex adjusted
% (95% CI)
Prefecture
Men
Women
% (95% CI)
p Value*
Lokha
6.8 (6.7 to 6.9)
7.6 (7.4 to 7.7)
7.2 (7.1 to 7.3)
0.81
Nakchu
17.0 (16.9 to 17.1)
15.8 (15.6 to 15.9)
16.6 (16.5 to 16.7)
0.61
Lingzhr
7.7 (3.8 to 11.6)
9.9 (6.5 to 13.3)
8.7 (5.7 to 11.7)
0.85
Total
11.0 (10.6 to 11.3)
10.9 (10.5 to 11.4)
10.9 (10.5 to 11.2)
0.70
*Indicates comparison of men versus women.
distance to nearest eye care services (village, county, or
Training, pilot testing, and quality control
prefectural doctor), sanitation and service (electricity) infra-
The TECA survey was preceded by 1 month of training and
structure, subsistence activities, and transportation options.
pilot testing (1999) and reliability testing (repeated in 2000).
Elevation was recorded for each village based upon available
The lead ophthalmologist instructed the clinical team, while
maps.
epidemiologists trained the interviewers, enumerators, and
The enumerators selected 40 households from the village
data managers. Before pilot studies, 2 days of field practice
register book using random number cards, and developed the
occurred in a village close to Lhasa where approximately 100
list of household members from the village census list. The
villagers were enumerated and examined.
enumerators then visited each selected household, obtained
Inter-rater reliability was tested between the two five
consent, and completed a household form which included
senses doctors sequentially and independently in separate
further details on access to piped water, cooking facilities,
pilot tests in each year, 1999 and 2000. The five senses
latrine, electricity, and primary occupation or income gen-
doctors achieved 92% or higher agreement on major
erating activity of household. All household members were
categorisation for presenting vision in the better eye:
enumerated directly when present, or indirectly by means of
vision 6/18 or better; 6/24 to 6/60; and vision less than
questioning the people available. Empty houses were
6/60. Additional training and testing occurred in the second
revisited. Each household received a referral slip with time
year.
and place for clinical examination. As often as possible, the
In each year, diagnostic accuracy of the ophthalmologists
enumerated individuals were escorted to the clinical exam-
was tested against the senior ophthalmologist through
ination site.
independent examination of 50 patients with low vision
and blindness. Agreement was tested for: (1) the principal
Clinical examination
cause of low vision or blindness; (2) the presence of
significant cataract (causing visual acuity ,6/18); and (3)
Clinical examination usually occurred in a central village
the presence of trachoma and signs of vitamin A deficiency.
building. Visual acuity testing, clinical examination, and
During the first year, reliability testing (among 50
interviewing all occurred at the central site.
residents) occurred in a village in Lokha prefecture, not
A five senses doctor tested presenting visual acuity
selected for the survey. The ophthalmologists achieved
separately in each eye using a ‘‘Tumbling E’’ chart at a
100% agreement for the basic clinical examination. They
distance of 6 metres. If the person was wearing glasses (for
agreed in 88.2% of cases that cataract was the principal
distance vision), then his/her visual acuity was measured
cause of low vision or blindness. The two cases where the
again without glasses. If the presenting visual acuity was
teams disagreed were resolved through discussion. For
,6/18 in either eye, pinhole visual acuity was assessed.
Lingzhr, a similar test was conducted and agreement was
comparable.
Ophthalmologist examination
Accuracy was determined by observation of interviews.
Ophthalmologists conducted basic eye examinations, which
Inter-rater agreement was evaluated by discussion following
included visual inspection of the lid and globe, and
each pilot study day.
ophthalmoscopic examination of the cornea, anterior cham-
The senior ophthalmologist (CT) actively supervised all
ber, and lens, using a slit lamp. Trachoma was graded
survey teams for a week at the start of the survey in all three
according to the WHO simplified system.2 Clinical evidence of
prefectures. Enumeration data were compared with more
vitamin A deficiency included assessment of Bitot spots,
detailed questions asked by the interviewers for utilisation of
night blindness, conjunctival xerosis, and corneal xerosis.
eye care services, completed for individuals with visual
Ophthalmologists dilated the pupils if visual acuity was
impairment.
,6/18 and not the result of corneal disease or phthisis bulbi,
and assessed the cause of vision loss with retinoscopy. In all
Data analysis and reporting
cases of cataract surgery the eye was assessed for cause of a
For data analysis and reporting, we sorted individuals into
failure to reach 6/18 or better.
three categories according to better eye presenting visual
Table 4 Causes of blindness (visual acuity ,6/60) by prefectures (% of total blindness)
No of
Cataract, not
Aphakia, not Corneal
Macular
Prefecture
blind
operated
corrected
opacity
degeneration
Glaucoma
Refractive error
Globe
Others
Lokha
84
51.2%
6.1%
10.7%
15.5%
2.4%
4.8%
6%
3%
Nakchu
96
59.0%
3.6%
9.6%
18.1%
1.2%
6.0%
0%
2.5%
Lingzhr
81
42.0%
3.7%
8.6%
13.6%
3.7%
3.7%
11.1%
13.6%
Total
261
50.7%
4.7%
9.7%
15.7%
2.5%
4.8%
5.7%
6.2%
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1446
Dunzhu, Wang, Courtright, et al
Table 5 Comparison of blindness prevalence (visual acuity ,6/60) age 50 and older,
Tibet prefectures versus Shunyi and Zhongshan regions
Age adjusted
Age and sex adjusted
% (95% CI)
Prefecture
Men
Women
% (95% CI)
Lokha
4.0 (3.3 to 4.7)
8.7 (7.5 to 9.9)
6.7 (5.7 to 7.7)
Nakchu
11.2 (9.4 to 13.0)
19.2 (16.1 to 22.3)
15.5 (13.0 to 18.0)
Lingzhr
4.1 (1.8 to 6.4)
6.3 (5.2 to 7.4)
5.2 (4.5 to 5.9)
Total
7.5 (6.6 to 8.4)
14.2 (12.0 to 16.4)
10.9 (9.3 to 12.5)
Shunyi5
1.7
3.5
2.8 (2.4 to 3.1)
Zhongshan4
2.9
3.5
4.4 (3.8 to 4.9)
acuity: vision 6/18 or better; 6/24 to 6/60; and vision less than
Of the 15 900 enumerated people, 12 644 were examined
6/60. Blindness was defined as a presenting visual acuity (in
for an overall response rate of 79.6%; highest in Nakchu
the better eye) of less than 6/60 (,20/200 or ,0.10)
(81.4%) and lowest in Lingzhr (76.9%). The response was
according to Chinese Ministry of Public Health guidelines.
highest among women (82.7%) than men (75.7%), and 86%
Visual impairment was defined as a presenting visual acuity
among people over age 50 years.
(in the better eye) of 6/24 to and including 6/60.
Prevalence estimates were calculated, with 95% confidence
Blindness and visual impairment
intervals, for the three major visual acuity categories, as well
The crude prevalence of blindness (presenting visual acuity of
as for the most common causes of blindness and low vision:
less than 6/60) was 2.3%. The age and sex adjusted
cataract, corneal opacities, refractive error, and disorganised
prevalence of blindness shown in Table 1 was 1.39% (95%
globe. Prefecture specific and overall prevalence estimates
CI 1.31 to 1.47). As expected, blindness increased with age; as
were calculated. Tibet census data were used to adjust the
shown in Table 2, residents over 70 years of age accounted for
overall prevalence estimates for age and sex. We used
58.6% of all blindness (51% for men and 63% for women). If
Mantel-Haenzel x2 test to evaluate age and sex differences
the three selected prefectures are representative of Tibet’s 2.4
in blindness prevalence.3
million residents, there are approximately 27 600 who are
The cataract blindness prevalence estimates include oper-
blind. Using the WHO definition of blindness (,3/60 or
ated and unoperated individuals. Unoperated cataract blind
,20/400, or ,0.05), the age and sex adjusted prevalence of
were defined as bilaterally blind individuals with cataract as
blindness was 0.89% (95% CI 0.84 to 0.94). Women had a
the principal cause of blindness in at least one eye. Operated
significantly higher prevalence of blindness, at 1.02% (95% CI
cataract blind patients were assumed bilaterally blind at the
0.95 to 1.09) than men, at 0.76% (95% CI 0.72 to 0.80).
time of operation if both eyes had undergone surgery, or if
Visual impairment (better eye presenting visual acuity of
the unoperated eye was blind at the time of surgery.
6/24 to 6/60), was found in 10.9% (95% CI 10.5 to 11.2) of the
population (age and sex adjusted). It was significantly higher
RESULTS
in Nakchu compared to other prefectures (Table 3).
Population sampled, enumerated, and examined
All randomly selected clusters were identified and examined
Causes of blindness
in Lhoka and Nakchu, 23 and 25 clusters, respectively.
Cataract was the most common cause of blindness, account-
However, in remote areas in both prefectures, a degree of
ing for 50.7% of all cases. The second leading cause of
substitution of villages occurred because the survey team
blindness was macular degeneration (15.7%), followed by
faced considerable difficulty identifying individual villages by
corneal opacity (9.7%) (Table 4). Treatable causes of
name. In Lingzhr, the survey team substituted three of the
blindness (cataract, uncorrected aphakia, and refractive
seven counties (constituting 43% of the sampled population)
error) accounted for approximately 60% of the total cases.
because of heavy rains and poor road conditions. They
Preventable causes of blindness (most corneal opacities and
substituted randomly selected clusters from the remaining
globe related conditions such as phthisis bulbi) accounted
available areas to achieve the targeted number of enumerated
for approximately 16% of the total. As there is no practical
people.
treatment for macular degeneration, we estimate that
Table 6 Comparison of visual impairment (visual acuity 6/24– 6/60) prevalence age 50
and older, Tibet prefectures versus Shunyi and Zhongshan regions
Age adjusted
Age and sex adjusted
% (95% CI)
Prefecture
Men
Women
% (95% CI)
Lokha
39.6 (38.6 to 40.6)
36.9 (36.1 to 37.8)
38.1 (37.5 to 38.8)
Nakchu
76.9 (71.0 to 83.0)
67.1 (61.0 to 73.0)
72.8 (70.0 to 76.1)
Lingzhr
27.5 (21.6 to 33.4)
42.1 (39.4 to 44.8)
42.1 (38.3 to 45.9)
Total
49.9 (47.0 to 52.8)
47.5 (44.2 to 50.8)
48.5 (46.1 to 50.9)
Shunyi5
16.0
20.0
18.2
Zhongshan4
NA
NA
25.5
NA = data not available.
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Blindness and eye diseases in Tibet
1447
about 75% of blindness in Tibet could be either prevented or
preclude the possibility of small foci of disease. It should be
treated.
noted that the WHO simplified grading of trachoma, not
In the working age population (age 15–50), 25 individuals
generally practised in China, is more restrictive than the
were found to be blind, of whom 36% were blind due to
Chinese grading system.
cataract, 20% due to refractive error, 16% due to corneal
Several limitations may affect the reliability of our study.
opacity, 8% due to globe, and 20% due to other causes.
Approximately 80% of the enumerated sample were exam-
Among the 2080 children under 15 years of age only eight,
ined (.85% in the 50+ age group). Under-represented were
0.39% (95% CI 0.17 to 0.76) were blind, four due to cataract,
people living in the most inaccessible terrain and/or at the
two due to corneal opacity, and one each due to disrupted
extremes of altitude. These people may have a high
globe and others. Based on TECA findings, approximately
prevalence of eye diseases and visual impairment. Also
1100 children in Tibet are blind, among whom one half could
under-represented were younger men working away from
have been or could be corrected with cataract surgery.
their village at the time of enumeration. Family members
There were only 34 children (0.3%) with evidence of
provided what were considered to be reliable estimates of the
clinical vitamin A deficiency (Bitot spots, night blindness or
visual function of these absentee household members: almost
corneal xerosis). Vitamin A deficiency was similar in all three
all were (reasonably) considered not to have significant
prefectures. We found no clinical cases of trachoma, either
visual impairment. In a number of villages in Lokha, it was
active or cicatricial.
suggested that there had been some substitution of house-
Cataract was defined as a white or grey pupil and a visual
holds, thus breaking randomisation. However, follow up
acuity of ,6/18 without a central corneal opacity, in a person
enumeration and examination of individuals in these villages
who was examined with a retinoscope. For the purposes of
during the following year did not substantiate broken
this study, a patient with a history of cataract surgery in
randomisation concerns.
either or both eyes was also defined as a cataract patient. The
In summary, blindness and visual impairment are sig-
prevalence of cataract was 5.2% overall and 13.8% for people
nificant public health problems in the TAR, with the most
over age 50.
elderly having rates of blindness between 12% (Lingzhr men)
and 33% (Nakchu men and women). As recognised in many
DISCUSSION
settings,6 women in Tibet bear two thirds of the burden of
blindness. Excess prevalence was not related to age, as
The prevalence of blindness found in Tibet is higher than that
women in all older (50+ years) age groups had a higher
reported for other regions of China, Zhongshan (Guangdong
prevalence of blindness compared to men.
Province)4 and Shunyi (Beijing Province).5 Comparing people
Based in part on the TECA findings, in June 2002 the
50 years of age and older, blindness prevalence in the TAR is
TAR Health Bureau launched a master plan to increase
about three times that of these provinces (Table 5). In all
the quality and quantity of eye care services in the TAR for
three studies, women over age 50 had about twice the
the next 10 years. Focusing first on cataract, the master
prevalence of blindness as men, similar to survey findings
plan follows the framework outlined in both the World
from other settings.6
Health Organization’s Vision 2020 ‘‘The Right To Sight’’,
The two surveys from Zhongshan4 and Shunyi5 also
and the Chinese national ‘‘Blindness Prevention and Eye
provided visual impairment findings, for people over age 50
Care’’ documents. Targets have been set and funds directed,
years. The prevalence of visual impairment in the TAR is
largely from foreign agencies working in Tibet, to improve the
about twice that found in the Zhongshan and Shunyi studies
skill of Tibetan eye care professionals through further
(Table 6).
training and supervision. In addition, community based
Unoperated cataract accounted for half of all blindness in
educational and promotion programmes are planned to
Tibet, similar to the studies in Zhongshan (61.5%) and
improve knowledge and use of services, particularly by women.
Shunyi (45.7%). The higher prevalence of cataract in Tibet1 is
likely to be the primary reason for the higher blindness
ACKNOWLEDGEMENTS
prevalence in Tibet compared to Shunyi or Zhongshan.
We would like to acknowledge the significant contributions of the
Cataract prevalence for people over age 40 is 9.6%, which is
Tibet Autonomous Region Health Bureau for organisational support,
slightly less than the prevalence reported by Hu et al of 11.8%.
the Tibet Development Fund (particularly Mr Ngapo Jigyuan, Mr
Because cataract prevalence increases with age, the
Taring Jigme, Mr Tseden Dorjee, Mr Osman) for logistical support,
number of blind and visually impaired people is likely to
the Seva Canada and Seva Foundation for funding support, foreign
increase in the TAR as life expectancy rises, unless specific
volunteers (Ken Baum, Stanley Chan, Jane Gardiner, Linda Harth,
interventions are implemented to address the problem.
Grace Li, Karol Mikulash, Peter Nash, Maura Santangelo, Pearl
Nakchu, the highest and most remote prefecture, was
Wieringa, Erik Fleischman, and Laurence Schenk) and collaborating
Tibetan ophthalmologists (Dr Tsering Wangdul, Dr Tseden Yangkyi,
found to have the highest prevalence of blindness and visual
Dr Chunwa). We are grateful to the Tibetan population for their
impairment, compared to Lokha and Lingzhr. The cause of
generous participation in the project.
this increased prevalence remains unclear from the TECA
data. The prevalence of cataract (both operated and
. . . . . . . . . . . . . . . . . . . . .
unoperated) was higher in Nakchu than in Lokha and
Authors’ affiliations
Lingzhr, but this was not statistically significant. The lack of
S Dunzhu, F S Wang, Tibet Autonomous Region Public Health Bureau,
statistical significance is likely to be a reflection of
Tibet
insufficient study power to detect the small differences
P Courtright, L Liu, K Noertjojo, K L Bassett, British Columbia Centre for
between prefectures.
Epidemiologic and International Ophthalmology, Canada
There is little clinical evidence of vitamin A deficiency.
P Courtright, Kilimanjaro Centre for Community Ophthalmology, Kenya
C Tenzing, A Wilkie, M Santangelo, K L Bassett , Seva Foundation,
However, our sample of children was inadequate to provide
Seva Canada
reliable estimates. Since isolated instances of vitamin A
deficiency were found, further investigation is warranted in
certain districts. Current vitamin A deficiency interventions
Series editors: W V Good, S Ruit
(nutrition education and vitamin A capsule distribution)
should continue. Although reported by Tibetan colleagues as
REFERENCES
a leading cause of eye disease, trachoma related corneal
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disease is not a cause of blindness in Tibet. This does not
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Dunzhu, Wang, Courtright, et al
2 Thylefors B, Dawson CR, Jones BR, et al. A simple system for the assessment of
5 Zhao J, Jia L, Sui R, et al. Visual acuity and quality of life outcomes in
trachoma and its complications. Bull World Health Organ 1987;65:477–83.
patients with cataract in Shunyi county, China. Am J Ophthalmol
3 Armitage P, Berry G, Matthers JNS. Statistical methods in medical research.
1998;126:515–23.
4th ed. Oxford: Blackwell Publishing, 2002.
6 Abou-Gareeb I, Lewellen S, Bassett KL, et al. Gender and blindness: a meta-
4 Li S, Xu J, He M, et al. A survey of blindness and cataract surgery in Doumen
analysis of population-based prevalence surveys. Ophthalmic Epidemiol
County, China. Ophthalmology 1999;106:1602–8.
2001;8:39–56.
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