INTRODUCTION
Bhutan, a landlocked nation with about 800,000 people,
is known for its high mountain ranges in the southern Himalayas. Gelephu,
located in Sarpang District, with a population of 48,776, is home to the
Central Regional Referral Hospital (CRRH)1. CRRH caters medical
services to central Bhutan including Sarpang, Bumthang, Trongsa, Dagana,
Zhemgang and Tsirang districts. The Ophthalmology Department in CRRH serves as
the referral center for these areas, offering eye care to over 132,950
individuals in the region1. The hospital’s ophthalmology department
is equipped to handle a wide range of eye conditions and offers services such
as routine eye examinations, cataract surgeries, and treatment for glaucoma and
other ocular diseases. Astigmatism is a type of refractive error, derived from
a Greek word, which has two components; “a” means absence, and “stigma” means a
point. It is a refractive error (ametropia) that occurs when parallel rays of
light entering the eye, when the accommodation is at rest, are not focused at
one point on the retina due to irregular curvature of the cornea or of the lens
surface2. Astigmatism commonly occurs with other forms of refractive
errors and is corrected by a cylindrical lens in a pre-determined axis.
Astigmatism can be categorized according to the positioning of focal
points/median, axis orientation, and magnitude.
In 2020, approximately 2.2 billion people worldwide lived
with visual impairment, amongst which at least one billion cases could have
been prevented3. Globally, Uncorrected Refractive Error (URE) is the
leading cause of moderate to severe visual impairment4. Evidence
suggests that South Asia has the largest number of people with URE, and
astigmatism is more prevalent in Asian populations than other refractive errors5,6.
The Bhutan School Sight Survey (BSSP) conducted in 2019 found that URE was the
main cause of visual impairment in children, with astigmatism being the most
prevalent (9.75%)7.
Astigmatism during infancy disrupts emmetropia and is
associated with an increased risk of amblyopia8-10. Early
identification and treatment of astigmatism in children is crucial to avoid
defects in their vision development and also pivotal for timely remedial
interventions11. It is associated with headaches of unknown origin
and concomitant strabismus12-14. If left uncorrected, this can lead
to social and economic consequences for both the patients and their families15-17.
Understanding the prevalence and determinants of astigmatism is necessary to
address this major cause of visual impairment.
All-age data on the prevalence and types of astigmatism is
not available in Bhutan. While Bhutan considers providing free spectacles to
its population, there is no evidence on the types of spectacles required. This
study was expected to generate data on prevalence and types of astigmatism, and
its association with demographic profile. This study will help us plan for
larger population-based studies on astigmatism in the country.
METHODS
This was a cross-sectional study conducted in the
ophthalmology department at the CRRH in Gelephu. It received ethical approval
from the Research Ethics Board of Health of Bhutan (REBH/ Approval/2021/118,
protocol ID: PO2021118, dated: 22/11/2021). Site and administrative clearances
were also granted by CRRH and the Policy and Planning Division, respectively.
Inclusion criteria included all individuals aged ≥ 6 years
availing ophthalmic services and diagnosed with astigmatism. Individuals < 6
years of age, those with a history of corneal injuries, history of any
intraocular surgeries, and history of pterygium surgery were excluded from the
study. Written informed consent was obtained from all the participants and for
participants aged less than 18 years, verbal assent was taken from their parent
or guardian.
All patients underwent ocular examination which included
uncorrected distance visual acuity assessment using a Snellen chart (Tumbling
E), refraction with a streak retinoscopy (Welch Allen) performed by an
optometrist to evaluate the amount of astigmatism, and fundus examination
performed by an ophthalmologist. Jackson’s cross-cylinder was used to determine
the final astigmatic error. Cycloplegic refraction using
cyclopentolate/tropicamide eye drops was done for children. All patients
diagnosed with astigmatism after this assessment were potential participants
for the study and were enrolled after informed written consent. Once enrolled,
further data regarding their demographics were gathered using structured
pro-forma. All data from the examination were noted on this pro-forma. For the
purpose of uniformity, astigmatism was defined as cylindrical refractive error
measured after refraction or cycloplegic refraction expressed in correcting
plus or minus cylinder form. It was further classified into different types
based on meridians, axis and magnitude as described in Box 1.
The data from the structured pro-forma was extracted,
double-entered to ensure the accuracy and quality of data, and validated using
Epidata Version 4.6. Data analysis was done using STATA/SE, version 14.1. The
correlation of different types of astigmatism between the two eyes were tested
using the Pearson correlation coefficient and categorical data were analyzed
with Chi-Squared test with Cramer’s V (types of astigmatism against age group,
gender, region, occupation, and education level) with the confidence level kept
at 95%. A p-value of less than 0.05 indicated a statistically significant
association.
Box 1. Diagnostic criteria for
astigmatism
|
A] Based on positions of focal points/meridional2
•
Simple
myopic astigmatism: If one focal point lies in front of the retina and the
other on the retina
e.g. Plano/-0.75x160.
•
Compound
myopic astigmatism: If both focal points lie in front of the retina e.g.
-1.00/-1.00x150.
•
Simple
hyperopic astigmatism: If one focal point lies behind the retina and the other on
the retina e.g. Plano/+1.00x70.
•
Compound
hyperopic astigmatism: If both focal points lie behind the retina e.g.
+1.25/+1.50x80.
•
Mixed
astigmatism: If one focal point lies in front of the retina and the other behind
the retina e.g. -0.50/+1.50x120.
B] Based on axis11,25
•
With
the rule astigmatism (WTR): If the axis of the cylinder falls within 180°±15°
•
Against
the rule astigmatism (ATR): If the axis of the cylinder falls within 90°±15°.
•
Oblique
astigmatism: If the axis of the cylinder falls other than 180°±15° and 90°±15°.
C] Based on magnitude23
•
Mild
astigmatism: If the cylinder falls <1.50D(0.25-1.25)
•
Moderate
astigmatism: If cylinder falls between 1.50D-2.50D
•
High
/ significant astigmatism: If cylinder is more than
2.50D
|
RESULTS
Characteristics of study participants
Of the 302 participants with astigmatism, 175 (57.9%) were
females. The mean age was 30.59 ± 18.9 years (range 6-94 years).
Table 1 shows that those in the age
group of 16-25 years had the highest proportion (28.8%) of astigmatism followed
by those in the age group of 6-15 years (22.5%). The majority of participants
were students (41.9%) followed by those with elementary occupations (15.3%),
which included manual workers, labourers, and cleaners.
Prevalence
and types of astigmatism
The overall prevalence of astigmatism in the individuals
availing ophthalmic services at CRRH was found to be 4.18%. The total number of
ophthalmic patients who availed the service during that period was used as the
denominator to find the prevalence. Table 2 shows the breakdown of different
types of astigmatism amongst males and females. Compound myopic astigmatism
(146 in the right eye and 139 in the left eye) was most common followed by
simple myopic astigmatism (91 in the right eye and 96 in the left eye) with
regards to meridional astigmatism. The most prevalent axis astigmatism was
with-the-rule astigmatism (161 in the right eye and 153 in the left eye) while
the least common axis astigmatism was oblique (12 in the right eye and 15 in
the left eye). Amongst both children and adults, mild astigmatism was the most
prevalent in both right and left eyes, as depicted in Table 3.
Table 1. Demographic profile of individuals availing ophthalmic services
at CRRH, Sarpang (N=302)
|
Categories
|
n (%)
|
|
Age group, years
6-15
|
68 (22.5)
|
|
16-25
|
87 (28.8)
|
|
26-35
|
43 (14.3)
|
|
36-45
|
39 (12.9)
|
|
46-55
|
23 (7.6)
|
|
56-65
|
25 (8.3)
|
|
66+
|
17 (5.6)
|
|
Sex
Male
|
127(42.1)
|
|
Female
|
175(57.9)
|
|
Occupation Managers
|
2(0.7)
|
|
Professionals
|
20(6.6)
|
|
Associate
professionals & technicians
|
6(2.0)
|
|
Clerical
support workers
|
3(1.0)
|
|
Services
& sales workers
|
11(3.7)
|
|
Skilled
agricultural, forestry & fishery workers
|
36(11.6)
|
|
Craft
related trade workers
|
4(1.3)
|
|
Plant
& machine operators and machine workers
|
4(1.3)
|
|
Elementary
occupation
|
46(15.3)
|
|
Armed
forces
|
9(3.0)
|
|
Students
|
126(41.9)
|
|
Religious
(Monk/nun)
|
6(2.0)
|
|
Unemployed
|
29(9.6)
|
|
Region West
|
5(1.7)
|
|
Central
|
289(95.7)
|
|
East
|
8(2.6)
|
|
Education No education
|
80 (26.5)
|
|
*Primary
school
|
42 (13.9)
|
|
†Lower-Middle
secondary school
|
86 (28.5)
|
|
$Higher
secondary school
|
51 (16.9)
|
|
Diploma/certificate
|
9 (3.0)
|
|
Bachelor's
degree & above
|
34 (11.2)
|
*Primary school – includes
Pre-Primary-Class VI; †Lower-Middle secondary school – includes Class VII-X;
$Higher secondary school – includes Class XI-XII
Monocular
visual acuity characteristics
The majority of participants (90.73%) had uncorrected visual
acuity between 6/12 and 6/60, as shown in Figure 1. However, 95.37% of them had
their visual acuity corrected by just having a refraction and being prescribed
glasses. Mean cylindrical powers for right and left eye were -1.16 ± 1.08 D and
-1.13 ± 1.04 D respectively.
Figure 1. Uncorrected and best corrected visual acuity of the
individuals availing ophthalmic services at CRRH; UCVA-uncorrected visual
acuity, BCVA-best corrected visual acuity
Association
between types of astigmatism with demographic profile
A Pearson’s Chi-squared test with Cramér's V was conducted to
evaluate the association between various types of astigmatism and demographic
variables, including gender, age group, region, education level, and
occupation. No significant associations were found between the types of
astigmatism (classified by meridional orientation, axis, and magnitude for both
the right and left eyes) and either gender or region. However, an association
was observed between different types of astigmatism with both age group and
education level (p < 0.05), with the exception of magnitude astigmatism,
where no socio-demographic characteristics were significantly associated. Axis
astigmatism exhibited an association with occupation (p < 0.05), while other
forms of astigmatism did not show any significant relationship with occupation
(Tables 4 and 5).
Table 2. Distribution of gender and
types of astigmatism in individuals availing ophthalmic services at CRRH,
Sarpang (N=302)
|
Types of astigmatism
|
Right eye optics
|
Left eye optics
|
|
Male Female
|
Male Female
|
|
|
n (%) n (%)
|
n (%) n (%)
|
|
Based on positions of focal points
|
Simple
myopic astigmatism
Simple hyperopic astigmatism
|
38
(41.8)
3 (75.0)
|
53
(58.2)
1 (25.0)
|
39
(40.6)
3 (60.0)
|
57
(59.4)
2 (40.0)
|
|
|
|
Compound myopic astigmatism
|
57 (39.0)
|
89 (61.0)
|
54 (38.8)
|
85 (61.2)
|
|
|
|
Compound hyperopic astigmatism
|
1 (100)
|
0 (0.0)
|
1 (100)
|
0 (0.0)
|
|
|
|
Mixed astigmatism
|
24 (50.0)
|
24 (50.0)
|
22 (48.9)
|
23 (51.1)
|
|
|
|
$Not applicable
|
4 (33.3)
|
8 (66.7)
|
8 (50.0)
|
8 (50.0)
|
|
|
Based on axis
|
*WTR
|
71 (44.1)
|
90 (55.5)
|
64 (41.8)
|
89 (58.2)
|
|
|
|
†ATR
|
50 (42.7)
|
67 (57.3)
|
50 (42.4)
|
68 (57.6)
|
|
|
|
Oblique
|
2 (16.7)
|
10 (83.3)
|
5 (33.3)
|
10 (66.7)
|
|
|
|
$Not applicable
|
4 (33.3)
|
8 (66.7)
|
8 (50.0)
|
8 (50.0)
|
|
|
Based on magnitude
|
Mild
|
81 (39.3)
|
125 (60.7)
|
82 (40.4)
|
121 (59.6)
|
|
|
|
Moderate
|
33 (52.4)
|
30 (47.6)
|
28 (47.5)
|
31 (52.5)
|
|
|
|
High
|
9 (42.9)
|
12 (57.1)
|
9 (37.5)
|
15 (62.5)
|
|
|
|
$Not applicable
|
4 (33.3)
|
8 (66.7)
|
8 (50.0)
|
8 (50.0)
|
|
|
|
|
|
|
|
|
|
*WTR-with-the-rule
astigmatism; †ATR-against-the-rule astigmatism; $ Not applicable-the
participant had astigmatism in only one eye
Table 3. Proportion of magnitude of
astigmatism in children and adults availing ophthalmic services at CRRH,
Sarpang (N=302)
|
Magnitude
|
|
Right eye optics
|
|
Left eye optics
|
|
Male
|
Female
|
Male
|
Female
|
|
|
n (%)
|
n
(%)
|
n (%)
|
n
(%)
|
Mild
|
Children
(6 -17 years)
|
27 (45.8)
|
32
(54.2)
|
29 (47.5)
|
32 (52.5)
|
|
Adults
(18+ years)
Moderate
|
54 (36.7)
|
93
(63.3)
|
53 (37.3)
|
89 (62.7)
|
|
Children
(6-17 years)
|
13 (68.4)
|
6
(31.6)
|
10 (66.7)
|
5
(33.3)
|
|
Adults
(18+ years)
High
|
20 (45.5)
|
24
(54.5)
|
18 (40.9)
|
26 (59.1)
|
|
Children
(6-17 years)
|
6 (50.0)
|
6
(50.0)
|
5 (45.5)
|
6
(54.5)
|
|
Adults
(18+ years)
*Not applicable
|
3 (33.3)
|
6
(66.7)
|
4 (30.8)
|
9
(69.2)
|
|
Children
(6-17 years)
|
1 (33.3)
|
2
(66.7)
|
3 (50.0)
|
3
(50.0)
|
|
Adults
(18+ years)
|
3 (33.3)
|
6
(66.7)
|
5 (50.0)
|
5
(50.0)
|
*Not applicable because
these participants had astigmatism in only one eye
Table 4: Chi-square test
of association between socio-demographic characteristics and types of
astigmatism (based on positions of focal points) for right and left eye optics
|
Socio-demographic charac-
teristics
(n=290)+
|
|
Right eye optics
|
|
|
Left eye optics
|
|
Statistical values
|
|
Simple Myopic
|
Simple Com- ComHyper- pound pound
opic Myopic Hyper-
opic
|
Mixed
|
Simple Myopic
|
Simple Com- ComHyper- pound pound
opic Myopic Hyper-
opic
|
Mixed
|
χ2 Cramér's p-value V
|
|
|
n (%)
|
n (%) n (%) n (%)
|
n (%)
|
n (%)
|
n (%) n (%) n (%)
|
n (%)
|
1st row statistical values for right eye & 2nd row for left eye
|
Sex
|
Male
|
38 (41.8)
|
3 (75.0)
|
57 (39.0)
|
1 (100)
|
24 (50.0)
|
39 (40.6)
|
3 (60.0)
|
54 (38.8)
|
1 (100)
|
22 (48.9)
|
4.924
|
0.13
|
0.295
|
|
Female
Age-group
|
53 (58.2)
|
1 (25.0)
|
89 (61.0)
|
0 (0.0)
|
24 (50.0)
|
57 (59.4)
|
2 (40.0)
|
85 (61.2)
|
0 (0.0)
|
23 (51.1)
|
3.555
|
0.112
|
0.47
|
|
6-15
|
24 (26.4)
|
1 (25.0)
|
26 (17.8)
|
0 (0.0)
|
14 (29.2)
|
25 (26.0)
|
2 (40.0)
|
24 (17.3)
|
0 (0.0)
|
13 (28.9)
|
|
|
|
|
16-25
|
24 (26.4)
|
0 (0.0)
|
52 (35.6)
|
0 (0.0)
|
9 (18.8)
|
24 (25.0)
|
0 (0.0)
|
52 (37.4)
|
0 (0.0)
|
8 (17.8)
|
73.726
|
0.252
|
p<0.001
|
|
26-35
|
11 (12.1)
|
0 (0.0)
|
29 (19.9)
|
0 (0.0)
|
3 (6.2)
|
10 (10.4)
|
0 (0.0)
|
27 (19.4)
|
0 (0.0)
|
3 (6.7)
|
|
|
|
|
36-45
|
17(18.6)
|
0 (0.0)
|
20 (13.7)
|
0 (0.0)
|
1 (2.1)
|
20 (20.8)
|
0 (0.0)
|
19 (13.7)
|
0 (0.0)
|
0 (0.0)
|
74.493
|
0.256
|
p<0.001
|
|
46-55
|
6 (6.6)
|
0 (0.0)
|
10 (6.8)
|
0 (0.0)
|
6 (12.5)
|
7 (7.3)
|
0 (0.0)
|
9 (6.5)
|
0 (0.0)
|
6 (13.3)
|
|
|
|
|
56-65
|
6 (6.6)
|
2 (50.0)
|
2 (1.4)
|
1 (100)
|
12 (25.0)
|
7 (7.3)
|
2 (40.0)
|
2 (1.4)
|
1 (100)
|
10 (22.2)
|
|
|
|
|
66+
Education
|
3 (3.3)
|
1 (25.0)
|
7 (4.8)
|
0 (0.0)
|
3 (6.2)
|
3 (3.1)
|
1 (20.0)
|
6 (4.3)
|
0 (0.0)
|
5 (11.1)
|
|
|
|
|
No education
|
29 (31.8)
|
3 (75.0)
|
28 (19.2)
|
1 (100)
|
15 (31.3)
|
30 (31.2)
|
3 (60.0)
|
26 (18.7)
|
1 (100)
|
16 (35.6)
|
|
|
|
|
Primary
|
16 (17.6)
|
0 (0.0)
|
15 (10.3)
|
0 (0.0)
|
11 (22.9)
|
18 (18.8)
|
0 (0.0)
|
14 (10.1)
|
0 (0.0)
|
8 (17.8)
|
47.654
|
0.203
|
p<0.001
|
|
Low-
er-Middle secondary
|
25 (27.5)
|
0 (0.0)
|
39 (26.7)
|
0 (0.0)
|
17 (35.4)
|
26 (27.1)
|
1 (20.0)
|
38 (27.3)
|
0 (0.0)
|
15 (33.3)
|
|
|
|
|
Higher secondary
|
13 (14.3)
|
0 (0.0)
|
32 (21.9)
|
0 (0.0)
|
5 (10.4)
|
14 (14.6)
|
0 (0.0)
|
32 (23.0)
|
0 (0.0)
|
5 (11.1)
|
|
|
|
|
Diploma/
certificate
|
3 (3.3)
|
1 (25.0)
|
4 (2.7)
|
0 (0.0)
|
0 (0.0)
|
3 (3.1)
|
1 (20.0)
|
4 (2.9)
|
0 (0.0)
|
0 (0.0)
|
39.392
|
0.186
|
p<0.01
|
|
Bachelor’s
degree & above
Occupation
|
5 (5.5)
|
0 (0.0)
|
28 (19.2)
|
0 (0.0)
|
0 (0.0)
|
5 (5.2)
|
0 (0.0)
|
25 (18.0)
|
0 (0.0)
|
1 (2.2)
|
|
|
|
|
Managers
|
0 (0.0)
|
0 (0.0)
|
1 (0.7)
|
0 (0.0)
|
0 (0.0)
|
1 (1.0)
|
0 (0.0)
|
1 (0.7)
|
0 (0.0)
|
0 (0.0)
|
50.822
|
0.210
|
0.363
|
|
Professionals
|
4 (4.4)
|
0 (0.0)
|
15 (10.3)
|
0 (0.0)
|
1 (2.1)
|
4 (4.2)
|
0 (0.0)
|
14 (10.1)
|
0 (0.0)
|
1 (2.2)
|
|
|
|
|
Ass. Prof.
& technicians
|
2 (2.2)
|
0 (0.0)
|
3 (2.1)
|
0 (0.0)
|
0 (0.0)
|
3 (3.1)
|
0 (0.0)
|
3 (2.2)
|
0 (0.0)
|
0 (0.0)
|
|
|
|
|
Clerical support workers
|
1 (1.1)
|
0 (0.0)
|
1 (0.7)
|
0 (0.0)
|
1 (2.1)
|
1 (1.0)
|
0 (0.0)
|
1 (0.7)
|
0 (0.0)
|
1 (2.2)
|
|
|
|
|
Services
& sales workers
|
1 (1.1)
|
0 (0.0)
|
7 (4.8)
|
0 (0.0)
|
3 (6.3)
|
1 (1.0)
|
0 (0.0)
|
7 (5.2)
|
0 (0.0)
|
2 (4.4)
|
|
|
|
|
Skilled
agri., forestry & fishery
|
10 (11.0)
|
1 (25.0)
|
11 (7.6)
|
1 (100)
|
10 (20.8)
|
12 (12.5)
|
1 (20.0)
|
9 (6.5)
|
1 (100)
|
10 (22.2)
|
|
|
|
|
Craft
related trade workers
|
1 (1.1)
|
0 (0.0)
|
2 (1.4)
|
0 (0.0)
|
1 (2.1)
|
2 (2.1)
|
0 (0.0)
|
1 (0.7)
|
0 (0.0)
|
1 (2.2)
|
|
|
|
|
|
Plant & machine operators
|
2 (2.2)
|
0 (0.0)
|
1 (0.7)
|
0 (0.0)
|
1 (2.1)
|
2 (2.1)
|
0 (0.0)
|
1 (0.7)
|
0 (0.0)
|
1 (2.2)
|
|
|
|
|
|
Elementary occupation
|
15 (16.5)
|
1 (25.0)
|
23 (15.9)
|
0 (0.0)
|
5 (10.4)
|
14 (14.6)
|
1 (20.0)
|
23 (16.7)
|
0 (0.0)
|
5 (11.1)
|
44.877
|
0.198
|
0.602
|
|
|
Armed forces
|
1 (1.1)
|
0 (0.0)
|
8 (5.5)
|
0 (0.0)
|
0 (0.0)
|
1 (1.0)
|
0 (0.0)
|
7 (5.1)
|
0 (0.0)
|
0 (0.0)
|
|
|
|
|
|
Students
|
45 (49.4)
|
0 (0.0)
|
56 (38.6)
|
0 (0.0)
|
21 (43.7)
|
45 (46.9)
|
1 (20.0)
|
54 (39.1)
|
0 (0.0)
|
20 (44.4)
|
|
|
|
|
|
Monks/ Nuns
|
3 (3.3)
|
1 (25.0)
|
1 (0.7)
|
0 (0.0)
|
1 (2.1)
|
2 (2.1)
|
1 (20.0)
|
2 (1.4)
|
0 (0.0)
|
1 (2.2)
|
|
|
|
|
|
Unemployed
|
6 (6.6)
|
1 (25.0)
|
16 (11.0)
|
0 (0.0)
|
4 (8.3)
|
8 (8.4)
|
1 (20.0)
|
15 (10.9)
|
0 (0.0)
|
3 (6.7)
|
|
|
|
|
+12 cases of ‘Not
applicable’ observations were omitted from the test.
Table 5: Chi-square test of
association between socio-demographic characteristics and types of astigmatism
(based on Axis) for right and left eye optics
Socio-demographic characteristics
(n=290)+
|
Right eye axis
|
Left eye axis
|
Statistical values
|
With the rule astigmatism
|
Against the rule astigmatism
|
Oblique astigmatism
|
With the rule astigmatism
|
Against the rule astigmatism
|
Oblique astigmatism
|
χ2
|
Cramér's V
|
p-value
|
n (%)
|
n (%)
|
n (%)
|
n (%)
|
n (%)
|
n (%)
|
1st row statistical values for
(Right Eye) & 2nd row for (Left Eye)
|
Sex
|
|
|
|
|
|
|
|
|
|
Male
|
71 (44.1)
|
50 (42.7)
|
2 (16.7)
|
64 (41.8)
|
50 (42.4)
|
5 (33.3)
|
3.449
|
0.109
|
0.178
|
Female
|
90 (55.9)
|
67 (57.3)
|
10 (83.3)
|
89 (58.2)
|
68 (57.6)
|
10 (66.7)
|
0.454
|
0.039
|
0.797
|
Age-group
|
|
|
|
|
|
|
|
|
|
6-15
|
50 (31.1)
|
13 (11.1)
|
2 (16.7)
|
48 (31.4)
|
14 (11.8)
|
2 (13.3)
|
50.071
|
0.294
|
p<0.001
|
16-25
|
60 (37.3)
|
20 (17.1)
|
5 (41.8)
|
60 (39.2)
|
20 (16.9)
|
4 (26.7)
|
26-35
|
21 (13.0)
|
21 (17.9)
|
1 (8.3)
|
20 (13.1)
|
18 (15.3)
|
2 (13.3)
|
36-45
|
13 (8.1)
|
24 (20.5)
|
1 (8.3)
|
13 (8.5)
|
23 (19.5)
|
3 (20.0)
|
46-55
|
6 (3.7)
|
15 (12.8)
|
1 (8.3)
|
5 (3.3)
|
16 (13.6)
|
1 (6.7)
|
56-65
|
6 (3.7)
|
16 (13.7)
|
1 (8.3)
|
4 (2.6)
|
16 (13.6)
|
2 (13.3)
|
56.969
|
0.316
|
p<0.001
|
66+
|
5 (3.1)
|
8 (6.9)
|
1 (8.3)
|
3 (1.9)
|
11 (9.3)
|
1 (6.7)
|
|
|
|
Education
|
|
|
|
|
|
|
|
|
|
No education
|
21 (13.0)
|
51 (43.6)
|
4 (33.3)
|
19 (12.4)
|
51 (43.2)
|
6 (40.0)
|
|
|
|
Primary
|
30 (18.6)
|
11 (9.4)
|
1 (8.3)
|
27 (17.7)
|
11 (9.3)
|
2 (13.3)
|
|
|
|
Lower-Middle secondary
|
55 (34.2)
|
22 (18.8)
|
4 (33.3)
|
53 (34.6)
|
24 (20.3)
|
3 (20.0)
|
43.001
|
0.272
|
p<0.001
|
Higher secondary
|
36 (22.4)
|
12 (10.3)
|
2 (16.7)
|
36 (23.5)
|
12 (10.2)
|
3 (20.0)
|
|
|
|
Diploma/certificate
|
3 (1.9)
|
5 (4.3)
|
0 (0.0)
|
3 (2.0)
|
5 (4.2)
|
0 (0.0)
|
|
|
|
Bachelor’s degree & above
|
16 (9.9)
|
16 (13.7)
|
1 (8.3)
|
15 (9.8)
|
15 (12.7)
|
1 (6.7)
|
42.558
|
0.273
|
p<0.001
|
Occupation
|
|
|
|
|
|
|
|
|
|
Managers
|
0 (0.0)
|
1 (0.9)
|
0 (0.0)
|
1 (0.7)
|
1 (0.9)
|
0 (0.0)
|
|
|
|
Professionals
|
11 (6.9)
|
9 (7.7)
|
0 (0.0)
|
11 (7.2)
|
8 (6.8)
|
0 (0.0)
|
|
|
|
Ass. Prof. & technicians
|
1 (0.6)
|
4 (3.4)
|
0 (0.0)
|
1 (0.7)
|
5 (4.2)
|
0 (0.0)
|
|
|
|
Clerical support workers
|
1 (0.6)
|
2 (1.7)
|
0 (0.0)
|
1 (0.7)
|
2 (1.7)
|
0 (0.0)
|
72.755
|
0.355
|
p<0.001
|
Services & sales workers
|
7 (4.4)
|
3 (2.6)
|
1 (8.3)
|
5 (3.3)
|
3 (2.5)
|
2 (13.3)
|
|
|
|
Skilled agri., forestry &
fishery
|
10 (6.3)
|
19 (16.2)
|
4 (33.3)
|
11 (7.2)
|
18 (15.3)
|
4 (26.7)
|
|
|
|
Craft related trade workers
|
2 (1.2)
|
2 (1.7)
|
0 (0.0)
|
2 (1.3)
|
2 (1.7)
|
0 (0.0)
|
74.596
|
0.362
|
p<0.001
|
Plant & machine operators
|
0 (0.0)
|
4 (3.4)
|
0 (0.0)
|
0 (0.0)
|
4 (3.4)
|
0 (0.0)
|
|
|
|
Elementary occupation
|
20 (12.5)
|
24 (20.5)
|
0 (0.0)
|
18 (11.8)
|
23 (19.5)
|
2 (13.3)
|
|
|
|
Armed forces
|
5 (3.1)
|
4 (3.4)
|
0 (0.0)
|
3 (2.0)
|
4 (3.4)
|
1 (6.7)
|
|
|
|
Students
|
95 (59.4)
|
21 (17.9)
|
6 (50.0)
|
92 (60.5)
|
22 (18.6)
|
6 (40.0)
|
|
|
|
Monks/Nuns
|
1 (0.6)
|
5 (4.3)
|
0 (0.0)
|
1 (0.7)
|
5 (4.2)
|
0 (0.0)
|
|
|
|
Unemployed
|
7 (4.4)
|
19 (16.3)
|
1 (8.3)
|
6 (3.9)
|
21 (17.8)
|
0 (0.0)
|
|
|
|
DISCUSSION
Refractive errors are the most common ocular problem
affecting all age groups. Globally, among the types of refractive errors, astigmatism
was the most common refractive error both in children and adults15.
This is the first study to evaluate the prevalence and types of astigmatism and
its association with the demographic profiles of individuals availing
ophthalmic services at CRRH, Gelephu, Bhutan. Most of the astigmatic errors
were within -1.50D. It was more common in adults which correlates with a
meta-analysis done in 201715. The study found that the overall
prevalence of astigmatism was 4.18% which is lower than the prevalence of
astigmatism (9.75%) in Bhutan projected by the BSSS 2019 study7. The
lower prevalence in this study may be due to the fact that the study period
coincided with the period soon after the national lockdown due to the COVID-19
pandemic. In this period, the number of patients visiting the hospital was
lower than usual times.
The global estimated pool prevalence (EPP) of
astigmatism in children and adults in Southeast Asia is 9.8% and 44.8% as of
201715. Contrary to these findings, our study revealed a prevalence
rate of 7.56% for children and 3.49% for adults. A potential reason for this
difference could be due to the variation in sample size, genetic differences
between the study populations and differences in examination techniques,
wherein cycloplegics were not used for refraction11. The higher rate
among children is concerning because uncorrected astigmatism during childhood
can impact normal visual development and result in amblyopia. Moreover,
astigmatism in children has been linked to abnormal binocular vision, such as
strabismus, and the earlier onset of myopia13. These children may
also experience headaches and symptoms of eye strain (asthenopia).
There is mixed data on the gender involvement of
astigmatism based on age. Studies amongst children, like one conducted in
Tunisia, have reported girls being affected more than boys18.
Amongst adults, studies in Singapore and North India have reported that males
are affected more than females6,19. Our study found that astigmatism
was more prevalent in women than in men. This may be because we included
participants of a wide age range [6 – 94 years]. A potential reason why females
tend to have more axis astigmatism than males may be because of the larger
degrees of upward palpebral fissure slant20.
Our study did not note significant associations between the
types of astigmatism (classified by the position of focal points, axis, and
magnitude for both the right and left eyes) and gender. A significant
association (p<0.001) was noted between astigmatism and age groups, wherein
children were affected more. This is likely because children have steeper
corneas, which flatten as they grow older21. A significant
association was also noted between astigmatism and higher education levels.
This is likely due to the requirement of more frequent close reading and
greater use of electronics amongst those with higher educational
qualifications. Similarly, a significant association (p<0.001) was also
noted between astigmatism (defined via axis) and students, who would require
more frequent close reading.
Limitations
This study was a single hospital-based study. Thus, the
prevalence findings cannot be generalized to the Bhutanese population. The
study period coincided with the period soon after the COVID lockdown lifting,
resulting in a smaller sample size.
CONCLUSION
The prevalence of astigmatism in individuals availing
ophthalmic services at CRRH was 4.18%. The majority of astigmatism was WTR,
compound myopic and mild astigmatism. Further studies are needed to investigate
the national prevalence of astigmatism, its types and its association with
demographic profile in children as well as adults.
ACKNOWLEDGEMENTS
We thank Central Regional Referral Hospital, Sarpang for
providing us with the clearance to conduct this study and MECRIT for training
us in scientific writing. We would also like to express our gratitude to all
patients who have kindly consented to participate in the study.
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|
AUTHORS CONTRIBUTION
SC
formulated the concept, collected data, wrote up, edited and reviewed the
manuscript.
TJ formulated the concept, wrote up, edited and reviewed the manuscript.
IPS formulated the concept, wrote up, edited and reviewed the manuscript.
Authors agree to be
accountable for all respects of the work in ensuring that questions related
to the accuracy and integrity of any part of the work are appropriately
investigated and resolved.
|
|
CONFLICT OF INTEREST
None
GRANT SUPPORT AND FINANCIAL DISCLOSURE
None
|