Download Risk factors for pterygium in an adult Jordanian population

ACTA OPHTHALMOLOGICA SCANDINAVICA 2004
Risk factors for pterygium in an
adult Jordanian population
Muawyah D. Al-Bdour and Mo’tasem M. Al-Latayfeh
Department of Ophthalmology, School of Medicine, Jordan University of Science and
Technology, Irbid, Jordan
ABSTRACT.
Purpose: To evaluate the risk factors for the development of pterygium in a
Middle Eastern country (Jordan) and to compare our findings with those from
other countries.
Methods: This study was conducted in Irbid District, in northern Jordan, a
region located 31 degrees north of the equator, with a stable, subtropical climate.
In this case control study, 96 adult subjects presenting with pterygium were
interviewed and compared to 192 control subjects who were group-matched for
age and sex. A standard questionnaire and eye examination were completed for
both groups.
Results: There was a strong positive association between pterygium and environmental factors. The most striking increase in the risk of pterygium occurred in
subjects who worked outdoors compared to those who worked indoors, with an
odds ratio of 5.47. Current and previous sunlight exposures were associated with
a higher risk of developing pterygium, with odds ratios of 3.54 and 4.52, respectively. Previous use of sunglasses represented a protective element, but the
protective role of recent use of sunglasses was not statistically significant.
Conclusion: There is a statistically significant association between outdoor work,
sunlight exposure and pterygium formation. Efforts should be made to educate
outdoor workers to wear sunglasses and brimmed hats. Public education should
focus on avoidance of unnecessary sunlight exposure.
Key words: Jordan – pterygium – sunlight exposure – sunglasses
Acta Ophthalmol. Scand. 2004: 82: 64–67
Copyright # Acta Ophthalmol Scand 2003.
Several modalities of surgical treatment
have been advocated, but the recurrence rate remains high (Lewallen
1989; Sebban & Hirst 1991; Sugar
1992; Dan et al. 1997).
Although a proportion of cases
appear to be inherited (Faraldi & Gracis
1976; Booth 1985; Hecht & Shoptaugh
1990), pterygium formation has been
linked to corneal and conjunctival
microtrauma caused by exposure to
sunlight and particulate matter such as
dust particles (Dimitry 1937; Dhir et al.
1967; Moran & Hollows 1984;
Mackenzie et al. 1992; Threlfall & English
1999).
Risk factors for the development of
pterygium have been evaluated in different parts of the world (Rojas &
Malaga 1986; Khoo et al. 1998; Saw &
Tan 1999), including the Middle East
(Youngson 1972; Hosni 1977; Norn
1982). This study was designed to evaluate the potential risk factors for the
development of pterygium in Jordan
and to compare our findings with
those from other countries.
doi: 10.1046/j.1600-0420.2003.00213.x
Material and Methods
Introduction
The term ‘pterygium’ describes a fleshy,
triangular or wing-shaped growth of
the conjunctiva that encroaches onto
the cornea. It is not simply a degenerative process arising from pinguecula, as
has been previously thought (Wong
1978; Hill & Maske 1989). More recent
reports have suggested that pterygium
is an active, invasive, inflammatory
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process associated with cellular proliferation, connective tissue remodelling
and angiogenesis leading to fibrovascular proliferation (Kwok & Coroneo
1994; Coroneo et al. 1999).
Pterygia are usually small and relatively benign, but they are common
(Luthra et al. 2001; Wong et al. 2001).
They cause considerable discomfort
and tearing, and may progress to
involve the central part of the cornea.
The study was conducted at the Princess Basma Teaching Hospital, which is
affiliated to the Jordan University of
Science and Technology, from July
1999 to April 2002. This hospital serves
the district of Irbid in the north of
Jordan, which is located 31 degrees
north of the equator and has a stable,
subtropical climate. A total of 96 adult
patients presenting with problems
related to pterygia were included in
ACTA OPHTHALMOLOGICA SCANDINAVICA 2004
the study. The next two consecutive
patients to present after each pterygium
patient in the same outpatient clinic
were selected as controls. All subjects
were group-matched for age and sex.
All subjects agreed to be included in
the study after the nature of the study
had been explained and they had been
interviewed by the ophthalmologist.
The same questionnaire was given to
all subjects in both groups. Each subject’s main occupation during the previous 7 years was classified as either
predominantly ‘indoor’ (such as office
workers, clerks, teachers, etc.) or ‘outdoor’ (such as taxi drivers, construction
workers, etc.) based on the nature,
location and circumstances of their
work. Each subject was questioned
about their current level of sunlight
exposure in average hours per day and
their exposure level 7 years previously.
In addition, their use of protective sunglasses at the time of the study and
7 years previously was recorded. Data
including age, gender, smoking and
previous surgical treatment were collected. All subjects were examined
using slit-lamp biomicroscopy. When
present, the size of the pterygium was
measured in millimetres from its apex
to limbus, using the slit-lamp beam.
Odds ratios (ORs) and 95% confidence intervals (95% CI) were calculated
to obtain the relative risk of developing
pterygium for each risk factor.
Results
A total of 96 pterygium subjects and
192 control subjects were included
in the study. The mean age of the
pterygium subjects at interview was
49.1 years (range 22–72 years), while
that of the control subjects was
48.2 years (range 25–70 years). In all,
83% of pterygium subjects were male,
as were 77.6% of control subjects. As
shown in Fig. 1, 54 pterygium subjects
(56%) had unilateral disease almost
equally distributed between the two
eyes, while 42 (44%) had bilateral disease. The average size of pterygium was
2.1 mm in the right eye and 1.9 mm in
the left eye. Twelve patients out of 96
had had previous surgical treatment for
pterygium.
The results shown in Table 1 demonstrate that those who worked predominantly outdoors were 5.74 times more
at risk of developing pterygium than
Fig. 1. Comparison between unilateral and bilateral disease among case subjects.
those who worked indoors. Current
and previous sunlight exposures (on
an average of 1 hour or more daily)
were strongly associated with a higher
risk of developing pterygium, with ORs
of 3.54 and 4.52, respectively. Previous
use of sunglasses was shown to be protective against pterygium formation.
However, the protective role of current
use of sunglasses was not statistically
significant. In addition, smoking did
not represent a statistically significant
risk factor for pterygium formation.
Bilaterality of the disease was independent of the studied risk factors, in that
the studied risk factors were not found
to increase the risk of bilateral involvement.
Discussion
The most striking increase in the risk of
developing pterygium occurred in subjects who worked in an outdoor environment compared with those who
worked indoors. This finding is comparable to that of similar studies evaluating the relationship between outdoor
work and pterygium conducted in different parts of the world (Rosenthal
et al. 1988; Mackenzie et al. 1992;
Nakaishi et al. 1997; Wong et al.
2001). In a study conducted in Japan,
the OR for the prevalence of pterygium
among outdoor workers as compared
to indoor workers was 2.1 (95% CI
1.68–2.45) (Nakaishi et al. 1997). This
Table 1. Comparison between pterygium subjects (cases) and control subjects.
Cases
Controls
Total
OR
95% CI
p-value
n
(%)
n
(%)
No. of subjects
96
(100)
192
(100)
288
Sex
Males
Females
80
16
(83)
(17)
149
43
(77.6)
(22.4)
229
59
Work
Outdoors
Indoors
62
34
(64.6)
(35.4)
48
144
(25)
(75)
110
178
5.47
3.3–9.1
< <0.005
Sun exposure 7 years previously
1 hour/day
78
(81)
< 1 hour/day
18
(19)
94
98
(49)
(51)
172
116
4.52
2.6–7.9
<0.005
Sunglasses 7 years previously
Absent
76
(79)
Present
20
(21)
87
105
(45)
(55)
163
125
4.59
2.7–7.9
<0.005
Current sun exposure
1 hour/day
70
< 1 hour/day
26
(73)
(27)
83
109
(43)
(57)
153
135
3.54
2.1–5.9
<0.005
Current sunglasses
Absent
56
Present
40
(58)
(42)
90
102
(47)
(53)
146
142
1.59
NS
NS
Smoking
Smoker
Non-smoker
(46)
(54)
102
90
(53)
(47)
146
142
0.75
NS
NS
44
52
OR ¼ odds ratio; 95% CI ¼ 95% confidence interval; NS ¼ not significant.
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ACTA OPHTHALMOLOGICA SCANDINAVICA 2004
association may be related to a higher
level of exposure to sunlight (Rojas &
Malaga 1986; Mackenzie et al. 1992;
Nakaishi et al. 1997; Threlfall &
English 1999) and possibly to a higher
level of exposure to dust (Dimitry 1937;
Mackenzie et al. 1992; Nakaishi et al.
1997) in outdoor workers. In our study,
outdoor workers were more likely to be
male, because outdoor occupations are
predominantly male vocations in
Jordan. This explains why the majority
of pterygium subjects were male.
Current and previous sunlight exposures were associated with a higher risk
of developing pterygium. The association was stronger for previous exposure
than for current exposure. This might
reflect the cumulative effect of exposure, whereby solar radiation may initiate ocular tissue changes that later
promote the development of pterygium
so that sunlight exposure is reflected in
later years of life by development of
pterygium. Our finding is consistent
with other findings in Singapore
(Khoo et al. 1998) and Australia
(Threlfall & English 1999). Several surveys have consistently shown that
countries near the equator have higher
rates of pterygia (Taylor 1981; Moran
& Hollows 1984; Saw & Tan 1999). The
theory that chronic exposure to sunlight causes pterygium seems to be
beyond any debate.
The effect of solar radiation on the
eye was studied thoroughly by Taylor
et al. (1992). The effects of visible radiation as well as ultraviolet-A and ultraviolet-B were evaluated. A positive
association was found between ocular
exposure to each band of radiation
(bands of visible radiation, UV-A,
UV-B) and the development of pterygium. Most plastic lenses in sunglasses
block substantial amounts of UV-A
and UV-B radiation (Rosenthal et al.
1988). Glass is slightly less effective in
blocking UV-B radiation (Rosenthal
et al. 1986). In our study, previous use
of sunglasses was shown to be protective against pterygium formation while
current use was not. In a study by
Khoo et al. (1998), neither previous
nor current use of sunglasses were
shown to have a protective role. Most
other studies have demonstrated that
the use of sunglasses has a protective
role to varying extents (Rosenthal et al.
1986, 1988; Mackenzie et al. 1992;
Threlfall & English 1999). One possible
explanation for the variation in the pro-
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tective role of sunglasses may be that
different types of sunglasses have been
used by both case subjects and control
subjects. Genetic attributes (Tan et al.
1997) and variable lifestyle behaviour
may also contribute to this variation. A
possible explanation for the nonprotective effect of recent use of sunglasses
is that subjects start wearing sunglasses
once the pterygium has already formed.
Although some previous studies
found a positive correlation between
smoking and pterygium formation
(Khoo et al. 1998), smoking was not
found to be a statistically significant
risk factor in our study.
As a method of recruiting subjects with
pterygium, the hospital-based study
design represents a practical alternative
to a large scale, community-based survey.
We incorporated several features into our
study design to reduce bias. For instance,
both pterygium and control subjects were
selected from the same clinic population
and interviewed using a standard questionnaire. Diagnosis was made by an
ophthalmologist using a slit-lamp. The
subjects were group-matched for age
and sex. Although the possibility of investigator bias was minimized by the similarity of the study procedure for both
groups, it could not be completely eliminated because it was impossible to mask
the interviewer to a patient with grossly
visible pterygium during a face-to-face
interview. Another limitation in our
study is that data on the average daily
ocular radiation dose were not available,
and therefore a dose–response relationship between sunlight exposure and
development of pterygium could not be
described. In addition, the relatively small
sample size might have made some factors, such as smoking, insignificant, in
contrast to some previous studies.
Conclusion
This study shows that outdoor work
and sunlight exposure are positively
associated with the development of
pterygium. Public education should
focus on encouraging people to take
appropriate protective measures, such
as wearing sunglasses and brimmed
hats when outdoors, and to avoid unnecessary sunlight exposure. Meanwhile,
further research is required to enable us
to better understand the relative contributions of different risk factors.
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Received on December 27th, 2002.
Accepted on October 18th, 2003.
Correspondence:
Muawyah D. Al-Bdour FRCSI (Ophth)
PO Box 141461
Amman 11814
Jordan
Tel: þ 962 6 535 3399
Fax: þ 962 6 535 3399
Email: [email protected]
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