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ASSOCIATION OF NET PTERYGIUM TISSUE MASS (DRYWEIGHT) IN DETERMINING
CHANGES IN OCULOVISUAL FUNCTIONS AND ANTERIOR CORNEAL CURVATURE RELA-
TIVE TO PTERYGIUM TYPES
NOOR SYAHIRA BINTI CHE ROSLI
DEPARTMENT OF OPTOMETRY AND VISUAL SCIENCE, KULLIYYAH OF ALLIED HEALTH SCI-
ENCES, INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA, JLN SULTAN AHMAD SHAH BAN-
DAR INDERA MAHKOTA 25200 KUANTAN,
PAHANG, MALAYSIA
syahirarosli5346@gmail.com
MOHD RADZI HILMI, PhD (Corresponding author)
DEPARTMENT OF OPTOMETRY AND VISUAL SCIENCE, KULLIYYAH OF ALLIED HEALTH SCI-
ENCES, INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA, JLN SULTAN AHMAD SHAH BAN-
DAR INDERA MAHKOTA 25200 KUANTAN, PAHANG, MALAYSIA
mohdradzihilmi@iium.edu.my
KHAIRIDZAN MOHD KAMAL, PhD (Corresponding Author)
DEPARTMENT OF OPHTHALMOLOGY, KULLIYYAH OF MEDICINE, INTERNATIONAL ISLAMIC
UNIVERSITY MALAYSIA, JLN SULTAN AHMAD SHAH BANDAR INDERA MAHKOTA 25200
KUANTAN, PAHANG, MALAYSIA
khairidzan@iium.edu.my
MD MUZIMAN SYAH MD MUSTAFA, PhD
DEPARTMENT OF OPTOMETRY AND VISUAL SCIENCE, KULLIYYAH OF ALLIED HEALTH SCI-
ENCES, INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA, JLN SULTAN AHMAD SHAH BAN-
DAR INDERA MAHKOTA 25200 KUANTAN,
PAHANG, MALAYSIA
syah@iium.edu.my
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ABSTRACT
Introduction: Dryweight in pterygium is more towards the fleshy appearance of the fibrous tissue. Aim:
The goal of this study was to determine the predictive ability of net pterygium tissue mass (dryweight)
on predicting changes in anterior corneal curvature and oculovisual functions relative to pterygium
types. Methodology: A total of 93 primary pterygium patients who visited an ophthalmology clinic were
selected as participants. The net pterygium tissue mass were obtained via freeze dry method subsequent
to pterygium excision using fibrin glue adhesive method. Best corrected visual acuity (BCVA) and con-
trast sensitivity function (CSF) were measured by using M&S Smart System II as measurement for oculo-
visual function, while the changes of anterior corneal curvature was measured using corneal topography.
Results: The mean and standard deviation for BCVA, CSF and SimK were 0.44 ± 0.30 LogMAR, 24.28 ±
17.66 % and 4.64 ± 4.18 D respectively. This study found that the predictive ability of pterygium dry-
weight with BCVA were strong in Type I and Type III while moderate in Type II with 13.10% (R2 = 0.131,
p < 0.05) in Type I. Slight increase trend were noted in both Type II with 53% (R2 = 0.530, p < 0.05) and
Type III, with 21.60% (R2 = 0.216, p < 0.05). For CSF, the predictive ability of pterygium dryweight were
strong in all types with Type I, Type II and III reported 21.6% (R2 = 0.216, p < 0.05), 31.8% (R2 = 0.318, p <
0.05), 28.9% (R2 = 0.289, p < 0.05) respectively. The predictive ability of pterygium dryweight for SimK
were strong in all types with contribution of 44.7% (R2 = 0.447, p < 0.05), 47.7% (R2 = 0.477, p < 0.05), 39.1%
(R2 = 0.391, p < 0.05) respectively. Conclusion: Net pterygium tissue mass (dryweight) is a strong factor in
predicting changes of oculovisual functions and anterior corneal curvature in relation to pterygium types.
Keywords: Pterygium, dryweight, best corrected visual acuity, contrast sensitivity function, anterior
corneal curvature.
INTRODUCTION
Pterygium is a wing-shaped abnormal growth of the fibrovascular tissue characterized by a be-
nign proliferation of local conjunctiva that often crosses the limbal of cornea and extends into corneal sur-
face (Chui et al., 2011). Based on the anatomical structure, pterygium can be divided into cap (the leading
edge which also known as pterygium apex), head (the vascular area that invades the cornea) and body in
which the connective tissue spreading on top of the cornea (Liu et al., 2013; Anguria et al., 2014). At early
stage, pterygium is usually asymptomatic. However, dry eye related manifestations may be present, such
as burning, itching, and/or tearing.(Liu et al., 2013; Hilmi et al., 2019; Hilmi et al., 2019). This could hap-
pen due to unstable tears distribution (Hilmi et al., 2019). It is an established fact that as pterygium pro-
gresses, it induced unwanted corneal astigmatism, reduction in contrast sensitivity function as well as
visual acuity (Coroneo, DiGirolamo & Wakenfield, 1999; Chandrakumar et al., 2013).
Currently, the pathogenesis of pterygium is still debatable, however hereditary, inflammation
and environmental factors, including long-term exposure of ultraviolet (UV) on the ocular surface were
noted as possible etiologies (Coroneo, DiGirolamo & Wakenfield, 1999; Liu et al., 2013; Anguria et al.,
2014). There are few grading scales available in which has and can be used to classify the type of pterygi-
um. In 1997, Tan and his co-workers (Tan et al., 1997) proposed a clinical grading of pterygium which
was based on the translucency appearance of pterygium tissue. The authors described pterygium into
three types; Type I pterygium (atrophic- the episcleral vessels unobscured), Type II pterygium (interme-
diate- the episcleral vessels partially obscured) and Type III pterygium (fleshy- the episcleral vessels are
totally obscured). Other than that, pterygium also can be classified based on the size, encroachment and
extension of its tissue onto cornea (Maheswari, 2003; Popat et al., 2014; Shelke et al., 2014). Thus, this
study aimed to evaluate the effects of pterygium types on changes in oculovisual function based on the
net pterygium tissue mass (NTPM).
MATERIALS AND METHODS
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A cross-sectional prospective study was conducted in a University-based Ophthalmology Clinic
(IIUM Eye Specialist Clinic, IIUM Kuantan). All participants were recruited based on voluntary sampling.
Participant who fulfill the inclusion criteria were selected in this study. The inclusion and exclusion crite-
ria of this study are participant who has an established diagnosis of primary pterygium, both gender with
age range from 20 to 70 years old, both unilateral and bilateral pterygium is included, double head pter-
ygium is excluded, free from any history of ocular trauma, surgery, free from any ocular diseases and
never wear contact lenses (Mohd Radzi et al., 2017; Hilmi et al., 2019). Diagnosis of pterygium was done
by a consultant ophthalmologist (KMK). The sample size for his study was calculated by using Power
and Sample Size Calculation Software Version 3.1.2. (PS Software, Nashville, TN, USA).
Prior to study commencement, informed consent was obtained with approval obtained by Inter-
national Islamic University Malaysia (IIUM) research ethical committee (IREC) (IIUM/310/G13/4/4-125)
and this study comfort to the recommendation of the tenets of the Declaration of Helsinki. Standard op-
tometric examination were performed in all participants which includes dry refraction, auto-refraction,
best corrected visual acuity (BCVA), slit-lamp examination and contrast sensitivity function (CSF) were
measured. BCVA and CSF were evaluated using M&S Smart System II. Changes on anterior corneal cur-
vature was evaluated using Zeiss Atlas 995TM Corneal Topographer (Carl Zeiss Meditec Inc, Dublin, US).
Freeze-dried pterygium tissue samples known as net pterygium tissue mass (NTPM) were obtained
based on methodology that has been described in detail (Hilmi et al., 2019).
All statistical analyses were done using IBM predictive analytical software (SPSS). Changes in
BCVA, CSF and SimK value between pre and 3-months post-surgical excision of pterygium (Mohd Radzi
et al., 2017). Comparison between pre- and post-surgical excision was done using paired T-test, while
Pearson’s correlation test was performed to determine the association of oculovisual functions parame-
ters (BCVA and CSF) and anterior corneal curvature (SimK) induced by NPTM relative to the pterygium
types. Comparative analysis on magnitude changes in BCVA, CSF and SimK values between all pterygi-
um types were done using one-way analysis of variance (ANOVA). Magnitude changes in all parameters
were based on changes between baseline (pre-surgical) with 3-months post-surgical. P < 0.05 was set as
the level of significance.
RESULT
Out of 93 patients involved in this study, 50.5% (n = 47) was male and 49.5% (n = 46) were fe-
males. All pterygium were classified based on Tan’s classification of pterygium (Tan et al., 1997) which
comprised of 30 (Type I - atrophic), 32 (Type II - intermediate) and 31 (Type III - fleshy) primary pterygi-
um. All data were normally distributed based on ratio of skewness and kurtosis of within 2.50 (George
and Mallery, 2010). At baseline, the mean and standard deviation (SD) for BCVA, CSF and SimK were
0.44 ± 0.30 LogMAR, 24.28 ± 17.66% and 4.64 ± 4.18D respectively. Paired t-test revealed that there were
significant differences between BCVA, CSF and SimK between the baseline pre-surgical and post-surgical
3 months (p < 0.05), as shown in Table 1 below.
Table 1. Comparison of BCVA, CSF and SimK between Pre & Post-pterygium Excision (N=93)
Variables
Baseline (mean ± SD)
Post 3 months (mean ± SD)
P-value*
BCVA (logMAR)
0.44±0.30
0.12±0.04
< 0.05
CSF (%)
24.28±17.66
6.32±0.89
< 0.05
Sim K (D)
4.64±4.18
0.57±0.45
< 0.05
*Paired T-test
Based on Pearson’s correlation test, increasing trend was noted with stronger association was
found with increase of pterygium types. For BCVA, moderate association was found for type I pterygium
with 0.361 and increase steadily with 0.464 for type II. Type III pterygium was found strongly associated
with changes in BCVA. For CSF, moderate association was found in all pterygium types (type I: 0.465,
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type II: 0.537 and type III: 0.564). Whereas for changes in SimK, strong association was found in all pter-
ygium types (type I: 0.669, type II: 0.626 and type III: 0.690). Correlation findings were summarised in
Table 2 below.
Table 2. Association of NPTM with Changes in BCVA, CSF and SimK (N = 93)
Variables
Correlation, r
p-value
Type I
Type II
Type III
Type I
Type II
Type III
BCVA
0.361
0.464
0.728
p < 0.05
p < 0.05
p < 0.05
CSF
0.465
0.537
0.564
p < 0.05
p < 0.05
p < 0.05
SimK
0.669
0.626
0.690
p < 0.05
p < 0.05
p < 0.05
Based on Paired T-test findings, magnitude changes for all measured parameters were found sta-
tistically significant with increasing trends of changes towards higher grade of pterygium. Type III pter-
ygium was found induce the largest changes followed by type II and I respectively for all parameters
measured. The magnitude changes are shown in Table 3 below.
Table 3. Magnitude Changes of BCVA, CSF and SimK between Type I, Type II and Type III Pterygium
Variables
Types of Pterygium (n=93) Mean ± SD
P-value*
Type I (n=30)
Type II (n=32)
Type III (n=31)
BCVA (log-
MAR)
0.02 ± 0.04
0.33 ± 0.20
0.58 ± 0.21
a: < 0.05
b: < 0.05
c: < 0.05
CSF (%)
0.33 ± 0.76
15.19 ± 9.35
37.87 ± 10.00
a: < 0.05
b: < 0.05
c: < 0.05
SimK (D)
1.30 ± 0.64
2.90 ± 1.57
7.97 ± 4.16
a: > 0.05
b: > 0.05
c: < 0.05
*ANOVA: One way analysis of variance
a: Pair of Type I and Type II
b: Pair of Type II and Type III
c: Pair of Type I and Type III
DISCUSSION
Previous studies stated that presence of pterygium could lead to the changes in the appearance of
the corneal itself as well as can induce increment of corneal astigmatism (Coroneo et al., 1999), reduction
in both contrast sensitivity function and visual acuity (Oh and Wee, 2010; Mohd Radzi et al., 2017). How-
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ever, it is difficult to determine the actual impact of pterygium on the oculuvisual function as each pter-
ygium is unique and different for each patient. Previous reports (Tan et al., 1997; Sandra et al., 2014)
commented that pterygium recurrence could be related to the fleshiness appearance of the pterygium.
The whitish fleshiness appearance of pterygium has been suggested as the active site of proliferation of
fibroconnective pterygium tissue (Sandra et al., 2014; Mohd Radzi et al., 2017). An attempt was made re-
cently (Mohd Radzi et al., 2019) to quantify the dry-weight of tissue known as Net Pterygium Tissue
Mass (NPTM), to signify the actual pterygium tissue mass that present on the corneal surface. Thus, this
study aimed to determine the impact of NPTM on changes in BCVA, CSF and SimK in primary pterygi-
um patients.
BCVA is an important parameter as it represents the visual status of the eye. It is an established
fact that pterygium affects visual acuity as it progresses (Maheshwari, 2007; Chui et al., 2011; Anguria et
al., 2014, Mohd Radzi et al., 2017). And it is worth to note that as BCVA affected, CSF could also be affect-
ed as anterior corneal curvature changed due to corneal compression as pterygium progresses from lim-
bus towards central cornea. Previous works (Oh and Wee, 2010; Sandra et al., 2014; Mohd Radzi et al.,
2017) had reported that changes in CSF is important factor as in some pterygium, BCVA not significantly
affected, while CSF effect was more prominent. This could be due to types of pterygium which could be
atrophic or intermediate, in which less whitish appearance presence which in return does not fully cov-
ered the visual axis. Another reason for this is the thickness of pterygium (Mohd Radzi et al., 2018) which
also contribute this notion. A thicker pterygium tissue could further signify active proliferative disorders
in which could lead to higher grade of pterygium such as type III ptergyium. Sandra et al., (2014) had
commented that type I could be less affected in both BCVA and CSF compared to type II, and recent
study (Hilmi et al., 2018; Norazmar et al., 2019) showed clear demarcation effect between type I and III,
which suggest fleshy pterygium could induce more effect on both BCVA and CSF. This current study
findings also in agreement with both studies (Sandra et al., 2014; Norazmar et al., 2019)
With regards to changes in SimK, it needs to be emphasised that pterygium morphology can var-
ies from a pterygium to another. A patient might come with smaller pterygium size, in which should not
significantly affect vision. However, clinical evidence (Hilmi et al., 2018) showed that it does not follow
specific rules such as a larger size, would likely to have worse BCVA and CSF, or vice versa. Thus, fleshi-
ness appearance is an important criteria as it could signify higher percentage of NTPM. Previous studies
(Maheshwari, 2007; Mohd Radzi et al., 2017) has reported that corneal compression occur due to indenta-
tion of corneal curvature. Although it was not stated reason of this, it can be postulated that pterygium
tissue could be the possible reason as pterygium tissue is an active proliferative tissue (Hilmi et al., 2019;
Norazmar et al., 2019; Hilmi et al., 2019; Hilmi et al., 2019). In fact, there are several studies (Azemin et al.,
2014; Che Azemin et al., 2014; Che Azemin et al., 2015; Che Azemin et al., 2016) that commented on the
angiogenesis factor of pterygium in which reflects the presence of fibrovascular components of pterygi-
um which in line with classification of pterygium itself.
This present study results revealed that there are significant correlation and relationship between
the NPTM (dryweight) on BCVA, CSF and SimK (p<0.05). Changes in oculovisual function (BCVA and
CSF) have been described previously based on the size, area, length and redness of pterygium tissue.
(Maheswari, 2007; Popat et al., 2014; Shelke et al., 2014). To the best of our knowledge, no study has been
done on evaluating NPTM (dryweight) with regard to changes in BCVA, CSF and SimK based on pteryg-
ium types. This present study would like to highlight that types of pterygium is an important factor that
needs to be evaluated in determining the caused of changes in BCVA, CSF and SimK.
CONCLUSION
Types of pterygium is an important characteristics that need to be evaluated in order to have better un-
derstanding on how does pterygium affects oculovisual functions.
ACKNOWLEDGEMENT
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This study was funded by International Islamic University Malaysia (IIUM) under Research Initiative
Grant Scheme (RIGS16-129-0293).
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