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Citation: Mohamed-Noor J, Abd-Salam D. Refractive errors and
biometry of primary angle-closure disease in a mixed Malaysian population. Int
J Ophthalmol 2017;10(8):1246-1250
Refractive errors and biometry of primary
angle-closure disease in a mixed Malaysian population
Jelinar Mohamed-Noor, Dhaniah Abd-Salam
Department
of Ophthalmology, Hospital Kuala Lumpur, Jalan Pahang, Kuala Lumpur 50586,
Malaysia
Correspondence
to: Jelinar Mohamed-Noor; Dhaniah binti Abd Salam. Department of
Ophthalmology, Hospital Kuala Lumpur, Jalan Pahang, Kuala Lumpur 50586,
Malaysia. JelinarMNoor@hotmail.com; dhaniah1453@yahoo.co.uk
Received:
2016-11-26
Accepted: 2017-02-06
Abstract
AIM: To
assess the refractive status, anterior chamber depth (ACD) and axial length
(AL) of patients with primary angle-closure disease (PACD).
METHODS: Retrospective
cohort. Data was collected from charts of all PACD patients treated from April
2013 to December 2015. Analysis was done on 137 patient charts with complete
biometric data. Patient demographics, PACD type, refractive status (spherical
equivalent), ACD and AL were studied.
RESULTS: The
median age of 137 subjects [53 with primary angle-closure suspects (PACS), 27
with primary angle-closure (PAC) and 57 with primary angle-closure glaucoma
(PACG)] was 68y (range 21-88y). The majority was Chinese (n=68; 49.6%)
and most of them were women (n=75; 54.7%). The distribution of myopia (n=51;
37.2%) and hyperopia (n=49; 35.8%) was similar. The ACD was shallower in
myopes compared to hyperopes (P=0.02) and emmetropia (P=0.049)
but the AL was not significantly different between groups. There were no
patients blind from PACG.
CONCLUSION: Both
myopia and hyperopia can occur in PACD. Despite a shallower ACD in angle
closure myopes, the AL was not different between groups.
KEYWORDS:
primary angle-closure suspect; primary angle- closure; primary
angle-closure glaucoma; anterior chamber depth; axial length
DOI:10.18240/ijo.2017.08.10
Citation: Mohamed-Noor J, Abd-Salam D. Refractive errors and biometry of primary
angle-closure disease in a mixed Malaysian population. Int J Ophthalmol
2017;10(8):1246-1250
INTRODUCTION
Glaucoma
has long been recognized as a leading cause of blindness. The scale of this
problem will increase with future population growth and increasing life
expectancy. The global prevalence of glaucoma for population aged 40-80y is
3.54% and the prevalence of primary angle-closure glaucoma (PACG) is highest in
Asia (1.09%)[1]. This number is expected to
increase each year.
PACG
is responsible for the vast majority of bilateral blindness in East Asia[2-3], Singapore[4]
and India [5-7]. The risk
factors for PACG include hyperopia, a short axial length (AL), shallow anterior
chamber depth (ACD) and increased lens thickness[8-11]. It has been reported that hyperopic subjects have
shorter ALs and shallower ACDs, which predispose them to angle-closure[12-13]. Yong et al[14] found that amongst Chinese in Singapore, hyperopia
(52%) and shallow ACD was seen in half of the patients with angle-closure.
Generally
myopia has been shown to be associated with primary open angle glaucoma (POAG)[15-17]. Therefore, with the increasing
prevalence of myopia in Asia one would expect an increase in the prevalence of
POAG and possibly a reduction in the prevalence of PACG[18-20]. In addition it is also thought that myopia has a
protective effect against PACG. However, recent studies have reported the occurrence
of myopia in angle closure subjects[14,21].
These studies[21-22] described
findings in a homogenous population but little is known of the spectrum of
glaucoma cases namely primary angle-closure disease (PACD) in Malaysia which is
of mixed ethnicity.
Currently there are not many published data on PACD in Malaysia.
Liza-Sharmini et al [23-24] found
that primary angle-closure (PAC) is not uncommon in Malays and they often
present with more advanced disease compared to Chinese. In addition, aggressive
disease progression was observed in Malays with the onset of optic neuropathy.
However, the study subjects were from different socioeconomic background and
this may influence the severity and aggressiveness of the disease.
The
aim of this study was to evaluate the refractive status and ocular biometric
parameters of subjects with PACD. The occurrence of blindness among these
subjects was also assessed.
SUBJECTS AND METHODS
This
study is confined to consecutive subjects with PACD seen at a tertiary hospital
in Malaysia. Data was collected from records of all patients with angle closure
who attended the glaucoma clinic from April 2013 to December 2015. Ethics
approval was obtained from the Medical Research and Ethics Committee Malaysia
and the study was done in accordance with the tenets of Declaration of
Helsinki.
PACD
was comprised of patients categorized as primary angle-closure suspects (PACS),
PAC and PACG. PACS was defined as an eye with narrow angles, at least 180o
iridotrabecular contact (ITC), and an intraocular pressure (IOP) of 21 mm
Hg or less in the absence of glaucomatous optic neuropathy (GON) or peripheral
anterior synechiae (PAS). PAC was defined as the presence of at least 180o
ITC and a raised IOP of more than 21 mm Hg, or PAS, but without glaucomatous
optic neuropathy (GON). PACG was defined as eyes with PAC associated with GON
and corresponding glaucomatous visual field (VF) defects. GON is defined as a
loss of neuroretinal rim with a vertical cup-to-disc ratio of ≥0.7 or an
inter-eye asymmetry of ≥0.2, notching attributable to glaucoma, or both. The
glaucomatous VF defects are reproducible in at least 2 consecutive VFs, of ≥2
contiguous points with P<0.01 loss or greater, or ≥3 contiguous points
with P<0.05 loss or greater on pattern deviation plot, or abnormal
Glaucoma Hemifield Test. The extent of blindness, defined as having a best
corrected vision of less than 3/60 or an inability to count fingers at 3 m in
the better eye, was assessed.
All
patients had laser peripheral iridotomy. Key exclusion criteria were: patients
with secondary glaucoma such as neovascular and uveitic glaucoma, previous
ocular surgeries and records with incomplete data were excluded. If both eyes
were eligible, the better eye was selected.
The
patient’s demographics, visual acuity, refractive status and biometrics were
analyzed. The spherical equivalent (SE) was calculated based on the patient’s
objective refractive status. They were categorized as myopia (<-0.5 D),
emmetropia (-0.5 D to +0.5 D) or hyperopia (>+0.5 D). Patients were
categorized as having moderate myopia if the SE was ≤-2.0 D to -5.0 D and high
myopia if the SE was ≤-5.0 D. The central ACD and AL were obtained from an
immersion A-scan biometry (Quantel Medical Compact Touch, USA), which is a
non-contact method. This avoids indentation on the cornea and minimizes errors
in measuring the AL and ACD.
Statistical
analysis was performed using SPSS Version 20.0. Descriptive statistics will be
utilized for selected variables. The results will be presented as frequencies
and percentage for categorical data. The numerical data which is normally
distributed will be presented as mean and standard deviation (SD), while median
and range (minimum and maximum) will be presented for numerical data which is
not normally distributed. In comparing numerical data which is normally
distributed between two groups independent t-test will be used in
analysis and Mann-Whitney test will be used if the numerical data is not normally
distributed. In comparing numerical data which is normally distributed between
more than two groups one-way ANOVA test will be used in analysis, while
Kruskal-Wallis test will be used if the numerical data is not normally
distributed. Pearson’s Chi-square test will be used to study association
between categorical data, while Fishers exact test will be used if assumptions
of Pearson’s Chi-square test are not met. The probability values of less than
0.05 (P<0.05) were considered as statistically significant.
RESULTS
A
total of 137 charts of patients with complete data were studied. Those with
PACD were categorized into 3 subgroups i.e. PACS, PAC and PACG. There
were 53 with PACS, 27 with PAC and 57 with PACG. Their age ranged from 21-88y,
median age was 68y. There were more Chinese (n=68; 49.6%) and most were
women (n=75; 54.7%) (Table 1).
Table
1 Demographic features of the study population
|
Characteristic
features |
PACS (n=53) |
PAC (n=27) |
PACG (n=57) |
P |
Total (n=137) |
|
Subgroup
proportion, % |
38.7 |
19.7 |
41.6 |
|
100 |
|
Median
age years (min to max) |
67 (53 to
83) |
70 (21 to
82) |
66 (40 to
88) |
0.451a |
68 (21 to
88) |
|
Ethnicity
(%) |
|
|
|
|
|
|
Chinese |
27 (50.9) |
12 (44.4) |
29 (50.9) |
|
68 (49.6) |
|
Non-Chinese |
26 (49.1) |
15 (55.6) |
28 (49.1) |
0.834b |
69 (50.4) |
|
Gender
(%) |
|
|
|
|
|
|
M |
18 (34.0) |
13 (48.1) |
31 (54.4) |
|
62 (45.3) |
|
F |
35 (66.0) |
14 (51.9) |
26 (45.6) |
0.094b |
75 (54.7) |
Statistical
test: aKruskal-Wallis; bChi-square.
There
was a similar distribution of myopia (n=51; 37.2%) to hyperopia (n=49;
35.8%) with more myopes amongst Chinese (Table 2). Interestingly, there were
more hyperopes amongst PACS (41.5%) but more myopes (59.3%) amongst the PAC
group. However, in the PACG group there was an almost equal distribution of
myopes (35.1%) to hyperopes (38.6%) (Table 3). The ACD was shallower in myopes
compared to hyperopes (P=0.022) and emmetropia (P=0.049).
However, there was no difference in AL between groups (Table 4).
Table
2 Refractive status of Chinese to non-Chinese n (%)
|
Ethnicity |
Myopia |
Emmetropia |
Hyperopia |
Total |
|
Chinese |
26 (51.0) |
20 (54.1) |
22 (44.9) |
68 |
|
Malay |
16 (31.3) |
12 (32.4) |
16 (32.7) |
44 |
|
Indian |
8 (15.7) |
5 (13.5) |
9 (18.3) |
22 |
|
Others |
1 (2.0) |
0 (0) |
2 (4.1) |
3 |
|
Total
(n) |
51 |
37 |
49 |
137 |
Table
3 Refractive status across subgroups
|
Refractive
status |
PACS (n=53) |
PAC (n=27) |
PACG (n=57) |
P |
Overall (n=137) |
|
Mean
SE (SD) |
0.47
(1.86) |
-0.86
(1.81) |
-0.12
(2.27) |
0.023*c |
-0.04
(+2.08) |
|
Hyperopia
(>+0.50 D) |
|
|
|
|
|
|
n (%) |
22 (41.5) |
5 (18.5) |
22 (38.6) |
|
49 (35.8) |
|
Mean, D (SD) |
+2.21
(+1.32) |
+1.83
(+0.66) |
+1.86
(+1.15) |
0.585c |
+2.01
(+1.19) |
|
Emmetropia
(+0.50 to -0.50 D) |
|
|
|
|
|
|
n (%) |
16 (30.2) |
6 (22.2) |
15 (26.3) |
|
37 (27.0) |
|
Median (min to max, D) |
0.00
(-0.38 to +0.50) |
+0.13
(-0.50 to +0.50) |
+0.13
(-0.50 to +0.50) |
0.896a |
0.00
(-0.50 to 0.50) |
|
Myopia
(<-0.50 D) |
|
|
|
|
|
|
n (%) |
15 (28.3) |
16 (59.3) |
20 (35.1) |
|
51 (37.2) |
|
Median (min to max, D) |
-1.75
(-3.00 to -0.63) |
-1.75
(-4.50 to -0.73) |
-1.81
(-7.40 to -0.62) |
0.558a |
-1.75
(-7.4 to -0.62) |
SE:
Spherical equivalent. *PACS vs PAC P=0.03; PAC vs
PACG P=0.31; PACS vs PACG P=0.31. Statistical test: aKruskal-Wallis;
cOne way ANOVA.
Table
4 Refractive status across all groups
|
Biometry |
Hyperopia
(n=49) |
Emmetropia
(n=37) |
Myopia (n=51) |
P |
|
Median
SE (min to max, D) |
+1.75
(+0.63 to +5.50) |
0.00
(-0.50 to +0.50) |
-1.75
(-7.40 to -0.62) |
|
|
Anterior
chamber depth, median (min to max) |
2.66 (2.03
to 4.07) |
2.64 (2.11
to 3.4) |
2.46 (1.85
to 4.2) |
0.042*a |
|
Axial
length |
|
|
|
0.481c |
|
Mean (SD) |
22.73
(0.92) |
22.90
(0.92) |
22.95
(0.98) |
|
|
Range |
20.52 to
25.03 |
20.53 to
24.45 |
20.42 to
26.38 |
*aPairwise comparison myopia vs emmetropia
P=0.049; Myopia vs hyperopia P=0.022; Emmetropia vs
hyperopia P=0.972. cPairwise comparison myopia vs emmetropia
P=0.972; Myopia vs hyperopia P=0.507; Emmetropia vs
hyperopia P=0.705. Statistical test: aKruskal Wallis; cOne
way ANOVA.
Of
the 51 myopic angle closure patients in our study, majority had low myopia 34
(66.7%), 14 (27.5%) had moderate (<-2.0 D to -5.0 D) and 3 (5.9.0%) had high
(<-5.0 D) myopia.
DISCUSSION
In
our study on PACD, majority were women (54.7%) with a preponderance of Chinese
(49.6%). This is similarly seen in a study by Yong et al [14], where 64% of 427 angle-closure patients were mostly
women and majority were Chinese (92.3%). This may be attributed to the
underlying racial distribution of Singapore where Chinese make up 76.1% of the
resident population[25]. In Malaysia, 68.8% of
the population comprise of Malays and other Bumiputera groups, followed by
Chinese 23.2%, Indians 7.0% and other ethnic groups 1%[26].
However, despite this differing pattern of racial distribution in Malaysia, the
ratio of Chinese to non-Chinese with PACD i.e. PACS, PAC and PACG, was
similar. This may be explained by the high prevalence of angle-closure found in
Chinese[9,27-28].The
study also showed that 22% of 427 angle-closure subjects had myopia but
hyperopes was still prevalent amongst PACS and PACG[14].
However, in analyzing the refractive status of our patients with angle-closure
in our study, we found there was an almost equal distribution of myopes (37.2%)
to hyperopes (35.8%). This may be due to our small study population which has a
similar distribution of non-Chinese to Chinese. Hence, as shown in our study
myopia in angle closure is not as rare as was previously believed.
The
rate of high myopia among all angle closure subjects has been reported to be
between 1.6% to 2.6%[8,14]. A
study by Lowe[8] reported that 5.5% (7 of 127
eyes) of patients were myopes and 1.6% (2 of 127 eyes) had high myopia (≤6.0
D). Another study by Chakravarti and Spaeth[21] reported
a high myopia rate of 1.9% of 322 angle-closure patients. These studies differ
in the population that was studied. Although our study was based on 137
patients with complete biometric records, the rate of high myopia (2.2%) among
all angle-closure patients was comparable to other studies.
Interestingly,
we also found that the ACD was shallower in myopes compared to hyperopes and emmetropia
but the AL was not significantly different between groups. This is not
surprising as smaller anterior segments, namely a shallower anterior chamber
width, as measured by optical coherence tomography, have been found in Asian
eyes[29]. This was in contrast to the study by
Yong et al[14], where myopic angle-
closure glaucoma subjects had longer axial and vitreous cavity length but the
ACD was similar in all groups. Our subjects may have lenticular myopia or
underlying cataract but the lens thickness measurements were not available in
our patient record.
Epidemiologic
studies have shown a higher prevalence of myopia amongst Chinese compared to
Western population[9,27-28].
Environmental factors are believed to induce elongation of the AL resulting in
axial myopia[30]. In our study, despite a similar
distribution of myopes to hyperopes amongst PACD, there were more myopia
amongst Chinese compared to non-Chinese. Hence, angle-closure is not uncommon
in myopes especially in individuals with inherent shallow anterior chamber
dimensions as seen in a proportion of Chinese. This supports the current
thinking that ACD dimension is an important risk factor in the development of
angle-closure glaucoma.
In
the study by Liza-Sharmini et al[23-24], both eyes of the study subjects were included into
the study and assessed individually, 27.8% to 30.4% was found to be blind from
PACG. In our study we found no patients blind as a result of PACG because we
only studied the vision in the better eye as blindness was defined as having a
best corrected vision of less than 3/60 or an inability to count fingers at 3 m
in the better eye. Thus, the definition of blindness was different between the
two studies. Another possible
reason is that our study subjects are from an urban population who are better
educated and where health care is easily accessible.
The
strengths of this study lies in the spectrum of PACD that was studied. This
includes PACS, PAC and PACG. Our study had an almost equal distribution of
Chinese to non-Chinese despite the prevailing racial distribution in this
country. Among the limitations of our study is that it is a retrospective
study. Therefore, a fair amount of essential data could not be retrieved or
assessed. The study population was small and all parameters were confined to
available data in the patient’s chart. We also could not evaluate the lens
thickness, lens vault, ciliary body thickness, iris dimension, anterior chamber
width and volume between ethnic groups. These may be important parameters to assess
as it will help us better understand the mechanism of angle-closure glaucoma in
our population.
In
conclusion, angle-closure glaucoma can occur in both myopes and hyperopes at an
almost equal frequency. Myopic angle-closure glaucoma is not rare and myopia is
not a protective factor against angle-closure as was previously believed.
Importantly, increase public awareness and education are essential in early
detection and treatment of glaucoma.
ACKNOWLEDGEMENTS
First
of all, we would like to thank the Director General of Health Malaysia for his
permission to publish this article. We thank our colleagues from Clinical
Research Centre of Hospital Kuala Lumpur, who provided insight and expertise
that greatly assisted the research.
Conflicts
of Interest: Mohamed-Noor J, None; Abd-Salam D, None.
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