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Comparison of ultrasound
biomicroscopy and spectral-domain anterior segment optical coherence tomography
in evaluation of anterior segment after laser peripheral iridotomy
Xiao-Yun Ma1,2, Dan
Zhu2, Jun Zou3, Wen-Jie Zhang1, Yi-Lin Cao1
1Department of Plastic and
Reconstructive Surgery, Shanghai Ninth People’s Hospital, Shanghai Jiao
Tong University School of Medicine, Shanghai Key Laboratory of Tissue
Engineering, National Tissue Engineering Center of China, Shanghai 200011,
China
2Department of Ophthalmology, Shanghai Guanghua
Integrative Medicine Hospital, Shanghai 200052, China 3Department of Ophthalmology, Shanghai Tenth People’s Hospital, Tongji
University, Shanghai 200072, China
Correspondence to: Jun Zou. Department
of Ophthalmology, Shanghai Tenth People’s Hospital, Shanghai Tongji University, 301 Yanchang
Middle Road, Shanghai 200072, China. zoujun70@126.com
Received: 2015-04-15
Accepted: 2015-07-13
Abstract
AIM: To
quantitatively assess narrow anterior chamber angle using spectral-domain anterior
segment optical coherence tomography (SD-AS-OCT) and
ultrasound biomicroscopy (UBM),
and to evaluate the correlations and
consistency between SD-AS-OCT and UBM.
METHODS:
Fifty-five eyes from 40
patients were examined. Patients were diagnosed with primary
angle-closure glaucoma (PACG) remission (11 eyes from 8
patients), primary angle closure
(PAC, 20 eyes from 20 patients)
and PAC suspect (24 eyes from 12
patients). Each eye was examined by SD-AS-OCT and UBM after laser peripheral
iridotomy (LPI). The measurements of SD-AS-OCT
were angle open distance (AOD), anterior chamber angle
(ACA), trabecular iris angle
(TIA), and trabecular iris
space area (TISA). UBM measurements were AOD and TIA. Correlations of AOD500
and TIA500 between UBM and AS-OCT were assessed. All
parameters were analysed by SPSS 16.0 and MedCalc.
RESULTS:
ACA, TIA and AOD measured by SD-AS-OCT reached a maximum at
the temporal quadrant and minimum at the nasal quadrant. TISA
reached the maximum at the inferior and minimum at the
superior quadrant. Group parameters of
AOD500 and AOD750 showed a linear positive correlation, and AOD750 had less
variability. UBM outcomes of AOD500 and TIA500 were significantly smaller than
those of SD-AS-OCT. The results of the two techniques were correlated at the
superior, nasal and inferior quadrants.
CONCLUSION:
Both UBM and SD-AS-OCT are
efficient tools for follow-up during the course of PACG. We recommended using
parameters at 750 µm anterior to the sclera spur for the screening and
follow-up of PACG and PAC. The two methods might be
alternatives to each other.
KEYWORDS: primary angle-closure glaucoma; ultrasound biomicroscopy;
spectral-domain
anterior segment optical coherence tomography; laser peripheral
iridotomy
DOI:10.18240/ijo.2016.03.16
Citation: Ma XY, Zhu D, Zou J, Zhang WJ, Cao YL. Comparison of ultrasound biomicroscopy and
spectral-domain anterior segment optical coherence tomography in evaluation of
anterior segment after laser peripheral iridotomy. Int J Ophthalmol 2016;9(3):417-423
INTRODUCTION
Glaucoma is the
leading cause of irreversible blindness worldwide. Quigley and
Broman[1]
predicted
that the prevalence of primary angle-closure glaucoma (PACG) would reach 21
million (26% of all types of glaucoma) by 2020. The incidence and prevalence of
PACG also differ among races[2-3]. Currently,
China has the
largest number of PACG patients, and is expected to have 48% of the total
incidence by 2020[1].
Follow-up surveys of primary angle closure suspect (PACS) eyes showed that 22%-28% of them progress to
primary angle closure (PAC) within a few years[4-5]. PACS can be diagnosed early by
certain ways, such as slit-lamp, gonioscopy, ultrasound
biomicroscopy
(UBM) and Pentacam. If treated early and safely, some
patients with PACS may not progress to PACG or blindness. In China, there is an
urgent need
to develop simpler, more efficient and economic examinations.
UBM
has been used
in imaging and quantitative evaluation of anterior ocular segments
since the
1990s. It allows in vivo observation
of the anatomy and pathology of the anterior segments, from the conjunctiva and
cornea to the iris and basal vitreous body, which provides
significant information on glaucoma, cysts, neoplasms, trauma and foreign
bodies. UBM also provides biometric information of anterior segment structures,
such as anterior chamber (AC) depth, anterior chamber angle (ACA), and iris
thickness. UBM provides more detailed information compared to slit-lamp,
gonioscopy or B-scan examinations for diagnosis and follow-up of PAC eyes[6].
Optical
coherence tomography (OCT) is a widely used non-invasive fundus imaging
technique. Since the first application of OCT in the cornea in 2002[7],
anterior segment-optical coherence tomography (AS-OCT)
has developed rapidly. There are two major OCT platforms on the market:
time domain-optical coherence tomography (TD-OCT) and spectral (or
Fourier) domain-optical coherence tomography (SD/FD-OCT).
With a higher
imaging resolution than UBM, AS-OCT makes it easier for the operator and software
to identify ACA structures[8], such as:
the scleral spur (SS), iris surface, Schwalbe’s line, even
trabecular meshwork (TM), and Schlemm’s canal[9]. This provides
more precise analysis of the angle opening distance (AOD) from the SS, ACA, trabecular iris
angle (TIA), and trabecular iris space area (TISA).
Glaucoma
research has often been conducted by TD-AS-OCT. RetinaScan-3000 OCT (NIDEK) is
a high-speed SD-OCT that uses dual diode lasers with wavelengths of 880
nm. It is capable of conducting 53 000 A-scans per second with a 7
μm axial and
20 μm
transverse resolution, providing high-quality imaging
(4
μm OCT
digital resolution) with shorter measurement time and fewer artefacts
than TD-AS-OCT[10]. RetinaScan-3000
is designed mainly for ocular fundus assessment, but with a forehead attachment
and a switch to the anterior segment mode, it is capable of assessing anterior
segments, including corneal thickness and ACA parameters.
Correlation of AC parameters between SD-AS-OCT and UBM has rarely been investigated.
Therefore, we designed this study to compare the utilisation of images from UBM
and SD-AS-OCT, and to assess the ACA in narrow angle patients.
SUBJECTS AND METHODS
From January
to December 2014, we recruited 40 patients (29 female; mean age 67.2±9.0y)
from the Department of Ophthalmology, Shanghai Tenth People’s Hospital of
Tongji University, who were diagnosed with PAC, PACS
or PACG following systematic eye examination, including medical history,
slit-lamp examination (Haag-Streit,
Bern, Switzerland),
non-contact tonometry (CT-80; Topcon, Tokyo, Japan), corneal
thickness
measurement (RetinaScan 3000; NIDEK, Gamagori, Japan), gonioscopy(Volk
Optical Inc., Mentor, OH, USA) and automated perimetry (Octopus 900; Haag-Streit, Koeniz,
Switzerland) measurement. All subjects were of Chinese
ethnicity. Patients with severe systemic diseases, history of optical
surgery or laser treatment, or diseases and pathological
structures
that might have interfered with observation of the cornea, AC, iris or pupil were
excluded. Fifty-five eyes from 40 patients received laser peripheral
iridotomy (LPI) that was performed by the same experienced doctor using the
combination of argon and neodymium:yttrium-aluminum-garnet (Nd:YAG) laser. Argon laser was set at 500
to 1000 mW power with a spot size of 50 μm for a duration of 0.1s. Nd:YAG was
set at 3 to 5 mJ. The study protocol was approved by the Ethics Committee of Shanghai Tenth People’s Hospital of
Tongji University. Written informed consent was obtained from
each patient after explanation of the purpose and possible consequences of
the study.
All patients
underwent imaging with SD-OCT (RetinaScan 3000;
NIDEK, Gamagori, Japan) under ordinary room light. Patients
were asked to gaze at the inward illumination to minimise eye movement. Scans were centred on the
limbus to visualise the ACA and were taken in the nasal,
temporal, superior and inferior quadrants (0, 3, 6 and 9 o’clock positions)
using the anterior segment programme. This programme
automatically
overlaid valid images selected from 50 scans of the same location. The operator
repeated this process and chose the best images and calculated parameters
(AOD at 500
µm and 750 µm from the SS (AOD500 and AOD750), ACA, TIA, and TISA (Figure
1) with the
built-in software.
Figure
1 Anterior chamber angle in SD-AS-OCT image A: AOD: The distance from the corneal
endothelium to the anterior iris perpendicular to a line drawn along the
trabecular meshwork at 500 µm or 750 µm from the scleral spur; TISA: The areas
bounded by the corneal endothelium, trabecular meshwork, and anterior iris
surface out to a distance of 500 µm or 750 µm from the scleral spur; TIA: The
angle measured with the apex in the scleral spur and the arms of the angle
passing through a point on the trabecular meshwork 500 µm from the scleral spur
and a perpendicular point on the iris. B: ACA: The angle measured with the apex
at the angle recess and the arms of the angle passing through a point on the
trabecular meshwork 500 µm from the scleral spur and a perpendicular point on
the iris. 1: Scleral spur.
All patients
underwent imaging with UBM (UD-6000; Tomey Corporation, Nagoya, Japan) under
bright conditions
following SD-AS-OCT. Following topical anaesthesia, an appropriately sized
eye cup was placed on the sclera of the eye being examined, with normal
saline as the couplant. Scans were taken in the nasal, temporal, superior and
inferior quadrants. Measurements were taken three times and the operator chose
the best image (when the iris was located on the reference line and its length
was shortest). The mean value of three repetitions was
used for
statistical analysis. UBM measurements were AOD500 and TIA500.
Statistical
Analysis Statistical analysis was performed using SPSS version
16.0 (Chicago, IL, USA) and MedCalc version 12.7.0.0 (Ostend, Belgium).
Differences in mean values of parametric data among eyes of different patients
were analysed
using the independent-sample Student’s t-test. Correlation between two groups
of data collected by SD-AS-OCT was examined. The Pearson
correlation test was used to evaluate correlations between measurements.
Bland-Altman plots were used to evaluate limits of agreement of
AS-OCT and UBM. P<0.05 was
considered
statistically significant.
RESULTS
Fifty-five
eyes from 40
patients were
available for analysis. Complete ophthalmic examination
revealed PACG remission in 11 eyes from 8 patients, PAC (the fellow eye of the
acute PACG
eye, with gonioscopy revealed peripheral anterior
synechiae, 20
eyes from 20 patients) and PACS in 24 eyes from 12 patients. There
was no significant difference in mean intraocular pressure (IOP) measured
by non-contact tonometry before LPI (15.36±2.90 mm
Hg)
and after LPI
(15.12±3.20 mm Hg；P=0.477). The corneal thickness (514±30.19
μm) did not
differ significantly between the sexes or according to pathological stage (P>0.05).
None
of the patients experienced rose of IOP, acute
PACG or progressive loss of vision after LPI. The SS could be
identified in all SD-AS-OCT images, and 82.7% (182/220) of
UBM images (Figure
2).
Figure
2 Images of ACA from
SD-AS-OCT and UBM A: SS is clearly shown (white
arrows) in both SD-AS-OCT and UBM. SD-AS-OCT
(left) had a
disadvantage in displaying the angle recess area and structures behind the iris;
B: ACA image
by SD-AS-OCT (left) and UBM (right) after LPI.
SD-AS-OCT measurements of ACA
after LPI are summarised in Table 1. Measurements at 500 µm from SS were linearly correlated with those at
750 µm (P<0.01). ACA, TIA and AOD measured by AS-OCT reached the
maximum at temporal quadrant and minimum at nasal quadrant，but for TISA, the maximum value
appeared to be at the inferior quadrant and minimum value at the superior
quadrant. UBM showed similar distributions of angle width to OCT. Measurements using UBM and
SD-AS-OCT
were correlated at the superior, temporal and inferior quadrants,
but Pearson correlations were not significant in the nasal quadrant (Table 2). UBM yielded
significantly smaller measurements compared with SD-AS-OCT (Paired t-test, P<0.01). No evidence of outliers
from normal distribution was seen for any of the indices.
Table 1
Mean values of angle parameters by
AS-OCT after LPI
|
Parameters |
Superior |
Inferior |
Nasal |
Temporal |
|
TIA500 (°) |
24.784±7.971 |
25.719±10.472 |
23.411±8.463 |
26.425±7.398 |
|
TIA750 (°) |
22.589±6.158 |
23.178±8.615 |
21.566±7.342 |
23.400±6.755 |
|
ACA500 (°) |
16.046±6.641 |
14.739±6.320 |
12.913±6.312 |
16.449±5.866 |
|
ACA750 (°) |
16.079±5.795 |
15.296±6.455 |
13.728±6.162 |
16.294±5.855 |
|
AOD500 (mm) |
0.244±0.098 |
0.246±0.103 |
0.228±0.092 |
0.259±0.086 |
|
AOD750 (mm) |
0.317±0.106 |
0.326±0.147 |
0.304±0.120 |
0.332±0.109 |
|
TISA500 (mm2) |
0.084±0.040 |
0.094±0.060 |
0.084±0.037 |
0.093±0.033 |
|
TISA750 (mm2) |
0.150±0.060 |
0.165±0.098 |
0.153±0.064 |
0.163±0.061 |
TIA: Trabecular
iris angle; ACA: Anterior chamber angle; AOD: Angle opening
distance; TISA: Trabecular iris space area.
Table 2
Mean values and Pearson correlation
of TIA500 and AOD500
measured by UBM and AS-OCT
|
Quadrants |
TIA500 (°) |
AOD500 (mm) |
||||||||
|
UBM (SD) |
AS-OCT (SD) |
t |
P
|
Pearson P |
UBM (SD) |
AS-OCT (SD) |
t |
P
|
Pearson P |
|
|
Superior |
10.109 (10.196) |
24.784 (7.971) |
-10.795 |
0.000 |
0.002 |
0.08 (0.097) |
0.244 (0.098) |
-10.711 |
0.000 |
0.005 |
|
Inferior |
15.385 (10.979) |
25.719 (10.472) |
-6.308 |
0.000 |
0.007 |
0.148 (0.133) |
0.246 (0.103) |
-5.108 |
0.000 |
0.016 |
|
Nasal |
17.368 (11.857) |
26.425 (7.398) |
-3.662 |
0.001 |
0.498 |
0.154 (0.104) |
0.228 (0.092) |
-4.248 |
0.000 |
0.333 |
|
Temporal |
17.094 (10.416) |
23.411 (8.463) |
-6.014 |
0.000 |
0.017 |
0.159 (0.123) |
0.259 (0.086) |
-5.903 |
0.000 |
0.017 |
TIA: Trabecular iris angle; AOD:
Angle opening distance; UBM: Ultrasound biomicroscopy; AS-OCT: Anterior
segment-optical coherence tomography; SD: Standard deviation.
TIA500 and
AOD500 were chosen to analyse consistency between UBM and SD-AS-OCT examinations (Table
3). Agreement
of AOD500 and TIA500 measurements was illustrated with Bland-Altman plots (Figure
3). The mean
value and mean difference of AOD500 were 0.191 µm and 0.11 µm, respectively,
and 3.6% (2/55) of measurements were out with the 95% limits. The mean
ratio of AOD500 was 1.97, and 1.8% (1/55) of measurements were
out with
the
95% limits.
The mean value and mean difference of TIA500 were 20.0° and 10.2°, respectively,
and all measurements were within the 95% limits. The mean ratio of TIA500 was
1.79, and 5.4% (3/55) of measurements were out with the 95% limits.
Figure
3 Bland-Altman plots
of AOD500 and TIA500 measured by UBM and AS-OCT. A and C: The differences of TIA500 and AOD500
measured by UBM and AS-OCT. B and D: The ratios of TIA500 and AOD 500 measured
by UBM and AS-OCT. The ratio variations are much bigger when the mean values
are smaller.
Table 3
Mean difference and ratio between results of UBM and AS-OCT together with 95% limits
of agreement
|
Parameters |
AS-OCT - UBM |
AS-OCT/UBM |
||||||
|
|
Mean (95%) |
Range |
1.96×SD |
Mean ratio |
Mean (95%) |
Range |
1.96×SD |
|
|
AOD500 |
0.11±0.05 |
0.11 (0.01, 0.20) |
0.19 |
0.10 |
1.97±0.60 |
1.97 (0.79, 3.14) |
2.35 |
1.18 |
|
TIA500 |
10.15±4.72 |
10.2 (0.9, 19.4) |
18.5 |
9.25 |
1.79±0.48 |
1.79 (0.86, 2.73) |
1.87 |
0.94 |
AOD: Angle opening distance; TIA: Trabecular iris angle; SD: Standard deviation.
Measurements
of 500 μm and 750 μm from SS were analysed for coefficient of variation (Table 4). Coefficient of
variation was smaller for measurements at 750 µm.
Table 4
Coefficient variation of 500 µm and 750 µm measurements %
|
Measurements |
500 µm from SS |
750 µm from SS |
|
TIA |
34.26 |
31.83 |
|
ACA |
42.20 |
39.77 |
|
AOD |
41.41 |
37.71 |
|
TISA |
47.75 |
44.66 |
TIA: Trabecular iris angle; ACA: Anterior chamber angle; AOD: Angle opening
distance; TISA: Trabecular iris space area; SS: Sclera spur.
DISCUSSION
The ACA is an
important structure in the diagnosis and treatment planning of PACG. It has
been shown previously that there is no significant difference in ACA
between Chinese and Caucasian people[3].
However, Chinese people tend to have flatter keratometry, thicker
peripheral iris, and more forward iris root and ciliary body, therefore, they
have a more crowded AC and narrower ACA compared to Caucasian people[3].
LPI is the
first-line treatment for PAC, because it relieves pupil blockage, flattens
the iris, widens ACA, and improves aqueous humour outflow[11].
It is
reported
that LPI
results in a significant increase in ACA width in eyes with narrow angles[6,12].
However, the mechanism of PACG in Chinese people often involves
non-pupillary
block[13]. It was recommended that clinicians should
follow the progress of PAC eyes even after successful LPI, because LPI might
not resolve goniosynechia caused by non-pupillary
block[14-15]. Long-term follow-up
shown
that, despite
the presence of a patency LPI, a large proportion of PACG eyes require further
treatment, such as anti-glaucoma medications, peripheral
laser iridoplasty, or surgical therapy to control IOP[4,16].
Some studies
have verified that OCT and UBM show excellent performance in identifying eyes
with narrow angles[4,17-18]. SD-AS-OCT shows excellent
reproducibility, sensitivity and ability to identify ACA structures[19-20]. However, the measurements were
mostly done only at the nasal and temporal quadrants to avoid influence by the
eyelids. Moreover, outward illumination was applied during the examination to
achieve better image quality. Patients with narrow angles should be
examined in as many orientations as possible to gain a comprehensive assessment
of goniosynechia. Using SD-AS-OCT, we managed to image four
quadrants of the limbus using inward illumination, which minimised eye movement
and provided credible results. We found that ACA, TIA and AOD measured by SD-AS-OCT reached a maximum
at the temporal quadrant and a minimum at the superior quadrant. The maximum value of
TISA appeared
to be at the inferior quadrant and minimum value at the nasal quadrant.
Measurements by UBM and SD-AS-OCT were correlated at the
superior, nasal and inferior quadrants, which was consistent with previous
findings[21-22].
The TM is the
primary drainage structure for aqueous humour and is intimately related
to the pathophysiology of glaucoma. The TM extends for 500-800
μm from the
SS[23-24]. It is believed that there is
no
significant association between TM width and angle parameters[23].
In the current study, the coefficient of variation of the 500 µm
group was larger than that of the 750 µm group in every quadrant. We speculated that
structures like the plateau iris and recess of peripheral iris might have more
influence on parameters at 500 µm, which means that AOD750 would be more
steady and accurate in reflecting the scale of aqueous humour
outflow
blockade than AOD500, and help clinicians to estimate goniosynechia.
Therefore, we recommend using parameters at 750 µm anterior to the SS for
screening and follow-up of narrow angles.
Currently,
TD-AS-OCT, Pentacam or Orbscan are widely used for AC measurements[3].
Some studies have compared SD-OCT and UBM in terms of the quantitative angle
measurements and suggested that they do agree[8,25]. Radhakrishnan
et al[18] have compared the
specificity and sensitivity of gonioscopy, TD-AS-OCT and UBM in identifying
narrow angles. The ACA parameters measured by OCT and UBM had similar mean
values, reproducibility, and sensitivity and specificity
profiles. Mansouri et al[26] compared the
accuracy in measurement of the ACA by UBM and TD-AS-OCT. They found that AS-OCT measurements are significantly
correlated with UBM measurements but show poor agreement with each other. They
think that TD-AS-OCT cannot replace UBM for the quantitative assessment of the
AC angle. In
the current study, we used SD-OCT instead of TD-OCT. AOD500 and TIA500 in
superior, inferior, nasal and temporal quadrants were examined, and the average
values were accepted for analysis of correlation between the techniques. Bland-Altman plots were used to
evaluate whether these two different techniques could be alternatives in
clinical use. As demonstrated in Figure 3, for the same quadrant in
the same eye, the smaller the mean value of the two methods, the greater the
ratio between them. This indicated that as the iris root approaching the
TM, it was
hard for UBM to discern the presence of goniosynechia or outflow block. In
other words, UBM had a higher probability to underestimate TIA and AOD in
narrow angles. This might explain why patients could keep a relatively low and
stable IOP while UBM examinations revealed a wide range
of goniosynechia.
UBM requires
patients to be in the supine position. Although topical anaesthesia
is applied,
contact between the eye cup and couplant still make patients uncomfortable.
Moreover, the eye cup and the couplant may affect the angle structure by
gravity and pressure. AS-OCT is a newer instrument that requires patients to be
in the seated position and there is no contact with the eyeballs, which makes
it more practical and the ACA structure is more similar to the natural
configuration. RS-3000 AS-OCT had the disadvantage of displaying angle recess
area and structures behind the iris but could gave the precise location
of the SS and identified the separation between the iris root
and the TM (Figure
2). UBM was
unable to resolve different tissues when the separation between them was too
small. Both UBM and AS-OCT could show the SS with high
reproducibility (Figure 2), which means TIA (use SS as vertice
while measuring) should produce a smaller measuring error than ACA (use summit
of AC as
vertice while measuring). In the current
study, TIA500
and AOD500 measurements by two methods were correlated in every quadrant except
for the nasal quadrant. The two groups had statistically significant
difference, even though they were not significantly different in clinical
application[6,20]. Our findings were consistent with the study
of Wang et
al[20],
they compared
ACA width measurements by UBM and high and low-resolution TD-OCT, and
found that low-resolution OCT was similar to UBM for most of the studied angle
measurements, but high-resolution OCT tended to give larger
measurements compared to low-resolution OCT and UBM. The difference in
resolution between the three methods, the outer illumination of high-resolution
OCT, different image processing algorithms, and the air-cornea and cornea-aqueous humour
interface
distortion of coherent light may have contribute to the differences. This
might be an explanation to the results carried out by Mansouri et al[26].
Aptel et
al[27] used SD-AS-OCT and TD-AS-OCT to
measure AC parameters in healthy participants, and the two devices were
consistent for all the parameters except for the AC depth
and SS angle.
The extent of
goniosynechia could influence the treatment choices for PAC and PACG.
Comparing the images obtained from our two techniques, we believed that SD-AS-OCT has
a major
advantage over UBM in estimating AC width. The resolution difference between
UBM and SD-AS-OCT might be responsible for the measurement error. First, the
RS3000 OCT had better axial resolution of 7 μm compared to 50 μm
provided by UD-6000 UBM. OCT could give the precise
location of the SS, while the lack of image contrast made UBM incapable of such
discernment when the separation between the TM and iris root was too
small.
Second, the two methods might not have scanned at the same location, which
could have led to the different results. With a real-time scanning
system and inward aiming light, it was much easier for SD-AS-OCT to locate the
exact same target limbus position. UBM required patients to follow the external
guidance light, meaning that the probe was perpendicular to the target tissue.
The reproducibility depended on the operator’s experience and patient’s
coordination. In the current study, we tried to eliminate this error by
repeating UBM three times. Moreover, the UBM and SD-AS-OCT images were
processed with a built-in programme, and the different analytical
software of
the two procedures might have accounted for the discrepancy in the results.
SD-AS-OCT has better definition of interfaces
between different tissues and less background noise, which
might be
helpful for the software to recognize and calculate. The
low
resolution of UBM could have caused minute differences that accumulated
into a
significant difference in the calculation of angle recess area.
There were
some limitations to the current study that might be improved in future studies.
First, all the patients had narrow ACAs. Comparison of UBM and SD-AS-OCT for
evaluation of open angles needs further investigation. Second, we
chose inward rather than outward guidance light to minimise eye movement and
aimed for the natural configuration of the ACA. However, whether the
measurements with the two type of guidance light were consistent
should be
validated. Third, because the coherent light was not perpendicular to the
target tissue, the image clarity was not as good as in some previous studies
that used outward guidance light. Improvement in analytical
software and
new image processing algorithms should be developed.
In conclusion, both UBM and SD-AS-OCT are efficient tools for
follow-up during the course of PACG. However, SD-AS-OCT was capable of
providing angle images with fine anatomical structures, which was more useful
in quantitative assessment of a narrow or closed angle. ACA parameters measured
by SD-AS-OCT were well correlated with those from UBM. SD-AS-OCT provided
larger measurements of TIA500 and AOD500 compared to UBM in patients with
narrow ACA, but this was not clinically significant. Parameters measured by
SD-AS-OCT at 750 µm anterior to the SS appear to be less variable than those at
500 µm and are useful clinically. We recommend using parameters at 750 µm
anterior to the SS for screening and follow-up of PACG and PAC. With real-time
monitoring of imaging, SD-AS-OCT is a non-contact apparatus with high
resolution; it is user friendly and is a promising method
for screening individuals at risk for developing PACG.
ACKNOWLEDGEMENTS
Conflicts of Interest: Ma XY, None; Zhu D,
None; Zou J, None; Zhang WJ, None; Cao YL, None.
REFERENCES
1 Quigley HA, Broman AT. The
number of people with glaucoma worldwide in 2010 and 2020. <ii>Br J
Ophthalmal</ii> 2006;90(3):262-267. [CrossRef] [PubMed] [PMC free article]
2 Wang N, Wu H, Fan Z. Primary
angle closure glaucoma in Chinese and Western populations. <ii>Chin Med J
</ii>2002;115(11):1706-1715.
3 He M, Foster P, Johnson GJ,
Khaw PJ. Angle-closure glaucoma in East Asian and European people. Different
diseases? <ii>Eye (Lond) </ii> 2006;20 (1):3-12. [CrossRef]
[PubMed]
4 Thomas R, George R, Parikh R,
Muliyil J, Jacob A. Five year risk of progression of primary angle closure
suspects to primary angle closure: a population based study. <ii>Br J
Ophthalmol </ii> 2003;87(4):450-454. [CrossRef]
[PubMed]
5 Liza-Sharmini AT, Sharina YN,
Dolaboladi AJ, Zaid NA, Azhany Y, Zunaina E. Clinical presentation, severity
and progression of primary angle closure in malays. <ii>Med J Malaysia
</ii> 2014;69(1):21-26. [PubMed]
6 Dada T, Mohan S, Sihota R,
Gupta R, Gupta V, Pandey R. Comparison of ultrasound biomicroscopic parameters
after laser iridotomy in eyes with primary angle closure and primary angle
closure glaucoma. <ii>Eye (Lond) </ii>2007;21(7):956-961. [CrossRef]
[PubMed]
7 Wirbelauer C, Scholz C,
Häberle H, Laqua H, Pham DT. Corneal optical coherence tomography before and
after phototherapeutic keratectomy for recurrent epithelial erosions.
<ii>J Cataract Refract Surg </ii> 2002;28(9):1629-1635. [CrossRef]
8 Reinstein DZ, Gobbe M, Archer
TJ. Anterior segment biometry: a study and review of resolution and
repeatability data. <ii>J Refract Surg </ii> 2012;28(7):509-520. [CrossRef] [PubMed]
9 Sharma R, Sharma A, Arora T,
Sharma S, Sobti A, Jha B, Chaturvedi N, Dada T. Application of anterior segment
optical coherence tomography in glaucoma. <ii>Surv Ophthalmol</ii>
2014;59(3):311-327. [CrossRef] [PubMed]
10 Savini G, Carbonelli M,
Barboni P. Spectral-domain optical coherence tomography for the diagnosis and
follow-up of glaucoma. <ii>Curr Opin Ophthalmol </ii>
2011;22(2):115-123. [CrossRef] [PubMed]
11 Tarongoy P, Ho CL, Walton DS.
Angle-closure glaucoma: the role of the lens in the pathogenesis, prevention,
and treatment. <ii>Surv Ophthalmol </ii> 2009;54(2):211-225. [CrossRef] [PubMed]
12 Lee KS, Sung KR, Shon K, Sun
JH, Lee JR. Longitudinal changes in anterior segment parameters after laser
peripheral iridotomy assessed by anterior segment optical coherence tomography.
<ii>Invest Ophthalmol Vis Sci </ii>2013;54(5):3166-3170. [CrossRef]
[PubMed]
13 Liang Y, Friedman DS, Zhou Q,
Yang XH, Sun LP, Guo L, Chang DS, Lian L, Wang NL; Handan Eye Study Group.
Prevalence and characteristics of primary angle-closure diseases in a rural
adult Chinese population: the Handan Eye Study. <ii>Invest Ophthalmol Vis
Sci </ii> 2011;52(12):8672-8679. [CrossRef]
[PubMed]
14 Ang LP, Aung T, Chew PT.
Acute primary angle closure in an Asian population: long-term outcome of the
fellow eye after prophylactic laser peripheral iridotomy.
<ii>Ophthalmology</ii> 2000;107(11):2092-2096. [CrossRef]
15 Yan YJ, Wu LL, Wang X, Xiao
GG. Appositional angle closure in Chinese with primary angle closure and
primary angle closure glaucoma after laser peripheral iridotomy.
<ii>Invest Ophthalmol Vis Sci </ii>2014;55(12):8506-8512. [CrossRef]
[PubMed]
16 Ramani KK, Mani B, George RJ,
Lingam V. Follow-up of primary angle closure suspects after laser peripheral
iridotomy using ultrasound biomicroscopy and A-scan biometry for a period of 2
years. <ii>J Glaucoma </ii>2009;18(7):521-527. [CrossRef] [PubMed]
17 Dada T, Sihota R, Gadia R,
Aggarwal A, Mandal S, Gupta V. Comparison of anterior segment optical coherence
tomography and ultrasound biomicroscopy for assessment of the anterior segment.
<ii>J Cataract Refract Surg </ii> 2007;33(5):837-840. [CrossRef] [PubMed]
18 Radhakrishnan S, Goldsmith J,
Huang D, Westphal V, Dueker DK, Rollins AM, Izatt JA, Smith SD. Comparison of
optical coherence tomography and ultrasound biomicroscopy for detection of
narrow anterior chamber angles. <ii>Arch Ophthalmol </ii>
2005;123(8):1053-1059. [CrossRef] [PubMed]
19 Schuman JS. Spectral domain
optical coherence tomography for glaucoma (an AOS thesis). <ii>Trans Am
Ophthalmol Soc</ii> 2008;106:426-458.
20 Wang D, Pekmezci M, Basham
RP, He M, Seider MI, Lin SC. Comparison of different modes in optical coherence
tomography and ultrasound biomicroscopy in anterior chamber angle
assessment.<ii> J Glaucoma </ii>2009;18(6):472-478. [CrossRef] [PubMed]
21 Mansouri K, Burgener N,
Bagnoud M, Shaarawy T. A prospective ultrasound biomicroscopy evaluation of
changes in anterior segment morphology following laser iridotomy in European
eyes. <ii>Eye (Lond) </ii>2009;23(11):2046-2051. [CrossRef]
[PubMed]
22 See JL, Chew PT, Smith SD,
Nolan WP, Chan YH, Huang D, Zheng C, Foster PJ, Aung T, Friedman DS. Changes in
anterior segment morphology in response to illumination and after laser
iridotomy in Asian eyes: an anterior segment OCT study. <ii>Br J
Ophthalmol </ii> 2007;91(11):1485-1489. [CrossRef] [PubMed] [PMC free article]
23 Tun TA, Baskaran M, Zheng C,
Sakata LM, Perera SA, Chan AS, Friedman DS, Cheung CY, Aung T. Assessment of
trabecular meshwork width using swept source optical coherence tomography.
<ii>Graefes Arch Clin Exp Ophthalmol </ii> 2013;251(6):1587-1592. [CrossRef] [PubMed]
24 Gold ME, Kansara S, Nagi KS,
Bell NP, Blieden LS, Chuang AZ, Baker LA, Mankiewicz KA, Feldman RM.
Age-related changes in trabecular meshwork imaging. <ii>Biomed Res
Int</ii> 2013;2013:295204. [CrossRef]
25 Emanuel ME, Parrish RK 2nd,
Gedde SJ. Evidence-based management of primary angle closure glaucoma.
<ii>Curr Opin Ophthalmol</ii> 2014;25(2):89-92. [CrossRef] [PubMed]
26 Mansouri K, Sommerhalder J,
Shaarawy T. Prospective comparison of ultrasound biomicroscopy and anterior
segment optical coherence tomography for evaluation of anterior chamber
dimensions in European eyes with primary angle closure. <ii>Eye (Lond)
</ii> 2010;24(2):233-239. [CrossRef]
[PubMed]
27 Aptel F, Chiquet C, Gimbert
A, Romanet J, Thuret G, Gain P, Campolmi N. Anterior segment biometry using
spectral-domain optical coherence tomography. <ii>J Refract Surg
</ii> 2014:30(5):354-360. [CrossRef] [PubMed]
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