Morphology of Trabeculectomy Filtering Blebs using Anterior
Segment Optical Coherence Tomography: A Comparison of Two
Methods
Rita Pinto Proença
1
, Joana Ferreira
1,2
and João Paulo Cunha
1,2
1
Department of Ophthalmology, Central Lisbon Hospital Center, Lisbon, Portugal
2
Nova Medical School, Universidade Nova de Lisboa, Lisbon, Portugal
Keywords: Glaucoma, Imaging, Optical Coherence Tomography, Trabeculectomy, Filtering Blebs.
Abstract: Anterior segment imaging optical coherence tomography (AS-OCT) can be a useful aid in glaucoma surgery.
Recent studies have shown its importance in both the preoperative morphologic evaluation of glaucoma
patients as well as postoperative evaluation of filtering bleb functionality. Our purpose is to evaluate post-
trabeculectomy filtering and non-filtering bleb characteristics in both time-domain OCT (TD-OCT,
Visante™, Carl Zeiss) and spectral-domain OCT (SD-OCT, Heidelberg Spectralis ® anterior segment
module), assess the usefulness of AS-OCT in evaluating postoperative filtering bleb function and compare
both methods results. AS-OCT as a useful exam in determining functioning and non-functioning bleb
characteristics. SD-OCT with an anterior segment module had a better performance in examining fine bleb
features and performed better than in previous studies in examining deeper structures.
1 INTRODUCTION
Trabeculectomy has been performed for the treatment
of glaucoma since 1968. Optimal results of this
surgical technique depend on the formation of a
filtering bleb (Cairns JE, 1968). Bleb morphology is
an indicator of shunt function and a predictor of bleb-
related complications (Picht G et al., 1998; Hu C et
al., 2003; DeBry PW et al., 2002; Soltau JB et al.,
2000).
Color photography (Cantor LB et al., 2003; Wells
AP et al., 2004), ultrasound biomicroscopy
(Yamamoto T et al., 1995), confocal microscopy
(Messmer et al., 2006; Labbe A et al., 2005),
conventional optical coherence tomography (OCT)
(Savini G et al., 2005) and time-domain anterior
segment (AS) OCT (Leung CK et al., 2007; Singh M
et al., 2007) have all been studied has potential exams
for analysing bleb characteristics.
AS-OCT imaging has been used to correlate bleb
structure and function, showing morphologic features
that may help distinguish between successful and
failed blebs (Singh M et al., 2007) (Meziani L et al,
2016) (Napoli PE et al., 2014). Spectral domain
optical coherence tomography (SD-OCT) is an
imaging modality that uses Fourier transformation of
reflected light from ocular structures to determine
depth data. Bleb imaging with OCT is useful as it is a
non-contact imaging method, in contrast to
ultrasound biomicroscopy (Drexler W et al., 1999 and
2001) (Khamar MB et al., 2014).
This study aimed to evaluate post-trabeculectomy
filtering and non-filtering bleb characteristics in both
time-domain OCT (TD-OCT, Visante™, Carl Zeiss)
and spectral-domain OCT (SD-OCT, Heidelberg
Spectralis ® anterior segment module), assess the
usefulness of AS-OCT in evaluating postoperative
filtering bleb function and compare both methods
results.
2 MATERIALS AND METHODS
2.1 Subject Groups
Observational case series conducted at the
Ophthalmology Department of the Central Lisbon
Hospital Center (CHLC) between January and
September of 2016.
Twenty eyes of 20 patients who had undergone
limbal-based trabeculectomy with intraoperative use
of mitomycin-C 0.02% and had at least 6 months of
follow up were included. All patients had primary
open angle glaucoma with an uncontrolled intraocular
ProenÃ
˘
ga R., Ferreira J. and Cunha J.
Morphology of Trabeculectomy Filtering Blebs using Anterior Segment Optical Coherence Tomography: A Comparison of Two Methods.
DOI: 10.5220/0006335804140419
Copyright
c
2017 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
pressure (IOP) despite maximum medical therapy.
Exclusion criteria were other types of glaucoma,
previous glaucoma surgery or ocular hypotension.
Eyes were classified in 2 groups according to
trabeculectomy outcome: failed blebs (FBs) and non-
failed blebs (NFBs). NFBs were defined as eyes with
post-operative IOP 18mmHg or a reduction of 35%
in pre-operative IOP without ocular hypotensive
medication. The remaining blebs were classified as
FBs.
Bleb structures were assessed with both TD-OCT
and SD-OCT in terms of wall thickness and
reflectivity, microcysts, bleb cavity, visualization of
the internal ostium, scleral flap and subflap space.
IOP and slit lamp morphology were also recorded.
Patient's informed consent was obtained before
participation in this study. The principles of the
Declaration of Helsinki were respected and the study
was approved by our institutional Ethics Committee.
2.2 Study Procedures
Patients were consecutively recruited and seen at
CHLC Ophthalmology department. A complete
demographic and background history was recorded.
A full ophthalmological examination was performed
with IOP measurement using Goldmann applanation
tonometry, slit lamp examination with a particular
focus in bleb pattern and fundoscopy. In the same
visit patients were examined with both time-domain
OCT (TD-OCT, Visante™, Carl Zeiss) and spectral-
domain OCT (SD-OCT, Heidelberg Spectralis ®
anterior segment module).
2.2.1 Intraocular Pressure
IOP was measured before pupillary dilation with
Goldmann applanation tonometry and a mean of 3
measurements was taken.
2.2.2 Spectral Domain Optical Coherence
Tomography Imaging
Blebs were examined with both time-domain OCT
(TD-OCT, Visante™, Carl Zeiss) and spectral-
domain OCT (SD-OCT, Heidelberg Spectralis ®
anterior segment module) in the same day, by the
same operator.
SD-OCT was performed using an anterior
segment adaptation lens in the optical system of the
scanning element to focus the OCT beam in the
anterior segment.
For the imaging, the patient was seated in front of
the OCT and asked to look down and fixate an
external point. The lid was gently manually elevated
by the observer to display the superior bulbar
conjunctival bleb.
Each trabeculectomy bleb was scanned at least
twice and the best image was selected. Scans were
oriented radially to the corneoscleral limbus to try to
include both scleral flap and maximum bleb height in
the same scan.
The obtained images were analysed qualitatively.
Qualitative assessment was based on visualization of
bleb structures 1) wall bleb thickening relative to
conjunctival-episcleral appearance, classified as
thickened or not thickened 2) wall reflectivity defined
as a uniform or multiform according to the presence
of hyporeflective spaces in the bleb wall 3) presence
of microcysts (small, round hyporeflective spaces
located at the surface of the bleb) 4) bleb cavity
(subepithelial hyporeflective space limited by
conjunctival tissue superficial to the sclera or scleral
flap 5) internal keratotrabaculectomy ostium 6)
scleral flap 7) subflap space.
Bleb characteristics were analysed in FBs and
NFBs in both methods.
2.2.3 Bleb Pattern
Slit lamp bleb morphology was analysed and blebs
were classified as cystic, diffuse or flattened. An
anterior segment photography of each bleb was
recorded for documentation.
2.2.4 Statistical Analysis
Demographics and clinical characteristics of patients
were described with frequencies (percentages) and
with mean (SD: standard deviation).
Normality assumption of the residuals was
verified using Kolmogorov–Smirnov goodness-of-fit
test. Nonparametric Chi-Square test was applied to
compare both methods.
A level of significance α=0.05 was considered.
Data were analysed using the Statistical Package for
the Social Sciences for Windows (IBM Corp.
Released 2013. IBM SPSS Statistics for Windows,
Version 22.0. Armonk, NY: IBM Corp.)
3 RESULTS
3.1 Patient Demographics and Clinical
Characteristics
A total of 20 eyes of 20 patients (13 males) were
imaged. One patient was excluded due to severe
hypotonia.
The FB group was comprised of 10 patients and
the NFB group of 9 patients. Mean age was 67.7 ±
9.57 years in the FB group and 72.1 ± 12.01 years in
the NFBs group.
Pre-operative IOP was reduced from 26.1 ±
5.97mmHg to 16.1 ± 4.1mmHg in the FB group with
ocular hypotensive medication and from 27.1 ±
5.06mmHg to 13.9 ± 2.85mmHg in the NFB group.
Mean interval between trabeculectomy and study
assessment was 39.33 ± 13.78 months in the FB group
and 31.5 ± 20.55 months in the NFB group.
No statistically significant differences in these
characteristics were found between groups.
Four patients in the FB group required additional
surgery (needling). The characteristics of both groups
are summarized in Table 1.
3.2 SD-OCT versus TD-OCT
Bleb characteristics were analysed in FBs and NFBs.
The utility of SD-OCT versus TD-OCT imaging in
showing bleb features was considered. Results are
summarized in table 2. Figures 1, 2 and 3 show
examples of bleb images in both methods.
In successful blebs, bleb wall thickening (88.8%
vs 77.8%), multiformity (88.8% vs 77.8%),
microcysts (100% vs 66.7%) and bleb cavity (88.8%
vs 77.8%) were visualized in a greater proportion
with SD-OCT than with TD-OCT. In spite of this
trend, these values were not statistically significant.
SD-OCT showed the scleral flap, subflap space
and internal ostium in a smaller proportion of blebs
than TD-OCT. This difference was not statistically
significant.
Table 1: Demographic and clinical characteristics of the patients by group.
NFB (n=10) FB (n=9) p
Sex
2F 8M 4F 5M -
Age (years)
67.7 ± 9.57 72.1 ± 12.01 0.54
Preoperative IOP (mmHg)
26.1 ± 5.97 27.1 ± 5.06 0.35
Postoperative IOP (mmHg)
16.1 ± 4.11 13.9 ± 2.85 0.11
Mean interval between
trabeculectomy and OCT
(months)
39.33 ± 13.78 31.5 ± 20.55 0.62
Additional surgery
4 0 -
Table 2: Structures visualized in FB and NFBs in both methods.
Bleb SD-OCT TD-OCT p value
Wall
thickening
Total
FB
NFB
15/19 (78.9%)
8/9 (88.8%)
7/10 (70%)
13/19 (68.4%)
7/9 (77.8%)
6/10 (60%)
0.71
1
1
Multiform
wall
Total
FB
NFB
13/19 (68.4%)
8/9 (88.8%)
5/10 (50%)
8/19 (42.1%)
7/9 (77.8%)
1/10 (10%)
0.19
1
0.14
Microcysts
Total
FB
NFB
13/19 (68.4%)
9/9 (100%)
4/10 (40%)
10/19 (52.6%)
6/9 (66.7%)
4/10 (40%)
0.50
0.20
1
Bleb Cavity
Total
FB
NFB
16/19 (84.2%)
8/9 (88.8%)
8/10 (80%)
11/19 (57.9%)
7/9 (77.8%)
4/10 (40%)
0.15
1
0.17
Scleral
Flap
Total
FB
NFB
13/19 (68.4%)
6/9 (66.7%)
6/10 (60%)
15/19 (78.9%)
7/9 (77.8%)
7/10 (70%)
0.71
1
1
Subflap
space
Total
FB
NFB
8/19 (42.1%)
5/9 (55.5%)
3/10 (30%)
12/19 (63.1%)
7/9 (77.8%)
5/10 (50%)
0.33
0.65
0.65
Internal
ostium
Total
FB
NFB
6/19 (31.6%)
3/9 (33.3%)
3/10 (30%)
12/19 (63.1%)
7/9 (77.8%)
5/10 (50%)
0.10
0.15
0.65
3.3 SD-OCT in Successful versus
Failed Blebs
Cystic spaces in the bleb wall were present in
functioning blebs more than in non-functioning blebs
in a statistically significant value (p<0.01).
A trend was also present for a more multiform
wall in functioning blebs. Results are summarized in
Table 3.
There was no other feature of failed blebs vs
successful blebs statistically significant.
4 CONCLUSIONS
This is the first study to compare characteristics of
functioning and non-functioning bleb in both Time-
Domain OCT (TD-OCT, Visante ™, Carl Zeiss) and
Spectral-Domain OCT (SD-OCT, Spectralis®
Heidelberg former segment module).
Functioning blebs present thickened and
multiform walls, with more microcysts, with a better
visualization of the bleb cavity, greater heights of
hyporeflective cavity, as well as better visualization
of the scleral flap, subflap space and ostium.
Table 3: Structures visualized in FB and NFBs in SD-OCT.
FB NFB p value
Wall thickening
8/9 (88.8%) 7/10 (70%) 0.58
Multiform wall
8/9 (88.8%) 5/10 (50%) 0.14
Microcysts
9/9 (100%) 4/10 (40%)
0.01
Bleb Cavity
8/9 (88.8%) 8/10 (80%) 1
Scleral Flap
6/9 (66.7%) 7/10 (70%) 1
Subflap space
5/9 (55.5%) 3/10 (30%) 0.37
Internal ostium
3/9 (33.3%) 3/10 (30%) 1
FB NFB p value
Wall thickening
8/9 (88.8%) 7/10 (70%) 0.58
Multiform wall
8/9 (88.8%) 5/10 (50%) 0.14
Microcysts
9/9 (100%) 4/10 (40%)
0.01
Bleb Cavity
8/9 (88.8%) 8/10 (80%) 1
Scleral Flap
6/9 (66.7%) 7/10 (70%) 1
Subflap space
5/9 (55.5%) 3/10 (30%) 0.37
Internal ostium
3/9 (33.3%) 3/10 (30%) 1
Figure 1: SD-OCT with arrows representing microcysts and bleb cavity.
Figure 2: SD-OCT and TD-OCT of a functioning bleb.
Figure 3: SD-OCT and TD-OCT of a non-functioning bleb.
Figure 4: Anterior Segment Photography of a cystic, diffuse and flattened bleb.
Microcysts were the structure that provided a
better discrimination between functioning blebs and
non-functioning blebs (p<0.01)
SD-OCT allows better visualization of thin wall
structures (multiformity, thickness and microcysts)
than TD-OCT. Despite its worse performance in the
observation of structures that need greater tissue
penetration and its greater difficulty in obtaining
wide-field images, this device has produced better
results than previous studies done without an anterior
segment adapter.
Some of our work limitations are the small
number of patients included, different follow-up
times and the higher number of anti-hypertensive
medications done by patients with non-functioning
blebs, which might affect conjunctival light
transmission and, consequently, the exam results.
AS-OCT is a simple, non-contact, reproducible
method for analysing the morphology of
trabeculectomy blebs. It is a useful exam in
evaluating the functionality of the bleb, aiding in the
clinical characteristics observed in the slit-lamp and
detecting early signs of the filtration bleb failure.
REFERENCES
Cairns JE. Trabeculectomy. Am J Ophthalmol 1968; 66:
673–9.
Cantor LB, Mantravadi A, et al. Morphologic classification
of filtering blebs after glaucoma filtration surgery: the
Indiana Bleb Appearance Grading Scale. J Glaucoma
2003;12: 266 –71.
DeBry PW, Perkins TW, Heatly G et al. Incidence of late-
onset bleb-related complications following
trabeculectomy with mitomycin. Arch Ophthalmol
2002; 120: 297–300.
Drexler W, Morgner U, Kartner FX et al. In vivo ultrahigh
resolution optical coherence tomography. Opt Lett
1999; 24: 1221–3. 20. Drexler W, Morgner U, Ghanta
RK et al. Ultrahighresolution Ophthalmic Optical
Coherence Tomography. Nat Med 2001; 7: 502–7.
Hu C, Matsuo H, Tomita G et al. Clinical Characteristics
and Leakage of Functioning Blebs after
Trabeculectomy with mitomycin-C in Primary
Glaucoma Patients. Ophthalmology 2003; 110: 345–
52.
Labbe A, Dupas B, Hamard P, Baudouin C. In Vivo
Confocal Microscopy Study of Blebs after Filtering
Surgery. Ophthalmology 2005;112:1979 – 86.
Leung CK, Yick DW, Kwong YY, et al. Analysis of Bleb
Morphology after Trabeculectomy with Visante
Anterior Segment Optical Coherence Tomography. Br
J Ophthalmol 2007;91:340 – 4.
Khamar MB, Soni SR, Mehta SV, Srivastava S, Vasavada
VA. Morphology of Functioning Trabeculectomy
Blebs using Anterior Segment Optical Coherence
Tomography. Indian J Ophthalmol. 2014 Jun;
62(6):711-4.
Messmer EM, Zapp DM, Mackert MJ, et al. In vivo
confocal microscopy of filtering blebs after
trabeculectomy. Arch Ophthalmol 2006; 124: 1095–
103.
Meziani L1, Tahiri Joutei Hassani R, El Sanharawi
M, Brasnu E, Liang H, Hamard P, Baudouin C, Labbe
A. Evaluation of Blebs After Filtering Surgery With
En-Face Anterior-Segment Optical Coherence
Tomography: A Pilot Study. J Glaucoma. 2016
May;25(5):e550-8.
Napoli PE1, Zucca I2, Fossarello M2. Qualitative and
quantitative analysis of filtering blebs with optical
coherence tomography. Can J Ophthalmol. 2014
Apr;49(2):210-6.
Picht G, Grehn F. Classification of filtering blebs in
trabeculectomy: biomicroscopy and functionality. Curr
Opin Ophthalmol 1998; 9: 2–8.
Savini G, Zanini M, Barboni P. Filtering blebs imaging by
optical coherence tomography. Clin Experiment
Ophthalmol 2005;33: 483–9.
Singh M, Chew PT, Friedman DS, et al. Imaging of
trabeculectomy blebs using anterior segment optical
coherence tomography. Ophthalmology 2007;114 :47–
53.
Soltau JB, Rothman RF, Budenz DL et al. Risk factors for
glaucoma filtering bleb infections. Arch Ophthalmol
2000; 118: 338–42.
Wells AP, Crowston JG, Marks J, et al. A pilot study of a
system for grading of drainage blebs after glaucoma
surgery
. J Glaucoma 2004;13: 454 – 60.
Yamamoto T, Sakuma T, Kitazawa Y. An ultrasound
biomicroscopic study of filtering blebs after mitomycin
C trabeculectomy. Ophthalmology 1995;102:1770 – 6.