Morphology of Trabeculectomy Filtering Blebs using Anterior

Segment Optical Coherence Tomography: A Comparison of Two

Methods

Rita Pinto Proença

, Joana Ferreira

1,2

and João Paulo Cunha

1,2

Department of Ophthalmology, Central Lisbon Hospital Center, Lisbon, Portugal

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

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

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

Multiform

wall

Total

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

0.14

Microcysts

Total

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

Bleb Cavity

Total

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

0.17

Scleral

Flap

Total

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

Subflap

space

Total

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

Internal

ostium

Total

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.

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