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01 Würzburg Bleb Classification Score

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Original Paper
Ophthalmologica 2008;222:408–413
DOI: 10.1159/000161555
Received: April 19, 2007
Accepted: April 20, 2007
Published online: October 10, 2008
Interobserver Variability of the
Würzburg Bleb Classification Score
Thomas Klink Sybille Schrey Uta Elsesser Janine Klink
Günther Schlunck Franz Grehn
Department of Ophthalmology, Julius Maximilian University, Würzburg, Germany
Abstract
Background: The Würzburg bleb classification score (WBCS)
serves to assess filtering blebs in a standardized fashion. The
purpose of this prospective masked agreement study was to
evaluate the WBCS interobserver variability. Methods: The
WBCS provides a scheme to grade clinical bleb morphology.
It evaluates the following parameters: vascularity, corkscrew
vessels, encapsulation, microcysts and bleb height. Thus, 113
eyes of 104 consecutive patients at various times after surgery were examined (slit lamp biomicroscopy) by 3 ophthalmologists with each observer being unaware of the findings
reported by the others. To calculate the interobserver variability of the WBCS, the interobserver consistency and absolute agreement were determined with an intraclass correlation coefficient (ICC) using a 2-way random model. Results:
The ICC values of a single rater’s judgment were: vascularity
+0.62, corkscrew vessels +0.67, encapsulation +0.63, bleb
height +0.53, microcysts +0.52 and total score +0.74. The ICC
values of the mean of all 3 raters were: +0.83 vascularity,
+0.86 corkscrew vessels, +0.84 encapsulation, +0.77 bleb
height, +0.76 microcysts and +0.90 total score. Conclusion:
The WBCS is a bleb morphology score with high levels of interobserver consistency and absolute agreement in clinical
practice.
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Introduction
Scarring of the filtering bleb is the main reason for
failure of penetrating glaucoma surgery. Recently, several
wound healing modulating agents have entered routine
clinical practice [1, 2]. In order to guide their use, a thorough slit lamp examination is essential and allows for a
timely start of wound-modulating therapy [2–8]. In clinical practice, scoring systems offer a framework for structured patient examination and facilitate the interpretation of clinical findings. The Würzburg bleb classification score [5] (WBCS) was designed to allow for a
well-structured assessment of filtering bleb morphology.
Since 1998, the WBCS is regularly used in experimental
investigations and clinical routine, especially as a basis
for intensified postoperative care [1, 9–13]. Recently published grading systems for filtering blebs use criteria similar to the WBCS [2, 3, 8]. Here we analyze the interobserver variability of the WBCS as a prerequisite for its
consistent use in clinical routine.
Materials and Methods
From July to October 2004, 113 eyes of 104 consecutive patients, who had undergone primary fornix-based trabeculectomy
for medically uncontrolled primary or secondary open-angle
glaucoma or chronic angle-closure glaucoma, were enrolled in a
prospective masked agreement study at the Würzburg University
Eye Hospital. The patients had undergone surgery between 2 days
Dr. Thomas Klink
Universitäts-Augenklinik Würzburg
Josef-Schneider-Strasse 11, DE–97080 Würzburg (Germany)
Tel. +49 931 201 20610, Fax +49 931 201 20490
E-Mail klink_t@klinik.uni-wuerzburg.de
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Key Words
Bleb grading ⴢ Glaucoma surgery ⴢ Filtering bleb ⴢ
Trabeculectomy
and 10 years prior to the examination (median 67 days). The study
was approved by the local ethics committee, and informed consent was obtained from all participants.
All eyes were examined once (slit lamp biomicroscopy) by 3
ophthalmologists at different clinical training levels (F.G., T.K.,
S.S.) with each observer being unaware of the findings reported
by the others. A fourth person (U.E.) selected the patients and
dispensed and collected the data entry forms.
The WBCS evaluates vascularity, corkscrew vessels, encapsulation, microcysts and bleb height (table 1). Most parameters
are scored from 0 to 3, as compared to standard photographs
(fig. 1). The presence of microcysts is scored from 0 to 3 according to thirds of the bleb area bearing microcysts (fig. 2) and bleb
height is estimated as multiples of corneal thickness [5, 10, 11].
Finally, the total score was calculated (vascularity, corkscrew
vessels, encapsulation and microcysts, examples of scoring:
fig. 3, 4). After recording their bleb evaluation, the observers received additional patient data [intraocular pressure (IOP), diagnosis and time of follow-up]. Based on the filtering bleb evaluation and the additional patient data, the investigators noted their
therapeutic decisions from the options available: no therapy; increasing dose of steroids; 5-fluorouracil injections; antiglaucomatous medication; needling the filtering bleb; a new surgical
approach.
Statistical analysis was performed using SPSS for Windows
statistical software (version 13.0, SPSS, Chicago, Ill., USA). An
analysis was performed to determine the consistency and absolute agreement between the observers concerning bleb morphology, in order to reflect the clinical reproducibility of the WBCS.
For bleb morphology, the consistency and absolute agreement of
a single rater’s judgment and of the mean of all 3 raters were calculated with the intraclass correlation coefficient (ICC) using a
2-way random model [14]. The single rater’s judgment is a singlemeasure ICC value, which gives information about the expected
consistency and absolute agreement between single users of the
WBCS. The mean of all 3 raters is an average-measure ICC value,
which gives the expected consistency and absolute agreement between groups of 3 investigators using the WBCS. Levels of agreement obtained with the ICC statistics of 1 0.81 were defined as
excellent agreement, levels between 0.61 and 0.80 were defined as
good agreement, levels between 0.41 and 0.60 were defined as
moderate agreement, levels between 0.21 and 0.4 were defined as
fair agreement and levels less than 0.21 were defined as poor
agreement. The statistical analysis of therapeutic decisions was
performed with cross-classified tables (␬ values).
Table 1. Parameters and scoring of the WBCS
Parameters
Scoring
Vascularity
3 = avascular
2 = similar to adjacent conjunctiva
1 = increased
0 = massive
3 = none
2 = in one third
1 = in two thirds
0 = entire bleb
3 = none
2 = in one third
1 = in two thirds
0 = entire bleb
3 = entire bleb
2 = lateral or medial of the flap
1 = over the scleral flap
0 = none
multiples of corneal thickness
Corkscrew vessels
Encapsulation
Microcysts
Bleb height
ic angle-closure glaucoma. Intraoperatively, 8 eyes had
received no antimetabolites, 11 had received 5-fluorouracil and 94 had received mitomycin C.
Grading of Bleb Morphology
For all eyes, the consistency and absolute agreement of
a single rater’s judgment and of the mean of all 3 raters
were calculated with the ICC (established by Landis [14])
using a 2-way random model. With slit lamp examination, the consistency and absolute agreement of a single rater’s judgment were: vascularity +0.62/+0.62, corkscrew vessels +0.68/+0.67, encapsulation +0.63/+0.63,
bleb height +0.56/+0.53, microcysts +0.53/+0.52 and total
score +0.74/+0.74 (table 2). The means of all raters were
in this setting: +0.83/+0.83 for vascularity, +0.87/+0.86
for corkscrew vessels, +0.84/+0.84 for encapsulation,
+0.80/+0.77 for bleb height, +0.77/+0.76 for microcysts
and +0.90/+0.90 for total score (table 2).
In total, 113 eyes of 104 consecutive patients (63 male,
41 female) were examined. Both eyes of 5 male and 4 female patients were included. The mean interval between
surgery (trabeculectomy) and bleb grading was 334.4 8
637.6 days (range 2–3,516 days, median 67 days). The
mean age of all patients was 62.3 8 13.06 years. Overall,
74 eyes suffered from primary open-angle glaucoma, 35
from secondary open-angle glaucoma and 4 from chron-
Therapeutic Decisions
The assessment of therapeutic decisions showed an
agreement of all 3 observers in 88 (78%) eyes. In all other
cases, at least 2 observers decided for the same therapy.
There was no case of total disagreement among all 3 graders. In order to compare the therapeutic decisions among
the single raters we used cross-classified tables with ␬ values. The ␬ values indicate moderate (0.556) to good (0.662
and 0.706) agreements (table 3).
Würzburg Bleb Classification Score
Ophthalmologica 2008;222:408–413
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Results
Vascularity
avascular
similar to adjacent conjunctiva
increased
massive
Microcysts
Corkscrew vessels
in one third
in two thirds
entire bleb
under high magnification
Encapsulation
Fig. 1. Standard photographs of the WBCS.
in one third
entire bleb
Discussion
B
B
Fig. 2. Diagram of where to search for the presence of microcysts
according to thirds of the bleb area bearing cysts (scored 0–3; see
table 1). Early after the operation, microcysts appear above the
scleral flap (A) and are found nasally and temporally of the scleral flap during follow-up (B).
410
Ophthalmologica 2008;222:408–413
Klink/Schrey/Elsesser/Klink/Schlunck/
Grehn
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A
Adequate healing of the filtering bleb area is the key to
successful penetrating glaucoma surgery. Therefore, early detection of bleb scarring is essential as it guides the
individualized application of antimetabolites [1]. With
slit lamp examination as the mainstay of decisive diagnostics, scoring systems provide guidelines for a wellstructured observation of clinical findings and their
proper representation on record. This is of particular interest when different observers monitor the same patient,
and benefits less-seasoned examiners in particular. The
idea of the Würzburg bleb classification score (WBCS)
was to establish an objective and reproducible grading
system [5]. To date, several bleb classification schemes
have been proposed. The Indiana Bleb Appearance Grading Scale (IBAGS) [3] and the bleb classification according to Sacu et al. [2] are grading systems for filtering
blebs, which used criteria similar to the WBCS. The most
recent bleb grading system is the Moorfields Bleb Grad-
Fig. 3. Filtering bleb 2 weeks after trabeculectomy, overfiltration
with a total bleb score of 4 (vascularity: 0, corkscrew vessels: 0,
encapsulation: 3, microcysts: 1).
Fig. 4. Filtering bleb 4 weeks after trabeculectomy, working well
with a total bleb score of 11 (vascularity: 2, corkscrew vessels: 3,
encapsulation: 3, microcysts: 3).
Table 2. Slit-lamp examination: interobserver consistency and absolute agreement for all eyes (n = 113)
Measures
Consistency/absolute agreement
Vasc.
CSV
Encap. Micro. BH
TS
Single rater’s judgment
consistency
absolute agreement
consistency
absolute agreement
0.62
0.62
0.83
0.83
0.68
0.67
0.87
0.86
0.63
0.63
0.84
0.84
0.74
0.74
0.90
0.90
Mean of all 3 raters
0.53
0.52
0.77
0.76
0.56
0.53
0.80
0.77
Consistency and absolute agreement were calculated with the intraclass correlation coefficient using a 2-way
random model for a single rater’s judgement and the mean of all 3 raters. Vasc. = Vascularisation; CSV = corkscrew vessels; Encap. = encapsulation; Micro. = microcysts; BH = bleb height; TS = total score.
ing System (MBGS), which goes back to a telemedicine
study [4, 8]. Sacu et al. [2] used the WBCS as a basis for
their score, and expanded it by the parameters dimension
of avascularity, conjunctival transparency, hemorrhage
and thin-cystic avascular configuration. In a prospective
clinical trial, Sacu et al. [2] showed that the detection of
corkscrew vessels and microcysts in the first 2 weeks after
surgery may serve as prognostic indicators of subsequent
IOP development and outcome of surgery. Corkscrew
vessels were associated with an increased IOP and microcysts with a reduced IOP after 12 months of follow-up [2].
All other parameters did not correlate with long-term
outcome. The IBAGS evaluates 4 parameters (bleb height,
horizontal extent, vascularity and Seidel test), and its reproducibility was established using filtering bleb photo-
graphs [3]. The IBAGS shows a high consistency and absolute agreement between different observers. Unfortunately, the first report does not specify if the single or
average ICC values were provided [3]. The single ICC val-
Würzburg Bleb Classification Score
Ophthalmologica 2008;222:408–413
Table 3. Agreement in therapeutic decisions among the single
Measure of the agreement (␬)
Absolute number of agreement (%)
Grader
A-B
Grader
A-C
Grader
B-C
0.706
96 (85)
0.662
90 (80)
0.556
83 (73)
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graders using cross-classified tables (␬ values; n = 113 eyes; percentage in parentheses)
References
412
ment. Both, the IBAGS and MBGS do not consider microcysts as these scores were designed to evaluate bleb
photographs, which often fail to depict microcysts, even
if present clinically. However, the work of Sacu et al. [2]
indicates a relevant positive predictive value for microcysts, which makes their inclusion in a bleb score desirable. The consistency and absolute agreement of bleb
height as scored by the WBCS was comparable to the
IBAGS and slightly inferior to the MBGS [16].
Consistency and absolute agreement of all other WBCS
parameters were good (single ICC) or excellent (average
ICC). The WBCS registers bleb encapsulation rather than
bleb size (MBGS) or bleb extent (IBAGS), since indications for a scarring demarcation may deserve particular
attention. ICC values for encapsulation were similar or
higher than for the extension measures depicted in the
IBAGS [16]. With a similar rationale, the WBCS scores
the presence of corkscrew vessels, which are easy to detect
and which gave a good ICC in our study. The average
measure ICC values for vascularity were comparable for
all 3 bleb-grading systems [16]. We chose a cross-sectional study design to include filtering blebs at various stages
of conjunctival wound healing.
To assess the absolute agreement of therapeutic decisions after WBCS grading and evaluation of additional
clinical data, we analyzed the ␬ values in cross-classified
tables comparing all 3 investigators. A complete agreement of all 3 examiners in 78% appears quite reasonable.
Other bleb scoring schemes have not yet been analyzed
in this regard.
In summary, our data indicate that the WBCS is feasible for standardized filtration bleb analysis with satisfactory interobserver variability. The WBCS might be of
particular value when postoperative care of a single patient is provided by different ophthalmologists, as it aids
consistent evaluation and documentation of the clinical
findings.
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The WBCS was the first standardized bleb grading
system used in a prospective clinical study to evaluate the
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prognosis of bleb function and surgical outcome [9, 10].
The WBCS grades each bleb characteristic from 0 to 3,
which might give less fidelity compared to the MBGS, for
example, but has advantages in clinical routine for its
simplicity.
Our data reveal that not all WBCS parameters were
unequivocally graded: microcysts and bleb height were
detected with moderate consistency and absolute agree-
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