The main aim of our prospective study was to investigate whether there is an agreement between postoperative IOP and the WBCS. Klink et al.
established a semi-quantitative score and classified the filtering blebs before and after clear cornea phacoemulsification as ‘favourable’ when they reached a WBCS of 10 points or more, and ‘unfavourable’ if less than 10 points were scored [13
]. Using this classification of ‘success’ of bleb morphology as detectable with slit lamp biomicroscopy, we found only poor agreement to our defined target IOP (Table ). But after expanding the definition of ‘success’ on the morphological findings, we found fair agreement between the attainment of at least 7 points (к 0.273) and our target IOP (Table ). Based on these findings we conclude that the WBCS is applicable in clinical practice. It is very interesting to compare these results with those published by Klink et al
. Even though they did not find any prognostic value of the early WBCS bleb score for the long-term success of TE (20% pressure reduction with reference to the pretreated IOP level and an upper IOP limit of 21 mmHg without glaucoma medication), they found that bleb score of more than 8 points in the first two weeks after TE seemed to be associated with a lower IOP (≤12 mmHg) 1 year postoperatively, while patients with a total bleb score of less than 7.0 two weeks postoperatively showed a higher IOP [25
]. Our study compares the WBCS and a defined target IOP at the same time, but nonetheless we found a similar ‘cut off’ on the WBCS scale. The fact that in our study 21 out of 25 eyes reaching a WBCS of
10 points also achieved the target IOP (84%) indicates that the WBCS works well in predicting IOP control when at least ten points are attained.
In addition, we looked for agreements between single items of the WBCS and the postoperative IOP. We found a fair agreement between the occurrence of microcysts and reaching the target pressure. This is in accordance with Picht et al.
] and Sacu et al.
]. In contrast, our data reveal that excessive vascularisation shows a fair agreement to higher IOP postoperatively but we found no agreement between the presence of corkscrew vessels and IOP, nor between presence of bleb encapsulation and IOP.
Our study strengthens the clinical utility of the WBCS with good interobserver consistency, and absolute agreement in assessment of the factors vascularisation, corkscrew vessels and bleb score (excluding microcysts). The item bleb height was evaluated with excellent consistency and absolute agreement. In comparison, the data of Klink et al.
revealed that bleb height was detected with moderate consistency and absolute agreement, whereas consistency of all other parameters were good (single ICC) or excellent (average ICC) [18
Morphological slit-lamp biomicroscopy grading systems like the WBCS, the IBAGS or the MBCS only allow describing the surface and the superficial layers of the bleb. Even though there exist newer methods of describing filtering blebs, for example examining the internal bleb structure using ultrasound biomicroscopy [26
], anterior segment optical coherence tomography [14
] and in-vivo confocal microscopy [15
], the WBCS remains an important tool to describe morphological appearance in clinical practice, as it is easy to use in routine practice, non-invasive and cost-efficient. Further, consistent evaluation is given by satisfactory interobserver variability as shown by Klink et al.
] as well as by our data. Nevertheless, the new imaging methods might provide additional information and prognostic indicators. Also, as wound healing is modulated by the use of anti-TGFβ2 antibodies [33
] and Mitomycin C supplemented with Cross-Linking Hyaluronic Acid [36
] the use of WBCS and other classification systems remains necessary for a careful examination of the developing filtering bleb to recognize early bleb failure.
The main aim of filtering surgery is to achieve low levels of intraocular pressure in order to prevent further visual field loss [37
]. Therefore, the success after TE can be measured by the achievement of a certain level of IOP. As shown in a recently-published study by Rotchford et al.
, there exist currently 92 different IOP-based definitions of success [38
]. For our study, we defined ‘success’ concerning IOP as reaching a target pressure of less or equal to 21 mmHg and IOP reduction of at least 20% of the preoperative level without any antiglaucoma medication and without any additional interventions. Using this definition of success, clinical outcomes following fornix-based TE within the last two years at our clinic were satisfying. 73.7% of our study group were classified as ‘successful’ and reached the target pressure defined above.
If additional interventions are excluded from our definition of success, the success rate increases to 77.2%. This result is comparable with other studies, which report similar success rates (between 73.9% and 76%) using the same definition of success [3
We are aware that the ultimate goal of any bleb classification system is to predict the development of IOP over longer post-intervention periods. As agreement between WBCS and target IOP is a necessary precondition, this study only compares target IOP and WBCS at the same time to evaluate the usability and overall correlation of the WBCS and IOP in clinical practice. Therefore, no subgroup splitting according to time after surgery has been done and two examines with different levels of experience have been chosen. A larger study is ongoing to investigate the agreement of the WBCS score at early postoperative visit (<3 month and at 3 month) with the WBCS score at a later timepoint (6, 12 and 24 month). In this subsequent study we want to know if the <3 or 3 month WBCS score predicts the outcome (IOP and success) of eyes after trabeculectomy after 6, 12 and 24 month post surgery.