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K. Laaser, F. Bock, C. W. Roessler, K. Gottschalk, R. Rejdak, U. Schloetzer-Schrehardt, F. E. Kruse, A. G. M. Juenemann; Objective Quantification of Bleb Vascularisation After Trabeculectomy Using a Semiautomatic Method. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3371.
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Vascularisation of filtering blebs is a major risk factor for bleb failure. In order to evaluate therapeutic interventions a precise and reproducible quantification of the degree of vascularisation is necessary. Aim of the present study was to establish a new method for objective quantification of bleb vascularisation: a semiautomatic, quantitative image analysis based on threshold analysis.
This pilot study included 15 patients with primary open-angle glaucoma (POAG) and 5 patients with pseudoexfoliation OAG (PEXG) during a 6 months follow-up period after trabeculectomy. All trabeculectomies were performed with mitomycin C (0.3mg/ml) by one surgeon. In three consecutive examinations at 1 month, 3 months and 6 months the bleb was documented using analog color photographs according to a standardized protocol (slit lamp photograph in down-gaze, 10fold magnification). The morphometric analysis of the bleb vascularisation was performed using a digital image analysis software (cell^F: Olympus Hamburg, Germany). For the detection of the vessels a grey scale picture optimized by a filter set was used. The vascularisation of the bleb was given as percentage of the total bleb area.
The semiautomatic analysis was possible in all photographs. During follow-up, the vascularised area of all blebs decreased from 14.8 ± 4.5% (1 month) to 10.1 ± 3.2% (3 months) (p< 0.001) and to 6.3 ± 2.7% (6 months) (p< 0.001) (p< 0.001, 1 to 6 months) of the whole bleb area. The overall reduction of vascularisation was 8,9 ± 4,1% in the POAG group and 7,4 ± 2,1% in the PEXG group. The difference between both groups was not significant (p= 0,29).
In accordance with the clinical qualitative evaluation the decrease of bleb vascularisation during six months follow up could be quantitatively identified. This study shows that an objective assessment of the filtering bleb vascularisation is possible and improves the subjective qualitative evaluation. A possible clinical implication of this semiautomatic, quantitative image analysis is to identify the necessity and the optimal time point for postoperative interventions.
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