Sonographic bleb visualisation after PAUL glaucoma implant surgery

Bleb characteristics in the area around the plate following glaucoma drainage device (GDD) surgery are difficult to evaluate on slit lamp examination. Ultrasound sonography could be used for more detailed visualisation. The aim of this study was to describe bleb configuration after PAUL glaucoma implant (PGI) surgery and evaluate the possible correlation with intraocular pressure (IOP) in order to derive new markers for evaluating GDD function.

Patients underwent a 15 MHz ultrasound examination (Compact Touch, Quantel Medical) after undergoing PGI implantation. The filtering bleb dimensions were measured and bleb configuration was assessed along with documentation of all clinical data.

A total of 70 eyes from 65 patients were included. 55 eyes (78.6%) had a double-layered bleb whereas 15 eyes (21.4%) had a bleb with only one compartment (six eyes, 8.6% above; nine eyes, 12.9% below the plate). The total height of both compartments averaged 3.52 mm. The average IOP was 13.03 mm Hg. There was a significant correlation between single and double-layered blebs (p<0.01) with regard to IOP (one compartment: 16.47 mm Hg vs two compartments: 12.09 mm Hg). There was no significant correlation between total bleb height (p=0.143) or bleb extension (T: p=0.629; L: p=0.742). However, total bleb height showed an inverse association with IOP. Blebs with a height >2 mm had significantly lower mean IOP than those having <2 mm bleb heights (p=0.041).

Sonography is a suitable modality to evaluate bleb characteristics after PGI implantation. Blebs with a double fluid layer are significantly correlated with lower IOP values. Bleb height has an inverse association with IOP, with higher blebs (>2 mm) showing a significantly lower IOP.