Confocal Microscopy of Filtering Blebs after Trabeculectomy

Filtration surgery is the most effective method of lowering intraocular pressure (IOP) in patients with insufficient medical control. It consists in facilitating the drainage of the intraocular fluid (IOF) from the anterior chamber to the subconjunctival space and subsequent lowering of IOP. The formation of filtration blebs (FB) and the processes of scarring occurring in the conjunctiva are of particular importance in glaucoma surgery. In many cases, the appearance of FB does not match the IOP values, and what causes the failure after trabeculectomy often remains unclear. Often, over time, there is a change in the structure of the FB, as fibrous tissue grows, which prevents the IOF drainage. Laser scanning in vivo confocal microscopy is a non-invasive study allowing the production of layered images at the microstructural level with high resolution of both the cornea and other structures of the anterior ocular surface.

To evaluate the morphological structure and function of filtering blebs after trabeculectomy using in vivo confocal microscopy taking into account the type of implant and when the surgery was performed.

The study included 33 patients, 46 eyes with glaucoma. Twenty-six of the eyes had primary open-angle glaucoma (POAG), 18 eyes had pseudoexfoliative glaucoma and 2 eyes had juvenile glaucoma. All patients underwent trabeculectomy with fornix-based flap, and three of the eyes underwent retrabeculectomy. Mitomicyn C (MMC) was administered intraoperatively to all patients. The study of the filtering bleb was performed by in vivo confocal microscopy (CFM) (Heidelberg Retina Tomograph II (HRT II) /Rostock Cornea Module/ (Heidelberg Engineering GmbH, Heidelberg, Germany), the period from trabeculectomy and examination being from 1 year to 22 years. An Express implant was placed in 14 eyes, Ologen implant in 7 eyes, and 25 eyes had no implant placed. In the analysis of the morphological structure of the filtering blebs, three indicators were evaluated: the type of epithelium, the type of stroma, and blood vessels.

Statistical significance was established with regard to the function and morphological structure of the filtering bleb (p=0.009). Blebs with fine collagen mesh and dense collagen mesh demonstrate good function. In the case of blebs with insufficient function, those with a dense collagen network and hyper-reflective tissue predominated and there were no blebs with a fine collagen network, and in non-functioning blebs most common were those with a pronounced collagen network and hyper-reflective tissue. With regard to vascularization, we found that the functioning blebs in the shortest postoperative period were dominated by those with one blood vessel (stage 1) and there was no stage 3, with weak tortuosity, while in non-functioning blebs in the late postoperative period, there was moderate to severe vascularization and tortuosity (p=0.037), (p=0.043), (p=0.047), (p=0.021). The type of implant affects the tortuosity of the blood vessels of the filtering bleb (p=0.026). The blebs with Express implants show a slight tortuosity, followed by the blebs with Ologen implants. The highest percentage of highly kinked blood vessels occurred in blebs without an implant.

In vivo confocal microscopy is an innovative method which allows visualization of the internal structure of the filtering blebs at a cellular level, giving us a new insight into the ongoing healing processes, premising the function of the filtering blebs after glaucoma surgery.