Prospective observation of filtration blebs in high-risk eyes with limbal-based conjunctival flap

Updates on the utility of anterior segment optical coherence tomography in the assessment of filtration blebs after glaucoma surgery

The formation of filtration blebs is the main drainage mechanism for reducing intraocular pressure after traditional incisional glaucoma surgery such as trabeculectomy and non-penetrating deep sclerotomy. Early and short-lasting blebs may also occur after canaloplasty. Bleb formation also plays an important role after the implantation of glaucoma drainage devices, including Minimally Invasive Glaucoma Surgery devices. Anterior segment optical coherence tomography (AS-OCT) is a rapid and non-invasive high-resolution imaging technique that has evolved in recent years to become a routine examination. Anterior segment optical coherence tomography (AS-OCT) provides key information in the assessment and follow-up of glaucoma surgery, especially in the assessment of filtration blebs. Thus, bleb morphology can be qualitatively classified into diffuse, cystic, encapsulated and flattened, and AS-OCT imaging can also provide several quantitative parameters of the bleb, such as total bleb height, bleb fluid-filled cavity height, bleb wall thickness, number of microcysts and trabeculectomy opening size. These parameters could have an impact on clinical management during follow-up because they may predict the success or failure of the surgery in the early and late postoperative periods. Additionally, they may also guide the procedures used to increase filtration and reduce intraocular pressure, such as bleb needling and laser suture lysis.

Factors related to filtration-bleb morphology after Ex-PRESS® surgery

Purpose

We investigated the factors influencing the morphology of filtration blebs after Ex-PRESS^® surgery. We analyzed the thickness of the bleb wall and the height and the volume of blebs.

Methods

This was a retrospective non-randomized study. After excluding patients who had undergone an additional glaucoma surgery, we analyzed the cases of 145 consecutive patients (180 eyes) who underwent trabeculectomy with Ex-PRESS® for the first time at Toyama University Hospital and were followed for >1 year. We used anterior segment optical coherence tomography to analyze the morphology of the blebs after Ex-PRESS surgery. We also examined potential influencing factors including age, central corneal thickness, type of glaucoma (primary open-angle glaucoma [POAG] or pseudo-exfoliation glaucoma [PEXG]), preoperative intraocular pressure (IOP), postoperative IOP, history of trabeculotomy, and operation method: Ex-PRESS surgery only, or simultaneous cataract surgery.

Results

Ex-PRESS surgeries significantly decreased the IOP from 24.5 ± 8.8 mmHg to 11.1 ± 3.4 mmHg after 1 year (P < 0.001). The cases with higher blebs, larger volume of blebs, and thinner bleb wall had better surgical outcomes.

Conclusion

Advanced age, higher postoperative IOP, PEXG, and simultaneous cataract surgeries were found to decrease the volume and height of blebs. Younger age, higher postoperative IOP, POAG, and simultaneous cataract surgeries were found to thicken the wall of blebs. Among the younger patients, there were many cases in which surgery was unsuccessful in spite the large volume of blebs. The reason for this may be that the wall of the bleb is thick.