Table 3 Comparison of corneal invasion by filtering bleb (CIFB) and overhanging filtering bleb (OFB)

Slit lamp examination

Conjunctival subsidence line is present in the early stage. The filtering bleb intrudes into the cornea in a zigzag shape (serrations), and is closely connected with the cornea and cannot be moved. The filtering bleb is flat without any overhang. In severe cases, the bleb can cover the pupil area, and appears polycystic without any sagging

The filtering bleb extends over the limbus, overhangs the corneal surface, forming a pocket-like structure. The sagging bleb does not break through the Bowman membrane or enter the corneal stroma. Most of these blebs can be easily moved

Ultrasound biomicroscopy and optical coherence tomography

The filtering bleb is polycystic. The corneal epithelium and Bowman membrane disappear in the area covered by the filtering bleb, and the corneal stroma becomes thinner

The corneal stroma does not become thinner. The Bowman membrane under the bleb is intact

Intraoperative findings

Tight adhesion between the filtering bleb tissue and the cornea and scarring are present. Needle insertion is difficult. The filtering bleb cannot be easily separated from the cornea. The posterior boundary of the filtering bleb is obviously adhered. The internal orifice of the filtering bleb moves forward toward the transparent cornea

Blunt separation can be achieved. The posterior boundary does not show adhesions, and the internal orifice of the filtering bleb is not displaced. The corneal wound remains transparent after healing

Pathological examination

The resected surface is covered with squamous epithelium, which is thickened in some areas. Proliferative capillaries, loose connective tissue, and scattered fibroblasts are present under the epithelium. The Bowman membrane is destroyed and has disappeared, and part of the corneal stroma is thinner

The Bowman membrane under the bleb is intact. No channel connected with the cavity of conjunctival filtering bleb is present