Objective: We studied the control of intraocular pressure(IOP) by various types of blebs after non-penetrating trabeculectomy(NPT) and the difference between bleb formation after penetrating trabeculectomy(PT) and that after NPT.

Methods: The filtering blebs of 45 yeys from 40 patients after NPT were studied using ultrasound biomicroscopy. They were grouped into four types, and the space under the scleral flap was classified into three types. The filtering blebs and the space under the scleral flap were correlated with IOP level.

Results: Overall, 40% of the blebs were L(low-reflective) type, 16% H(high-reflective) type, 16% E (encapsulated) type, and 29% F(flattened) type, but in good IOP control cases 59% of the blebs were L type, 14% H type, 14% E type, and 14% F type. L type blebs were found in 94% of eyes with good IOP control.

Conclusions: Though filtering blebs of the L type could produce sufficient IOP reduction, blebs after NPT showed a greater tendency to become flattened than after PT. Additional systematic therapy must be designed to maintain the L type of filtering blebs after NPT.