Not 100% sure but the link on Trabeculectomy provides more information for your perusal.

"After surgery, the eye fluid drains through the newly created passage to a reservoir, known as a filtering bleb, which is created during surgery from the normal covering of the eye. This bleb appears as a blister like bump on the white of the eye"
http://www.nurseseyesite.nhs.uk/glaucoma/optionsfortreatment...

Also:
"לאחר הניתוח נוצרת כרית סינון דקיקה בין לובן העין ללחמית, המהווה מעבר בין חלל העין למחזור הדם"
http://www.doctors.co.il/ar/6244/גלאוקומה: הגנב השקט של הראי...

seems to match this definition:
"surgery by which a flap of sclera is created in the eye wall, allowing aqueous humor to percolate out of the eye and underneath the conjunctiva"
http://www.drugs.com/dict/filtering-bleb.html

To be certain, I'd wait for Eytan to confirm/refute if time allows.