Late-Onset Inadvertent Bleb Formation following Pars Plana M3 Molteno Implant Tube Obstruction

To report a case of inadvertent bleb formation presenting 18 months after pars plana M3 Molteno implant tube obstruction in a patient with mixed mechanism glaucoma.

An 84-year-old Caucasian male with mixed mechanism glaucoma underwent slit-lamp examination, gonioscopy, colour anterior segment photography and anterior segment optical coherence tomography (AS-OCT).

An inadvertent bleb developed 18 months after pars plana implant tube re-positioning with a 6/0 Vicryl tie ligature. The bleb was located in the area anterior to the implant plate; it was characterised by a thin, transparent, avascular and multi-cystic wall, with a visible stoma at the posterior edge of the bleb. The bleb was functioning as demonstrated by an intraocular pressure of 6 mm Hg at presentation and a punctate fluorescein uptake pattern of the bleb wall. The bleb over the plate of the Molteno implant was non-functioning, likely secondary to tube obstruction by vitreous in the early postoperative period. AS-OCT showed a tract from the anterior chamber commencing at an entry wound through a corneal tunnel to the posterior stoma at the base of the inadvertent bleb.

We hypothesise that the pathophysiologic factors resulting in an inadvertent bleb are a result of a combination of apoptosis, late-onset wound dehiscence and internal gaping of a centrally placed corneal wound. In addition, aqueous hydrodynamic factors may play a role.