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Surgical technique, management affects bleb formation around Molteno implant
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The structure of blebs surrounding Molteno implants develops through a series of stages, a recent study in cadaver eyes determined. Final thickness and permeability of the capsule may be influenced by the surgical technique and postoperative management, the study authors said.
Anthony C. B. Molteno, FRCS, FRACO, and colleagues at the University of Otago Medical School in Dunedin, New Zealand, and elsewhere studied 75 autopsy eyes or surgical pathology specimens. All were obtained 4 days to 23 years after implantation of a Molteno implant for the treatment of primary or secondary glaucoma.
In eyes that underwent two-stage insertion, the authors found that after first part of the insertion (without aqueous outflow), the episcleral plates of the Molteno implants became encapsulated by an avascular collagenous layer 20 µm to 60 µm thick.
During the second stage, with delayed aqueous drainage and temporary increase of intraocular pressure to 25 to 35 mm Hg, permeable capsules of about 190 µm to 250 µm thick are produced. These have fewer fibrovascular than fibrodegenerative components, the authors said.
Nonligatured implants, with immediate aqueous flow, produced capsules 300 µm to 600 µm thick, the authors noted. The capsules were composed of an outer fibrovascular layer and an inner fibrodegenerative layer of approximately equal thickness.
The authors noted that three-stage insertion of a modified Molteno implant, with temporary direction of aqueous flow onto the conjunctival surface, produced the thickest capsules, of 375 µm to 700 µm. The resulting capsules were composed entirely of dense fibrovascular tissue without a fibrodegenerative layer. according to the authors.
The study is published in the November issue of Ophthalmology.