Ahmed valve encapsulation as a main cause of its implantation failures

Objective. To study the relationship of post-operative ocular hypertension with the encapsulation of Ahmed valve’s plate. Methods. The standard Ahmed valve implantation was performed in 238 patients aged 18-86 with multiple glaucoma surgeries (39 %), secondary neovascular (36 %), pseudophakic (23 %), juvenile (8 %), uveal (5 %) and post-traumatic (2 %) glaucomas. A routine ophthalmic examination was performed in 1 week, 1, 3, 6, 9, 12 and 36 months after surgery. Results. Excision of the fibrous capsule as the only way to cope with post Ahmed valve ocular hypertension was performed on 16 patients 3-36 months after surgery. Macro- and microscopic analysis of the excised capsules was done. In all cases, preparations of 1.2-2.2 mm thickness were obtained. We found a bilaminar structure of the capsule, the inner surface consisting of densely-packed collagen fibers, whereas the outer layer is represented by a loose fi-brovascular layer. Suspension of encapsulation is possible at initial stages of scarring, by applying ocular massage, needling, revision of the surgical area, and injection of antimetabolites.

refractory glaucoma, encapsulated filtering bleb, Ahmed drainage system