Pathophysiology of artificial aqueous drainage in primate eyes with molteno implants

Single-plate Molteno implants were installed in two stages in glaucomatous monkey eyes. This device shunts aqueous from the anterior chamber to periocular orbital tissues. The mechanism of aqueous filtration and absorption was explored using flow studies, fluorescently labeled microspheres and histological examination of tissues. Flow studies indicated that the capsule around the explant functions by a passive mechanism, shunting aqueous into the extracellular space. Outflow is proportional to capsule surface area. Latex microspheres (0.2 mum and smaller) passed freely through the capsule, giving the impression of an open sieve. The presence of microspheres in the episcleral wall of the capsule indicates that all surfaces contribute to filtration. A concentration gradient of particles in the extracapsular space, away from the bleb surface, suggests that the capsule itself limits filtration rate.