Synthetic scleral reinforcement materials. II. Collagen types in the fibrous capsule

Attainment of a steady state in fibrous-capsule formation around a polymeric implant is indicative of minimization of the foreign-body response, and is characterized by thin capsule walls, few macrophages, and the replacement of type III collagen with type I collagen within the capsular matrix. We implanted four general types of extraocular band materials (porous, solid, composite, and patched) in rabbit eyes, and examined the proportions of types III and I collagen in the surrounding fibrous-capsule walls at intervals after surgery. Immunohistochemical analysis showed that 18 months after implantation of the band materials, the capsules adjacent to the porous-material surfaces had virtually no type III collagen remaining, while the solid-surface-material capsules still contained more than trace amounts (greater than 5%). In that the bands were implanted around the outside of the globe, which provides a dynamic environment in constant motion, it may be that the cellular ingrowth permitted by the porous materials increased the stability of the implants, thereby lessening the foreign body response and allowing the collagen replacement characteristic of the steady state to be completed. In contrast the solid-surface implants, which had little cellular ingrowth, may have continued to undergo sufficient micromovement within the capsule walls to sustain a low-level activation of the wound-healing response, resulting in thicker capsule walls and residual type III collagen a year and a half after implantation surgery.