Vol.29 No.1 Original Article PDF

Use of hollow polymethylmethacrylate as an orbital implant

Archimedes Lee D. Agahan, MD, Alexander D. Tan, MD

To establish the physical properties of a low-weight hollow polymethylmethacrylate (PMMA) implant and determine its suitability as an orbital implant.

Hollow implants were molded by fusing 2 half-sphere shaped implants made from medical-grade PMMA powder. The water absorption capacity, bulk density, and hardness of the hollow implants were determined. Twelve patients were randomly divided into two equal groups: one group receiving the standard solid acrylic implant and another receiving the hollow PMMA implant. The anophthalmic socket was examined for complications due to surgery and type of implant used. Serial CT (computed tomography) scans were performed to detect implant migration.

The hollow PMMA implant had the following physical properties: water absorption = 0.65%, bulk density = 0.57 g/cm3 , and hardness = 71.2kg. Most of the implants remained in the socket at least 6 weeks in both groups with 1 case of early implant extrusion in the solid acrylic group. Small degree of implant migration was observed on CT scan in 4 patients in the solid acrylic group and 3 in the hollow PMMA group at 12 weeks follow-up. In the solid acrylic group, the implant migrated posteriorly in those that were eviscerated and anteriorly in those that were enucleated. No pattern was observed in the type of operation and direction of the implant migration in the hollow PMMA group.

Hollow polymethylmethacrylate implants are comparable substitutes for solid acrylic implant. Multicenter clinical trials with adequate sample size and longer follow-up are needed to establish the long-term stability of the implant.