An orbital implant’s function is to replace lost orbital volume, maintain the structure of the orbit, and impart motility to the overlying ocular prosthesis. Implants may be grouped according to the materials from which they are manufactured: inert materials, such as glass, silicone, or methylmethacrylate; and biointegrated materials, such as hydroxyapatite, porous polyethylene, and aluminum oxide (Fig 8-1). Biointegrated materials are designed to be incorporated by soft-tissue ingrowth from the socket.
Inert spherical implants provide comfort, have low extrusion rates, and are considered an appropriate cost-effective choice in patients not requiring implant integration. Disadvantages of nonporous implants include the possibilities of decreased motility and implant migration. Spheres of inert materials may be wrapped in sclera, polyglactin mesh, or autogenous materials (eg, fascia, dermis, or muscle) to provide a substrate for attachment of the extraocular muscles. Inert implants transfer motility to the prosthesis only through passive movement of the socket. Buried motility implants with anterior surface projections push the overlying prosthesis with direct force and can improve prosthetic motility.
Porous implants allow for direct attachment of the extraocular muscles as well as drilling and placement of a peg to integrate the prosthesis directly with the moving implant (see Fig 8-1B). Peg placement is usually carried out 6–12 months after enucleation to allow for complete vascular biointegration. Although pegged porous implants offer excellent motility, they also have a higher rate of postoperative complications, including inflammation and exposure. In fact, most porous implants are never pegged and are still able to achieve adequate motility.
After enucleation, implants are placed either within the Tenon capsule or in the muscle cone behind the posterior Tenon capsule. After evisceration, implants are placed either behind or within the sclera. Spheres may be covered with materials such as sclera (homologous or cadaveric), autogenous fascia, or polygalactin mesh, which serve as further barriers to migration and extrusion. Secure closure of Tenon capsule over the anterior surface of an anophthalmic implant is an important barrier to potential later exposure. A dermis-fat graft may be placed instead of an implant or to increase the surface area of the conjunctiva. As the conjunctiva reepithelializes over the dermis, it adds to the socket surface area.
Figure 8-1 Orbital implants. A, Examples of various orbital implants (from left to right): silicone, 18 mm; hydroxyapatite, 20 mm; porous polyethylene, 20 mm; silicone, 22 mm. B, Various pegs and rescue screws for integrated orbital implants.
(Courtesy of Christine C. Nelson, MD.)
Figure 8-2 Superotemporal migration of an orbital implant secondary to displacement of the extraocular muscles.
(Courtesy of M. Reza Vagefi, MD.)
Extraocular muscles should not be crossed over the front surface of a spherical implant or purse-stringed anteriorly because the implant will migrate when the muscles slip off the anterior surface (Fig 8-2). Muscles sutured into the normal anatomical locations, either directly to the implant or to wrapping material (sclera, autogenous fascia, polygalactin mesh) surrounding the implant, allow superior motility and prevent implant migration.
Following enucleation or evisceration surgery, an acrylic or silicone conformer is placed in the conjunctival fornices to maintain the conjunctival space that will eventually accommodate the prosthesis.
Wladis EJ, Aakalu VK, Sobel RK, Yen MT, Bilyk JR, Mawn LA. Orbital implants in enucleation surgery: a report by the American Academy of Ophthalmology. Ophthalmology. 2018;125(2):311–317.
An ocular prosthesis is generally fitted 4 weeks after enucleation or evisceration. The ideal prosthesis is custom fitted to the exact dimensions of the patient’s conjunctival fornices after postoperative edema has subsided (Fig 8-3). Eviscerations may be more amenable to prosthetic fitting. Premade or stock eyes are less satisfactory cosmetically, and they also limit prosthetic motility. In addition, they may trap secretions between the prosthesis and the socket. Typically, the patient might remove the prosthesis once a month for cleaning.
Figure 8-3 Right anophthalmic socket with an acceptable functional and cosmetic outcome.
(Courtesy of Keith D. Carter, MD.)
The American Society of Ocularists is an international nonprofit professional and educational organization founded by technicians specializing in the fabrication and fitting of custom ocular prosthetics. Its website includes information for both patients and physicians (www.ocularist.org).
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.