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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Ocular prosthesis | 2/6 | https://en.wikipedia.org/wiki/Ocular_prosthesis | reference | science, encyclopedia | 2026-05-05T07:31:20.544903+00:00 | kb-cron |
=== Integrated implants (porous) === The porous nature of integrated implants allows fibrovascular ingrowth throughout the implant and thus also insertion of pegs or posts. Because direct mechanical coupling is thought to improve artificial eye motility, attempts have been made to develop so-called 'integrated implants' that are directly connected to the artificial eye. Historically, implants that directly attached to the prosthesis were unsuccessful because of chronic inflammation or infection arising from the exposed nonporous implant material. This led to the development of quasi-integrated implants with a specially designed anterior surface that allegedly better transferred implant motility to the artificial eye through the closed conjunctiva and Tenon's capsule. In 1985, the problems associated with integrated implants were thought to be largely solved with the introduction of spherical implants made of porous calcium hydroxyapatite. This material allows for fibrovascular ingrowth within several months. Porous enucleation implants currently are fabricated from a variety of materials including natural and synthetic hydroxyapatite, aluminium oxide, and polyethylene. The surgeon can alter the contour of porous implants before insertion, and it is also possible to modify the contour in situ, although this is sometimes difficult.
==== Hydroxyapatite (HA) ==== Hydroxyapatite implants are spherical and made in a variety of sizes and different materials (coralline/synthetic). Since their approval by the Food and Drug Administration in 1989, spherical hydroxyapatite implants have gained widespread popularity as an enucleation implant and was at one point the most commonly used orbital implant in the United States. The porous nature of this material allows fibrovascular ingrowth throughout the implant and permits insertion of a coupling device (PEG) with reduced risk of inflammation or infection associated with earlier types of exposed integrated implants. Hydroxyapatite is limited to preformed (stock) spheres (for enucleation) or granules (for building up defects). One main disadvantage of HA is that it needs to be covered with exogenous material, such as sclera, polyethylene terephthalate, or vicryl mesh (which has the disadvantage of creating a rough implant tissue interface that can lead to technical difficulties in implantation and subsequent erosion of overlying tissue with the end stage being extrusion), as direct suturing is not possible for muscle attachment. Scleral covering carries with it the risk of transmission of infection, inflammation, and rejection. A 2008 study showed that HA has a more rapid rate of fibrovascularization than MEDPOR, a high-density porous polyethylene implant manufactured from linear high-density polyethylene.
==== Porous polyethylene (PP) ==== Development in polymer chemistry has allowed introduction of newer biocompatible material such as porous polyethylene (PP) to be introduced into the field of orbital implant surgery. Porous polyethylene enucleation implants have been used since at least 1989. It is available in dozens of prefabricated spherical and non-spherical shapes and in different sizes or plain blocks for individualized intraoperative customizing. The material is firm but malleable and allows direct suturing of muscles to implant without wrapping or extra steps. Additionally, the smooth surface is less abrasive and irritating than other materials used for similar purposes. Polyethylene also becomes vascularized, allowing placement of a titanium motility post that joins the implant to the prosthesis in the same way that the peg is used for hydroxyapatite implants. PP has been shown to have a good outcome, and in 2004, it was the most commonly used orbital implant in the United States. Porous polyethylene fulfills several criteria for a successful implant, including little propensity to migrate and restoration of defect in an anatomic fashion; it is readily available, cost-effective, and can be easily modified or custom-fit for each defect. The PP implant does not require to be covered and therefore avoids some of the problems associated with hydroxyapatite implants.
==== Bioceramic ==== Bioceramic prosthetics are made of aluminium oxide (Al2O3). Aluminium oxide is a ceramic biomaterial that has been used for more than 35 years in the orthopedic and dental fields for a variety of prosthetic applications because of its low friction, durability, stability, and inertness. Aluminium oxide ocular implants can be obtained in spherical and non-spherical (egg-shaped) shapes and in different sizes for use in the anophthalmic socket. It received US Food and Drug Administration approval in April 2000 and was approved by Health and Welfare, Canada, in February 2001. Aluminium oxide has previously been shown to be more biocompatible than HA in cell culture studies and has been suggested as the standard reference material when biocompatibility studies are required to investigate new products. The rate of exposure previously associated with the bioceramic implant (2%) was less than most reports on the HA or porous polyethylene implant (0% to 50%).