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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Ocular prosthesis | 3/6 | https://en.wikipedia.org/wiki/Ocular_prosthesis | reference | science, encyclopedia | 2026-05-05T07:31:20.544903+00:00 | kb-cron |
==== Conical orbital implant (COI) and multipurpose conical orbital implant (MCOI) ==== The safe and effective sphere (still popular and easy to use) was supplemented with the pyramid or COI implant. The COI has unique design elements that have been incorporated into an overall conical shape, including a flat anterior surface, superior projection and preformed channels for the rectus muscles. 5-0 Vicryl suture needles can be passed with slight difficulty straight through the implant to be tied on the anterior surface. In addition, this implant features a slightly recessed slot for the superior rectus and a protrusion to fill the superior fornix. As of 2005 the newest model is the multipurpose conical orbital implant (MCOI), which was designed to address the issues of the postoperative anophthalmic orbit being at risk for the development of socket abnormalities including enophthalmos, retraction of the upper eyelid, deepening of the superior sulcus, backward tilt of the prothesis, and stretching of the lower eyelid after evisceration or enucleation. These problems are generally thought to be secondary to orbital volume deficiencies which is also addressed by MCOIs. The conical shape of the MCOI more closely matches the anatomic shape of the orbit than a spherical implant. The wider anterior portion, combined with the narrower and longer posterior portion, allows for a more complete and natural replacement of the lost orbital volume. This shape reduces the risk of superior sulcus deformity and puts more volume within the muscle cone. Muscles can be placed at any location the surgeon desires with these implants. This is advantageous for cases of damaged or lost muscles after trauma, and the remaining muscles are transposed to improve postoperative motility. In anticipation of future peg placement there is a 6 mm (0.24 in) diameter flattened surface, which eliminates the need to shave a flat anterior surface prior to peg placement. Both implants (COI and MCOI) are composed of interconnecting channels that allow ingrowth of host connective tissue. Complete implant vascularization reduces the risk of infection, extrusion, and other complications associated with nonintegrated implants. Additionally, both implants produce superior motility and postoperative cosmesis.
==== Pegged (motility post) implants ==== In hydroxyapatite implants, a secondary procedure can insert an externalized, round-headed peg or screw into the implant. The prosthesis is modified to accommodate the peg, creating a ball-and-socket joint. After fibrovascular ingrowth is completed, a small hole can be drilled into the anterior surface of the implant. After conjunctivalization of this hole, it can be fitted with a peg with a rounded top that fits into a corresponding dimple at the posterior surface of the artificial eye. This peg thus directly transfers implant motility to the artificial eye. However, the motility peg is mounted in a minority of patients. This may partially be due to problems associated with peg placement, whereas hydroxyapatite implants are assumed to yield superior artificial eye motility even without the peg. 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.
== Implant movement == Implant and prosthesis movement are important aspects of the overall cosmetic appearance after enucleation, and are essential to the objective of crafting a lifelike eye similar in all aspects to the normal fellow eye. There are several theories of improved eye movement, such as using integrating prosthetic material, pegging the implant, covering the implant (e.g. with scleral tissue), or suturing the eye muscles directly to the prosthetic implant. The efficiency of transmitting movement from the implant to the prosthesis determines the degree of prosthetic motility. Movement is transmitted from traditional nonporous spherical implants through the surface tension at the conjunctival–prosthetic interface and movement of the fornices. Quasi-integrated implants have irregularly shaped surfaces that create an indirect coupling mechanism between the implant and prosthesis that imparts greater movement to the prosthesis. Directly integrating the implant to the prosthesis through an externalized coupling mechanism would be expected to improve motility further. Despite the reasoning stating that hydroxyapatite orbital implants without a motility peg would yield a superior artificial eye motility, when similar surgical techniques are used, unpegged porous (hydroxyapatite) enucleation implants and donor sclera-covered nonporous (acrylic) spherical enucleation implants yield comparable artificial eye motility. In two studies, there were no differences in maximum amplitude between hydroxyapatite and acrylic or silicone spherical enucleation implants, thus indicating that the implant material itself may not have a bearing on implant movement as long as the muscles are attached directly or indirectly to the implant and the implant is not pegged. The motility of a nonintegrated artificial eye may be caused by at least two forces: