After an enucleation or evisceration, the orbit will most likely require volume replacement with an
orbital implant. One must make the decision on porous versus non-porous implants, spherical versus non-spherical. The implants come in various shapes and sizes. One of the oldest models is called the Allen implant which came with many facets and grooves through which the muscles would attach. I will focus this discussion on the most frequently used implants and the ones that I am most familiar with and use the most.
The acrylic sphere is the most basic implant. Acrylic, or methylmethacrylate, is a non-porous material which means that there will be no fibrovascular ingrowth of the surrounding tissues into the implant. I find that this implant is best used in cases of trauma, such as a severe gunshot wound to the orbit, where extraocular muscles are unidentifiable. In this case, the muscles will not be reattached to the implant. Rather, the implant can be placed into the orbit and the tenon’s capsule and conjunctiva sewn over the top. If fibrovascular ingrowth is sought after, then this implant can be wrapped in a scleral shell or other biomaterial. There is no need for windows to be cut into the shell. The orbital tissues will integrate into the shell itself.
Implants made of silicone are also available through FCI Ophthalmics. This non-porous implant is similar to an acrylic implant, but slightly more pliable. The same applications apply as stated above.
Silicone Implant
Porous polyethylene, or Medpor, which is manufactured by Porex Surgical Group, is my favorite implant. It has the advantage of promoting fibrovascular ingrowth, which decreases the chances of extrusion and improves motility, but it is also less abrasive than other porous implants, such as hydroxyapatite.
Porous Polyethylene
The implant can be wrapped in a scleral shell, windows cut in the shell and the native extraocular muscles sewn into place allowing the belly of the muscle to be in contact with the exposed polyethylene. The surface is nonabrasive so extrusion is rare.
As an alternative, a polyethylene implant called the SST is also made. This implant has premade suture holes in the anterior surface. The implant is made this way to avoid having to wrap the implant since the muscles can be sewn directly to the porous implant. Extrusion rates are decreased because the anterior surface is smooth.
BioEye® makes an implant out of hydroxyapatite. This is a coral-like material that has the same structure and composition as human bone. This porous material promotes fibrovascular ingrowth of tissue.
Hydroxyapatite
The disadvantage I find with this implant is that the surface is abrasive and can lead to extrusion or exposure of the implant which can promote bacterial invasion and infection. Similar to polyethylene, the hydroxyapatite spheres can be wrapped in a scleral shell and muscles attached after windows are made in the shell.
A bioceramic orbital implant made of aluminum oxide is a new generation of porous implants made by FCI Ophthalmics. It does not dissolve in body fluids and does not release soluble components. The bioceramic implant is lighter in weight, less brittle and much smoother than the hydroxyapatite implant. A protein coating that forms after insertion prevents the implant from being recognized as a foreign body.
Bioceramic Implant
The mesh wrapped bioceramic implant can be placed directly into the orbit and the muscles attached without the need for a shell.
Mesh Wrapped Bioceramic Implant
Pegging is an option of any of the porous implants, most commonly done with hydroxyapatite. Instruments seen below, manufactured by Innovia LLC and distributed by FCI, can be used. The thought behind pegging is that it improves motility by allowing the pegged surface to fit into a corresponding groove in the back of the prosthesis creating almost a ‘snap’ like fit.
FCI Ophthalmics
As an alternative, a magnetic coupler can also be used. These spherical implants are manufactured by Porex and come with a magnet on the anterior surface of the implant. The ocularist will place a corresponding magnet on the posterior surface of the prosthesis for increased motility.
I personally do not peg or use magnetic couplers. I find that patients have good motility with proper attachment of the extraocular muscles directly to the scleral shell. Also, pegging creates a potential track from exterior to the middle of the implant which can promote infection and lead to extrusion.
I find the sphere introducer, manufactured by FCI Ophthalmics, to be of great value in inserting the spherical implant into the scleral shell.
Insertion of the wrapped implant can also be performed using this introducer, but I like to use the plastic hollow tube that comes with each Medpor implant.
One other implant that was recently released on the market that I will briefly mention is the orbital tissue expander also manufactured by FCI Ophthalmics (click here for video). This is a fantastic implant that can be used in anophthalmic children. This implant is fixated to the lateral orbital rim using the attached T-plate. Serial injections of saline are performed allowing the implant to slowly expand and simulate growth of the natural eye, thus promoting growth of the bony orbit.
Orbital Tissue Expander
Again, this implant is best for children who are dependent on a growing eye for development of the socket. Use of this implant avoids the necessity for repeat trips back to the operating room to exchange implants for larger ones as the child grows.
In summary, many spherical orbital implants exist and can be used to fill the orbit after enucleations or eviscerations. I prefer and most commonly use the porous polyethylene implant made by Porex Surgical. It is easy to use with low morbidity. It promotes tissue ingrowth allowing improved implant motility but is smooth enough to decrease chances of extrusion.
Have a question or comment on this article? Use the "Comment" link above to leave your thoughts, and the author will respond.