Ocular prosthesis
The ocular prosthesis roughly takes the shape of a convex shell and is made of medical grade plastic acrylic.
The earliest known evidence of the use of ocular prosthesis is that of a woman found in Shahr-I Sokhta, Iran[1] dating back to 2900–2800 BC.
Since microscopic research has shown that the eye socket showed clear imprints of the golden thread, the eyeball must have been worn during her lifetime.
In addition to this, an early Hebrew text references a woman who wore an artificial eye made of gold.
[3] Roman and Egyptian priests are known to have produced artificial eyes as early as the fifth century BC constructed from painted clay attached to cloth and worn outside the socket.
These were crude, uncomfortable, and fragile and the production methodology remained known only to Venetians until the end of the 18th century, when Parisians took over as the center for artificial eye-making.
Shortly following the introduction of the art of glass eye-making to the United States, German goods became unavailable because of World War II.
One solution to this problem has been demonstrated recently in a device based on an LCD which simulates the pupil size as a function of the ambient light.
The most basic simplification can be to divide implant types into two main groups: non-integrated (non-porous) and integrated (porous).
[4][7] Nonintegrated implants contain no unique apparatus for attachments to the extraocular muscles and do not allow in-growth of organic tissue into their inorganic substance.
[7] Porous enucleation implants currently are fabricated from a variety of materials including natural and synthetic hydroxyapatite, aluminium oxide, and polyethylene.
[12] 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.
[13] 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.
[9] It is available in dozens of prefabricated spherical and non-spherical shapes and in different sizes or plain blocks for individualized intraoperative customizing.
[9] The material is firm but malleable and allows direct suturing of muscles to implant without wrapping or extra steps.
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.
[15] Aluminium oxide ocular implants can be obtained in spherical and non-spherical (egg-shaped) shapes and in different sizes[9] for use in the anophthalmic socket.
[12] 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.
[12] As of 2005 the newest model[needs update] 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.
However, because the so-called ball and socket are separated by layers of Tenon's capsule, imbricated muscles, and conjunctiva, the mechanical efficiency of transmission of movement from the implant to the prosthesis is suboptimal.
[6][19][21] Although it is generally accepted that integrating the prosthesis to a porous implant with peg insertion enhances prosthetic movement, there is little available evidence in the literature that documents the degree of improvement.
Traction sutures or clamps may be applied to the horizontal rectus muscle insertions to assist in rotating and elevating the globe during the ensuing dissection.
An appropriately sized implant should replace the volume of the globe and leave sufficient room for the ocular prosthesis.
A temporary ocular conformer is inserted at the completion of the pro- cedure and is worn until the patient receives a prosthesis 4 to 8 weeks after surgery.
An elective secondary procedure is required to place the coupling peg or post in those patients who desire improved prosthetic motility.
Technetium bone or gadolinium-enhanced magnetic resonance imaging scans are not now universally used, but they have been used to confirm vascularization before peg insertion.
Living with an ocular prosthesis requires care, but oftentimes patients who have had incurable eye disorders, such as micropthalmia, anophtalmia or retinoblastoma, achieve a better quality of life with their prostheses.
It is generally recommended to leave the prosthesis in the socket as much as possible, though it may require some cleaning and lubrication, as well as regular polishing and check-ups with ocularists.
