ocular prosthesis ocular prosthesis an ocular prosthesis, artificial eye or glass eye is a type of craniofacial prosthesis that replaces an absent natural eye following an enucleation, evisceration, or orbital exenteration. the prosthesis fits over an orbital implant and under the eyelids. though often referred to as a glass eye, the ocular prosthesis roughly takes the shape of a convex shell and is made of medical grade plastic acrylic. a few ocular prostheses today are made of cryolite glass. a variant of the ocular prosthesis is a very thin hard shell known as a scleral shell which can be worn over a damaged or eviscerated eye. makers of ocular prosthetics are known as ocularists. an ocular prosthesis does not provide vision; this would be a visual prosthesis. someone with an ocular prosthesis is altogether blind on the affected side and has monocular (one sided) vision. for a functional replacement, or "bionic eye", see visual prosthesis. human ocular prosthesis of brown color cat with an ocular prosthesis. history prosthetic eye and glasses made for an injured world war i soldier by pioneering plastic surgeon johannes esser "making glass eye", c. 1915–1920. artificial glass eye being moulded under heat, 1938 the earliest known evidence of the use of ocular prosthesis is that of a woman found in shahr-i sokhta, iran dating back to 2900–2800 bc. it has a hemispherical form and a diameter of just over 2.5 cm (1 inch). it consists of very light material, probably bitumen paste. the surface of the artificial eye is covered with a thin layer of gold, engraved with a central circle (representing the iris) and gold lines patterned like sun rays. on both sides of the eye are drilled tiny holes, through which a golden thread could hold the eyeball in place. 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. 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. the first in-socket artificial eyes were made of gold with colored enamel, later evolving into the use of glass (thus the name "glass eye") by the venetians in the later part of the sixteenth century. 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. but the center shifted again, this time to germany because of their superior glass blowing techniques. shortly following the introduction of the art of glass eye-making to the united states, german goods became unavailable because of world war ii. as a result, the us instead made artificial eyes from acrylic plastic. production of modern ocular prosthetics has expanded from simply using glass into many different types of materials. in the united states, most custom ocular prostheses are fabricated using pmma (polymethyl methacrylate), or acrylic. in some countries, germany especially, prostheses are still most commonly made from glass. limits of realism ocularist surgeons have always worked together to make artificial eyes look more realistic. for decades, all efforts and investments to improve the appearance of artificial eyes have been dampened by the immobility of the pupil. 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. implant types and chemical construction there are many different types of implants, classification ranging from shape (spherical vs egg (oval) shaped), stock vs custom, porous vs nonporous, specific chemical make-up, and the presence of a peg or motility post. the most basic simplification can be to divide implant types into two main groups: non-integrated (non-porous) and integrated (porous). nonintegrated implants though there is evidence that ocular implants have been around for thousands of years, modern nonintegrated spherical intraconal implants came into existence around 1976 (not just glass eyes). 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. such implants have no direct attachment to the ocular prosthesis. usually, these implants are covered with a material that permits fixation of the extraocular recti muscles, such as donor sclera or polyester gauze which improves implant motility, but does not allow for direct mechanical coupling between the implant and the artificial eye. non-integrated implants include the acrylic (pmma), glass, and silicone spheres. polymethyl methacrylate (pmma) (acrylic) polymethyl methacrylate (pmma), commonly known as acrylic, is a transparent thermoplastic available for use as ocular prosthesis, replacement intraocular lenses when the original lens has been removed in the treatment of cataracts and has historically been used as hard contact lenses. pmma has a good degree of compatibility with human tissue, much more so than glass. although various materials have been used to make nonintegrated implants in the past, polymethyl methacrylate is one of the implants of choice. 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 introduction in 1989 when an implant made from hydroxyapatite received food and drug administration approval, 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%). 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. 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. and 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