Ocular prosthesis - AbsoluteAstronomy.com

An ocular prosthesis or artificial eye (a type of Craniofacial prosthesis

Craniofacial prosthesis

Craniofacial prostheses are prostheses made by individuals trained in anaplastology or maxillofacial prosthodontics who medically help rehabilitate those suffering from facial defects caused by disease , trauma or birth defects...

) replaces an absent natural eye

Human eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...

following an enucleation, evisceration, or orbital exenteration. The prosthetic fits over an orbital implant and under the eyelid

Eyelid

An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...

s. 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 prosthetics today are made of cryolite

Cryolite

Cryolite is an uncommon mineral identified with the once large deposit at Ivigtût on the west coast of Greenland, depleted by 1987....

glass. A variant of the ocular prosthesis is a very thin hard shell known as a sclera

Sclera

The sclera , also known as the white or white of the eye, is the opaque , fibrous, protective, outer layer of the eye containing collagen and elastic fiber. In the development of the embryo, the sclera is derived from the neural crest...

l shell which can be worn over a damaged eye. Makers of ocular prosthetics are known as ocularist

Ocularist

An ocularist is someone who specializes in the fabrication and fitting of ocular prostheses for people who have lost an eye or eyes due to trauma or illness...

s. An ocular prosthetic does not provide vision; this would be a visual prosthetic. Someone with an ocular prosthetic is totally blind

Blindness

Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...

on the affected side and has monocular (one sided) vision

Visual perception

Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...

which affects depth perception

Depth perception

Depth perception is the visual ability to perceive the world in three dimensions and the distance of an object. Depth sensation is the ability to move accurately, or to respond consistently, based on the distances of objects in an environment....

History

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 BCE. 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 (Yer. Ned. 41c; comp. Yer. Sanh. 13c). Roman and Egyptian priests are known to have produced artificial eyes as early as the fifth century BCE 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 WWII. As a result, the US instead made artificial eyes from acrylic plastic.

Modern ocular prosthetics has expanded from simply using glass into many different types of materials.

Limits of realism

Ocularists and eye surgeons have always worked together to make the most realistic artificial eye. For decades, all efforts and investments to improve the appearance of artificial eye are neutralized by the immobility of the pupil. A solution to this problem has been demonstrated recently. The device is based on a LCD which simulates the pupil size as a function of the ambiant 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 non porous, 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: nonintegrated (non-porous) and integrated (porous).

Nonintegrated implants

Though there is evidence that ocular implants have been around for thousands of years (already cited reference 2) 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

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)

PMMA 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 (see poly(methyl methacrylate)).

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 (PMMA) 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, aluminum oxide, and polyethylene

Polyethylene

Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

.

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/ Chinese).

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 was 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

Polyethylene terephthalate

Polyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...

, or vicryl

Vicryl

Vicryl is an absorbable, synthetic, braided suture, manufactured by Ethicon Inc., a subsidiary of Johnson and Johnson. It is indicated for soft tissue approximation and ligation. The suture holds its tensile strength for approximately three to four weeks in tissue, and is completely absorbed by...

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 recent study has shown that HA has a more rapid rate of ﬁbrovascularization than
Medpor.

Porous polyethylene (PP)

MEDPOR is a high-density porous polyethylene (Medpor)
Implant manufactured from linear high-density polyethylene.
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 aluminum oxide (Al₂O₃). Aluminum oxide is a synthetic 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.
Aluminum oxide ocular implants can be obtained in spherical and non-spherical (egg-shaped) shapes and in different sizes for use in the anophthalmic socket
The bioceramic implant is available in spherical and egg-shaped models 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.

Aluminum 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, 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.1 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 multipurpose conical porous polyethylene orbital implant (MCOI) (Porex Medical) 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. And in anticipation of future peg placement there is a 6-mm 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 eye.
However, the motility peg is mounted in only a minority of patients. This may partially be the result of 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 ideal 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. (1) The rubbing force between the posterior surface of the artiﬁcial eye and the conjunctiva that covers the implant may cause the artiﬁcial eye to move. Because this force is likely to be approximately equal in all directions, it would cause comparable horizontal and vertical artiﬁcial eye amplitudes. (2) An artiﬁcial eye usually ﬁts snugly in the conjunctival space (possibly not in the superior fornix). Therefore, any movement of the conjunctival fornices will cause a similar movement of the artiﬁcial eye, whereas lack of movement of the fornices will restrict its motility.
Imbrication of the rectus muscles over a nonintegrated implant traditionally was thought to impart movement to the implant and prosthesis. Like a ball-and-socket joint, when the implant moves, the prosthesis moves. 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. Moreover, the concern is that imbrication of the recti over nonintegrated implants actually can result in implant migration. The recent myoconjuctival technique of enucleation is an alternative to muscle imbrication.

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.
And although the porous implants have been reported to offer improved implant movement, these clearly are more expensive and intrusive, requiring wrapping, and subsequent imaging to determine vascularization and pegging to provide for better transmission of implant movement to the prosthesis, and also are prone to implant exposure.

Age and size of the implant may also affect the motility, since in a study comparing patients with hydroxyapatite implants and patients with nonporous implants, the implant movement appeared to decrease with age in both groups. This study also demonstrated improved movement of larger implants irrespective of material.

Surgical procedure

Essentially the surgery follows these steps:

Anesthesia
Conjunctival peritomy
Separation of the anterior Tenon’s fascia from the sclera
Pass sutures through rectus muscles
Rectus muscles disinserted from the globe
Rotate and elevate the globe
Open Tenon’s capsule to visualize optic nerve
Cauterize necessary blood vessels
Divide the nerve
Remove the eye
Hemostasis is achieved with either cautery or digital pressure.
Insert orbital implant.
If necessary (hydroxyapatite) cover the implant with wrapping material before
Attach the muscle (if possible) either directly (PP) or indirectly (HA) to implant.
Create fenerations in wrapping material if necessary
For HA implants drill 1 mm holes as muscle insertion site
Draw Tenon’s fascia over implant
Close Tenon’s facia in one or two layers
Suture conjunctiva
Insert temporary ocular conformer until prosthesis is received (4–8 weeks later)
After implant vascularization an optional secondary procedure can be done to place a couple peg or post.

Also under anesthesia

Create conjunctival incision at the peg insertion site
Create hole into implant to insert peg or post
Modify prosthesis to receive peg/post.

The surgery is done under general anesthesia with the addition of extra subconjunctival and/or retrobulbar anesthetics injected locally in some cases.
The following is a description of the surgical procedure performed by Custer et al.:

The conjunctival peritomy is performed at the corneal limbus, preserving as much healthy tissue as possible. Anterior Tenon’s fascia is separated from the sclera. Blunt dissection in the four quadrants between the rectus muscles separates deep Tenon’s fascia.

Sutures may be passed through the rectus muscles before their disinsertion from the globe. Some surgeons also suture one or both oblique muscles. 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. Tenon’s capsule may be opened posteriorly to allow visualization of the optic nerve. The vortex veins and posterior ciliary vessels may be cauterized before dividing the nerve and removing the eye. Alternatively, the optic nerve may be localized with a clamp before transection. Hemostasis is achieved with either cautery or digital pressure.

The orbital implant is inserted at the time of enucleation. An appropriately sized implant should replace the volume of the globe and leave sufficient room for the ocular prosthesis. Enucleation implants are available in a variety of sizes that may be determined by using sizing implants or calculated by measuring globe volume or axial length of the contralateral eye.

In the past, spherical nonporous implants were placed in the intraconal space and the extraocular muscles were either left unattached or were tied over the implant. Wrapping these implants allows attachment of the muscles to the covering material, a technique that seems to improve implant movement and reduce the incidence of implant migration. Porous implants may be saturated with antibiotic solution before insertion. Because the brittle nature of hydroxyapatite prevents direct suturing of the muscles to the implant, these implants are usually covered with some form of wrapping material. The muscles are attached to the implant in a technique similar to that used for spherical non-porous implants. The muscles may be directly sutured to porous polyethylene implants either by passing the suture through the implant material or by using an implant with fabricated suture tunnels. Some surgeons also wrap porous polyethylene implants either to facilitate muscle attachment or to reduce the risk of implant exposure. A variety of wrapping materials have been used to cover porous implants, including polyglactin or polyglycolic acid mesh, heterologous tissue (bovine pericardium), homologous donor tissue (sclera, dermis), and autogenous tissue (fascia lata, temporalis fascia, posterior auricular muscle, rectus abdominis sheath).
Fenestrations in the wrapping material are created at the insertion sites of the extraocular muscles, allowing the attached muscles to be in contact with the implant and improving implant vascularization. Drilling 1-mm holes into the implant at the muscle insertion sites is performed to facilitate vascularization of hydroxyapatite implants. Tenon’s fascia is drawn over the implant and closed in one or two layers. The conjunctiva is then sutured. 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. That procedure is usually delayed for at least 6 months after enucleation to allow time for implant vascularization. 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. Under local anesthesia, a conjunctival incision is created at the peg insertion site. A hole is created into the porous implant to allow insertion of the peg or post.
The prosthesis is then modiﬁed to receive the peg or post. Some surgeons have preplaced coupling posts in porous polyethylene implants at the time of enucleation. The post may spontaneously expose or is externalized in a later procedure via a conjunctival incision.

Notable people with prosthetic eyes

Baz Bastien
Baz Bastien
Aldege "Baz" Bastien was a Canadian professional ice hockey goaltender, head coach and general manager. He played five games for the Toronto Maple Leafs in 1945, but received most of his playing accolades while with the Pittsburgh Hornets of the American Hockey League...

– ice hockey player, coach (right eye)
Sammy Davis, Jr.
Sammy Davis, Jr.
Samuel George "Sammy" Davis Jr. was an American entertainer and was also known for his impersonations of actors and other celebrities....

– singer (left eye)
Peter Falk
Peter Falk
Peter Michael Falk was an American actor, best known for his role as Lieutenant Columbo in the television series Columbo...

– actor (right eye)
Nick Griffin
Nick Griffin
Nicholas John "Nick" Griffin is a British politician, chairman of the British National Party and Member of the European Parliament for North West England....

– BNP Member of European Parliament and leader (left eye)
Jeff Healey
Jeff Healey
Norman Jeffrey "Jeff" Healey was a blind Canadian jazz and blues-rock vocalist and guitarist who attained musical and personal popularity, particularly in the 1980s and 1990s.-Early life:...

- Canadian blues guitarist (both eyes)
Leo McKern
Leo McKern
Reginald "Leo" McKern, AO was an Australian-born British actor who appeared in numerous British and Australian television programmes and movies, and more than 200 stage roles.-Early life:...

– actor (left eye)
Claus Schenk Graf von Stauffenberg
Claus Schenk Graf von Stauffenberg
Claus Philipp Maria Justinian Schenk Graf von Stauffenberg commonly referred to as Claus Schenk Graf von Stauffenberg was a German army officer and Catholic aristocrat who was one of the leading members of the failed 20 July plot of 1944 to assassinate Adolf Hitler and remove the Nazi Party from...

– German career army officer and resistance leader (left eye)
Robert Thurman
Robert Thurman
Robert Alexander Farrar Thurman is an influential and prolific American Buddhist writer and academic who has authored, edited or translated several books on Tibetan Buddhism. He is the Je Tsongkhapa Professor of Indo-Tibetan Buddhist Studies at Columbia University, holding the first endowed chair...

– writer (left eye)
Mo Udall
Mo Udall
Morris King "Mo" Udall was an American politician who served as a U.S. Representative from Arizona from May 2, 1961 to May 4, 1991...

– politician (right eye)
Carl Ouellet
Carl Ouellet
Carl Joseph Yvon Ouellet is a retired Canadian professional wrestler. He has worked for, among other promotions, the World Wrestling Federation, World Championship Wrestling, Extreme Championship Wrestling, and Total Nonstop Action Wrestling.-Beginnings:Carl Ouellet debuted in 1987...

– Canadian professional wrestler (right eye)

External links

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