Pretutorial
Tutorial
Introduction
Mark R. Levine, MD
The search for the ideal orbital implant began in 1885 when Mules placed a glass spherical implant into an eviscerated socket. One year later, Frost introduced a similar implant into Tenon's capsule following an enucleation procedure.1,2 The Mules sphere revolutionized anophthalmic socket surgery by replacing lost orbital volume and diminishing socket contracture. Ideally, an appropriately sized implant must be centrally placed with sufficient space remaining to allow a fitting of a prosthesis with at least 2 mm of volume and 4 mm of central thickness.
Recent advances in enucleation and evisceration surgery began in 1989 with the introduction of hydroxyapatite orbital implants by Dr. Arthur Perry. Before 1989, there were three types of implants. One was an implant of acrylic or silicone buried in the muscle cone behind posterior Tenon's capsule to establish a centrally placed implant. Another type of implant was a quasi-integrated implant such as the Allen implant and Iowa implant, which lead to the universal implant (Slide 1 and Slide 2). The Iowa implant uses mounds that couple to the convexities on the posterior surface of the prosthesis; these mounds were later reduced in size to form a universal implant.3 The third type of implant used prior to 1989 was an exposed integrated implant, which, when successful, was most effective, but more often led to implant extrusion from infection or epithelial breakdown (Slide 3 and Slide 4).
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In 1989, Perry designed a well-tolerated integrated hydroxyapatite orbital implant made from sea coral.4 The porous nature of the material allowed fibrovascular ingrowth throughout the implant and permitted insertion of a coupling device without inflammation or infection, as was commonly seen with the exposed integrated implants. This was, therefore, a true buried integrated implant. Since that time, porous implants have been fabricated from natural or synthetic hydroxyapatite, aluminum oxide and polyethylene. The potential benefits of porous implants included improved prosthetic motility and a lower incidence of implant migration and extrusion. However, implant exposure occurred (Slide 5).
Subsequently, surgeons wrapped porous implants to facilitate muscle attachment and reduce the risk of implant exposure. Wrap material included polyglactin mesh, bovine pericardium, human donor sclera, dermis and dura mater, autogenous fascia lata, temporalis fascia and posterior auricular muscle. Fenestrating the wrapping material allowed the attached muscles to contact the implant or posterior fat to improve implant vascularization.5
An elective secondary procedure was performed to enhance motility, if desired, with a coupling peg or post. The pegging system was modified from an early polycarbonate peg, to a peg and sleeve system, and then to a biocompatible titanium peg system (Slide 6, Slide 7, Slide 8). The pegging can be performed only after implant vascularization, which takes approximately 6 months from implant surgery. Implant vascularization can be verified by technetium bone scan, magnetic resonance imaging, scanning with gadolinium or computed tomography scanning with contrast. Lack of vascularization ultimately will lead to infection, inflammation, epithelial breakdown and extrusion.5
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Although porous implants represented a significant advancement in ophthalmic surgery, limitations existed. Complications included implant exposure (Slide 9 and Slide 10), discharge, conjunctival thinning, pyogenic granuloma, implant infection and persistent pain and discomfort. These complications seemed to be related to surgical technique, wrapping material and host factors. In addition, implant exposure rates (37.5%) after peg placement were higher than the exposure rate in unpegged implants.6,7 Unique complications associated with pegging included pegs falling out, pyogenic granuloma around the peg or in the peg hole, improper peg placement causing poor transfer of movement, conjunctival overgrowth of the peg and excessive movement with clicking or popping.
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Although improvements in implant design have led to better cosmesis and motility, questions remain. The fundamental questions are fivefold:
- What is the cost of the implants?
- Is there a difference between porous and nonporous implants in terms of implant motility?
- What are the complication rates of porous and nonporous implants?
- What is the complication rate of pegging?
- What is the value of wrapping material?
Cost
Hydroxyapatite implants cost approximately $650 and porous polyethylene implants cost approximately $520, compared to acrylic and silicone enucleation spheres, which cost $15 to $50. In addition, charges for non-autogenous wrapping material vary from $100 to $500, and other charges can be incurred, including costs for imaging studies to establish vascularization, facility charges for pegging, ocularist expenses and costs of a reoperation for complication of porous implant exposure or pegging complications.
Implant Motility
A report by the American Academy of Ophthalmology, authored by Philip Custer, MD, and colleagues, concluded that "Based on one randomized clinical trial, spherical alloplastic nonporous and nonpegged porous enucleation implants provide similar implant and prosthetic motility when they are implanted using similar surgical techniques. Coupling the prosthesis to a porous implant with a motility peg or post appears to improve prosthetic motility, but there are few available data in the literature that document the degree of the improvement."5,8
Complication Rates of Porous and Nonporous Implants and Pegging
Custer and colleagues summarized in their assessment that exposure rates of porous implants were similar to or higher than what was reported for acrylic spheres and silicone spheres. In addition, implant exposure rate after peg placement was higher than the exposure rate in nonpegged implants as described by Jordan and others.6,7
Wrapping Material
Wrapping material allows attachment of the muscles to the covered material; this seems to improve movement and to add additional tissue as a barrier between Tenon's capsule and the implant, reducing exposure from the prosthetic tissue drag. Consideration in wrapping material must be taken due to the potential for infectious disease and prion transmission. Although no reports of disease transmission from donor sclera have been reported, segments of human immunodeficiency virus genome have been identified in preserved human sclera.9 Dura mater implants may pose the greatest risk of prion transmission of Creutzfeldt-Jakob disease.10 Processed bovine pericardium may be of concern in transmitting infectious prions from cattle with bovine spongiform encephalopathy (mad cow disease).11
Variability exists among reported exposure rates for porous and nonporous implants, most likely due to variations in surgical technique and the type of wrapping material. In today's medical world, with declining reimbursements, pragmatic cost-cutting and the possibility of pay for performance looming ahead, surgeons must increase their surgical case load per day in an efficient manner and minimize complications and reoperations.
In enucleation surgery, an 18-mm to 20-mm porous implant wrap with autogenous fascia lata with anterior placement of the extraocular muscles provides optimal outcomes. Autogenous grafts are believed to be superior to fresh or preserved homogenous grafts because the autogenous graft does not cause immune reactions or inflammation and has less chance of being absorbed.12 Access holes in the fascia lata for extraocular muscle insertion and a posterior hole allow for vascularization. The anterior placement of the extraocular muscles combined with autogenous fascia lata favors fewer complications. Slight vaulting of the prosthesis ensures less prosthetic drag without impairing motility. If a patient is dissatisfied with motility, then consideration is given to pegging.
In evisceration surgery, better motility is a result of less anatomic disruption of the extraocular muscles. The insertion of an 18-mm porous implant in a scleral pouch, which has had expansion sclerotomies at its equators, allows for vascularization and anterior scleral closure without tension. The prosthesis is slightly vaulted to reduce drag.
Implant pegging, when needed, is best performed on patients who underwent enucleation, as the complication rate is less than for patients who underwent evisceration. In addition, healing difficulties may occur in patients who require pegging after enucleation who are diabetic or have systemic disease, such as sarcoidosis, or collagen vascular disease.
Finally, elderly patients with reduced motility due to age are best served with an acrylic sphere for both enucleation and evisceration, as cost and longevity become a factor.
- Mules PH. Evisceration of the globe with artificial vitreous. Trans Ophthalmol Soc. 1885;5:200-206.
- Gougelmann HP. The evolution of the ocular motility implant. Int Ophthalmol Clinics. 1976;10:689-711.
- Jordan DR, Anderson RL, Nerad JA, Allen L. A preliminary report on the Universal Implant. Arch Ophth. 1987;105:1726-1731.
- Perry AC. Integrated orbital implants. Adv Ophthalmic Plast Reconstr Surg. 1990;8:75-81.
- Custer PL, Kennedy RH, Woog JJ, et al. Orbital implants in enucleation surgery: A report by the American Academy of Ophthalmology. Ophthalmology. 2003;110(10):2054-2061.
- Jordan DR, Chan S, Mawn L, et al. Complications associated with pegging hydroxyapatite orbital implants. Ophthalmology. 1999;106(3):505-512.
- Jordan DR. Problems after evisceration surgery with porous orbital implants. Ophthal Plastic Reconstr Surg. 2004;20(5):374-380.
- Custer PL, Trinkaus KM, Fornoff J. Comparative motility of hydroxyapatite and alloplastic enucleation implants. Ophthalmology. 1999;106(3):513-516.
- Seiff SR, Chang JS Jr., Hurt MH, Khayam-Bashi H. Polymerase chain reaction identification of human immunodeficiency virus-1 in preserved human sclera. Am J Ophth. 1994;118:528-530.
- Anson JA, Marchand EP. Bovine pericardium for dural grafts: Clinical results in 35 patients. Neurosurgery. 1996;39:764-768.
- Nunery WR. Risk of prion transmission with the use of xenografts and allografts in surgery. Ophthal Plast Reconstr Surg. 2003;17:389-394.
- Remulla HD, Rubin PA, Shore JW, et al. Complications of porous spherical orbital implants. Ophthalmology. 1995;102:586-593.