In our experience, anophthalmic sockets reconstructed with aluminum oxide implants appear to have less postoperative tissue inflammation than sockets in which HA implants have been placed [56]. Problems (e.g., exposure) encountered with its use are similar to those seen with other porous implants [9, 55, 62, 115]. The more inert nature of these implants is a potentially critical advantage in minimizing socket inflammation. As with other currently available porous orbital implants, aluminum oxide is less expensive than the Bio-Eye (an unwrapped Bioceramic implant is US $450, a Vicryl mesh-wrapped Bioceramic implant is US $495).

Summary for the Clinician

■Porous orbital implants permit fibrovascular ingrowth. Implant fibrovascularization potentially reduces the risk of migration, extrusion, and infection.

■HA (Bio-Eye), porous polyethylene (MEDPOR), and aluminum oxide (alumina, Bioceramic) are currently the most widely accepted porous orbital implant materials.

■Complications with porous orbital implants are uncommon and include exposure and infection.

■Porous orbital implants permit direct coupling of the implant to an overlying prosthesis. Peg systems are the most commonly utilized coupling mechanism.

14.3Orbital Implant Selection in Adults

There continues to be little consensus regarding orbital implant material and design preference [115]. Surgeons have their own preferences regarding the use of spherical versus shaped, wrapped versus unwrapped, and pegged versus unpegged implants. Implant cost, insurance reimbursement, and marketing pressures also have a role in implant selection. In a 2004 survey of orbital surgeons, of 1,919 primary orbital implants used following enucleation, porous polyethylene was used in 42.7% of cases, followed by coralline HA (27.3%), nonporous alloplastic (PMMA, silicone) implants (19.9%), dermis fat grafts (7.2%), Bioceramic (1.8%), synthetic HA (0.9%), and mammalian bone (0.2%) [110]. The trends reported in this survey are reflective of a usage pattern in those responding to a nonrandom survey with a 31.4% response rate and do not suggest clinical superiority based on scientific evidence or statistical analysis [110].

When deciding which implant to use in an adult patient, we divide the various implants into three useful categories:

1.Porous spheres that may potentially be pegged (e.g., coralline or synthetic HA, porous polyethylene MEDPOR, aluminum oxide Bioceramic).

2.Quasi-integrated implants (e.g., mounded PMMA Universal implant, mounded porous polyethylene Quad MEDPOR) [3, 4, 48, 86].

3.Traditional nonporous sphere (e.g., PMMA, silicone).

If the patient is healthy and roughly between the ages of 15 and 65 years old, a porous implant (aluminum oxide, HA) that can potentially be pegged is our first choice. The porous implant with a peg will be associated with the highest degree of movement [34, 115]. If a peg is not being considered, the advantages of using a porous spherical implant are diminished as the movement associated with a nonpegged porous spherical implant is equal to that of a wrapped nonporous spherical implant [17, 21, 24]. However, the advantages of fibrovascular ingrowth and the potentially diminished risk of implant migration remain substantial reasons to consider using a porous implant even when pegging is not contemplated [102]. Trichopoulos and Augsburger reported implant migration in 11 of 68 nonporous implant cases (16.2%) but in only 1 of 190 porous cases (0.5%) [114]. Implant migration was associated with poor prosthetic motility and suboptimal cosmesis due to enophthalmos and deep superior sulcus deformity in all cases [114].

A quasi-integrated implant such as the Universal (mounded PMMA) or MEDPOR Quad implant (mounded) is an alternative consideration to the porous spherical implants if pegging is not a consideration but potentially improved motility is desired. The mounded surface of the Universal or MEDPOR Quad implant o ers improved motility over a standard sphere as a result of the indirect coupling that occurs between the mounds on the implant and the posterior surface of the prosthesis.Proper placement and meticulous closure of the Tenon capsule and conjunctiva are essential when using one of these mounded implants [4, 86]. Di culty putting these implants into the socket and the risk of exposure deter many from using them. The PMMA mounded implant is significantly less expensive (US $275) than HA, porous polyethylene, or aluminum oxide.

A nonporous sphere (e.g., PMMA, silicone), wrapped, centered within the muscle cone, and attached to each of the rectus muscles is another alternative if pegging is not a consideration and budgetary restraints limit the use of porous implants. Although reasonable prosthetic

movement occurs in most cases, motility of the artificial eye is limited compared to that often observed following placement of a buried, mounded implant or a porous pegged implant. Because prosthetic movement is only

14 passively coupled to the buried sphere, the artificial eye may lag behind the contralateral normal eye on attempted horizontal or vertical gaze. A nonporous implant simply placed into the orbit, without a wrap and without connection to the rectus muscles, is the least-desirable choice in our view as it o ers little movement, and the implants are prone to migrate over time, most commonly into the superotemporal space. A decentered implant can make fitting of a custom artificial eye problematic.

Nonporous spherical implants are frequently considered in maturing patients (seventh decade or beyond), debilitated or immunocompromized individuals, and patients with diabetes or a history of periorbital radiation therapy as they would not be good candidates to consider peg placement. A traditional nonporous sphere (e.g., PMMA, silicone) wrapped and centered in the muscle cone and connected to the rectus muscles is our typical approach. Maturing patients in good health and seeking to maximize potential prosthesis motility may be candidates for a quasi-integrated (or buried integrated) porous implant (e.g., Universal implant or MEDPOR Quad implant).

Summary for the Clinician

■Healthy patients between 15 and 65 years old are generally good candidates for a porous orbital implant following enucleation or evisceration surgery.

■Debilitated or immunocompromized individuals and patients with diabetes or a history of periorbital radiation should receive a nonporous implant.

■Nonporous spherical implants (e.g., PMMA or silicone) are less expensive than the newer generation of porous implants. However, nonporous implants do not permit fibrovascular ingrowth or implant–prosthesis coupling and may have a greater risk of migration or extrusion.

14.4Orbital Implant Selection in Children

Adult orbital volume is achieved by 12–14 years of age [118]. It has also been shown in normal pediatric individuals that 80% of adult orbital volume is reached by 5

years of age [8]. Historically, enucleation early in childhood is believed to contribute to the underdevelopment of the involved orbital bone structure with secondary facial asymmetry [5, 73, 103, 112]. More recent studies have indicated that obvious secondary cosmetic facial asymmetries may not have always been a by-product of pediatric enucleation but rather a result of orbital irradiation early in life [11, 38, 40, 42]. It is recognized, however, that orbital soft tissue volume is a critical determinant of orbital bone growth, and that adequate volume replacement following enucleation is a critical factor in continued orbital growth [11, 30, 72, 118]. The ocular prosthesis is also believed to be an important factor in minimizing orbital growth retardation and preventing periorbital asymmetries [36].

Our current approach in children less than 5 years of age undergoing enucleation surgery is to place a wrapped, nonporous sphere implant (e.g., PMMA, silicone), generally at least 16or 18-mm diameter centered within the muscle cone and connected to each of the rectus muscles and the inferior oblique muscle. Implant exchange, typically with a larger porous orbital implant, can be considered in the teenage years.

Another option for volume replacement in children (less than 5 years) is autogenous dermis fat grafts. These grafts may undergo hypertrophy and perhaps contribute to orbital bone growth [36, 89, 91, 97]. Dermis fat grafts have traditionally been used most frequently after extrusion of an orbital implant or removal of a migrated implant if there is some loss of conjunctival tissues and shortened furnaces.Conjunctival epithelium will migrate over the anterior surface of the dermis fat graft and potentially expand the conjunctival surface area. Disadvantages of dermis fat grafts include an unpredictable rate of absorption with resulting superior sulcus deformity and orbital volume deficiency. In addition, there is little or no transfer of eye socket movement to the overlying prosthesis, resulting in an artificial eye with little natural motility.

Formerly in children between the ages of 5 and 15 years, we have advocated nonporous implants, either a PMMA mounded implant (e.g., Universal) or a wrapped sphere (e.g., PMMA, silicone). As with younger patients, implant exchange with a porous orbital implant was then considered at a later time. The main reason for this was that we do not feel children younger than 15 years of age are good candidates for pegs. Regular follow-up visits and proper prosthesis care are important components for maintaining a healthy peg. In our experience, children often do not adequately care for their prostheses. Since the motility obtained with a mounded implant is superior to the nonpegged spherical implant, we have generally

advocated this type of implant [4, 86]. There is now an increasing trend to use porous implants in pediatric patients [26, 44, 117]. We have successfully placed porous spherical implants following childhood (5–15 years) enucleation and now consider the use of HA or aluminum oxide implants in many preteen and teenage patients undergoing enucleation surgery. Pegging is not a consideration until the child is mature enough to take care of the prosthesis and maintain follow-up visits. Importantly, the radiopaque nature of HA on imaging and potential limitations on postoperative external beam irradiation are no longer significant concerns or strong contraindications to the use of HA following enucleation for retinoblastoma [7, 25, 26].

Summary for the Clinician

■Approximately 80% of adult orbital volume is achieved by 5 years of age.

■Adequate volume replacement with an appropriately sized implant and overlying prosthesis is believed to be a critical determinant of continued orbital bone development.

■Children under the age of 5 typically receive a nonporous orbital implant that can be replaced later in life with a porous implant.

■Pediatric patients older than 5 may be candidates for porous orbital implants.

14.5Volume Considerations in Orbital Implant Selection

Removal of an eye following enucleation or evisceration creates an orbital soft tissue volume deficiency.Insu cient volume replacement results in a postnucleation socket syndrome that may consist of an abnormally deep superior sulcus, upper eyelid ptosis, an anophthalmic appearance, and lower eyelid malposition and may require a larger-than-desirable prosthesis [22, 65, 67, 113]. Proper implant volume may be determined either preoperatively or intraoperatively (enucleation cases) from the axial length of the eye or by determining the volume of fluid the enucleated eye displaces in a graduated cylinder [22, 67, 113]. Several authors have reported considerable interpatient variability of axial length and globe volume, with globe volumes varying between 6.9 and 9.0 ml [22, 67, 113]. Kaltreider and Lucarelli have shown that the axial length minus 2 mm (or A-scan minus 1 mm) approximates the implant diameter for optimal volume replace-

ment in emmetropic and myopic individuals [65, 67]. Custer and Trinkaus suggested a graduated cylinder be used to measure the volume of fluid displaced by an enucleated eye [22].

Approximately 70–80% of the volume of an individual’s normal globe should be replaced with an orbital implant [22, 67]. This generally allows for a prosthetic volume that is ideally 2.0 to 2.5 ml [26]. While the upper limit of prosthetic volume is around 4.0 ml, larger prostheses often result in progressive lower eyelid laxity and malposition due to the weight of the prostheses on the eyelid and the projection of the anterior surface of the artificial eye. Larger prostheses may also have limited socket excursion [65]. An 18-mm sphere has a volume of 3.1 mm, a 20-mm sphere has a volume of 4.2 ml, and a 22-mm sphere has a volume of 5.6 ml. Theoretically, the volume of the enucleated globe minus 2.0–2.5 ml gives the ideal implant size to use [22]. The calculated implant size is often greater than 22 mm with this technique. Unfortunately, implants larger than 22 mm may have a higher exposure rate and if too large will hinder fitting of an acceptable custom prosthesis [74, 113]. In most adults, we typically use 20to 22-mm spherical implants following enucleation and 18to 20-mm implants after evisceration procedures. In pediatric patients, slightly smaller implants may be required depending on the patient’s age and orbital development. Individualization of the implant size is important in optimizing orbital volume replacement and in achieving the best possible aesthetic result [22, 65–67, 113].

Summary for the Clinician

■Insu cient orbital soft tissue volume replacement following enucleation may result in an abnormally deep superior sulcus, upper eyelid ptosis, an enophthalmic appearance, and lower eyelid malposition and may require a larger- than-desirable prosthesis.

■It is estimated that 80% of the volume of an individual’s normal globe should be replaced with an orbital implant. The artificial eye volume is ideally 2.0–2.5 ml.

■A variety of formulas and techniques have been suggested to calculate the recommended implant size. Generally, most adults should typically receive a 20to 22-mm spherical implant following enucleation and an 18to 20-mm implant after an evisceration procedure.

material is helpful in preventing implant exposure [81, 85, 101, 102, 114]. Avoiding autologous/homologous tissue donor materials eliminates the theoretical risk of immunologic reactions and transmission of infectious agents, and it is less expensive if the cost of wrapping tissue is avoided and operating time is diminished [114]. Another advantage of the unwrapped orbital implant is that there is no wrapping to act as a possible barrier to the fibrovascular ingrowth within the porous sphere [85].

In a 2003 survey, the majority of respondents (59%) preferred not to wrap orbital implants [110]. Two previous studies showed no significant di erence in exposure rates between wrapped and unwrapped porous polyethylene [9, 81, 102, 114]. Trichopoulos and Augsburger [114] reported very low exposure rates (2.1%) in 190 unwrapped porous orbital implants (HA, porous polyethylene), while Perry and Tam [102] found no exposure in 21 unwrapped porous implants (HA, porous polyethylene). It has been suggested that implant wrapping may not be a protective barrier to implant exposure [114]. A potentially lower exposure rate in unwrapped implants has been attributed to more complete vascularization of the unwrapped implant as well as adherence of the rectus muscle/Tenon layer directly to the anterior surface of the implant, which may minimize wound tension [85, 111]. It may also be due to posterior implant placement and a meticulous layered closure [85, 102]. Long et al. [85] demonstrated that unwrapped HA implants provide the same motility as sclera-wrapped implants. They suggested a more rapid vascularization of unwrapped implants facilitated early integration of tissue in the orbit, which helped maintain the position of the extraocular muscles and ensured excellent implant motility [85]. Placement of an unwrapped implant without muscle attachment during enucleation surgery as an alternative may simplify the procedure, decrease operating room time, reduce the total cost of the procedure, avoid creating a second surgical site for harvesting autogenous wraps, and eliminate the risk of disease transmission [85, 110, 111].

In contrast to some of the arguments reviewed, we advocate using an implant wrap (polyglactin 910 mesh;

Fig. 14.4a, b) material when implanting HA and aluminum oxide spherical implants. One of the principle advantages of implant wraps is that they permit meticulous adherence of the rectus muscles to the implant surface. Our technique includes attachment of the rectus muscles to the implant approximately 5 mm anterior to their normal anatomical position (Fig. 14.4c) [58, 60]. The rectus muscles end up with their insertions very close to each other.We have been advancing the medial and lateral rectus muscles further over the anterior implant surface so that the muscle attachment sites are nearly adjacent. It is possible that a more anterior muscle attachment helps keep the porous implant seated in good position and may facilitate fibrovascularization of the most anterior portion of the implant, which is where orbital implant exposures frequently occur. We also typically reinsert the inferior oblique muscle to the wrap just below the normal anatomic insertion of the lateral rectus muscle.

With secondary orbital implantation surgery (to replace a migrated or absent implant), localizing the four rectus muscles is essential to identifying the location of the muscle cone. Centering the implant within the muscle cone is the ideal anatomical position for a new implant.Reattaching the muscles to the wrapped implant is important as the extraocular muscles may not have been in their normal anatomic position prior to their isolation. Attachment helps keep the muscles oriented and the implant anatomically centered, helping to reestablish a more natural conjunctival space and it is hoped a more comfortable and better-fitting prosthesis. The centered implant with attached muscles also leads to improved prosthetic motility in most cases. A common misconception is that the extraocular muscles, once transected from the globe (in a prior enucleation procedure), retract into the orbit, precluding their later localization. Fortunately, the fibrous connective tissue framework of the orbit remains intact and prevents the extraocular muscles from retracting into the posterior eye socket [46]. The extraocular muscles are straightforward to localize in the majority of anophthalmic sockets with or without a previously placed implant [46].

Summary for the Clinician

■Advantages of orbital implant wrapping include facilitating implant insertion into the socket as well as permitting simple and meticulous attachment of the rectus muscles to the implant surface.

■Disadvantages of orbital implant wraps include additional costs and the potential barrier to implant fibrovascularization.