Fig. 41.1
Ocular implants . Acrylic, porous polyethylene, hydroxyapatite (from right to left)
The HA implant may be inserted wrapped or unwrapped. The unwrapped HA implants, however, have a much higher surface exposure rate. The cause of the erosion is likely due to multiple factors, but one of the reasons is the rough surface of the HA implant, which causes it to erode through the thin conjunctiva and Tenon’s layers [13–16]. Thus, most surgeons wrap the HA implant prior to insertion.
Hydroxyapatite appears to be biocompatible, nonallergenic, nontoxic, and nonbiodegradable [17–21]. When implanted into soft tissue, the porous HA matrix is infiltrated by host fibrovascular tissue [22–24]. The extraocular muscles can be directly attached to the wrapping material of the implant, producing very good implant movement. Following complete vascularization of the implant, a hole can be drilled into the implant and a motility peg placed, directly coupling the implant to the prosthesis, thus maximizing the prosthetic motility.
The porous polyethylene implant also has the advantage of allowing fibrovascular ingrowth of the implant [23, 24]. It, too, can be inserted either wrapped or unwrapped, but there has not appeared to be an increased exposure rate in the unwrapped state. Thus, an advantage of the PPE implant is that wrapping the implant is not required. The material is soft enough to allow direct suturing of the muscle onto the surface of the implant, producing excellent implant motility. A system that utilizes a titanium peg that can be placed into the anterior surface of the implant and couples the implant and prosthesis has recently been developed, and this system further improves prosthetic motility. The PPE appears to be biocompatible, nonallergenic, nontoxic, and nonbiodegradable.
Early results with both of these implants are very encouraging, but it takes many years to accurately assess the success and failure rates of a new design. A recent report utilizing a synthetic bioceramic implant wrapped in polyglactin mesh has also been promising (FCI, Cedex, France) [25]. More anterior placement of the rectus muscles also appears to reduce exposure problems with the mesh. There have also been concerns regarding the transmission of HIV virus or even prions from sclera or dura [26–30].
Dermis-Fat Grafts
Dermis-fat grafts (DFG) are often not thought of as ocular implants, but in children, a DFG is an excellent primary choice to consider. The extraocular muscles can be sutured directly to the graft, increasing its motility. The significant graft atrophy that is sometimes seen in adults’ sockets following DFG placement is unusual in the pediatric socket. There have even been cases where the DFG has grown too much in the pediatric socket and has later needed to be debulked [31]. As one can see in the in the following list of “ideal” implant characteristics, the DFG demonstrates many of these properties.
The “Ideal” Implant
With 110 years of experience and a plethora of materials that have been implanted in the orbit, the “ideal” implant should offer the following:
- 1.
It should be easy to use and readily available.
- 2.
It should compensate for the volume loss of the eye in a manner that imitates the natural condition as closely as possible.
- 3.
The implant should become incorporated within the orbital tissues and have a direct attachment to the extraocular muscles.
- 4.
It should allow for maximum movement of the prosthesis, thus maximizing the rehabilitation potential of the patient.
- 5.
The implant should be biocompatible and should not cause any inflammatory, rejection, allergic, or carcinogenic reactions by the tissues.
- 6.
The material should not be biodegradable.
- 7.
It should not cause a fibrotic reaction that could lead to a contracted socket.
- 8.
Complications related to the implant should not occur. No extrusions, exposures, infections, or displacements of the implant should result.
- 9.
It should provide maximal stimulus for growth of the bony orbit and facial structures.
The Reconstructive Plan
Orbital Growth
The early growth of the face and orbital area in the child is rapid. At 3 months of age, the face is only about 40% of that of an adult. But at 2 years it has reached approximately 70% of the adult dimensions and by 5.5 years attains 80% of its adult size. An anophthalmic orbit or an orbit with a severely microphthalmic eye can have devastating effects on the bony orbital growth and affect the overall facial development. Orbital soft tissue volume is a critical factor in orbital bone development. Therefore, replacing the orbital soft tissue volume is essential in continued orbital bone growth. This should be kept in mind when choosing an implant. For example, in a 6-month-old child who is being enucleated, a solid or porous implant would have to be relatively small because the orbit is small. Such a small implant will have an adverse effect on the overall orbital growth. To compensate for a small implant and to provide adequate orbital volume, an increasingly larger prosthetic shell will be required. This anteriorly placed shell will not have the same stimulatory effect as an appropriate-size implant, and the larger prosthesis will ultimately produce another set of problems, such as reduced motility, increased lower lid laxity, and increased discharge due to a suboptimal fit.
Ocular Implants in Younger Children
Patients younger than 5 years of age have typically received a nonporous implant as this has facilitated easier replacement with a larger porous implant later in childhood or adolescence. In children 3 years of age and under who undergo an enucleation, most of the oculoplastic contributors in this text prefer dermis-fat grafts as the primary ocular implant. At less than 3 years of age, the orbit still needs to undergo significant growth. Autogenous dermis-fat grafts have been shown to stimulate orbital growth in infants and children, often resulting in near normal orbitofacial development [32]. The grafts tend to grow as the child grows and in many cases obviate the need for additional volume augmentation when the child is older. The DFG seems to simulate the forces that were provided by the globe. Therefore, in children 3 years of age or less who need an implant (due to retinoblastoma, trauma, congenital problems, etc.), a dermis-fat graft is an excellent choice.
Between 3 and 6 years of age, recommendations vary as to which is the best implant to use. The orbit still has a significant amount of growth to undergo. A DFG offers all the previously mentioned advantages and is an excellent implant choice in this age group. However, the orbit is bigger and can accommodate a larger implant, so some surgeons prefer to insert a spherical implant. Some authors prefer a spherical nonporous implant for children less than 5 years of age preferably wrapped nonporous sphere implant (PMMA, silicone), at least 16–18 mm diameter centered within the muscle cone [33–35]. There has, however, recently been a reported use of hydroxyapatite porous sphere implants used in children as young as 4 months. Based on this study of over 531 children treated with HA implants following enucleation, the ideal HA implant size for a patient less than 4 months was 16 mm, 4 months to 1 year was 18 mm, 1–2 years of age was 18–20 mm, and greater than 2 years of age was 20 mm [36].
This brings up another concern, however, that in this younger age group, there is the distinct possibility that additional surgery may be required at a later date. Depending on the original problem, this may be due to tumor recurrence or the need to replace a small implant with a larger implant for volume considerations. If a porous or solid implant is used in a young child, the problem, as mentioned previously, involves the need to place the maximum size implant that can fit into a small, developing orbit. A small implant may not provide sufficient stimulation for orbital growth or in later years become a volume deficiency problem. A porous implant can also be very difficult to remove because of the fibrovascular ingrowth into the implant. The surgeon may want to consider the porous implant better as a permanent implant and, if additional surgery is a future possibility, recognize that either a DFG or a nonporous implant would be considerably less damaging to the orbital contents if additional surgery was in fact required.
In considering the possibility that additional orbital volume augmentation might be required in the future, a secondary implant can be placed in a socket that has had a DFG placed previously. In the infant or child, the DFG usually provides all the volume augmentation needed, as previously mentioned, and in some instances has even required debulking [31]. If, in a rare situation, there is still a need for volume augmentation, then after the graft has had time to completely heal, the DFG can be split open and a secondary implant of the desired size inserted behind the graft. The dermis is then sutured closed. An alternative is to place hydroxyapatite or other materials through a subperiosteal incision to increase mass behind the DFG [21]. With the advent of hydrogel expanders, however, the solution to the problem is even simpler, since a much smaller incision can be made in the dermis to allow a small, dehydrated spherical expander to be placed deep intraconally. The wound is then secured with 2 sutures of 5–0 Vicryl. The spheres range in hydrated volume from 2 to 5 mL which expands from a 5 to 8 mm diameter range dehydrated to from 16 to 22 mm when hydrated.
Tissue Expanders
In cases of early childhood enucleation, tissue expanders have been used to stimulate orbital bony growth. In the past inflatable expanders were used, but our preference today, again, is for osmotic hydrogel expanders if there is significant orbital and fissure asymmetry that requires intervention (see Chap. 39 for more details).
Ocular Implants in Older Children
In children older than 6 years of age , the orbit has reached 80% or more of its adult dimensions. Porous implants offer particular advantages to this age group. An adult-size implant can be used, and the advantages of the porous implants over the solid implants have been discussed. Dermis-fat grafts can still be used in this group, but orbital growth is less of a concern [32].
Special Situations
Solid implants, acrylic and silicone, are still used by many surgeons and have a consistent success rate [10]. They do not offer the theoretical advantages that the porous implants offer, but in trauma settings or conditions that may require implant removal in the future, the solid implants (acrylic and silicone) have their own advantages. Their smooth surface makes them easy to insert, and the lack of fibrovascular ingrowth makes them easy to remove if necessary. In the trauma setting where additional orbital reconstructive surgery may be needed, the surgeon should consider the ease of implantation and removal of these implants, should this be necessary. In the severely traumatized orbit, future volume augmentation may be required, bony reconstruction may be needed, and significant scarring and tissue contraction may occur. All these forces can cause an implant to become displaced or to extrude. Porous implants can be very difficult to remove, requiring sharp dissection.
Thus, the type of implant chosen should take all the abovementioned factors into consideration. Throughout the years, numerous authors have published their results using differing implant types and techniques, often with confusing and conflicting results. There are always multiple factors contributing to the success of any surgery. Besides the type of implant used, the surgical technique, the use of a wrapping material, and the type of material used all are extremely important. Studies examining the techniques and materials need to be continued to help us advance our technology. The DFG and the porous ceramic implants have yielded excellent results for the authors of this chapter.
Specific Procedures
Enucleation
One must be meticulous in identifying the correct eye for enucleation. It is recommended that numerous check systems be employed to eliminate the devastating event of removing the wrong eye. One suggestion is to employ a system that checks which eye is to be removed at several different stages. First, the nurse in the preoperative staging area asks the patient or parents which eye is to be removed and reviews the operative consent. If both the consent and patient are in agreement, the nurse places a small mark with a skin-marking pen above the brow of the eye to be enucleated. When the patient is brought back to the operating suite, the anesthesiologist again asks the patient which eye is to be removed. The circulating nurse witnesses this, checks for the correct location of the skin mark, and checks the operative consent. The final check is by the surgeon, reviewing the medical record and checking for the correct location of the skin mark over the eye to be enucleated. The patient is then examined. In cases of trauma, it is often obvious which eye is to be removed. However, in cases involving a retinoblastoma, for example, it may not be obvious. In such cases only the eye with the tumor is dilated, and indirect ophthalmoscopy is performed for tumor identification. Once the tumor is identified, the eye to be removed is then marked. Such a system of numerous checks guards against wrongful removal of a nondiseased eye.
The enucleation procedure is a relatively standard technique with the incorporation of minor personal variations. In prepping and draping the patient, the entire midface is exposed in the surgical field. This is very useful when soft tissue or eyelid work also needs to be performed, as in trauma cases. A plastic eye shield is placed in the nondiseased eye for protection. Traction sutures are placed at the lid margins of the operative eye. The superior and inferior fornices are preserved by the placement of a double-armed silk suture passed from the conjunctival surface full thickness through the lid and tied externally. A 360° conjunctival peritomy is made around the limbus. The medial and lateral rectus muscles are hooked, tagged with a double-armed 5–0 Vicryl suture, and severed from the globe with the Bovie cautery (using the Colorado Needle tip) (Fig. 41.2). A traction suture is placed on the globe at the stump of the insertion of both the medial and lateral recti. The inferior rectus and superior rectus are located, tagged, and severed from the globe. The inferior oblique and superior oblique are located and severed from the globe. These can also be tagged with a suture for attachment to the implant if desired.
Fig. 41.2
Enucleation procedure. (a) Superior rectus muscle is isolated on the muscle hook. (b) The muscle is tagged with a 5–0 Vicryl suture. (c) The muscle is severed from the globe with a monopolar cautery using the Colorado needle tip
Once all the muscles have been removed from the eye, the optic nerve is cut and the eye is removed. Various methods can be used to control bleeding from the cutting of the optic nerve. The nerve can be clamped for several minutes prior to cutting it. This technique should be avoided in situations involving an intraocular tumor, such as a retinoblastoma, where malignant cells may be pushed farther down the nerve. Another technique is to pack the socket with iced gauze pads immediately following the removal of the eye and apply pressure for 5 min. The gauze pads are gently removed, and the socket is examined for any signs of bleeding. If bleeding is present, the socket is again packed with iced gauze pads for 5 min. If bleeding is still present, which is unusual, the bleeding sites are located and cauterized with the bipolar cautery. Cautery is kept to a minimum to avoid extensive tissue damage and, if the optic nerve stump is cauterized, to avoid proximal nerve tissue injury. Additionally, gel foam soaked in thrombin can also be placed over the severed optic nerve to aid in hemostasis and left in the orbit.
Dermis-Fat Grafts
Harvesting
Even in the infant, a dermis-fat graft can be harvested. An accessible site is the lateral buttock area, which usually provides ample tissue even in the slimmest or youngest of patients (Fig. 41.3). Once the donor site is determined, the epithelium needs to be removed. This can be done by sharply dissecting the epidermis off exposing the dermal tissue, or various methods of dermabrasion can be employed, yielding pinpoint bleeding of the abraded dermis (Fig. 41.4). A 1- to 2-cm plug of dermal tissue with attached fat is desired. After the epidermis is removed, a scalpel blade is used to make a full-thickness dermal incision. The fatty tissue is bluntly and sharply dissected until the desired amount of fat is obtained. A larger diameter of fat is generally removed around the dermis graft. Care is taken to minimize the trauma to the graft. Excessive trauma to the graft will increase the amount of graft atrophy. To help stabilize the fat cell membranes, one author soaks the DFG in 50 units of regular insulin in 100 mL of normal saline. Once the graft is removed, the wound is closed primarily in layers. Deep, interrupted 3–0 polyglycolic acid sutures are used to close the deep layer. A 4–0 polyglycolic acid suture is used as either a running subcuticular stitch or as an interrupted horizontal mattress as the next layer to remove tension from the skin closure. Absorbable skin sutures are very useful in children. The skin is closed with a 5–0 fast absorbing gut suture. An alternative is a running subcuticular 4–0 Prolene or nylon suture, which is left in place for 10–14 days and then removed.
Fig. 41.3
Dermis-fat graft . The patient is positioned for harvesting a graft from the lateral buttock area
Fig. 41.4
Dermis-fat graft. The epithelium has been removed from the surface of the graft area
Implantation
After the enucleation has been completed, the DFG can be placed into the socket (Fig. 41.5). The volume of the DFG should be slightly more than the tissue removed. The four replaced recti muscle sutures are now secured to the appropriate positions at the edge of the dermis. The two oblique muscles can also be attached to the graft if desired. Tenon’s and conjunctival tissue are attached to the edge of the dermis using a running or interrupted 5–0 Vicryl suture. The conjunctiva need not be closed over the entire dermal plug. The conjunctival tissue will epithelialize over the dermis. This is very useful in situations where there is a shortage of conjunctiva. The fat will continue to prolapse until the conjunctiva is completely closed. However, excessive pressure should not be placed on the graft, and excess fat should be trimmed from the graft prior to complete closure of the conjunctiva (Fig. 41.6). An appropriate-size conformer is then placed in the socket. The conformer should not be so large as to place tension on the wound edges. A pressure dressing is applied (Fig. 41.7).
