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A secondary implantation procedure is best performed under local anesthesia with sedation. This allows the patient to assist the surgeon in identifying the rectus muscles by moving the normal eye as directed by the surgeon. After sedation, the eyelids and the anterior conjunctiva are infiltrated with bupivacaine hydrochloride with epinephrine and hyaluronidase. An antibiotic and an anti-inflammatory are also given.
Removing the Implant
The entire area is then prepped, including the inside of the socket, and the superior and inferior fornices are identified with a double-armed 4-0 silk suture. The lids are separated with a lid speculum and the implant is exposed with a horizontal incision over its anterior surface. Care is taken to create separate flaps of conjunctiva and Tenon's capsule. The conjunctival flaps are created inferiorly and superiorly into the depths of the fornix to the point of the fornix suture. The implant is then removed, with care taken to remove as much of the pseudocapsule as possible, since it may inhibit vascularization of the implant. If anesthesia is not adequate to permit the removal of the pseudocapsule, a retrobulbar injection should not be given at this time because it will inhibit the movement of the rectus muscles making them difficult to identify. Likewise, any additional anesthesia is given only as needed. The surgeon should proceed to identify the rectus muscles before giving the retrobulbar injection for removal of the pseudocapsule.
Identification and Evaluation of the Muscles
The rectus muscles are identified by instructing the patient to gaze in each quadrant so that the anophthalmic socked can be observed for tissue movement and for the location of the rectus muscles. If the rectus muscles are found to be attached to the existing implant, they are isolated and tagged as in an enucleation. If the rectus muscles are not found to be attached to the primary implant, they can usually be found in the fornices, since their check ligaments tend to prevent them from fully retracting into the orbit when released. Identification of the superior, inferior, medial, and lateral rectus muscles is confirmed by feeling for contractions during socket movement and by visual inspection using a 4X loupe.
Dissection of the Muscles
Each muscle is then tagged with 5-0 Vicryl suture. A retrobulbar block is administered through the posterior aspect of the socket and the muscle dissection is completed. Care is taken to avoid damage to the levator complex.
Preparation of the Orbit
The socket is then inspected for scarring that may have contributed to the migration of the primary implant, and all such scars are lysed to allow proper placement and to prevent migration of the new implant.
Determination of Implant Size
Proper sizing of the orbit is essential to avoid complications and to achieve an optimum fit of the implant to both the orbit and the artificial eye. An undersized implant may result in enophthalmos or a deep superior sulcus, and may necessitate weight-increasing modifications to the artificial eye which, in turn, induce lower lid sag and restricted motility. Conversely, an oversized implant increases the risks of wound dehiscence, exposure, infection, and may complicate the coupling of the artificial eye to the motility peg. An implant is of the proper size when its volume, added to the volume of the implant wrapping material and the volume of the artificial eye, equals the volume of the enucleated globe (Perry 1983). A set of graduated sizing spheres should be used to properly size the orbit.
Wrapping the implant
There are several benefits to wrapping the implant. These include: increased motility, ease of insertion, ease of muscle attachment, and decreased risk of exposure. The use of an unwrapped implant allows the rough surface of the hydroxyapatite material to snag on orbital tissues during insertion, and may also cause abrasion of the overlying tissues during movement, thereby increasing the risk of exposure. Prior to wrapping, the implant is sterilized and soaked in an antibiotic solution (80 mg gentamicin in 100 cc saline). The implant is placed in the scleral shell and the shell is sutured closed with 5-0 Vicryl sutures. The excess tissue is trimmed and marks are made at the attachment sites of the four rectus muscles and at the anterior pole of the implant. Small windows (5 mm x 7 mm) are cut at the attachment sites of the rectus muscles and the implant is inserted into the orbit. The four rectus muscles are then brought into contact with the implant by passing a double-armed 5-0 Vicryl suture through the anterior lip of the window and tying the muscles snugly to the opening. This contact between the hydroxyapatite material and the highly vascular muscle tissues ensures good vascularization of the implant (Perry 1991a, DePotter 1992, Ferrone 1992). The oblique muscles can be attached, according to the surgeon's preference. Fornix-deepening sutures may be used at this point, as needed, to provide space for the artificial eye to move in concert with this highly motile implant.
Dressings and Postoperative Care
A firm pressure dressing is maintained for 4 to 6 days, oral antibiotics are given for 1 week, and steroids (prednisone) are given 3 times daily for 4 days. Oral postoperative pain medication is also given as needed. The socket is evaluated after removal of the pressure dressing and, if the edema has subsided, the tarsorrhaphy sutures are removed. Topical antibiotics are applied 4 times daily for 4 weeks. The patient is generally ready for fitting with an artificial eye 6 to 8 weeks postoperatively.