Enucleation

Enucleation, or more accurately orbital exenteration, is indicated if the eyeball has collapsed because of trauma or perforated from an ulcer or laceration. Further, it should be considered whenever a chronic, painful eye condition can­not be resolved.

The lids are clipped, taking care to flush any hair clip­pings from the skin, eye, and conjunctiva. Irritating anti­septic solutions should be kept out of the unaffected eye, and they should not be allowed to pool on the surgery table near the downside eye. Once the skin is prepared for asep­tic surgery, lidocaine (1-2%) is injected subcutaneously around the entire circumference of the affected eye, at a distance of roughly 3 cm from the eyelid margins. This block typically results in paralysis of branches of the auric- ulopalpebral nerve, inducing eyelid paralysis; alternatively, the auriculopalpebral nerve can be blocked as described above (see the previous section in this chapter, Infectious Keratoconjunctivitis). A retrobulbar block of 5-10 cc of 1-2% lidocaine for a large goat is administered by introduc­tion of a 5-10 cm long, 18-20-gauge needle directed through the eyelid skin toward the apex of the orbit. Optimally, the lidocaine is deposited in the vicinity of the foramen orbitorotundum, which lies on a line from the center of the affected eye toward the opposite ear, at a level just ventral to the ipsilateral zygomatic bone. Successful anesthesia is signaled by ocular anesthesia, mydriasis of the pupil, paralysis of the retrobulbar muscles, and blind­ness, although these findings may variably exist in the pre­operative state.

A transpalpebral approach is most commonly employed (Irby 2017). If possible, the eyelids are sutured or clamped shut prior to incision of the eyelids. A circumferential inci­sion around the entire eye is made through the eyelid skin at a distance of roughly 1 cm from the lid margin. The inci­sion is extended through the subcutaneous tissues, taking care to not penetrate the underlying conjunctival sac. The canthal ligaments at the medial and lateral aspects of the eye are sharply transected. Once a subcutaneous surgical plane is established around the entirety of the incision, sur­gical scissors are used to remove the eyelid margins, retrob­ulbar muscles, and underlying conjunctiva and globe from the orbital cavity. During dissection, the surgeon should keep the scissors adjacent to the rim of the bony orbit while gradually deepening the incision around the entire circum­ference of the orbital cavity. Taking care not to apply firm retraction to the tissues to be extirpated, the surgeon should transect the orbital stalk at the back of the orbital cavity, thereby removing the eyelid margins, extraocular muscles, conjunctiva, and globe en masse. Once the orbital contents are removed, hemorrhage will become heavier, so this step should be taken only after the orbital contents have been entirely freed from the surrounding bone. Rather than attempt to suture the remaining optic stalk, packing of the orbital cavity with sterile roll gauze is recommended to limit hemorrhage. An everting mattress suture, Ford inter­locking pattern, or simple continuous pattern can be used to close the skin, with the surgeon taking care not to incor­porate any strands of roll gauze into the skin closure. The roll gauze should be removed when one or two suture placements remain in the skin. Hemostasis is achieved through hematoma formation within the closed orbital cavity. Postoperative antimicrobial and analgesic therapy is indicated, as are appropriate steps toward mitigation of potential myiasis. As with all surgeries, tetanus prophy­laxis is imperative.