Subconjunctival enucleation

The subconjunctival enucleation technique is the simplest and most rapid of these procedures, and the most frequently performed in small animals. Using this method, the globe is excised from its surrounding Tenon’s capsule with the majority of the surgical dissection limited to the sub-Tenon’s space. As a result, this method usually has less hemorrhage intraoperatively and less serum accumulation postoperatively. This technique does not usually remove the conjunctivae and lacrimal gland; however, the entire nictitating membrane is excised. Exposure of the deeper orbital tissues may be limited with this procedure because of the edematous bulbar conjunctiva, but can be enhanced by a lateral canthotomy.

In the subconjunctival procedure for enucleation, entry into the orbit is through the bulbar conjunctiva. After completion of draping around the palpebral fissure, a 5–10 mm lateral canthotomy may be performed to increase exposure (Fig. 4.9a). With blunt-tipped tenotomy, strabismus, or Metzenbaum scissors, the full-thickness lateral canthus is cut. Hemostasis is usually achieved by direct pressure with a surgical sponge, if necessary supplemented by point electrocautery. The bulbar conjunctiva and Tenon’s capsule are incised at the 12 o’clock position by curved Steven’s tenotomy, strabismus, or Metzenbaum scissors with blunt tips for about 3–5 mm posterior to the limbus, and the incision extended for 360° (Fig. 4.9b). Using the scissors’ blunt tips, the dissection plane between the sclera and Tenon’s capsule is extended deeper into the orbit until each extraocular muscle insertion is identified (Fig. 4.9c). After isolation with a muscle hook, the tendinous insertions of all of the extraocular muscles are incised. Transection of the extraocular muscle insertions, rather than through the muscle per se, minimizes hemorrhage. As each of the four major rectus muscle insertions is incised, the globe becomes more mobile. After incision of the retractor muscle and oblique muscle insertions, the globe will displace slightly forward.

Fig. 4.9 Enucleation – subconjunctival approach: In this procedure the globe is removed from Tenon’s capsule through a bulbar conjunctival incision at the limbus. After removal of the nictitating membrane, the eyelid margins are removed and permanently apposed. (a) The palpebral fissure is temporarily enlarged by a lateral canthotomy. The lateral canthus is incised by small tenotomy scissors for 5–10 mm. (b) The bulbar conjunctiva and Tenon’s capsule are incised 360° by curved Steven’s tenotomy or strabismus scissors a few millimeters behind the limbus. About 2–4 mm of bulbar conjunctiva are left attached at the limbus, to permit manipulation of the globe with forceps during the enucleation procedure. (c) By blunt–sharp dissection with curved tenotomy scissors, the extraocular muscle insertions to the globe are excised. The globe is rotated in different directions to provide the optimal exposure during the dissection process. (d) The optic nerve is clamped by curved hemostat and transected by curved enucleation or Metzenbaum scissors. Special care is required to prevent touching the posterior globe with the tips of the scissors during optic nerve incision. Once the optic nerve has been cut, the globe can be rotated forward for incision of any remaining fascial attachments. (e) The nictitating membrane is protracted by thumb forceps and its base clamped with two curved hemostats. The structure is excised by Mayo scissors. The lacrimal gland may be removed at this time from beneath the lateral orbital ligament. (f) The two layers of closure include apposition of the rostral portion of Tenon’s capsule by simple interrupted absorbable sutures. The skin–orbicularis muscle layer is apposed with simple interrupted non-absorbable sutures. (g) Two weeks following enucleation in a young Labrador Retriever and suture removal.

To sever the optic nerve and the adjacent posterior ciliary arteries, a small curved hemostat or enucleation forceps are carefully positioned posterior to the globe (Fig. 4.9d). With curved Metzenbaum scissors or the specially curved enucleation scissors, the optic nerve and surrounding blood vessels are transected just anterior to the hemostat. Placement of the scissors is critical to avoid any contact with the posterior sclera and to prevent inadvertent incision of the posterior segment of the eye. The globe is carefully removed from the orbit to permit placement of a ligature deep to the hemostat still clamped to the optic nerve and accompanying blood vessels. The orbit is now carefully examined for any bleeders, and ligatures or point electrocautery applied if needed.

If an intraorbital implant is not used, parts of the remaining extraocular muscles and periorbital fascia are apposed with 2-0 to 4-0 simple interrupted absorbable sutures to reduce the dead space within the orbit. The remaining bulbar conjunctiva and anterior Tenon’s capsule are apposed with 2-0 to 4-0 simple interrupted absorbable sutures. With closure of the bulbar conjunctiva, 4–6 mm of the eyelid margins (including the medial and lateral canthi, and nictitating membrane) are excised circumferentially with tenotomy or strabismus scissors. The nictitating membrane is protracted, and two hemostats are overlapped and clamped at its base (Fig. 4.9e). The remaining nictitating membrane, complete with gland, is excised by tenotomy or strabismus scissors. The remaining eyelids (including the septum orbitale) are closed and apposed with 3-0 to 5-0 simple interrupted non-absorbable sutures (Fig. 4.9f,g).

If an orbital prosthesis is planned, an 18–22 mm sterile silicone sphere (Jardon Eye Prosthetics Inc., Southfield, MI) or methyl methacrylate sphere (Storz Instrument Company, St Louis, MO) is usually selected (Fig. 4.10). The surface of the silicone sphere is scarified or roughened with several incisions via scalpel blade to roughen its smooth surface and facilitate orbital retention. The sphere is inserted, and the extraocular muscles and endorbita are apposed about the sphere. An alternative method is the placement of mesh implants on the anterior surface of the orbital rim to prevent postoperative eyelid and orbital shrinkage.

Fig. 4.10 Placement of a 14–22 mm silicone or methacrylate sphere after enucleation in the dog and cat. Two-layer closure is recommended with apposition of the dorsal and ventral periorbita and Tenon’s capsule with simple interrupted absorbable sutures, and the eyelid skin and orbicularis oculi muscle layer with simple interrupted non-absorbable sutures. In both cats and horses these orbital implants are more apt to extrude than in dogs.

(Modified with permission from Nasisse MP, van Ee RT, Munger RJ, Davidson MG 1988 Use of methyl methacrylate orbital prostheses in dogs and cats: 78 cases (1980–1986). Journal of the American Veterinary Medical Association 192:539–542.)

Transpalpebral (‘en bloc’) enucleation

The transpalpebral enucleation technique differs from the subconjunctival procedure in that the surgical entry starts at the level of the eyelids, and the deeper aspects of the eyelids and the entire palpebral, fornix, and bulbar conjunctivae, and nictitating membrane are excised (‘en bloc’ method). This technique is performed more frequently in the large animal species. Although more tissues are excised in this procedure, the conjunctival and corneal surfaces are avoided, thereby reducing the chance of orbital contamination and postoperative infection. This method is preferred when infections of the globe and conjunctival surfaces are present. Because the entire conjunctiva is excised, exposure and visualization of the deeper orbital tissues are facilitated.

After draping, the eyelids are apposed with simple continuous 3-0 to 4-0 sutures, thereby closing the palpebral fissure (Fig. 4.11a). The eyelid skin is incised circumferentially by scalpel blade about 6–8 mm from the eyelid margins to avoid the bases of the meibomian or tarsal glands (Fig. 4.11b). The skin incision is carefully deepened until the submucosa of the palpebral conjunctiva is reached. Then, with blunt dissection with Steven’s tenotomy, strabismus or Metzenbaum scissors, the incision is continued under the conjunctival fornices, and onto the globe and under the bulbar conjunctiva (Fig. 4.11c). The procedure continues using the same steps as the subconjunctival method. Dissection within the sub-Tenon’s space between the sclera and Tenon’s capsule will usually minimize hemorrhage. All of the extraocular muscles are severed at their insertions (Fig. 4.11d). Isolation, clamping by curved hemostat, incision of the optic nerve, and removal of the globe follow (Fig. 4.11e). The Vicryl® ligature is carefully positioned deep to the hemostat on the optic nerve stump.

Fig. 4.11 Enucleation – transpalpebral approach: In this technique the globe is removed with the eyelids sutured or clamped together. (a) The palpebral fissure is closed by suturing the eyelids together with a continuous non-absorbable suture. Alternatively, the eyelids can be clamped together by Allis or towel forceps. (b) The eyelid skin and orbicularis oculi muscle layers are incised for 360° to the level of the tarsoconjunctiva. The incision is usually about 6–8 mm from the eyelid margins to avoid the bases of the meibomian glands. (c) With the sutured eyelids clamped by Allis forceps, the dissection is continued by small curved Metzenbaum scissors around the conjunctival fornices and onto the globe. (d) Once the sub-Tenon’s space is entered about the globe, the different extraocular muscle insertions are isolated and transected. Hemorrhage is usually minimal as long as the surgical plane remains in the sub-Tenon’s space. (e) Once the posterior orbit is entered, the optic nerve is carefully isolated, clamped by a curved hemostat, and incised by curved scissors posterior to the clamp. (f) The first of two layers of closure consists of apposition of the orbital septum with simple interrupted or simple mattress absorbable sutures. (g) The second and last closure is apposition of the eyelid and orbicularis oculi muscle layer with simple interrupted non-absorbable sutures.

Closure of the anterior periorbital fascial tissues with simple interrupted 3-0 to 5-0 absorbable sutures, with or without an orbital prosthesis, helps to reduce the dead space within the orbit. The orbital septum within the eyelids is apposed with 3-0 to 4-0 simple interrupted or horizontal mattress absorbable sutures (Fig. 4.11f). The eyelid–subcutaneous layer is apposed using the same type of suture and suture pattern. The eyelid skin is apposed with several 3-0 to 4-0 simple interrupted non-absorbable sutures (Fig. 4.11g).