Chapter 17 General Principles and Techniques Anesthetic Considerations in the Ophthalmic Patient *Monitor for hyperthermia in cats. †Buprenorphine is a better analgesic than morphine in cats. ††Black box warning added by the FDA in October 2010 identified cases of renal failure and death in cats with repeated uses of meloxicam. Meloxicam is approved for single use only in cats in the U.S. Apply topical lubricating ointment to keep the tissue moist before surgical repair. Thoroughly irrigate and gently cleanse the wound with a dilute 10% Betadine solution. Identify the mucocutaneous junction, the meibomian glands in the tarsal plate, and the palpebral conjunctiva. Convert simple lacerations to a V-shaped defect with judicious wound debridement (scarify necrotic margins and smooth jagged edges), taking care to preserve as much tissue as possible (Fig. 17-4, A) if needed for alignment (optional). Place a marginal skin suture, ensuring that the lid margin has perfect alignment (Fig. 17-4, B). Leave the conjunctival tissue to heal on its own. Take care that knots and suture ends do not abrade the cornea by positioning them subcutaneously, or place knots on the outside of the eyelid by passing the suture through the eyelid. Use a simple interrupted or modified figure-8 cruciate suture (e.g., 4-0 to 5-0 Vicryl) with the knot ends directed away from the cornea to close the skin (Fig. 17-4, C, D). Space remaining skin sutures approximately 2 to 3 mm apart. If the nasolacrimal duct has been damaged by trauma near the medial canthus, stent it by first cannulating the nasolacrimal duct with 0 to 2-0 monofilament suture and then passing polyethylene or Silastic tubing over the suture and securing it to the skin near the medial canthus and the lateral canthus of the nostril (see inset, Fig. 17-4). A complete temporary tarsorraphy may be indicated to protect the cornea after repair of extensive eyelid injuries because of impaired eyelid functions and blink reflex (Fig. 17-5). Medicate the wound with a broad-spectrum ophthalmic antibiotic ointment such as neomycin/polymyxin/bacitracin for 14 days, and monitor for blepharospasm, tearing, or holding the eye closed (mucopurulent discharge is common with topical antibiotic ointments); this may indicate that a corneal ulcer has formed. Remove sutures at 10 to 14 days. Leave the cannula in place for 4 to 6 weeks. Place horizontal mattress sutures at the eyelid margins to appose them, using partial-thickness bites oriented parallel or perpendicular to the lid margin (see Fig. 17-5). Prepare a thin, sliding conjunctival flap by grasping the conjunctiva with ophthalmic tying forceps such as a 0.3 mm Colibri forceps approximately 2 mm from the limbus. Apply traction to tent the conjunctiva, and incise a few millimeters from the limbus with a pair of tenotomy scissors (Fig. 17-6, A). Elevate the cut edge, bluntly dissecting perilimbally with tenotomy scissors to separate the conjunctiva from the underlying sclera (Fig. 17-6, B). Using the tips of the tenotomy scissors directed at a 90-degree angle to the tissue, use sharp dissection to separate the episclera from the conjunctiva. Start the dissection at the free edge of the conjunctiva, and move the scissors proximally as the episclera is separated from the conjunctiva. Take care to prevent iatrogenic button-holes in the conjunctiva. After dissection, the conjunctival flap becomes much more mobile, reducing the chance of flap retraction. Position the flap over the defect after it has been debrided to remove any corneal epithelium. Be sure to debride the corneal epithelium off the corneal ulcer bed and edges before placing the tissue flap so the flap can integrate into the cornea. Dissect a hood flap from the bulbar conjunctiva dorsal to the lesion or from the bulbar conjunctiva as close to the lesion as possible (Fig. 17-7, A and B). Dissect half of the bulbar conjunctiva and separate it from the episclera as described previously; position it over the globe. Ensure that the conjunctiva lies flat on the cornea with no traction; this will occur if the episclera has been well dissected from the conjunctiva with tenotomy scissors (see Fig. 17-7, B). Place two absorbable sutures (6-0 to 8-0 Vicryl) at the limbus 180 degrees apart to position the flap over the cornea (Fig. 17-7, C). Provide tension across the free edge of the flap (not on the eye) to keep it in place over the cornea; corneal sutures are not required. Place partial-thickness sutures into the episclera or sclera in a simple interrupted pattern with 6-0 to 8-0 Vicryl (Gilger et al, 2007). If needed, place additional limbal sutures to further anchor the flap. Start a total or 360-degree conjunctival flap by making a 360-degree conjunctival incision 2 to 3 mm from the limbus, (Fig. 17-8, A and B). Carefully dissect the conjunctiva ventromedially from the episclera and the third eyelid tissues. If the graft has a great deal of retraction, dissect the episclera more proximally from the conjunctiva with tenotomy scissors, taking care not to cause button-holes in the conjunctiva. Suture the free edges of the conjunctiva together in a horizontal mattress pattern (Fig. 17-8, C and D) using absorbable suture (6-0 Vicryl or smaller). Ensure that the sutures are tight, so that no corneal contact is made by sutures and the conjunctival graft is sutured to itself and not to the cornea (Gilger et al, 2007). It is important to get epithelial-to-epithelial apposition without flap overlap. Medicate the eye with broad-spectrum ophthalmic antibiotics (see previous laceration medical management description) at least four times a day and atropine once or twice daily. In the nonadherent areas, trim the flap with tenotomy scissors under topical anesthesia with proparacaine 6 to 8 weeks after surgery, once the corneal lesion has healed, allowing the corneal attachment to atrophy and undergo fibrosis, thus minimizing scar formation. Loose and excess conjunctiva can be trimmed from the cornea to reduce the vascular reaction and subsequent scar, but do not remove the conjunctiva from the former corneal ulcer or defect. Scar remodeling occurs over several months; final results vary from an insignificant opacity to a dense leukoma. Exteriorize and extend the third eyelid by grasping it with forceps and elevating it. Pass a cutting needle with swaged-on 3-0 or 4-0 monofilament absorbable suture through the upper eyelid in the dorsolateral conjunctival fornix (Fig. 17-9, A). Direct the needle through the external surface of the third eyelid under the crossbar of the T-shaped cartilage, and exit through the external surface of the third eyelid on the opposite side of the cartilage. Alternatively, to reduce the chance of the suture rubbing on the cornea, direct the suture around the cartilage, but do not penetrate the conjunctiva on the bulbar surface of the third eyelid (Fig. 17-9, B). Direct the suture back through the dorsolateral conjunctival fornix and out the upper eyelid. Apply tension on the suture, pulling the third eyelid over the cornea. Tie the suture over a stent, with the ends long enough to tie a bow, so that the cornea may be inspected periodically (Fig. 17-9, C). As an alternative, use double-armed 3-0 to 2-0 nonabsorbable suture, and begin by placing the suture midway along the length of the third eyelid and then through the fornix. Using heavy scissors, make a wide lateral canthotomy to improve exposure (Fig. 17-10, A). You may wish to clamp the area to be cut with a straight hemostat before incising to reduce hemorrhage. Place a lid speculum (optional). Next, make a 360-degree bulbar conjunctival incision around the limbus using small blunt scissors, such as Stevens tenotomy or small Metzenbaum scissors (Fig. 17-10, B). At the level of the orbital rim, use curved Metzenbaum scissors to bluntly dissect down through the bulbar conjunctiva to the subtenon space to expose the extraocular muscle tendons. Incise the tendons with scissors close to the globe (Fig. 17-10, C). Optionally, use small hemostats to clamp these areas before cutting to reduce hemorrhage. The ability to freely rotate the globe almost 360 degrees indicates that at least the recti and oblique muscles are cut. Using a curved hemostat, clamp the tissues of the posterior pole of the globe, containing the optic nerve, retractor bulbi muscle, and associated vasculature (Fig. 17-10, D). Do not pull the globe or place any traction on the eye because this could avulse the optic nerve at the optic chiasm and blind the other eye. Leave the hemostat in place if space allows, or if necessary remove it before blindly incising the stalk with curved Metzenbaum or enucleation (more strongly curved) scissors about 5 to 10 mm posterior to the globe. Be sure to transect the optic nerve and avoid cutting the posterior sclera. Control hemorrhage from the orbit with direct pressure, hemostatic clamps, electrocautery, and/or calcium alginate. Avoid the optic nerve with cautery unless the equipment is appropriate for use around the brain or spinal cord such as Cameron-Miller cautery. Ligation of vessels and/or the optic nerve, although possible, is technically difficult and may not be necessary. Also remove the orbital lacrimal gland and all conjunctiva (Fig. 17-10, E). Remove the lid speculum and broadly incise the base of the nictitans; clamping before cutting may again reduce hemorrhage. Remove the entire nictitans, including cartilage and gland at the base. Remove the eyelid margins with heavy straight scissors, starting at the lateral canthotomy (Fig. 17-10, F). Fully excise the smooth hairless lid margin so that the skin edges will close without excessive dead space or tension. The medial canthal area must be removed. The medial canthus is closely adhered to its deeper attachments, so sharp dissection is sometimes required. Large vessels are occasionally encountered at the medial canthus. Copiously flush the orbit with sterile saline. Perform a wide lateral canthotomy using straight, heavy scissors such as a Mayo scissor (Fig. 17-11, A). Bluntly dissect the cut surface of each lid into an anterior skin-orbicularis oculi layer and a posterior tarsoconjunctival layer using a curved Metzenbaum scissor (Fig. 17-11, B). Continue blunt dissection medially until the medial canthus is reached. Remove the scissors, replace one blade of the scissor in the subcutaneous pocket just created, and cut the anterior layer parallel to the lid margin as close to the medial canthus as possible (Fig. 17-11, C). Close the lids with Allis tissue forceps or a 3-0 or 4-0 simple continuous suture with ends left long (Fig. 17-11, D). Use the lateral aspect of the forceps or suture to gently retract and rotate the dissected orbital contents medially, using blunt and sharp dissection of tissues around the lateral globe while clamping and then incising extraocular muscles close to their attachments on the globe (Fig. 17-11, E). Do not pull the globe or place any traction on the eye because this could avulse the optic nerve at the optic chiasm and blind the other eye. Clamp the tissues of the posterior pole of the globe with a hemostat; remove the hemostat and transect the tissues 5 to 10 mm posterior to the globe. Roll the globe out of the orbit from lateral to medial, and transect the remaining extraocular muscles, the medial canthal tendon, and the attachments of the medial canthus to the orbit from posterior to anterior (Fig. 17-11, F). Next, remove the nictitans, and excise any remaining conjunctiva (Fig. 17-11, G).
Surgery of the Eye
Anesthetic Considerations
TABLE 17-1
Surgical Techniques
Temporary Tarsorrhaphy
Conjunctival Flap
Hood Flap
360-Degree Conjunctival Flap
Third Eyelid Flap
Transconjunctival Enucleation
Lateral Enucleation
You may also need
Full access? Get Clinical Tree
