EYELID AKINESIA

In contrast to the powerful orbicularis muscle of the equine, ruminant species’ eyelids are much easier to open. However, any eyelid that is being held firmly shut by a patient should not be forced open for examination purposes unless the underlying disease process is known. Forceful attempts to open eyelids closed over a lacerated cornea may result in all the ocular contents being expelled into the examiner’s hand. In every instance, eyelids are most safely opened with the examiner’s hand(s) resting securely on the underlying orbit bones while the examiner’s fingers “walk” the lids open. Lids should not be forced open by direct application of pressure to the lid margins and thus to the underlying eyeball.

Eyelid akinesia is recommended as the safest way to open eyelids and is essential for standing ocular surgical procedures (nictitans, conjunctival or corneal surgery, etc.). Several methods are available to paralyze the upper eyelids, and akinesia should result within 5 minutes. In thinner-skinned animals (calves, sheep and goats), branches of the palpebral branch of the auriculopalpebral nerve may be palpated at any of a number of sites as branches cross the bony orbit rim dorsocaudal or dorsolateral to the eye along the zygomatic arch. One or more sites are cleansed, and topical anesthetic is injected subcutaneously (SQ, 1-5 ml/site) via a 20- to 25-gauge needle; the needle size and amount injected depend on the patient’s size. Nerve branches may not be palpable in adult cattle, but the palpebral nerves can be anesthetized as part of the Peterson Nerve Block (Figure 13-1). A 12-cm needle is inserted subcutaneously at the angle between the frontal and temporal processes of the zygomatic bone. This site is bounded by the zygomatic arch ventrally, the supraorbital process rostrally, and the coronoid process of the mandible caudally. The needle is directed caudally along the zygomatic arch and 10-20 cc of local anesthetic is infiltrated as the needle is advanced.

Figure 13-1 Peterson Nerve Block: a 12-cm needle is inserted subcutaneously at the angle between the frontal and temporal processes of the zygomatic bone. This site is bounded by the zygomatic arch (Z) ventrally, the supraorbital process (S) rostrally, and the coronoid process (C) of the mandible caudally.

Complete lower lid akinesia can be difficult to achieve in ruminants, and although specific nerve blocks have been described, the author prefers to use a 20- to 22-gauge spinal needle (7-12 cm) inserted 1 cm ventral to the lateral canthus and directed medially through the lower eyelid to diffusely infiltrate local anesthetic throughout the lower eyelid. Before injection, topical anesthesia is applied to the ocular surface, and the lower eyelid is supported with finger pressure applied from inside as the needle is advanced, thus also protecting the globe.

Complete akinesia and analgesia of the eye and orbit may be necessary in some cases. A Peterson nerve block can be used or a retrobulbar block can be performed. Pearce et al. showed greater distribution of anesthetic around target nerves and muscles with the retrobulbar block.

TOPICAL ANESTHESIA AND MEDICATION

Although some ruminants are surprisingly tolerant of eye examinations, the use of 0.5% proparacaine solution and other topical anesthetics are essential for certain ophthalmic procedures that require extensive touching or manipulation of the globe or conjunctiva. Topical anesthetic agents cause mild stinging upon installation and hyperemia of the conjunctiva and are mildly toxic to the corneal epithelium, thus resulting in a mild, diffuse corneal epithelial thickening and faint, diffuse fluorescein uptake after topical anesthetic administration. Complete external examination of the eye, including fluorescein staining, should always be performed before anesthetic installation. A repeated administration of topical anesthetic every 15 to 30 seconds for 3 to 5 minutes greatly enhances the depth of topical anesthetic.

Application to the eye of topical anesthetics or any other ocular solutions is most easily performed by gently spraying the medication or solution onto the surface of the eye. This technique conserves costly ophthalmic medications, can often be performed without touching the patient’s eyelids, and is very hygienic. If the spray device is kept clean, it can be used repeatedly over many days while maintaining sterility of the stock bottle. A very effective “squirt gun” can be made by drawing 1 to 3 ml of the ophthalmic stock solution into a tuberculin or 3-cc syringe. A 25-g needle attached to the syringe is removed from the needle hub after the syringe is filled by grasping it between index finger and thumb and bending it until the needle breaks off the hub. The end of the hub is still sharp, so the hub should not be held too close to the patient’s eye. The administrator’s hand should rest somewhere on the patient’s head during administration so that the hand will move away simultaneously to inadvertent movements of the patient’s head during spray administration and the patient’s eye will not bump the hub. A test spray before administration will ensure the medication is coming straight out of the syringe and is not being diverted to the side as a result of bending during needle removal.

TRANSPALPEBRAL OCULAR LAVAGE APPARATUS

The transpalpebral catheter can be an extremely valuable adjunct to topical ocular therapy in ruminants, notably bulls that are otherwise unsafe to treat. The devices are readily available through commercial suppliers^* or can be easily fabricated from polyethylene tubing (Figure 13-2). Medication infusion pumps can be attached to the catheters to help alleviate some handling of intractable patients, especially those with severe ocular disease that might need medication as often as every hour.

Figure 13-2 Materials necessary to make a transpalpebral ocular lavage apparatus.^*

The patient is sedated, and the skin at the exit point of the catheter in the area of the dorsolateral orbit rim is cleansed. The upper eyelid is paralyzed as described above and 3 to 5 cc of local anesthetic are infiltrated subcutaneously at the planned exit site. The tubing is secured within a hubless needle or onto a wound drain insertion needle. The needle tip is securely cushioned in the tip of the surgeon’s index finger, and the needle with tubing inside is held in the same palm. The surgeon’s hand is turned so the index fingernail is toward the cornea and is inserted in the palpebral fissure. The finger with the needle then pushes dorsally until it is touching the inside of the orbit rim (through the palpebral conjunctiva). The opposite hand should simultaneously pull the upper lid out from the globe and over the inserting finger before the needle is advanced from the fingertip to ensure the needle tip does not “buttonhole” a conjunctival fold close to the lid margin, which could prevent proper blinking after the tube is secured. The lid is released, and the same hand is used to push the needle-tubing unit through the upper lid staying just rostral to the bony rim. The tubing is carefully pulled through with the needle until the footplate resistance is felt, taking care that the footplate remains inside the conjunctival sac and is not pulled into the subcutaneous tissues of the dorsal eyelid. At this point, the eyelid should be manipulated to ensure that it moves freely and is not caught on the tubing. Small pieces of waterproof adhesive tape (“butterflies”) are placed around the tube and sutured to the skin just adjacent to the exit point from the lid to prevent retrograde movement of the tubing and footplate into the conjunctival sac. Cyanoacrylate glue is applied over the tape and tube, further securing it to the skin (Figure 13-3). Additional adhesive tape butterflies are placed along the length of the tubing as needed.

Figure 13-3 Four-year-old Angus bull with homemade transpalpebral ocular lavage apparatus consisting of size #190 polyethylene tubing with footplate flange. This was made by warming tubing over a match flame until it was softened; the tubing was then pressed gently against a metal surface. Footplate size and angulation of the tubing are easily customized.

CONGENITAL

Common congenital abnormalities of the orbit and globe in ruminants include microphthalmos (a smaller-than-normal eye usually with multiple associated ocular defects) and strabismus (Figure 13-4). Patients with microphthalmos (Figure 13-5 A and B) have correspondingly small orbit bones that will not develop normally. Patients with microphthalmos may have associated cardiac, abdominal wall, or caudal spinal closure defects, and a careful physical examination is warranted. Culling may be indicated; a heritable component has been reported in some dairy breeds. Microphthalmos and a wide spectrum of blinding and nonblinding ocular anomalies such as cataracts (Figure 13-6) can occur with chronic vitamin A deficiency in pigs.

Figure 13-4 A 3-day-old Hereford calf with hydrocephalus, variable strabismus and nystagmus, cardiac and vertebral defects.

Figure 13-5 A, Two-week crossbred piglet with bilateral microphthalmos. Piglet was born to a sow that was fed doughnuts and was severely vitamin A-deficient. B, Calf with microphthalmos. Other congenital abnormalities were found in this Jersey calf: wry tail and ventricular septal defect.

Figure 13-6 Three-week-old crossbred piglet with microphakia, cataract, and other congenital ocular anomalies. Piglet was born to a sow that was fed doughnuts and was severely vitamin A-deficient.

Unilateral or bilateral congenital strabismus of variable degree and direction may be seen in any species and may be seen associated with other physical and neurologic defects. Bilateral convergent strabismus (esotropia, Figure 13-7 A and B) with or without exophthalmos and nystagmus occurs in dairy cattle and may progress with age. Visual acuity is variable; the condition has been proven to be inherited in some dairy breeds and culling of affected animals may be indicated. If vision is impaired, affected animals may fail to thrive and have difficulty negotiating their environments.

Figure 13-7 A, A 4-week-old female Holstein calf with severe esotropia and a constant “star-gazing” head carriage was unable to walk without stumbling and could not eat from the ground. B, Dorsal oblique and lateral rectus muscle shortening procedures were performed with resultant marked improvement in the head position, vision, and behavior. The calf was maintained as a pet and was not bred. Such procedures are best referred to specialists.

EXOPHTHALMOS

Exophthalmos in adult cattle is usually attributable to either inflammatory disease or neoplasia. A simple history and clinical presentation can often differentiate between these two broad categories. Inflammatory causes of exophthalmos (foreign body, cellulitis, sinusitis, infected tooth, myositis, etc.) are usually peracute to acute in onset, with the patient exhibiting marked pain when the affected eye is retropulsed into the orbit and when the jaw is opened (Figure 13-8). Affected animals are often febrile, depressed, and reluctant to eat. Abnormal ipsilateral nasal odor and discharge may be present with concurrent sinus involvement. In contrast, exophthalmos due to orbital neoplastic diseases is of slower onset, and the patient is rarely in discomfort except in cases of exposure damage to the cornea. Exophthalmos should be distinguished from glaucoma (rare in ruminants) and proptosis (protrusion of the eye from the orbit usually due to trauma). In a ruminant, an eye protruding from its orbit associated with trauma often carries a grave prognosis and is usually associated with other craniofacial injuries and possibly neurologic signs. A proptotic eye may require enucleation if it is ruptured or extensive extraocular muscle avulsion exists. Regardless of cause, an exposed eye requires immediate and frequent cleansing and moistening. The eye and periocular tissues can be moistened in an emergency with sterile saline, sterile eye wash or with any number of contact lens solutions until medical attention is available.

Figure 13-8 Left unilateral exophthalmos in a cow.

ORBITAL INFLAMMATION AND CELLULITIS

As stated previously, orbit inflammatory disease in cattle usually has peracute to acute onset and may be caused by foreign body penetration, puncture wounds, sinusitis, or extension of a severe infection in the eye (panophthalmitis). Puncture wounds and foreign bodies can enter the orbital space through the facial skin, palpebral fissure, or mouth; all of these areas should be examined carefully, if possible, during the physical examination. However, examination of the oral cavity may be difficult or impossible because of the pain from opening the mouth. Pain with jaw movement may be extremely severe and result in complete anorexia in some patients. The pain is only rarely attributed to temporomandibular joint disease and is more likely a result of movement by the coronoid process of the mandible compressing the retrobulbar tissues. Adjacent muscles of mastication may also be inflamed. Additional physical examination findings may include fever, anorexia, depression, mild-to-severe exophthalmos with possible exposure keratitis, periorbital swelling, and pain (Figure 13-9). Inspection and manipulation of wounds or draining tracts may reveal the presence of a foreign body. Abnormal ipsilateral nasal odor and discharge may be present with concurrent sinus involvement; sinus swelling may be evident and sinus resonance after percussion may be reduced or absent. Ultrasound and radiographic examinations are helpful in locating foreign objects and ruling out fractures, sinusitis, lumpy jaw, or a large mass such as a tumor. Fistulograms can be performed if draining tracts are present. A tissue aspirate for culture and cytology can be useful to confirm the presence of bacteria. Additional information regarding diagnosis and treatment of sinus disorders can be found in Chapter 9.

Figure 13-9 Orbit cellulitis with severe secondary exposure keratitis caused by a wooden foreign body found in the retro-bulbar tissues in a cow.

Treatment is directed at protecting the cornea, treating inflammation, and correcting the reason for cellulitis. The cornea is treated with sterile artificial tear ointments as often as needed to maintain corneal lubrication; if corneal ulcers are present, standard medical or surgical ulcer treatment is indicated according to the severity of the ulcer. Ophthalmology texts should be consulted for specifics.

Orbit inflammation can be managed with hot packs 4 to 6 times a day, broad-spectrum antibiotics (based on bacterial sensitivity results) and antiinflammatory drugs. If the inflammation persists, surgical drainage may be necessary. Usually, over time, the swelling will localize and ventral drainage can be established. It may be possible to localize a fluid pocket by palpation or ultrasound. The site should be prepped and aspirated with aseptic technique. Ventral drainage is established while vital structures are avoided. Most orbital abscesses in cattle harbor Arcanobacter pyogenes and parenteral penicillin therapy is appropriate.

ORBITAL NEOPLASIA

An adult dairy cow with unilateral or bilateral exophthalmos of subacute to chronic onset is most likely lymphosarcoma (Figure 13-10A and B). Other orbital neoplasias are rare but do occur, primary to the orbit or as extensions from adjacent tissues. Excessive orbital fat or orbital fat prolapse (Figure 13-11A and B) should be ruled out by palpation, cytologic sampling, or biopsy. If a biopsy is performed, the conjunctiva must be closed over fat or extensive orbit fat prolapse can occur. Digital palpation of the retrobulbar area through the palpebral fissure after application of topical anesthesia is a useful adjunct examination (Figure 13-12). Orbital fat is soft, fluctuant and nonpainful to palpation; inflammatory lesions usually are painful and firm while lymphosarcoma or other neoplasias are nonpainful but firm.

Figure 13-10 A, A 7-year-old Holstein with subacute, unilateral exophthalmos. B, Orbit aspirate of lesion, showing typical appearance of lymphosarcoma. Neoplastic cells are predominantly large with a high nuclear to cytoplasmic ratio and a moderate variability to nuclear and cytoplasmic size. Several nuclei contain very prominent nucleoli. Centrally, a neoplastic cell is undergoing mitosis.

Figure 13-11 A, Orbital fat prolapse in an adult Shorthorn cross. B, Close-up view.

Figure 13-12 Digital palpation of palpebral fissure.

A complete physical examination should be performed—including careful cardiac auscultation and palpation of peripheral lymph nodes. Rectal examination is done with particular attention paid to uterine palpation and evaluation of regional lymph nodes. In some cases, the orbital mass or swelling may be felt adjacent or caudal to the globe by palpation posteriorly using a finger placed within the palpebral fissure after application of topical anesthesia. Fine needle aspiration of orbital tissues using a 20- to 22-g 7- to 12-cm needle with or without ultrasound guidance may be diagnostic (see Figure 13-10B). Serologic testing may be performed to assist in diagnosing lymphosarcoma.

Cows affected with lymphosarcoma usually die within 3 to 6 months, but a cow in late gestation may survive sufficiently long to deliver a healthy calf. In such cases palliative treatment to protect the eye and reduce ocular pain from exposure may be indicated. If the exophthalmos is mild and only slowly progressive and if parturition is imminent, topical artificial tear ointments 6 to 8 times a day may suffice.

Moderate, progressive exophthalmos or a longer time to parturition may require protection of the globe(s) by permanent complete tarsorrhaphy (Figure 13-13). After sedation and application of local and topical anesthesia, the 2- to 3-mm–wide eyelid margin is trimmed off and discarded. Lids are closed with 3-0 to 4-0 absorbable sutures in the fibrous tissue layer of the eyelid (tarsal plate) and subcutaneous tissues with or without skin. If exophthalmos is severe, enucleation (Figure 13-14A) or orbit exenteration (Figure 13-14B) may be recommended. In rare instances in very valuable cattle, an evisceration may be performed before placing a prosthesis (Figure 13-14C).

Figure 13-13 Permanent tarsorrhaphy on an 8-year-old Jersey 3 weeks prepartum.

Figure 13-14 A, Diagrammatic representation of enucleation. B, exenteration, and C, evisceration.

(Reprinted with permission from Slatter D: Fundamentals in veterinary ophthalmology, ed 3, Philadelphia, 2001, WB Saunders.)

PREPARATION OF PERIOCULAR TISSUES

Individual surgeons may have strong personal preferences for the type of tissue cleansing and preparation done before surgery, but some basics about periocular surgical preparations should be emphasized. Of utmost importance are protection of the eye and use of prep solutions that do not cause irritation or damage to the eye(s).

Sterile artifical tear ointments are used to protect the cornea before preparation procedures. However, ointments should never be used perioperatively if an intraocular procedure is planned. If artificial tear ointments are not used during preparation, an anesthetized patient’s eyelids should be manually closed whenever they open, and sterile saline or collyrium should be applied frequently to the cornea to prevent corneal desiccation.

Removal of hair from any surgical field is standard presurgical protocol but requires particular care near the eye. Some surgeons do not remove any hair at all before intraocular surgery because of their concern that small pieces of hair may not be completely rinsed from the conjunctival fornices and may enter the open eye during surgery. Other surgeons clip only long or dirty periocular hairs with scissors but do not use electric clippers or razors out of concern for damage and irritation of the sensitive skin of the eyelids. Using care and sharp clipper blades, an experienced surgeon can clip periocular hair without trauma to the patient. Chemical depilatories must not be used near the eye; waxes may cause eyelid swelling and irritation and damage to the eye surface if carelessly applied.

Extreme care must be taken to ensure all hair particles are removed from the conjunctival sac after clipping, particularly if the eye is to be opened during a planned intraocular surgery. A 20- to 22-g, 5- to 7-cm soft, flexible catheter can be attached to a 12- to 20-cc syringe filled with sterile saline and used to repeatedly lavage all of the recesses of the conjunctival sac and the bulbar surface of the membrane nictitans. The author uses the same syringe to thoroughly flush the upper and lower nasolacrimal puncta and ducts. A significant amount of exudate and debris residing within the nasolacrimal duct system can reenter the conjunctival sac during surgery and should be removed before any eye surgery.

Surgical prep detergents, such as povidone-iodine detergent scrubs, alcohol, hydrogen peroxide and chlorhexidine diacetate, should never be used near the eyes or anywhere there is a chance they could drip or run into the eyes. Chlorhexidine diacetate in particular can cause severe ocular disease and should be avoided. Povidone-iodine solutions (10% solution in sterile saline or sterile water) are acceptable sanitizers for the periocular skin. Five or more centrifugal scrubs beginning at the eyelid margins and circling outwards are performed alternating with sterile saline scrubs or rinses. Finally, povidone-iodine should be applied and left in place for several minutes.

Choices of surgical drapes are as varied as the surgeons that use them. The eye can be draped with a standard four-drape technique, a fenestrated drape, or specialized, nonfenestrated, self-adhesive eye drapes. The latter are most highly recommended for any type of intraocular surgery because their fenestration can be customized and the adjacent drape adheres beautifully to the lids and periocular facial skin and hair.

BASIC OPHTHALMIC SURGICAL INSTRUMENTATION

Minimal investment is required to purchase the few additional instruments necessary to perform the surgical procedures discussed in this chapter that would not be found in a standard soft tissue surgical pack.

A basic ophthalmic instrument set (Figure 13-15) suitable for eyelid, conjunctival, and simple corneal surgery includes: small towel clamps such as Schaedel’s; Bard-Parker #9 blade handle; small Mayo scissors; general suture scissors; small stitch scissors (Westcott); forceps such as Adson or Brown-Adson suitable for eyelid surgery in large ruminants; Allis tissue forceps useful during entropion surgery; forceps such as fine Bishop-Harmon suitable for eyelid surgery in small ruminants; 4 Hartman curved mosquito hemostats; four 6″ Kelly hemostats; Derf or other small needle holder; large, curved utility scissors with serrated blade (enucleation in adult cattle); small curved and straight Metzenbaum scissors; small ophthalmic scissors such as a Stevens or Westcott tenotomy scissors, a small needle holder appropriate for 5-0 to 6-0 or smaller suture such as an 11 mm, nonlocking, curved Castroviejo needle holder; small tissue forceps suitable for cornea and conjunctiva, such as 0.4 mm Colibri-type 1 × 2 or delicate 1 × 2 Bishop-Harmon; double-ended Martinez corneal dissector; Snellen or Desmarres lid forceps with solid lower plate; simple eyelid speculum, such as a 20-mm Barraquer; Desmarres lid retractors (2); and nonlinting sponges.^* A binocular magnifying loupe (see Figure 13-28A) is extremely useful for eye surgery in the field or hospital if better magnification systems are not available. Suture material appropriate for eye surgery should be available, including 4-0 silk for stay sutures and procedures such as tarsorrhaphies. Synthetic absorbable sutures, 4-0 to 7-0, with the smallest size needle available are suitable for corneal repair in smaller ruminants.

Figure 13-15 A basic ophthalmic instrument set.

Figure 13-28 A, Magnifying loupe and no. 15 blade used to excise squamous cell carcinoma from the lateral limbus in a cow before beta radiation. Q-tips are used in the opposite fornix to position the globe. B, Use of the strontium applicator.

ANESTHESIA

In many instances, these procedures can be done in a standing, sedated (10-20 mg xylazine IV) food animal. However, general anesthesia is certainly advantageous when a cow is fractious or has a severe lesion or for humane concerns.

If the surgery is to be done standing, adequate restraint with local and topical anesthesia is essential. The face is clipped and prepared for aseptic surgery. The cow is put in a chute or stanchion, and the head is tied snugly to the side. Local anesthesia has been described in a variety of ways. If a transpalpebral technique is used, local anesthetic should be deposited circumferentially 4 to 5 cm from the eyelid margins. To anesthetize the eye there are a few options. One possibility is to deposit 35 ml of 2% lidocaine in the retrobulbar cone using an 8.75 cm (3½ in) 18 gauge needle. Another way to provide analgesia to the retrobulbar area is with a Peterson nerve block (described under Eyelid Akinesia; see Figure 13-1). It is also possible to deposit anesthesia at 4 sites around the eye (Figure 13-16).

Figure 13-16 Injection sites for local anesthesia before transpalpebral enucleation in cattle. Five to 10 ml of lidocaine is injected at each site to produce anesthesia and proptosis.

(Reprinted with permission from Slatter D: Fundamentals in veterinary ophthalmology, ed 3, Philadelphia, 2001, WB Saunders.)

TRANSPALPEBRAL ENUCLEATION

After appropriate preparation and thorough nasolacrimal duct lavage, the eyelids are sutured together or clamped. A circumferential incision 1.5 cm away from the eyelid margin is made through the skin into the subcutaneous tissues of the eyelid but not through the conjunctiva. The lateral and medial canthal ligaments securing the eyelids to the orbit bones are transected. As traction is applied to the freed eyelids, dissection is continued caudally toward the orbit rim taking care to stay external to the conjunctival sac, which should remain closed. Close to the orbit rim the deep fascia forming the orbital septum is penetrated, and the extraocular muscles and tissues within the orbital cone can be visualized. In cases of panophthalmitis or when enucleation is necessary because of severe orbital cellulitis, the extraocular muscles and the other soft tissues within the periorbita should be excised as widely as possible or transpalpebral exenteration should be performed. Significant bleeding will occur in these cases. In other cases in which infection of the eye is not a concern, intraoperative bleeding is considerably lessened if each rectus muscle is transected at its tendon of insertion on the sclera. As each muscle is encountered, one blade of a Metzenbaum scissor is inserted between the muscle and sclera, and the scissor is pulled anterior toward the limbus before cutting, thus ensuring that the transaction occurs through muscle tendons, which bleed much less than the muscle belly. The dorsal and ventral oblique muscle insert deep to each respective rectus muscle and may have very short tendons of insertion. They are transected close to the sclera. After rectus and oblique muscle transection, the globe is grasped, and gentle traction is applied, thus making the retractor muscles that form a cone around the optic nerve easier to visualize. Traction on the globe should be minimal to decrease vagal nerve stimulation and avoid potential damage to the optic chiasm. With gentle medial traction on the globe, the surgeon should attempt to “strum” the optic nerve-retractor muscle cone using an approach from the dorsolateral side of the orbit. Once the location of the nerve has been confirmed, the same hand is used to position the blades of a large curved serrated utility scissor around the cone. The cone is rarely visualized directly because of variable amounts of orbital fat and hemorrhage; therefore digital palpation is important. One or two cuts of properly placed scissors will almost completely free the globe. It is held in one hand, and the remaining medial attachments severed. The entire third eyelid should be removed at this time. To prevent postoperative lacrimocele formation, it is recommended the lacrimal gland located in the periorbita of the dorsolateral orbit ventral to the orbit rim be surgically removed as well.

Meticulous hemostasis during enucleation is time-consuming, and in most cases not necessary. In the enucleation technique described above, no attempt is made to ligate the optic nerve and muscle cone because ligatures placed around the optic nerve and muscle cone are difficult to place, usually slip, result in tissue trauma in the process, may increase vagal stimulation, and can act as a foreign body inciting an inflammatory response. The orbit is packed with sponges and pressure is applied as closure commences, but all sponges are removed before the subcutaneous tissues are completely closed. An absorbable suture (no. 2-0) is used to close subcutaneous tissues; a nonabsorbable suture is used in the skin (Figure 13-17). A pressure bandage is applied for 24 hours and the pressure of the sutured incision combined with the bandage will almost always be adequate to stop hemorrhage. Drains are not necessary unless there is preexisting infection. Antibiotics should be given for 5 to 7 days after surgery.

Figure 13-17 Closure of the surgical site following enucleation in a cow.

TRANSPALPEBRAL EXENTERATION

Exenteration means the globe and as much of the ocular contents as possible are removed. For exenteration surgery, the dissection is done outside the extra ocular eye muscles and conjunctiva, all of which are removed with the globe (Figure 13-18A). For extensive SCC in cattle, this may be the preferred procedure.

Figure 13-18 A, A periocular incision is made and dissection performed outside the extraocular muscles to the orbital apex. B, The optic nerve and associated vessels are clamped, ligated, and transected.

(Reprinted with permission from Slatter D: Fundamentals in veterinary ophthalmology, ed 3, Philadelphia, 2001, WB Saunders.)

The same transpalpebral approach is recommended. The plane of dissection is against the bony orbit. All extraocular eye muscles are removed along with a substantial portion of the optic nerve (Figure 13-18B). If possible, a subcutaneous tissue layer is closed. A drain may be necessary for 48 to 72 hours. Skin is closed routinely.

EVISCERATION

Evisceration is the removal of the contents of the globe, leaving the cornea, sclera, extraocular muscles and adnexal structures in place. This is done before placing a silicon cosmetic prosthesis into the corneoscleral shell.

ACUTE HEAD TRAUMA WITH EYE INJURIES

Traumatic injuries to the head, orbit or globe are common in the ruminant. Serious head, ocular and orbital trauma are always emergencies. After injury, the patient’s head is restrained, if possible, to avoid additional, self-induced injury that occurs from rubbing the eye and periocular area against the chute, stanchion, stall, wall or forelimb. Examination or manipulation of the ocular or periocular tissues is avoided until adequate restraint and tranquilization are completed.