Surgery of the Eye

Chapter 17

Surgery of the Eye

General Principles and Techniques

Preoperative Concerns

Some periocular and ocular procedures are performed by general practitioners; however, many patients are referred to veterinary ophthalmologists. Surgical conditions commonly managed by general practitioners include emergency procedures (i.e., traumatic proptosis, eyelid lacerations, and corneal ulcers) and entropion or ectropion repair, tumor removal, and enucleation. Complicated or severe periocular diseases, corneal problems and intraocular procedures should be performed by persons with specialized training in veterinary ophthalmology.

Successful ophthalmic surgery requires a correct diagnosis, appropriate choice of surgical procedure and materials, attention to detail, and proper instrumentation and equipment. Each animal should be thoroughly evaluated for concurrent and contributing abnormalities. This evaluation should include a complete physical examination and appropriate diagnostics. Complete blood count (CBC) and serum chemistry panel are typical preanesthetic tests in older patients (see Chapter 4). If a heart murmur is present in an older patient, thoracic radiographs, echocardiography, and/or electrocardiography (ECG) may be appropriate, depending on the patient. Ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI) are helpful in defining orbital and retrobulbar disease. The normal flora of the conjunctival sac, cornea, eyelids, lacrimal ducts, and tarsal glands includes potential pathogens, so perioperative antibiotics are reasonable. Periocular tissues rapidly become inflamed and swollen when manipulated. This swelling can be minimized by preoperative systemic administration of non-steroidal antiinflammatory drugs (NSAIDs).

Preparation OF the Surgical Site

Liberally apply artificial tears or antibiotic ophthalmic ointment in both eyes to protect the corneas before clipping and preparing the skin and periocular tissue. Clip an area around the surgical site using a No. 40 clipper blade and an electric clipper. Do not use a vacuum to remove the clipped hair; rather, gently brush it away or use adhesive tape to collect it to prevent damage to the delicate eyelid tissue. Irrigate the conjunctival sac with eye wash or LRS to remove excess hair. Using gauze, cotton-tipped applicators or soft surgical sponges soaked in a diluted antiseptic solution like 10% povidone-iodine, prepare the skin for aseptic surgery. Do not use chlorhexidine, soap, detergents, or alcohol; these may damage the cornea. After surgery, protect the surgical site from rubbing, pawing, or scratching by administering analgesic and, applying a hard plastic protective E-collar.

Anesthetic Considerations

General anesthesia usually is required for ophthalmic surgery in small animals. Although topical anesthetics and minimal sedation are commonly provided with some procedures in human patients, the likelihood of further trauma to the eye is greater in the veterinary population when only mild sedation is used. The need for an immobile eye in a geriatric patient can present an anesthetic challenge. If the animal is older than 5 to 7 years, even with a physical status of I or II, CBC, comprehensive serum biochemistry profile, and urinalysis should be done. A careful physical examination should be performed with attention paid to auscultation of heart and lung sounds. Dogs or cats with cardiac murmurs presenting for elective surgery may need to undergo cardiac work-up before receiving a general anesthetic.

In many patients, induction needs to be performed in a manner that minimizes increases in intraocular pressure (IOP). Preoperative sedatives such as a benzodiazepine with an opioid can be helpful in achieving quiet, struggle-free induction (Table 17-1). Induction with a face mask may place pressure on or near the eyes and should be avoided. Propofol causes a decrease in IOP and is often the drug of choice for induction. Although etomidate can cause a decrease in IOP, if myoclonus occurs, IOP may sometimes increase. This is less likely to occur (but is still possible) when a benzodiazepine is administered beforehand. Use of ketamine in ophthalmic patients is controversial, and debate continues as to whether it increases IOP. Regardless, ketamine causes eye movements that are undesirable; thus its use as an induction agent is not recommended in surgeries where globe motion is problematic.

If possible, induce the animal in a quiet environment, where monitors are immediately available after intubation. With these patients, it is important to monitor blood pressure, heart rate, respiratory rate, ECG, end-tidal carbon dioxide (EtCO2), and pulse oximetry. Because the head is draped and often is turned away from the person administering anesthesia, simple monitoring techniques such as evaluating palpebral reflex, ocular movements or jaw tone often are not possible. Monitoring blood pressure, heart rate, respiratory rate, and EtCO2 can provide information on whether the anesthetic depth is adequate or appropriate. If neuromuscular blocking (NMB) agents are used, measuring EtCO2 is even more imperative to evaluate ventilation. A pulse oximeter with a sensor that can be secured to the tail is helpful because repositioning a sensor on the tongue may be difficult once surgery has begun. Masimo (Irvine, Calif.) makes a sensor for placement on the forehead of human neonatal patients that works well when secured to the underside of the base of the tail. Occasionally, hair must be removed before placement.

Monitoring of heart rate and ECG is very important during ophthalmic surgery because of the potential for initiation of the oculocardiac reflex. This reflex consists of a trigeminal (V) afferent and a vagal (X) efferent pathway. Traction on extraocular muscles or pressure on the eye itself can cause severe bradycardia; however, ventricular tachycardia, premature ventricular contractions, ventricular fibrillation, and asystole also may occur. If this reflex happens, manipulation of the eye must stop until a normal heart rate returns. If necessary, atropine (0.02-0.04 mg/kg IV) or glycopyrrolate (0.005-0.01 mg/kg, IV) may be given. Because atropine has a faster onset and an increased cardiac effect, it is the drug of choice in cases of severe bradycardia or sinus arrest. If the oculocardiac reflex persists, lidocaine may be injected into the rectus muscles to prevent transmission along the trigeminal afferent fibers. Atropine or glycopyrrolate has been used preoperatively to prevent this reflex; however, many patients are elderly and intolerant of tachycardia. For cardiac or geriatric patients, it may be reasonable to avoid giving an anticholinergic up front. Have glycopyrrolate or atropine available in the operating room (OR) with the appropriate dose already calculated, so it may be given rapidly IV if necessary.

Once the patient has been intubated, careful positioning is needed. Be sure to secure the endotracheal tube because the airway will be difficult to reach during the procedure. If there is concern about bending or kinking the endotracheal tube owing to positioning of the head, a wire-reinforced tube should be used. Because tear production decreases substantially during general anesthesia, the opposite eye should be lubricated every 2 hours. Reduced tear production may persist for 24 hours postoperatively, so continued application of a topical lubricant such as ophthalmic ointment for 1 to 2 days postoperatively is recommended. Also, make sure there is no pressure on the opposite eye if the patient is in lateral recumbency.

Pain and subsequent sympathetic response caused by ophthalmic surgery are considerably less than those induced by intraabdominal, orthopedic, or thoracic surgery. Therefore, a lighter anesthetic would be desirable, except that movement while under the anesthetic can cause a catastrophic injury to the eye. The anesthetic depth must be sufficient, so that the eye does not move. To accomplish this without marked hypotension, make sure the patient is hydrated before anesthesics are administered. In hypotensive patients on the ideal anesthetic plane, small boluses (3-10 ml/kg) of IV fluids can be administered. Ophthalmic patients are often geriatric and less tolerant of fluid boluses secondary to underlying cardiac disease. Furthermore, vascular compliance may be diminished, which makes the geriatric patient further susceptible to the vasodilation effects of general anesthetics. To counteract this vasodilation and subsequent hypotension small doses of either ephedrine or phenylephrine can help maintain adequate blood pressure in those patients. Another choice is to utilize neuromuscular blockade or a retrobulbar block to achieve an immobile eye and a lighter level of anesthesia. Ventilation must be supported manually or mechanically in all paralyzed patients.

Nondepolarizing muscle relaxants such as atracurium or vecuronium may be used and are very predictable (Box 17-1). Both drugs have an onset of about 3 to 5 minutes and last 20 to 35 minutes. The difference between the two is mainly in how they are metabolized. Atracurium is metabolized in the blood by plasma esterases, but it also undergoes nonenzymatic degradation called Hofmann elimination. Vecuronium is metabolized by the liver and is excreted in bile and urine. Reduced doses are required when used in patients with kidney or severe liver disease. Cis-atracurium is a stereoisomer of atracurium that is completely metabolized by Hofmann elimination. It is safe to use in patients with liver or kidney failure. Pancuronium has a longer duration of action of approximately 30 to 45 minutes. A large fraction is excreted unchanged by the kidneys and the remainder is excreted in bile or metabolized by the liver. Patients with liver or kidney disease can have a prolonged elimination time. Pancuronium is unique in its selective cardiac vagal blockade, causing a temporary increase in heart rate after it is administered.

A nerve stimulator is required to evaluate return of muscle function when nondepolarizing muscle relaxants are used. At least one twitch is needed for safe reversal. If the muscle relaxant has not worn off such that at least one twitch has returned, it is possible that a full reversal dose may be given, but the patient may still be weak and partially paralyzed. When three to four twitches are present, the dose of the reversal agent may be reduced, thereby reducing side effects. Even with four twitches and a full 5-second tetany, 50% of the neuromuscular receptors may be blocked, warranting a reduced amount of reversal agent. After reversal and prior to extubation, the twitches should be checked again to ensure adequate muscle strength. Atracurium is best reversed with edrophonium and atropine. Vecuronium and pancuronium are best reversed with neostigmine and glycopyrrolate. Anticholinergics are added to avoid potentially severe bradycardia and sinus arrest.

Whenever possible, extubation needs to be done in a quiet environment to avoid excitement and possible increases in IOP. Because of their sedating and analgesic effects, opioids are helpful in the postoperative period. Application of topical analgesics (i.e., proparacaine, lidocaine, or carbocaine) once after surgery reduces pain and blepharospasm. Chronic use of topical analgesics is toxic to the cornea and should be avoided. Because vomiting causes increased IOP, antiemetics may be needed prior to extubation or immediately afterward.

For enucleation, local adjunctive anesthesia may be considered preoperatively or intraoperatively to improve analgesia. Local anesthetics have been given as a retrobulbar injection (Myrna et al, 2010). To facilitate placement, this block may be placed at the end of surgery or after induction of general anesthesia. Retrobulbar injections may be given via an inferotemporal approach through the eyelid skin. To perform, use a 1.5 inch 22 g needle that is straight, or make a 20 degree bend midway in it. Point the needle through the skin just above the lower orbital rim at the junction of the lateral and middle thirds of the eyelid, and advance it through the periorbital fascia. Then, tilt the needle slightly dorsally and medially toward the orbital apex about 1 to 2 cm. Epinephrine may be included in the injection to improve hemostasis, but monitor heart rate as tachycardia may result.

Inherent risks of retrobulbar injection are potentially significant and include globe perforation, direct damage to the optic nerve, IV injection, retrobulbar hemorrhage, extraocular muscle myopathy, and intrathecal injection. An intrathecal injection leads to rapid loss of consciousness in an awake patient. Patients already under anesthesia will stop breathing and will need to have ventilator support until the intrathecal injection wears off. Another complication is an intraarterial injection, which may cause an immediate seizure. Systemic toxicosis is unlikely, but maximum doses should be checked and not exceeded in very small animals. Retrobulbar blocks without epinephrine are often performed after enucleation and closure of the orbital septum because presurgical blocks might increase surgical bleeding.


Potential pathogens in the normal flora of the conjunctiva, eyelids, cornea, lacrimal glands, and tarsal glands are one reason why perioperative antibiotics are often administered to animals having periocular or ocular surgery. Most often, the bacteria recovered from periocular flora are Staphylococcus and Streptococcus spp., and infected corneal ulcers can involve either Gram-negative or Gram-positive bacteria. Ophthalmic preparations containing bacitracin, polymyxin, and neomycin are often chosen for perioperative prophylaxis. Other frequently used topical antibiotics include erythromycin and oxytetracycline. Generally, systemic antibiotics are given for eyelid, intraocular, and orbital surgeries, whereas topical antibiotics are used for conjunctival and corneal surgeries. Systemic antibiotics should be given so that therapeutic blood levels can be assessed at the time of surgery (see Chapter 9).

Surgical Anatomy

The eyelids and orbit house and protect the eye (Fig. 17-1). Eyelids are mobile folds of skin that block light and protect the cornea. The upper lid is slightly larger and more mobile than the lower lid. Upper and lower lids join at the medial and lateral canthus and are stabilized by the medial and lateral palpebral ligaments. The width of the opening between the lids is controlled by opposing groups of muscles; the orbicularis oculi muscle closes the palpebral fissure, and the fissure is widened by the levator palpebrae superioris, the pars palpebralis of the sphincter colli profundus, and smooth muscles of the periorbita. The upper and lower lacrimal puncta, which drain excess tears from the ocular surface to the nose and pharynx via the nasolacrimal duct, are located just posterior to the eyelid margin about 2 to 5 mm from the medial canthus. The lacrimal caruncle is located near the medial canthus. It projects fine, small hairs; has sebaceous glands; and may be pigmented. Long hairs known as cilia project from the upper lid skin, but the lower lid is devoid of cilia. A tuft of long tactile hairs is seen at the dorsal medial margin of the orbit; this corresponds to human eyebrows.

Glands in the lid margins are similar to glands found elsewhere in the skin. Sebaceous glands open into follicles of the cilia on the upper lid. Both upper and lower lids have specially modified sebaceous glands, called the tarsal glands (meibomian glands). Duct openings of these glands are found in a shallow furrow immediately rostral to the mucocutaneous junction. The tarsal glands produce the outermost oily layer of the tear film and usually are visible through the conjunctiva. Sometimes very fine hair originates from the tarsal glands. This condition is called distichiasis. Ciliary glands (apocrine sweat glands) secrete into hair follicles or sebaceous glands, or directly onto the lid margin.

The special mucous membrane on the inner aspect of the lids is called the palpebral conjunctiva. At the level of the orbital rim, the palpebral conjunctiva reflects onto the eye to become the bulbar conjunctiva. The palpebral conjunctiva has goblet cells, whereas the bulbar conjunctiva is thinner and is without goblet cells. Conjunctival goblet cells secrete mucin, which produces the innermost layer of the tear film. Lymphatic nodules are found throughout the conjunctiva but are especially prominent on the bulbar surface of the third eyelid. Lymphatic drainage from the conjunctiva empties into the parotid lymph nodes. The third eyelid arises as a fold from the ventromedial aspect of the conjunctiva. It is very mobile and is able to cover the entire anterior face of the cornea. A T-shaped piece of hyaline cartilage stiffens the third eyelid. The gland of the third eyelid, a mixed seromucous gland that contributes the middle aqueous layer of tear film, surrounds the base of the cartilage.

The orbit is the cavity containing the eye, fat and the ocular adnexa. The bony orbital margin (frontal, lacrimal, and zygomatic bones) encompasses approximately four-fifths of the orbit circumference; the remainder is completed by the orbital ligament. The orbital ligament is a thick fibrous band connecting the zygomatic process of the frontal bone with the frontal process of the zygomatic bone. Both the orbicularis oculi muscle and the lateral palpebral ligament attach to the orbital ligament. The medial wall and part of the roof of the orbit are bony (frontal, lacrimal, presphenoid, and palatine bones). Five foramina are present in the medial wall: optic canal, orbital fissure, lacrimal canal, and two small ethmoidal foramina. The optic canal is rostral in the orbit and is traversed by the optic nerve and the internal ophthalmic artery. The orbital fissure between the basisphenoid and presphenoid bones gives passage to the oculomotor, trochlear, abducent, and ophthalmic nerves; the anastomotic branch of the external ophthalmic artery; and the orbital venous plexus. The retractor bulbi muscle originates in the orbital fissure. The rostromedial continuation of the orbit is the lacrimal canal, through which the nasolacrimal duct travels. The nasolacrimal duct connects to the two canaliculi, whose two puncta are found at the medial canthus. A fossa for the lacrimal gland is present in the ventral surface of the zygomatic process of the frontal bone, where the orbital ligament originates. The lateral wall and floor are formed by soft tissue, the medial pterygoid muscle, the temporal muscle, and the zygomatic gland. The maxillary artery and nerve cross the floor of the orbit near its apex. Orbital fat is present at the caudal pole of the eye, surrounding the optic nerve with spaces between extraocular muscles. This fat serves as a cushion and permits rotation and retraction of the eye. Extraocular muscles insert on the sclera and function to rotate and retract the eye. These muscles include the rectus muscles (dorsal, ventral, medial, and lateral), the oblique muscles (dorsal and ventral), and the retractor bulbi muscle. The orbit, extraocular muscles, and other orbital structures are covered with fascia (periorbital, muscular, and bulbar).

The contents of the eye are surrounded by an external fibrous coat: the transparent, multilayered cornea; and the yellow-white, opaque sclera (Fig. 17-2). The two meet at the corneoscleral junction or limbus. The cornea is usually less than 1 mm thick and is covered by a precorneal tear film; it has four layers: (1) epithelium with its basement membrane, (2) stroma, (3) Descemet’s membrane (basement membrane of endothelium), and (4) endothelium. The white part of the eye has four layers: conjunctiva, episclera (vascular layer), sclera proper (collagen fibers and fibroblasts), and lamina fusca (collagen bundles that intermingle with choroids and the ciliary body). The sclera is covered anteriorly by the conjunctiva; posteriorly, muscles insert around vessels and nerves, which penetrate its surface. The middle or vascular coat is the uvea, which consists of three continuous parts: choroid, ciliary body, and iris. The iris is seen through the cornea and regulates the size of the centrally located pupil. The ciliary body is a thick circular mound at the level of the limbus, which regulates the shape of the lens. The folds of the internal surface of the ciliary body are the ciliary processes that produce aqueous humor. The choroid lines, and is firmly attached to, the sclera. The retina lines the internal surface of the choroid to the level of the ciliary process. The retina is the nervous coat of the eye. Zonular fibers attach the equator of the lens to the ciliary process. The lens is transparent and elastic.

The interior of the eye is divided into chambers. The posterior segment, located posterior to the lens, is filled with the transparent jelly-like vitreous body. The space between the cornea and the lens is filled with aqueous humor and is divided into two chambers. The anterior chamber is the space between the cornea and the iris, and the posterior chamber is a narrow space between the iris and the lens.

Surgical Techniques

Eyelid Laceration Repair

Lacerated eyelids are commonly associated with traumatic injuries such as bite wounds and automobile injuries. They should be repaired as soon as possible to protect the cornea and maintain an effective blink reflex. Healing of lid lacerations by secondary intention may result in considerable fibrosis and distortion of the eyelids and lid margin, and secondary scarring of the corneal surface. Direct reapposition is possible if one-third or less of the lid margin is missing. More extensive injuries require advancement flaps or grafts for repair. Preservation of the eyelid margin and its associated structures is essential for normal eyelid function. No matter how thin a flap of tissue has been created by a laceration running parallel to the eyelid margin, it should not be excised (Fig. 17-3). If these flaps do not survive, the eyelid margin can be reconstructed.

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.

Conjunctival and Corneal Lacerations

Conjunctival lacerations without eyelid lacerations rarely require surgical repair because they heal rapidly. They are allowed to heal by secondary intention after debris has been removed and topical antibiotics applied. Conjunctival sutures are not necessary. Apply broad-spectrum topical ophthalmic antibiotics such as neomycin/polymyxin/bacitracin to prevent infection.

Deep corneal lacerations (>50% corneal stromal thickness) and perforations are surgical emergencies, and surgery should be performed as soon as they are discovered. These surgeries require an operating microscope and thus are best referred to a veterinary ophthalmologist. If a specialist is not available and the perforation or laceration site has plugged with fibrin or iris, medical management should be considered to try to prevent infection or stabilize the site until it can granulate by corneal vascularization. If the perforation site leaks aqueous humor for longer than 24 hours, enucleation or referral for corneal repair may be required.

For corneal perforations, use eye solutions rather than topical ointments because ointments may cause severe uveitis if they are absorbed into the anterior chamber. Evaluate the intraocular structures for evidence of additional trauma. Remove superficial foreign material embedded in the cornea with irrigation, forceps, and minimal dissection.

Medical treatment of a corneal perforation or laceration includes topical antibiotics, atropine, and systemic antibiotics. Antibiotics should be broad spectrum (e.g., ofloxacin for Gram-negative coverage, cefazolin 50 mg/ml in LRS [refrigerate] for Gram-positive coverage [1 drop every 1 to 2 hours for 24 to 48 hours, then every 4-6 hours]) until the lesion has vascularized. Corneal vascularization starts to develop after 3 to 5 days and grows on average 1 mm/day, so healing of a corneal perforation can take several weeks. If corneal vascularization does not develop; internal eye infection occurs; or the perforation site enlarges and leaks, surgery is necessary to repair or remove the eye. Atropine administered topically will reduce cycloplegia and minimize posterior synechiae. Systemic antibiotics with broad-spectrum coverage should also be used to try to prevent the development of internal eye infection.

For superficial corneal lacerations, a soft bandage contact lens reduces corneal exposure and will produce increased comfort. Adjunctive treatment also includes topical use of a tissue adhesive (n-butyl cyanoacrylate or absorbable methoxypropyl cyanoacrylate monomer). Remove any corneal epithelium over the ulcer bed, and dry the surface of the cornea with cellulose sponges or air. Using a 23 or 25 g needle or a similar applicator, apply a small volume (1 drop) of adhesive directly to the wound in a smooth, thin layer. Apply a restraint collar such as a hard E-collar until the ulcer has healed, typically in 7 to 28 days. Soft E-collars might allow the patient to rub the eye on objects like the floor and furniture, and would not be effective protection.

Adhesive polymerization occurs within a few seconds, and the material becomes very hard. Tissue adhesive may be considered for deep ulcers, but the heat from drying can cause corneal perforation. The adhesive has low tissue toxicity, is bacteriostatic, and inhibits melting of corneal stroma. Adhesive is extruded (2 to 4 weeks) as the cornea heals.

imageConjunctival Flap

Conjunctival flaps are used to treat deep corneal ulcers, descemetoceles, and small sealed corneal perforations. Conjunctival flaps typically are harvested from the bulbar conjunctiva and are integrated into the cornea with healing over a few weeks; they provide a protective covering that brings blood vessels and fibroblasts to facilitate healing. The flap remnant typically leaves a heavy, opaque scar. Plan the flap so it is several millimeters larger than the defect it must cover.

Perform a Seidel test to determine if small full-thickness corneal lacerations have sealed by placing sodium fluorescein on the cornea; then, without irrigation, observe to see whether a clear river of aqueous humor is running through the fluorescein (this indicates that the corneal perforation is not sealed). If the cornea leaks, these cases are best referred to an ophthalmologist because repair typically requires use of an operating microscope.

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.

imageHood Flap

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.

image360-Degree Conjunctival 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.

The third eyelid may be displaced centrally with the conjunctival graft over the eye. After the conjunctiva has been dissected from the episclera, it should stretch easily over the corneal surface (Fig. 17-8, C).

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.

Third Eyelid Flap

Third eyelid flaps serve as physiologic bandages to support and protect the cornea after trauma. They are easier to create than conjunctival flaps but should not be used on deep corneal ulcers, descemetoceles or corneal perforations, which usually are fragile and require visual monitoring to direct aggressive medication management (see p. 294).

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.

Enucleation or Exenteration

Enucleation is probably the most common orbital surgical procedure performed in small animal practice. Common indications for enucleation include irreparable corneal or intraocular injury, unmanageable endophthalmitis, intraocular neoplasia, severe proptosis, and intractable uveitis. An additional indication might include painful end-stage glaucoma, although this can be treated with globe-sparing procedures (intrascleral prosthesis). All other options should be considered before enucleation is performed, particularly for sighted or potentially sighted eyes. However, under the right circumstances, enucleation can provide rapid resolution to chronic painful eye disease, at the same time eliminating the need for topical medications in the affected eye (Cho, 2008).

Exenteration is indicated for intraorbital neoplasia or ocular neoplasia that has extended beyond the globe. Owners may be resistant to either procedure, despite the fact that it may improve the animal’s quality of life.

Transconjunctival, transpalpebral, and lateral enucleation techniques are described here. The technique chosen should reflect the pathologic circumstances of the eye to be removed, patient anatomy, and surgeon preference. With all techniques, excessive traction on the globe and optic nerve should be avoided (particularly in cats) because traction on the optic chiasm during enucleation has been reported to result in permanent postoperative blindness in the remaining eye. Ligation or cautery of the nasolacrimal openings in the surgery site may be considered in brachycephalic dogs. Histopathologic evaluation of the globe and any other removed tissue of concern should always be performed.

The transconjunctival enucleation technique is commonly used. Advantages of this approach compared with other methods include reduced orbital tissue loss (reduced postoperative orbital sinking) and reduced intraoperative bleeding. However, this technique may not be preferred for infectious conditions of the anterior segment, such as severely infected corneal ulceration. The sterile surgical site may be exposed to a contaminated ocular surface, allowing for possible spread of infectious agents into the orbit. This situation is worsened by rupture of the cornea because intraoperative pressure on the globe may expel infected material from the eye. In these cases, transpalpebral enucleation may be a better choice, especially in dogs (Cho, 2008).

Transconjunctival Enucleation

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.

A variation of subconjunctival enucleation improves access to the posterior pole of the globe and may reduce traction on the optic nerve. Begin the procedure by making a lateral canthotomy, and remove the lid margins and nictitans. The remainder of the globe dissection proceeds as for subconjunctival enucleation, as described earlier. With lid margins and nictitans out of the way from the start, additional surgical space is available around the globe.

To improve postoperative cosmesis following enucleation, several techniques have been employed in addition to closure of the orbital septum, including orbital mesh placement, sphere implantation, a combination of the two, and tissue reconstruction. Placing an orbital meshwork is simple. A taut continuous pattern of 3-0 to 5-0 monofilament nonabsorbable suture (nylon or polypropylene) is placed with bites 2 to 4 mm apart in the periosteum of the anterior orbital rim. Meshwork may be placed both horizontally and vertically. All gauze that has been placed in the orbit should be removed before the final bites are placed.

To avoid postnucleation cysts, excise all palpebral and bulbar conjunctival tissues before closing the lids. Close the lids in three layers. The orbital septum is the connective tissue layer lining the eyelid that originates from the orbital bone, and will move the entire head when pulled. Close the orbital septum within the eyelid (identified mainly by its strength in holding a needle or suture) with 3-0 to 5-0 long-lasting absorbable suture in a horizontal mattress or simple interrupted pattern. Effective closure of the orbital septum is the best way to prevent sinking of the orbit. Close subcutaneous tissues with 3-0 to 5-0 absorbable suture in a simple continuous pattern. Close the skin with 3-0 to 4-0 nylon simple interrupted skin sutures or 4-0 to 5-0 absorbable simple continuous subdermal sutures.

Lateral Enucleation

Advantages of the lateral approach include better visualization of retrobulbar tissues before the globe has been removed, especially in those with deep orbits; improved confinement of the ocular surface from the sterile surgical site; and retention of more orbital tissue than occurs with the transpalpebral technique. Disadvantages compared with the transconjunctival technique include greater loss of orbital tissue and potentially increased bleeding (because much of the dissection occurs more superficially than the subtenon space).

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).

Sep 11, 2016 | Posted by in SMALL ANIMAL | Comments Off on Surgery of the Eye
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