Eye

Anatomy

The eyelids function to maintain the health of the ocular surface. The eyelid muscles enable the lids to close over the ocular surface which helps distribute the pre-corneal tear film and protect the corneal and conjunctival surfaces from injury. Tactile cilia (lashes) sense approaching objects before they contact the globe, thus initiating the protective blink response. Glandular tissues secrete portions of the pre-corneal tear film (tarsal or Meibomian glands secrete the oily portion of the pre-corneal tear film and goblet cells of the conjunctiva secrete the mucinous portion of the pre-corneal tear film).

Important anatomic structures of the eyelids are illustrated in Figures 12-1A, B. The outermost surface of the eyelids is covered by relatively loose, haired skin in the dog and cat. Dogs usually have only upper eyelashes or cilia originating from the eyelid margin while cats do not have true eyelashes. On the lower eyelid, beneath the lid margin and parallel to the lid margin is a 1-2 mm wide zone of hairless skin. This nonhaired-haired demarcation is a surgical surgical landmark for entropion correction surgeries. Beneath the skin near the lid margins run the muscle fibers of the orbicularis oculi muscles. These muscle fibers (innervated by the palpebral branch of the facial nerve) run parallel to the lid margin and are responsible for eyelid closure. The upper eyelid has four muscles innervated by the occulomotor, facial, and sympathetic nerves that actively elevate the upper eyelid. Sensation to the eyelids is provided by the ophthalmic and maxillary branches of the trigeminal nerve. At the medial canthus, the medial palpebral ligament retracts the canthus medially; at the lateral canthus, the retractor anguli ligament/muscle retracts the lateral canthus laterally. Defects in the aforementioned liagamentous supportive structures may result in entropion and ectropion. Deep to the eyelid skin and orbicularis oculi muscles lies the connective tissue tarsal plate which contains the tarsal (Meibomian) glands. These glands are alligned perpendicular to the lid margin and there are approximately 30-40 per lid in dogs and cats. The gland openings may be seen with magnification along the lid margins. The tarsal plates are not as rigid in dogs and cats as in man, and their flaccidity may contribute to ectropion and entropion in some canine breeds. The innermost layer of the eyelids is the palpebral conjunctiva. This conjunctiva is firmly adherent to the tarsal plate area of the eyelids, but is loosely attached to the underlying eyelid stroma in the palpebral fornices.

Near the eyelid margins on the upper and lower lids, approximately 1-3 mm lateral to the medial canthus, are the openings (punctum) of the nasolacrimal duct system. These punctum lay at the medial most aspect of the cartilaginous tarsal plate and are just inside the eyelid margin on the palpebral conjunctival surfaces. The palpebral surface of the third eyelid conjunctiva at the medial canthus has a raised haired structure; the lacrimal caruncle.
 

Surgical Procedures

Temporary tarsorrhaphy

Temporary partial or complete closure of the palpebral fissure can be used to protect the globe following proptosis, extra- or intraocular surgery, or under conditions where the cornea may be overly exposed (e.g. palpebral nerve paralysis). If the temporary tarsorrhaphy is to be left in place for more than 48 hours, stents should be placed between the suture material and the eyelid skin to prevent the sutures pulling through the eyelid or cutting into the skin (Figures 12-2A, B). Pieces of sterilized “postal” rubber bands or a similar latex or silicon material make excellent stents for this purpose. If the tarsorrhaphy is to be maintained for more that 3-6 days, non-reactive suture such as monofilament or braided nylon is preferred to more reactive suture such as silk. Fine suture (5-0 to 6-0) with a small cutting needle allows proper placement of the suture. The needle should be passed first through the 4 mm x 6 mm stent and then through the eyelid skin 3-6 mm from the eyelid margin. By passing the needle into the tarsal plate, the needle should exit the eyelid margin at the level of the Meibomian gland openings. The needle should then be passed into the opposite lid margin at the Meibomian gland openings through the tarsal plate, and then out through the eyelid skin approximately 3-6 mm from the lid margin. The needle should then be passed through the stent material away from the lid, and then passed back through the stent material towards the lid. The needle is then passed through skin, tarsal plate, and Meibomian gland openings as previously described, across and through the opposite lid, and finally through the first piece of stent material so that the needle exits the same side of the stent material where the original suture bite took place. When finished, the completed suture pattern resembles a horizontal mattress pattern through eyelids and stents. Meticulous exit and entry of the needle at the Meibomian gland openings will result in excellent eyelid margin apposition with little to no risk of suture abrading the corneal surface. The suture should be tied tightly so that post-operative loosening and corneal abrasion by the suture may not occur.
 

Eyelid Laceration Repair

Full thickness eyelid lacerations that occur perpendicular to the eyelid margin are commonly seen secondary to fight wounds and other sharp trauma. Proper closure will result in a functional eyelid and a cosmetically acceptable palpebral fissure. The technique for eyelid laceration closure described may also be used to remove a full thickness eyelid tumor or to shorten an eyelid margin for correction of ectropion.

The skin, stroma, and conjunctiva of the eyelids are extremely vascular, and minimal debridement of damaged tissue following an eyelid laceration is recommended. Following surgical preparation of the skin and conjunctival surfaces with povidine iodine solution diluted with saline (10% povidine iodine solution diluted with saline to 1% final iodine concentration) and saline rinse, debridement of the wound with a scalpel blade is performed until the skin edge begins to hemorrhage. Closure of eyelid lacerations is performed with fine, absorbable suture (6-0 Vicryl) so as to appose the edges of the lacerated tarsal plate (Figure 12-3A-E). The first bite of the needle should enter the tarsal plate away from the lid margin and exit the tarsal plate close to the lid margin edge of the tarsal plate (Figure 12-3B). The needle is then passed to the opposite side of the wound and into the tarsal plate in the area closest to the lid margin to exit the tarsal plate away from the lid margin. If performed properly, the suture pattern approximates a horizontal mattress pattern with no suture passing through the palpebral conjunctiva (therefore there will be no possibility of suture rubbing the cornea) with the knot being tied and buried within the eyelid stroma away from the eyelid margin. A simple continuous pattern trailing away from the eyelid margin completes closure of the palpebral tarsal plate/conjunctiva with the final knot being buried within the eyelid stroma (Figure 12-3C). It is important to place suture bites so that no suture is passing through the palpebral conjunctiva that could abrade the corneal surface. A fine, braided, synthetic absorbable suture is preferred over larger, monofilament, and/ or catgut suture material, especially in thin-lidded dogs and cats. If the eyelid stroma is excessively swollen, or the patient is a large dog, additional simple interrupted sutures to close the more external orbicularis oculi muscle are indicated. Skin closure must be meticulous at the eyelid margin so as to result in a smooth, anatomic eyelid margin. Three suture patterns have been described to appose the eyelid margin skin. I prefer to use a simple horizontal mattress pattern (Figure 12-3D) using fine (4-0 to 6-0) nonabsorbable (silk or nylon) braided suture followed by simple interrupted skin sutures. A cruciate or “figure of eight” suture (Figure 12-3E) involving the lid margin followed by simple interrupted skin sutures also results in excellent closure. A well placed simple interrupted suture at the lid margin (Figure 12-3F) with the suture tags being tied back by subsequent simple interrupted sutures can result in excellent anatomic closure as well, but it is important to tie the suture tags in a manner that does not allow the suture tags or the knot to come in contact with and abrade the corneal surface. If eyelid closure is precarious due to tissue friability and/or swelling, temporary tarsorrhaphy sutures, one on either side of the wound closure, can help immobilize the lids and “splint” the lid until healing is complete and sutures are removed 10 days post-operatively.
 

Full Thickness Eyelid Wedge Resection for Correction of Ectropion

Ectropion is eversion of the lower eyelid margin resulting in spillage of tears onto the face (epiphora) and excessive exposure of the palpebral and bulbar conjunctiva and cornea. Ectropion is usually seen in those canine breeds with heavy facial skin, excessively long palpebral fissures, and/or lax tarsal plates (e.g. hounds, giant breeds, and sporting breeds). A simple technique for “tightening” lower lid ectropion involves a full thickness wedge resection of the lid to shorten the lid margin (Figure 12-4 A-E) with closure of the wound being similar to that described for eyelid laceration repair.

A smooth eyelid margin to help stabilize the precorneal tear film meniscus is desirable, so the wedge resection to shorten the lid margin is performed laterally (Figure 12-4B). There should be some tarsal plate left on each side of the wedge to allow for closure of the wound in two layers. The initial incision is made using a scalpel with a Jaeger lid plate inserted into the cul-desac to stabilize the eyelid (Figure 12-4B). The incisions should be made perpendicular to the eyelid margin (parallel to each other) to the level of the edge of the tarsal plate and then taper to a point that ends in the deepest recess of the cul-de-sac (Figure 12-4C). The incisions may also be made using a Metzenbaum scissor, with the shape of the excised wedge being the same as that described for scalpel excision using a lid plate. It is important that the initial incisions from the lid margin through the length of the tarsal plate be parallel to each other so that upon closure, there will be a straight, non-indented eyelid margin. Closure of the wound is in 2 (or 3) layers as for an eyelid laceration (Figures 12-4 D and E).
 

Eyelid Tumor Resection

Eyelid margin tumors are commonly seen in dogs. Meibomian gland adenomas, mast cell tumors, papillomas, melanomas, and squamous cell carcinomas may occur in the lid. In cats, eyelid neoplasia is uncommon and most tumors are malignant. A full thickness wedge resection as described for ectropion correction and a two-layer closure as described for eyelid laceration is used to remove most eyelid tumors.

Depending on the species (cats have tight lid margins compared to dogs with more lax margins) and breed (hounds and sporting breeds have more lax lids than do toy breeds such as miniature poodles), approximately 1/4 to 1/3 of an eyelid may be removed and closed in the manner listed above for ectropion correction. It is important to excise the eyelid with incisons through the tarsal plate area being made parallel to each other and perpendicular to the lid margin to maintain a smooth, anatomic lid margin after healing. 

If more than one-third of the lid margin is excised to obtain tumor free margins, closure may be complicated by inadequate surrounding tissue. This may result in excessive lid margin tension and poor lid function. A lateral canthotomy incision may enhance lid closure by allowing eyelid tissue to slide medially and be advanced to close the defect (Figure 12-5A-C). Following excision of the eyelid mass, a Metzenbaum scissor is used to cut full thickness from the lateral canthus to the depths of the cul-de-sac laterally being cautious so as to not cut the lateral orbital ligament. This incision (Figure 12-5B) yields less lateral tension, which allows for a more effective two-layer closure of the lid wound. Closure of the lateral canthotomy using the two layer technique leaves a small wound margin at the lateral canthotomy incision to heal by second intention (figure 12-5C).
 

If one-half or more of the eyelid margin must be excised for tumor excison, a semicircular sliding skin flap is constructed to close the resulting defect. Following excision of the lid mass and a releasing lateral canthotomy (Figure 12-6A), the semicircular skin flap is constructed by making a curved skin incision extending laterally from the end of the lateral canthotomy extending approximately 1.5-2.5 times the width of the void to be filled (Figure 12-6B). Excision of a Burow’s triangle of skin at the lateral terminus of the semicircular flap incision will minimize focal terminal distortion upon closure of the wound. The surgeon should use caution in making the skin incision and during undermining of the flap to not damage the superficial temporal artery located subcutaneously lateral to the lateral canthus. A two layer closure of the lid mass excision wound is followed by buried absorbable sutures placed to reduce dead space beneath the skin flap. The skin flap incision is closed in two layers up to the edge of the new lateral canthus. The newly formed eyelid margin created by the skin flap is left to heal by second intention. Complications may include trichiasis from facial hair, a flaccid lower eyelid that permits epiphora, or a flaccid upper eyelid (ptosis) due to excision of the levator palpebrae muscle in the original excision.
 

Entropion

Entropion is defined as inward turning/inversion of the eyelid(s). The condition is commonly seen in dogs and occasionally in cats resulting in frictional irritation of the conjunctival and corneal surfaces by eyelashes and/or facial hairs of the lid. This frictional irritation is painful and may lead to corneal ulceration, corneal neovascularization and deposition of pigment on the corneal surface (pigmentary keratitis). In severe cases, vision loss from corneal scarring and opacification, corneal perforation, and loss of the globe from deep corneal ulceration are possible.

In cats, lower lid entropion may be seen in brachycephalic breeds (e.g. Persians and Himalayans) as a conformational defect due to the shortened face. Spastic entropion occurs when an ocular irritant causes severe blepharospasm that leads to rolling in of the eyelid margin. Since the frictional irritation of the facial hairs on the corneal surface causes more pain, spastic entropion becomes a cycle of pain, blepharospasm, and corneal irritation with continued pain and blepharospasm. Spastic entropion may be seen in young cats (< 6 months of age) of the brachycepahlic breeds and in adult cats with corneal pain due to infectious (e.g. feline herpes virus-1) or irritation induced keratitis conditions.

In dogs, spastic entropion is seen in young puppies of breeds (e.g. Shar Peis, Chow Chows, and others) with excessive facial skin and laxity of eyelid structures such as the retractor anguli muscle or ligament. In some puppies, when neonatal ankyloblepharon resolves and the eyelids open at 2 weeks of age, the eyelid margins begin to roll inward due to heavy facial skin and eyelid laxity. In adult dogs, spastic entropion may be seen in animals that have a painful ocular condition leading to excessive blepharospasm similar to that described for cats.

Lower eyelid entropion in dogs is commonly seen in younger dogs (less than one year of age) due to deep-set globes and conformational defects of the eyelids and facial structures. Lower eyelid entropion may also have a spastic component which should be considered when surgically correcting the defect.

Upper eyelid entropion occurs in those heavy faced breeds (e.g. bloodhounds, Shar Peis, Chow Chows, mastiffs, and others) where the extreme weight of the forehead skin and upper lids and a lack of connective tissue structures leads to the upper eyelid margins rolling over onto the ocular surface with the upper eyelashes abrading the corneal surface. Upper eyelid entropion usually has a major spastic component similar to that caused by lower eyelid entropion.

Lateral canthal entropion occurs mostly in heavy faced breeds (e.g. Shar Peis, Chow Chows, mastiffs, St. Bernards, Bernese mountain dogs, English bulldogs, and others) where there is also laxity of the retractor anguli ligament/muscle. This allows the lateral canthal structures to roll inward causing frictional irritation to the cornea and conjunctiva. A spastic component may be seen in cases of lateral canthal entropion. In those breeds (St. Bernard, mastiffs, Bernese mountain dogs, Newfoundlands, and others) with excessively long palpebral fissures (macropalpebral fissure) and lax tarsal plates, a combination of lateral canthal entropion and lower lid ectropion with an upward “notching” of the upper eyelid margin is seen.

Medial canthal entropion is seen primarily in brachycephalic breeds (pugs, Shi Tzus, Lhasa Apsos, and others). The brachycephalic conformation results in the medial palpebral ligament being too tight causing the medial aspect of the upper and lower eyelids to roll inward. Frictional irritation to the corneal surface by the medial canthal hairs and lashes leads to medial corneal neovascularization and subsequent pigment migration (pigmentary keratitis). This form of entropion seldom appears to be painful to the patient and usually does not have a spastic component similar to other forms of entropion.

Temporary Everting Suture Technique for Treatment of Spastic Entropion

Temporarily everting the eyelid margins is an effective method of disrupting the cycle of frictional irritation, pain, and blepharospasm caused by spastic entropion. This technique should always be used in young animals prior to more permanent skin removal entropion repair. It is difficult to evaluate how much tissue needs to be removed in the young patient with entropion, and overzealous tissue removal may result in eyelid scarring and/or ectropion in later life. Likewise, in an adult animal with no history of previous entropion, the practitioner should identify the underlying source of pain, treat that condition, and temporarily evert the eyelids for pain relief rather than performing permanent entropion corrective surgery. A simple technique to evaluate for spastic entropion is to apply a drop of topical anesthetic (0.5% proparacaine) to determine if blepharospasm abates. If topical anesthetic use relaxes the blepharospasm and resulting entropion, a temporary everting technique maintained for 7-10 days may result in resolution of the entropion without tissue excision. Topical anesthetic is applied as a diagnostic test only and is contraindicated as therapy for spastic entropion. Topical anesthetics are epithelial toxic, and by deadening the ocular surface to pain and sensation, further damage to the corneal surface may occur.

Periocular hair is shaved and the skin is prepared with dilute povidine iodine and saline. Multiple everting sutures of either a braided or monofilament synthetic (polypropylene or nylon) suture material are placed in the skin. Either vertical mattress (Figures 12-7A-D) or horizontal mattress (Figure 12-7E) sutures are used. I prefer multiple small (5-0 or 6-0) sutures versus fewer larger (2-0 or 3-0) sutures. In young patients, thin, friable skin may not hold a larger suture, and if the suture pulls through the skin, entropion resumes, and a noticeable scar may be present from the resulting defect. Suture placement depends on how much entropion is present. If only the lower lid is involved, only everting sutures involving the lower lid are used. It is not uncommon in Shar Peis, Chow Chows, and bulldogs for entropion to affect the upper and lower lids and lateral canthus (Figure 12-7F), thus everting sutures are placed in all 3 areas (Figure 12-7G). For the vertical mattress suture technique, the first bite into the skin should be very close to the outside edge of the lid margin and the needle directed away from the lid margin. The second bite should be further away from the lid margin so that when the knot is tied with appropriate tension, the eyelid margin is everted from the ocular surface. The suture tag closest to the globe should be cut close to the knot so as to not abrade the cornea while sutures are present. The suture tag directed away from the lid margin should be long to allow for suture removal in 7-10 days. For the horizontal mattress technique, the first bite should be close to the lid margin and the exit site of the needle equally close to the lid margin. The second bite will be further from the lid margin with the needle path being parallel to the first needle tract/lid margin. After tying the suture, the knot is rotated away from the lid margin and suture tags are cut to avoid corneal irritation. Prevention of post-operative self-trauma (or trauma by the bitch if puppies are still nursing) is important. If the cornea is ulcerated, symptomatic care with topical antibiotic ointment with or without use of atropine for cycloplegia and pain relief is indicated. Sutures should be left in as long as possible (7-10 days) to reduce blepharospasm and recurrence of entropion.
 

Modified Hotz-Celsus Technique for Correction of Simple Entropion

The simplest technique for correction of lower or upper lid entropion is a modification of the Hotz-Celsus technique used in man. Skin is excised and wound edges are sutured in a manner that everts the entropic area of the lid margin (Figure 12-8A-D). Prior to surgery, it is important to estimate how much tissue must be removed to correct the entropion without causing ectropion. This determination is made based on experience, but there are techniques and surgical landmarks that will aid the surgeon. Prior to patient sedation, a drop of topical anesthetic is placed in the affected eye and the patient placed on an elevated table for examination. The surgeon should examine the patient with magnification without touching the face or periocular structures. This will assist the surgeon in accurately estimating the amount of tissue to be excised. After anesthetic induction, hair removal, and disinfection of the surgical site, the patient is placed in lateral recumbency for surgery. A Jaeger lid plate is placed to tense the eyelid and an incision is made with a scalpel. The saline moistened Jaeger lid plate is placed in the cul-de-sac and an assistant tenses the eyelid by lifting the lid with the lid plate (Figure 12-8 B). The surgeon uses thumb and index finger placed at the medial and lateral aspects of the area to be incised to tense the tissue for a smoother incision. The incision closest to the lid margin should be made at the level where the eyelid hair begins (lower eyelid) or about 1-2 mm away from the upper eyelashes (upper eyelid). The first incision should be made far enough from the lid margin to allow placement of sutures that will not abrade the cornea during healing. The surgical incisions and resulting wound should only be skin thickness, and no attempt should be made to remove orbicularis oculi muscle or tarsal plate structures. The second incision should be made distal to the initial incision at the point of greatest entropion and join the ends of the first incision in a smooth tapering fashion. The amount of tissue to remove is determined in the preoperative examination prior to sedation and by looking for a line of hair loss or skin discoloration due to the entropion. After the skin incisions, the skin is removed with the scalpel or a fine scissors. Following excision of tissue, the Jaeger lid plate should be removed and the skin sutured as it lies without tension (Figure 12-8C). The first nonabsorbable suture (4-0 or 5-0 monofilament or braided nylon or polypropylene) skin suture should approximately halve the wound defect. The next two sutures should be placed to divide the suture line into quarters. Since the second incision is in the form of an arc, it is longer than the initial skin incision that is parallel to and close to the lid margin. By utilizing a simple interrupted closure, bunching or “dog-ears” of one end of the suture line with a continuous suture pattern is prevented. The fine sutures should be placed close together (2-4 mm apart, depending on the size of the patient and suture size) and the suture tags closest to the eye should be cut close to the knot with the tags away from the eye being left longer. In animals with excessive preoperative blepharospasm and a spastic component to the entropion, intermittent vertical mattress sutures may be placed along the suture line to “overcorrect” the entropion until the skin sutures are removed at 10-14 days post-surgery (Figure 12-8D). In some cases, I “overcorrect” dogs of certain breeds (Chow Chow and Shar Peis) with vertical mattress sutures to prevent post-operative spasming with resulting suture contact of the corneal surface. Post-operative therapy consists of prevention of self-trauma, topical antibiotic ointment for treatment of corneal ulcers, systemic antibiotics, and non-steroidal anti-inflammatory drugs for pain.
 

“Arrowhead” Technique for Correction of Lateral Canthal Entropion

In those breeds with lateral canthal entropion but a normal length palpebral fissure (e.g. Shar Peis and Chow Chows), a modification of the Hotz-Celsus procedure (termed the “arrowhead” technique) may be used to evert the lateral canthal eyelid skin (Figure 12-9A-D). The Jaeger lid plate is used to tense the tissue, allowing smooth incision of the eyelid skin with a scalpel. The lid plate is placed in the lateral cul-de-sac and tensed upward by an assistant, simultaneously the surgeon tenses the lateral canthal tissue with the thumb and index finger on the upper and lower lids. The initial skin incisions should be approximately 2 mm from the lid margin along the upper and lower lids. Beginning about 6 mm from the lateral canthus, the skin incisions start to diverge from the lid margin and meet 5 mm lateral to the lateral canthus. (Figure 12-9B). This provides the surgeon additional tissue for closeing the resulting defect. The second incision begins at the medial-most extent of the first incision and gradually diverges from the first incisions. The point of intersection of the incisions lateral to the lateral canthus is dependent on how much eversion of the lateral canthus is necessary. In patients with minimal loose facial skin, closure of the “arrowhead” shaped skin incision may be adequate to correct the lateral entropion. In most dogs undergoing this procedure, however, a prosthetic lateral canthal ligament must be constructed to retract the lateral canthus and correct the defect. Prior to closure of the skin, blunt dissection is performed to undermine the skin over the lateral orbital ligament. Either a 4-0 monofilament nonabsorbable (nylon or polypropylene) or polydioxanone suture is used to first take a bite in the lateral most tip of the tarsal plate followed by passage of the suture through the periosteum over the orbital ligament. The surgeon may use two sutures (Figure 12-9C, upper) or a more complex placement of one suture (Figure 12-9C, lower) to pull the lateral canthus laterally and anchor it to the orbital ligament. Skin closure should begin at the lateral-most “point” of the “arrowhead” followed by a suture of the upper and then lower lid as for the traditional Hotz-Celsus technique (Figure 12-9D). In those dogs with upper, lower, and lateral canthal entropion, a skin incision of approximately 270° around the eyelid circumference (Figure 12-9E) may be made to result in correction of all abnormalities with one surgery. Temporary everting sutures as described for the Hotz-Celsus entropion correction are highly recommended in these patients. In patients with a macropalpebral fissure, this “arrowhead” correction technique corrects the entropion, but the ultimate exaggerated lateral placement of the lateral canthus may be cosmetically unacceptable, so the more complex lateral canthal reconstructive surgery described by Bigelbach is indicated.

Modification of Bigelbach’s Combined Tarsorrhaphy-canthoplasty Technique for Repair of Lateral Canthal Entropion and Lower Lid Ectropion

In those dogs where a combination of macropalpebral fissure and lateral retractor anguli ligament laxity results in lateral canthal entropion and lower eyelid ectropion (e.g. St. Bernards, mastiffs, Newfoundlands, and similar breeds), a technique to shorten the palpebral fissure and retract the lateral canthus has been described (Figure 12-10A-G).

First, the amount of eyelid to be excised must be determined. From 20 to 30% of the lateral-most upper and lower lids may be removed and still retain normal function and an acceptable cosmetic appearance. The upper and lower eyelid margins are notched with a scissor or scalpel an equal distance from the lateral canthus (Figure 12-10B). The distance from these notches to the lateral canthus (D) is measured. Extending from the lateral canthus, sweeping upward and downward from the lateral canthus and following the general curvature of the eyelids, two skin incisions are made with a scalpel (Figure 12-10C). These incisions are two times D in length. The tips of the two curved incisions are connected by a vertical skin incision, and full thickness lid incisions are made from the original notches to the tips of the sweeping skin incisions using either a scissor or a Jaeger lid plate and a scalpel (figure 12-10D). The skin of the incision triangle is removed with scissor or scalpel, and the full thickness eyelid triangles from the upper and lower lids are removed with scissors (Figure 12-10E). The tarsal plate edges and ends of the severed orbicularis muscle of the upper and lower lids are tacked to the lateral orbital ligament with absorbable suture (5-0 Vicryl or 4-0 PDS) in the same manner as described for the “arrowhead” lateral canthal entropion repair (Figure 12-10E). The upper and lower eyelid stroma is sutured to the subcuticular fascia of the face in a buried, continuous pattern with the same absorbable suture (Figure 12-10F). The skin is closed to align the lateral canthus with the center of the vertical connecting incision (Figure 12-10G) using a single horizontal mattress suture of 4-0 braided nylon or silk. The remainder of the skin incision is closed with simple interrupted sutures.
 

Medial Canthoplasty to Correct Medial Entropion and to Shorten the Palpebral Fissure (Roberts and Jensen “pocket-flap” Technique).

Reconstruction of the medial canthus in brachycephalic breeds of dogs may correct medial entropion and reduce frictional irritation to the cornea that causes pigmentary keratitis. In addition, the shortening of the palpebral fissure reduces exposure of the cornea, enhances total closure of the lids during blinking and during sleep, reduces frictional irritation from nasal fold trichiasis, and may help to prevent proptosis in predisposed exophthalmic dogs.

The eyelid is grasped in the center with tissue forceps and tensed laterally. A #15 Bard-Parker scalpel (or #64 Beaver blade) is used to split the medial aspects of both eyelids (Figure 12-11A) to a depth of approximately 1-1.5 cm to create dorsal and ventral “pockets” (Figure 12-11B). The dissection plane is such that the superficial portion includes the skin, orbicularis muscle and the deep portion is the tarsal plate and conjunctiva. If a simple medial canthoplasty is being performed for medial entropion correction, the dissection extends from the medial canthus laterally to a point 1-2 mm from the nasolacrimal punctae. If the surgery is intended to reduce the size of the palpebral fissure, the dissection can be extended beyond the punctae. It is important to keep the plane of dissection external to the nasolacrimal punctae and their ducts if the dissection extends lateral to the punctae. Using a small tenotomy scissor, the upper and lower eyelid margins are excised from the lateral-most extent of the dissection back to the medial canthus (Figure 12-11C). A strip no more than 2 mm wide should be excised. Next, the tenotomy scissor is passed such that one blade is within the dorsal “pocket” and one blade is within the dorsal cul-de-sac (Figure 12-11D). The tarsal plateconjunctival tissue is cut perpendicular to the lid margin for a distance of approximately 1-1.5 cm, thus creating a “flap” of tissue based at the medial canthus-upper eyelid (Figure 12-11E). The conjunctival surface of the “flap” is scarified with a scalpel to produce slight hemorrhaging. A small needle armed with 5-0 braided silk or synthetic absorbable suture (Vicryl) is passed through the lower eyelid skin into the ventral-most fornix of the ventral “pocket” and out through the eyelid margin opening (Figure 12-11F). The 5-0-suture needle pierces the tip of the dorsal “flap”, and the needle is then passed back down into the deep fornix of the ventral “pocket” (Figure 12-11G) and then out through the skin (Figure 1-11H). When the suture is pulled tight ventrally, this will anchor the “flap” within the deep recess of the ventral “pocket”. If absorbable suture is used, a small, partial thickness skin incision is made prior to tying the suture, and the suture knot is buried under the skin surface. If nonabsorbable suture (e.g. silk) is used, the external suture is knotted over a stent in the same manner as that described for temporary tarsorrhaphy. This inhibits the suture cutting into the skin and eases removal of the suture once the wound is healed. The edges of the skin margin of the lids can be closed in two layers similar to closure of a lid laceration (Figure 12-3).

The surgeon should realize that this technique sacrifices the upper nasolacrimal duct. If the dissection extends laterally beyond the ventral nasolacrimal punctum, the inferior duct, although patent, will not likely be functional and epiphora will result. If the dissection extends laterally beyond the punctae, the dorsal “flap” may incorporate Meibomian gland tissue. In this case, excision of glandular tissue prior to burying the “flap” within the “pocket” will prevent cyst formation at a later date due to buried glandular tissue. If the lacrimal caruncle on the palpebral surface of the third eyelid is large with long hairs growing from its surface, the surgeon may wish to excise this tissue and allow for healing by second intention to prevent future frictional irritation of the cornea by the lacrimal caruncle hairs.
 

Introduction

Conjunctival and corneal surgical procedures are performed to obtain tissue for diagnostic purposes or to reestablish the cornea’s anatomic and functional integrity. Important goals for the surgeon include the maintenance of corneal clarity and curvature to preserve adequate optical function. Multiple variables determine the best course of surgical therapy for individual cases, with the primary goal of attaining the best visual outcome for the patient. Prior to proceeding with most corneal and conjunctival procedures, it is ideal to consult with and consider referral to a veterinary ophthalmologist. Consultation with an ophthalmologist will assist in attaining the best possible clinical outcome for the patient.

Anatomy

Surgery of the conjunctiva and cornea requires a working knowledge of the anatomy and physiology of these structures. This knowledge will aid the surgeon in appropriate tissue handling, thereby decreasing surgical trauma and increasing surgical success. The conjunctiva is composed of stratified epithelium overlying a thin layer of loose connective tissue. The palpebral conjunctiva begins at the internal margin of the eyelids and extends posteriorly, reflecting back onto the globe at the level of the fornix, where it becomes the bulbar conjunctiva. The bulbar conjunctiva lies loosely on the surface of the eye until reaching the perilimbal region, where the conjunctiva, underlying denser connective tissue called Tenon’s capsule, and sclera become more tightly united. The conjunctival epithelium becomes continuous with the corneal epithelium at the limbus. Lymphatic follicles, goblet cells, blood vessels, and sensory nerves are located in the connective tissue layer of the conjunctiva. Lymphatics drain toward the eyelid commissures, and subsequently to the submaxillary lymph node medially and the parotid lymph node laterally. Goblet cells are individual glandular structures responsible for production of the inner mucin layer of the tear film. Increased densities of goblet cells are noted in the lower nasal and middle fornices and palpebral conjunctiva. The conjunctival vasculature is supplied by the anterior ciliary arteries, which are branches of the external ophthalmic artery, and most of the conjunctival venous drainage is provided by the deep facial vein. Sensory innervation is supplied by the ciliary nerves from the ophthalmic branch of the trigeminal nerve. The conjunctiva is the most exposed mucous membrane of the body and functions to prevent corneal desiccation, facilitate mobility of the lids and globe, and provide a structural and physiological barrier against opportunistic and pathogenic microbial organisms and foreign materials.

The cornea is the anterior fifth of the outer fibrous tunic of the globe, the remainder of which is provided by the sclera. In the dog, the cornea measures 15 mm horizontally and 14 mm vertically, while the cat cornea is slightly larger measuring 17 mm horizontally and 16 mm vertically. Corneal cross-sectional anatomy consists of five layers, with a thickness of approximately 400 to 800 µm in the dog and 470 to 830 µm in the cat. The outermost layer is the epithelium, comprised of five to seven stratified squamous cells, which are in a constant state of renewal every seven to ten days. A basement membrane lies beneath the epithelium, followed by corneal stroma, which provides approximately 90% of the corneal thickness. Descemet’s membrane is the acellular basement membrane of the corneal endothelium, which is a single layer of cells adjacent to the aqueous humor of the anterior chamber.

The cornea functions to protect and support the intraocular contents and to transmit and refract light. To accomplish these functions, the cornea is avascular, has low cellularity, and maintains a relative state of dehydration by a pumping mechanism in the endothelium and lipophilicity of the epithelial and endothelial layers. The corneal layers are thus nourished by the precorneal tear film, aqueous humor, and perilimbal vasculature. The corneal stroma is transparent and consists of parallel bundles of collagen comprising lamellae that span the entire corneal diameter and lie in layered sheets to provide most of the stromal volume. Low numbers of specialized fibroblasts called keratocytes, and leukocytes along with extracellular matrix comprise the remainder of the stroma. The corneal curvature and structural composition in the dog allows for approximately 40 to 42 diopters of refraction, and represents the most powerful refractive surface of the eye.

Instrumentation and Surgical Preparation

Surgical success improves with the appropriate use of specific ophthalmic surgical instruments. A comprehensive review of ophthalmic surgical instrumentation is beyond the scope of this chapter, however a discussion of required equipment is provided. Most surgical procedures involving the conjunctiva and cornea are performed more accurately using magnification. An operating microscope is ideal, although head loupe magnification of 2.5 to 4.5x with appropriate lighting is adequate for many cases.

Ophthalmic surgical instruments are more delicate and have finer tips than general surgical instruments, and specialized care is required to maintain instruments in the best condition. Surgical trays that keep instruments separate and protect the tips should be utilized, and gas sterilization is ideal to maintain instrument life. In contrast to instruments used in general surgery, many ophthalmic instruments have rounded handles and should be held like writing instruments. Many instruments also have spring handles instead of the more traditional finger rings for opening and closing blades. These qualities help minimize hand and arm movements, allowing finger movements to predominate, which provides finer surgical control.

Instruments required for conjunctival and corneal surgeries include tissue forceps, scissors, scalpel handles and blades, and needle holders that accommodate small needles and fine suture. Tissue forceps have three basic designs with regard to the teeth and appositional surfaces. Colibri-style and Castroviejo forceps have protuberant teeth, which aid in grasping and stabilizing tissues without crushing force. Colibri-style forceps are curved, which allow manipulation of tissue while keeping the handle of the instrument out of the magnified surgical field. Bishop-Harmon and similar forceps have teeth at right angles to each other and the handle. These forceps stabilize cut edges, where both sides of the tissue may be gently grasped. The third type of forceps has no teeth, only smooth appositional platforms. These instruments are indicated for tying fine suture material (eg. 6-0 and smaller). They should not be used to grasp tissues, as adequate fixation may only be obtained with crushing force resulting in possible damage to the tissue and instrument. Some Castroviejo and Colibri-style forceps incorporate a tying platform for suture behind the teeth. If the tying platform on these instruments is used, care is taken to avoid grasping and damaging suture with the forceps teeth.

Ophthalmic surgical scissors that are frequently utilized include blunt and sharp tipped tenotomy scissors. Blunt tips are usually preferred, as they are less likely to penetrate delicate tissues. Stevens tenotomy scissors, with ring finger holds, and Wescott scissors, with spring handles are our preference.

The scalpels and handles that are typically used in corneal surgery are Beaver brand. The handles are rounded and should be held like a pencil, and the blades are designed in various shapes. A #64 Beaver blade has a curved tip and cutting surfaces on the tip and on one side of the blade. This blade is used for performing corneal grooves as well as undermining keratectomy sites. Another instrument that may be used for keratectomies is a Martinez corneal dissector, which has a slightly curved semisharp blade allowing for dissection between parallel lamellae.

Needle holders have fine curved or straight tips, with either locking or non-locking handles. Most surgeons use slightly curved locking needle holders for corneal and conjunctival procedures. Needles should be positioned in the holders so that the shaft of the needle is perpendicular to the tips of the holders. Spatulated needles with swaged on suture are preferred to minimize disruption of corneal layers. Size 6-0 suture or smaller should be used with ophthalmic needle holders, as larger needles may damage the instrument. In general, 7-0 or 8-0 multifilament absorbable suture material is utilized for conjunctival and corneal procedures in small animals.

Proper patient preparation and positioning are essential for conjunctival and corneal procedures. Most cases require general anesthesia, though some may be performed with topical anesthetic and sedation or short acting anesthetic agents. Anesthetic risk and general patient health are vital considerations, and preoperative evaluation should include a complete physical examination as well as appropriate bloodwork. Excess hair should be carefully trimmed or clipped from the face, and unless infection is suspected and cultures are desired, any discharge or debris should be cleaned from the eye. Surgical scrub solutions should not be applied to the eye, and many antiseptic solutions are irritating to the conjunctival and corneal tissues. Dilute povidone solution (1:10 to 1:50 of the 10% stock solution) is non-toxic and may be gently applied to the eye by lavage and then removed by rinsing with sterile saline. A cottontipped applicator soaked in dilute povidone-iodine is used to clean the cul-de-sacs. In preparation for most conjunctival and corneal procedures, the patient is placed in dorsal recumbency, with the head positioned so that it is stable and the cornea of the eye to be operated is parallel to the table. An eyelid speculum provides increased exposure of the eye and aids visualization of the surgical field, or alternatively, suture may be passed through the skin of the eyelid, parallel to the margin, to aid in retraction of the lids. Hemorrhage should be carefully controlled with dilute (approximately 1:10,000) epinephrine and sterile cotton tip applicators or cellulose sponges. It is essential that the cornea be kept moistened throughout the surgical procedure and is accomplished by dripping saline onto the eye every twenty to thirty seconds. In addition to an eyelid speculum, stay sutures may be placed to stabilize the globe and expose the areas of surgical interest. Stay sutures are placed using 5-0 or 6-0 non-absorbable suture, with the needle passed partial thickness through the sclera and parallel along the limbus. To avoid penetrating the globe, the needle should be nearly parallel to the surface of the sclera is it is passed through the tissue. Tags should be tied and left long to allow manipulation without obstructing the visual field (Figure 12-12). Caution is used to avoid traumatizing the cornea when the stay sutures are manipulated. In general, the globe is stabilized by grasping the tissue near the area of interest, thereby minimizing globe rotation. Tension on the globe caused by tissue retraction is not appropriate, and tension that causes deformation of the globe is dangerous to the health of the eye.
 

Surgical Techniques

Lacerations

Conjunctival and corneal lacerations are traumatic injuries that often require very different approaches. Preliminary evaluation of conjunctival lacerations should allow the surgeon to localize the wound and assess the extent of the injury. Local swelling, hemorrhage, and patient discomfort may obscure the injury and general anesthesia may be required to explore the wound. The sclera, nasolacrimal system, cornea, and intraocular structures should be assessed for evidence of trauma. The patient is positioned in dorsal recumbency and magnification used to accurately assess the injury. An eyelid speculum or stay sutures are placed to increase exposure. If warranted, the nasolacrimal ducts should be cannulated and flushed to ensure patency. A 22 to 24-gauge intravenous catheter with the stylette removed may be used to cannulate the ducts, and the lids may be stabilized with Bishop-Harmon forceps. Instruments that will assist in wound exploration include Colibri or Castroveijo forceps to grasp the tissues and rotate the globe. Gentle and thorough flushing should be performed with sterile saline. Necrotic tissue should be carefully excised and hemorrhage should be controlled. The wound is systematically explored and evaluated for corneal and scleral injury, trauma to the extraocular muscles and periorbital tissues, and the presence of foreign material. Evidence of extensive trauma increases the short and long term chances of vision-threatening complications, such as endophthalmitis, intraocular hemorrhage, or retinal detachment. A description of surgical repair of extensive globe or orbital trauma is beyond the scope of this chapter, and referral to a veterinary ophthalmologist should be considered. If the wound is obviously contaminated, culture samples should be obtained. A conjunctival wound that is smaller than one centimeter, or one with copious drainage is allowed to heal by second intention. If the wound is larger than one centimeter, closure with 6-0 absorbable suture in a simple continuous pattern is appropriate. Care is taken to avoid suture tags or knots contacting the corneal surface.

Corneal lacerations are assessed differently than conjunctival lacerations. An important to determine the depth of the injury as early as possible. Full or partial thickness lacerations should be differentiated by evaluating for prolapse of intraocular contents, collapse of the anterior chamber, presence of blood or fibrin in the anterior chamber, or a positive Seidel test (apply fluorescein dye to the eye, and look for drainage of aqueous humor from the laceration). If a lens capsule rupture has occurred, lens removal may be required to save the eye from severe lens-induced uveitis. If the laceration is near the limbus, the conjunctiva and underlying sclera should be examined for injury. Assessing for the presence of vision, or of a consensual pupillary light reflex can determine the prognosis for vision prior to proceeding with surgery. In some cases of severe intraocular trauma, the owner and veterinarian must decide whether to attempt to save an avisual globe or consider a salvage procedure, such as enucleation or intraocular prosthesis. For these reasons, referral to a veterinary ophthalmologist is encouraged in cases of fullthickness corneal laceration.

Full thickness corneal lacerations require surgical repair. The patient is anesthetized and carefully prepared with minimal neck restraint or manipulation of the globe. The patient is positioned in dorsal recumbency and use of an operating microscope is preferred. Prolapsed uveal tissue is either replaced with the aid of a viscoelastic agent and gentle separation of adhesions or excised if the prolapsed tissue is severely desiccated. Fine tipped Colibri forceps are used for corneal and iridal manipulations. Manipulation of iris tissue may cause significant hemorrhage, which must be controlled to avoid serious damage to the eye. Use of 1:10,000 dilute epinephrine will decrease hemorrhage and careful use of a fine-tipped cautery is sometimes necessary. Viscoelastic agents are used to maintain the formation of the anterior chamber while the corneal wound is assessed and repaired. Prior to completion of closure of a full thickness laceration, most of the viscoelastic agent should be flushed from the anterior chamber and replaced with a balanced salt solution.

Corneal tissue does not stretch, so the edges of corneal lacerations, whether full or partial thickness, should not be debrided or excised. Superficial lacerations may heal without surgical repair by application of prophylactic topical antimicrobial ointment. Many lacerations are deep and irregular, requiring placement of interrupted sutures to appose the edges. Sutures should be placed at approximately 75-90% corneal depth using 7-0 or 8-0 absorbable braided suture. In placing corneal sutures, the needle should be directed perpendicular to the corneal surface, approximately one millimeter from the wound edge, depending on the nature of the laceration. As the needle is advanced, the needle holders are rotated and repositioned to allow adequate suture depth and have the needle exit at approximately the same distance on the opposite side of the wound. The suture is tied, using a tying platform, usually with two or three throws on the first knot, so the wound edges are apposed and not crushed. The first suture should be placed near the middle of the laceration, with subsequent sutures placed to divide the remaining length of the wound until closure is complete. Spacing between sutures is usually one millimeter, but adjustments may be necessary for irregular lacerations. Post-operative care is described in the final section of the chapter, and the eye should be reevaluated in five days.

Conjunctival and Corneal Biopsy

The most common indication for conjunctival and corneal biopsies is to identify the cause of abnormal tissue proliferations or chronic inflammatory processes that are not responsive to medical management. Incisional biopsies for sampling small and freely moveable or pedunculated conjunctival lesions may be performed with topical anesthetic and sedation or short acting anesthesia. Unless culture is desired, the eye should be aseptically prepared with dilute povidone iodine solution. Adequate exposure often necessitates placement of an eyelid speculum. A drop of dilute epinephrine or 2.5-10% ophthalmic phenylephrine placed in the eye prior to biopsy will decrease hemorrhage. Incisional biopsies are obtained by stabilizing and placing gentle tension on affected tissue with Colibri or Castroveijo forceps. Stevens or Wescott scissors are used to incise the lesion towards its base, and the excised tissue should be placed in a cassette in ten percent buffered formalin and submitted for histologic evaluation. Conjunctival incisions of less than one centimeter in length do not require primary closure and will heal by second intention. Defects that are larger than one centimeter should be closed with 6-0 absorbable suture in a continuous pattern. Care should be taken to avoid allowing suture or knots to contact the corneal surface. Post-operative care is summarized in the final section of the chapter, and the patient should be rechecked in five to seven days.

If the tissue of interest is expansive or seems firmly adhered to the underlying sclera, there should be suspicion of possible intraocular involvement and more extensive disease. Though an incisional biopsy is still an appropriate initial approach, referral should be considered for ocular ultrasound and additional surgical options. If the lesion is near the limbus, or if it involves the cornea, a superficial keratectomy may be required, as described in a later section of this chapter.

Keratotomy

The primary indications for keratotomies are spontaneous chronic corneal epithelial defects (SCCEDs) that occur in middle-aged to older dogs. These lesions are also known as indolent ulcers, indolent erosions, and boxer ulcers. Ophthalmic examination typically reveals a chronic (weeks in duration), superficial, variably painful, non-infected, and non-progressive erosion or ulceration with a characteristic lip of loose epithelium surrounding the border of the defect. Many patients are reported to have sustained an ocular injury, but the lesion does not heal with topical therapy in an appropriate length of time. Diagnosis is made by clinical signs with the aid of fluorescein staining to evaluate for wicking of stain beneath the poorly adherent corneal epithelium at the edge of the lesion. No specific treatment has been shown to be effective in all cases, but successful therapy has included debridement, striate or punctate keratotomies, corneal gluing, third eyelid flaps, contact lens application, and superficial keratectomies. Most SCCEDs will heal with debridement and keratotomy, but approximately 20 to 30% of animals will require additional surgical procedures and referral to a veterinary ophthalmologist should be considered. To perform debridement of the defect, topical anesthesia is applied, and the patient manually restrained or sedated. Rarely, patients may require short-acting general anesthesia. A dry cotton tipped applicator is swabbed from the center of the lesion peripherally, peeling away loose epithelium in the process. Once the cotton swab is wet with tears, it is less effective and should be exchanged for a dry swab. Epithelium that is poorly adhered to the abnormal underlying stroma is debrided easily with this technique. Debridement is considered complete when a margin of more adherent corneal epithelium is encountered during swab application. The resultant defect will in many cases be considerably larger than the original lesion. For best results in healing, a punctate or striate keratotomy is performed following debridement. Striate (grid) keratotomy is technically easier to perform, with a lower risk of globe injury than punctate keratotomy. Patient restraint may be manual, or sedation or short acting anesthesia may be used. Loupe magnification for the surgeon is ideal. Topical anesthetic is applied, and a 25-gauge needle is held at an approximate 45° angle to the corneal surface with the bevel directed away from the cornea. The surgeon’s hand should rest on the table or on the patient’s muzzle. The tip of the needle is then used to lightly scratch the corneal surface, and the pressure applied should be enough to cause a very faint needle mark in the corneal tissue. The scratches extend from normal epithelium across the defect and back into normal epithelium. The resultant grid consists of faint scratches approximately one millimeter apart, crossing in various directions over the lesion. The owner should be warned that the animal will show increased ocular discomfort for several days following the procedure. If successful, complete corneal healing should occur within two to three weeks. These patients should be treated to prevent infection and control inflammation, as described in the Post-Operative Care section, and they should be rechecked in three to seven days to ensure there is no evidence of infection or ulcer deepening.

Superficial Keratectomy

Corneal and limbal proliferations of abnormal tissue and SCCEDs are the most common indication for superficial keratectomies. Keratectomy is also indicated in the preparation of the cornea to receive a conjunctival flap or graft. Ideally, referral to a veterinary ophthalmologist should be considered, as the benefits of an operating microscope and advanced microsurgical skills will increase the success of surgery. The depth of the lesion should be considered prior to surgery, so that surgical planning may include a conjunctival flap if the lesion extends deeper than 30% of corneal thickness. If the lesion to be excised is deeper than approximately 75% of the cornea or if it is full thickness, more advanced or adjunctive surgical procedures may be required, necessitating referral to an ophthalmologist.

The patient is anesthetized, prepared for surgery and positioned in dorsal recumbency. An eyelid speculum and stay sutures are placed as needed to increase exposure of the eye. Topical dilute epinephrine (1:10,000) is used to control hemorrhage. A #64 Beaver blade is used to create a square or circular corneal groove surrounding the lesion. The groove should extend into slightly deeper corneal stroma than the deepest aspect of the lesion (Figure 12-13A). If the lesion is close to the limbus, the groove is made in a semicircular fashion around the lesion and adjacent to the limbal margin. Fine tipped Colibri or Castroviejo forceps are used to grasp the grooved edge of the cornea, and either a #64 Beaver blade or a Martinez corneal dissector is used to undermine the abnormal tissue. If a blade is used, it is held so that the blade is nearly parallel to the corneal surface and small circular motions used to undermine the lesion. A Martinez corneal dissector is held so that the dissecting blade is parallel to the corneal surface, and a sweeping motion is used to advance the instrument (Figure 12-13B). If the limbus is involved, the dissecting instrument is carefully advanced under the limbal tissue approximately two millimeters, using care to remain parallel to the ocular surface. Diseased conjunctiva that is adjacent to a limbal lesion is elevated using regular Colibris forceps and excised using tenotomy scissors. The conjunctiva at the margin of the lesion is tented and a small incision is made. The scissors are then advanced to bluntly undermine the conjunctiva prior to extending the incision, eventually elevating the entire affected region so that the only remaining conjunctival tissue attachments are at the limbus. Curved tenotomy scissors and forceps are then used to incise along the limbus and remove the affected corneal and conjunctival tissue en bloc.

The resulting corneal defect if it is less than 30% of corneal thickness does not require a conjunctival flap. If the limbus is involved, a conjunctival advancement, or hood flap may be performed to protect the limbal region and close the orbit. Keratectomy beds > 30% corneal thickness require a graft or flap to re-establish the structural integrity of the cornea, and some of these techniques are described in the following section. Post-operative medications are described in the final section of the chapter, and these patients should be rechecked in three to five days.
 

Conjunctival Flaps and Grafts

Conjunctival flaps and grafts differ in that flaps are attached to the tissue of origin with an intact blood supply, whereas grafts are completely severed from the donor site and must be revascularized from the recipient site to survive. The most common indication for conjunctival flap construction is to repair a loss of corneal integrity caused by keratomalacia, surgical wounds, and traumatic injuries. Corneal sequestra are an additional indication in cats. If corneal tissue is lost, as with keratomalacia, and a corneal perforation has resulted, tissue replacement with keratoplasty procedures may be indicated in addition to conjunctival flap techniques, necessitating referral to a veterinary ophthalmologist. The inciting cause and severity of corneal disease dictates which of the techniques described here are appropriate for use in individual patients. The benefits of conjunctival flaps include provision of physical support to weakened corneal tissue, a direct blood supply to naturally avascular tissue, and a source of cellular components to accelerate healing. Overall, the success rate of conjunctival flap procedures is approximately 90%, however, failure of adhesion, excessive tension resulting in flap dehiscence, flap necrosis, continued leakage of a ruptured globe, and refractory keratomalacia, are examples of complications that may occur following conjunctival flap surgery. In most cases, referral to a veterinary ophthalmologist should be considered, as surgical experience and technique are factors in establishing a successful outcome.

Conjunctival Pedicle Flap

Conjunctival rotating pedicle flaps are the most common type of flap performed by veterinary ophthalmologists. The patient is anesthetized, prepared routinely for ophthalmic surgery and positioned in dorsal recumbency. Use of an operating microscope is recommended for best results. An eyelid speculum and stay sutures should be placed to aid in exposure of the surgical field. The corneal recipient bed is prepared using fine tipped Colibri forceps for stabilization, and the cornea is grooved around the perimeter of the lesion with a #64 Beaver blade. The groove may be rounded or squared, depending on surgeon preference, and the affected stroma within the confines of the groove is removed by a superficial keratectomy. If a keratectomy is not performed, a surgical blade, cellulose sponges, and fine corneal scissors are used to freshen the edges of the corneal defect. The width or diameter of the defect is approximated, and a correspondingly sized or larger piece of conjunctival tissue is obtained for the flap. The donor conjunctival site is typically the dorsolateral bulbar conjunctiva, due to the ease of access and relatively loose adhesions to the underlying connective tissue. However, if the lesion is markedly closer to the ventral limbus, a ventrally based flap may be more appropriate. The base of the flap, which will remain attached to the donor tissue, should be located such that the flap is vertically oriented when positioned over the corneal defect; this reduces friction and drag caused by eyelid motion. In designing a flap, the surgeon plans the width of the flap base to be approximately one millimeter wider than its distal margin. The free or distal margin of the flap is designated by drawing an imaginary horizontal line across the cornea from the ventral aspect of the corneal lesion to the donor bulbar conjunctiva (Figure 12-14A). Due to curvature of the globe, the resultant conjunctival flap will be slightly longer than necessary; however, it is easier to trim away excess tissue than it is to supplement a flap that is too small. Hemorrhage is controlled by use of dilute epinephrine (1:10,000) cellulose sponges, and cotton tipped applicators. The conjunctival tissue is tented gently using regular Colibri or Castroviejo forceps, and a small incision is made using blunt tipped tenotomy scissors approximately two millimeters posterior to the limbus. Conjunctival tissue is undermined by blunt dissection with tenotomy scissors prior to enlarging the incision, and the elevated tissue should be thin, allowing visualization of the scissor blades through the conjunctiva (Figure 12-14B). Care must be taken during dissection to avoid closing the scissor blades until they are completely withdrawn from tissue, as inadvertently cutting small holes in the flap will weaken its integrity. The incision is extended to the predetermined distal point of the flap, staying as close to the limbus as possible. The distal flap margin is then incised by directing the scissors posterior and cutting perpendicular to the initial incision. This incision is approximately one millimeter greater than the horizontal width of the corneal lesion. The third conjunctival incision is parallel to the initial perilimbal incision, with the scissors directed toward the base of the flap. This third incision should be parallel to but shorter than the initial incision to maintain vascular supply to the flap.

As the flap is rotated, the surgeon must ensure that the non-epithelialized surface of the conjunctiva is placed in contact with the corneal recipient site. Placement of the flap with the conjunctival epithelial surface in contact with the corneal defect will result in failure. The donor tissue is positioned over the corneal defect, and should lie where placed without continued traction or tension. If there is tension on the flap, the conjunctival tissue is further undermined to release residual remnants of the white connective tissue, Tenon’s capsule. The flap is initially sutured with 7-0 to 9-0 multifilament absorbable suture using simple interrupted sutures placed at the corners of the corneal defect. Needle bites should include approximately one millimeter of flap tissue, and the needle should then enter the cornea at the base of the lesion, along the edge of the defect. The needle should then exit the normal corneal tissue one to two millimeters from the wound margin. The needle is passed cautiously so as to not penetrate the anterior chamber. If inadvertent penetration into the anterior chamber occurs, the suture is completely removed and placed in a different location. The perforation site will heal spontaneously, though some uveitis may occur. Ideally, the suture should penetrate to a depth that approximates 75-90% of the corneal thickness, though slightly shallower suture bites are acceptable for conjunctival flaps. Suture should be tied with two to three throws on the first knot, and the knot should be tied so as to appose but not crush tissue. Additional interrupted sutures are placed by dividing the distance between the initial sutures in half, then in half again, until sutures are spaced approximately one millimeter apart around the three exposed sides of the flap. The fourth side of the corneal lesion covered by the flap of conjunctival tissue close to the limbus is not sutured, as this would compromise vascular supply to the flap. A simple continuous suture pattern may be used to suture the three sides of the flap rather than interrupted sutures. After corneal suturing, two anchoring sutures are placed from the base of the flap to the limbus on each side. These sutures help to decrease flap tension on the corneal recipient site. Closure of the conjunctival donor site is unnecessary, but may be performed with a simple continuous pattern of 7-0 to 8-0 multifilament absorbable suture. Figure 12-14C demonstrates the appearance of the flap sutured to the corneal surface. The patient should be treated as described in the Post-Operative Care section, and a recheck examination should be scheduled in five to seven days.

Five to eight weeks after surgery and following complete healing of the corneal wound the vascular supply to the flap may be severed to improve the cosmetic appearance of the eye. Ideally, corneal vasculature should reach the surgical site prior to incising the flap. Incising the flap is performed with manual restraint or with a combination of light patient sedation and ocular topical anesthesia. A drop of dilute epinephrine or 2.5 to 10% ophthalmic phenylephrine will help to control hemorrhage. The bridge portion of the flap, which is not attached to the cornea, is gently elevated with Castroviejo forceps, and a blunt tipped scissor blade is inserted between the flap and the corneal surface. As the scissor blades are closed the flap is cut and the free margin retracts toward the limbus. The remaining tag of tissue is then trimmed near the limbal attachments. Complications of this procedure include necrosis of the remaining island graft, iatrogenic corneal ulceration from the scissors, and mild ocular discomfort for 2 to 3 days while the conjunctival incisions heal. Patients should be treated for five to seven days with prophylactic topical antimicrobials, and rechecked in two to three weeks.
 

Conjunctival Bridge Flap

The indications for performing conjunctival bridge flaps are similar to those for pedicle flaps. However, some ophthalmic surgeons feel that bridge flaps are more appropriate for exophthalmic breeds, providing for increased protection of the corneal surface during healing. The technique is similar to that described for pedicle flaps, with the exceptions described here. There is no distal or free margin to bridge flaps. The parallel conjunctival incisions extend 180° around the bulbar conjunctiva, leaving attachments dorsally and ventrally. The freed central portion of the flap is then placed onto the surface of the cornea, so that the lesion is completely covered (Figure 12-15). Only the medial and lateral edges of the corneal lesion are sutured to the corresponding edges of the conjunctival flap. Suturing the dorsal and ventral aspects of the flap would compromise vascular supply. Anchoring sutures are placed from the edges of the flap through the limbal tissues, both dorsally and ventrally. Postoperative management is similar to that for pedicle flaps, and these flaps are often severed after complete corneal healing occurs (5 to 8 weeks postoperatively) to release the nonadherent dorsal and ventral aspects of the tissue bridge.

Conjunctival Hood Flap

Conjunctival hood, or advancement flaps are indicated for perilimbal lesions of the cornea (Figure 12-16). The corneal recipient bed is prepared as described for rotating pedicle flaps. A perilimbal conjunctival incision is made by tenting the tissue with Colibri-style forceps and incising it with tenotomy scissors. The conjunctiva is then undermined in a direction radiating outward from the initial incision, extending posteriorly toward the fornix. The perilimbal incision is then extended to a distance one to two millimeters beyond the corneal lesion. The conjunctival tissue is advanced over the corneal defect. Interrupted sutures using 6-0 to 7-0 multifilament absorbable suture are placed from the edges of the advanced conjunctiva through the limbus so that the conjunctival hood completely covers the corneal lesion without tension. The conjunctiva is sutured to the edge of the corneal defect with absorbable multifilament 7-0 to 8-0 suture material. Postoperative management techniques are similar to those described for pedicle flaps.
 

360° Conjunctival Flap

The 360° conjunctival flap causes severe visual compromise and is considered a salvage procedure when most of the corneal surface has been severely damaged. The procedure is technically easier to perform than other conjunctival flaps, as no corneal sutures are needed. A perilimbal conjunctival incision is performed for 360°, and the conjunctival tissue is undermined posteriorly. The tissue is advanced over the cornea, and the cut edges of the conjunctiva are sutured in a simple interrupted or continuous pattern with 7-0 multifilament absorbable suture. Patient care postsurgically is described later.

Conjunctival Graft

Conjunctival grafts are performed by completely excising a portion of conjunctival tissue and then suturing the free tissue graft to a corneal defect. The graft provides structural support to the cornea, however the benefits of an intact vascular supply and cell-mediated healing provided by a flap are absent as the graft has no vascular supply. Indications for performance of a conjunctival graft are limited to chronic, inactive lesions that involve greater than 75% of corneal stromal loss. Corneal vascularization should be present at or near the edge of the corneal defect. Preparation of the corneal recipient bed is described earlier with conjunctival pedicle flap construction. The conjunctival donor graft is usually harvested from the dorsal or lateral bulbar or tarsal conjunctiva. The conjunctiva is incised with tenotomy scissors and undermined. The final donor graft should approximate the shape of the recipient bed, and should be approximately two millimeters larger in diameter. The conjunctival graft is carefully placed onto the corneal defect with the non-epithelialized surface in contact with the cornea. The suture material and suturing technique is similar to that described for conjunctival flaps. Initially, the four corners or quadrants of the graft are sutured to the cornea. Additional sutures should be placed so that the distances between the previously placed sutures are divided equally. Post-operative management is similar to that described for conjunctival pedicle flaps.

Post-Operative Care

Post-operative care is similar for many patients following corneal or conjunctival surgery. Frequent recheck examinations are recommended in most cases to monitor for progress or possible postoperative complications. Broad spectrum topical antimicrobials are indicated to prevent post-operative infection and should be applied three times daily. More specific and aggressive therapy may be required in cases where established infection is recognized by culture and microbial sensitivity, and application frequency should be increased to every two to four hours in some cases. Autologous serum has antiproteolytic properties that inhibit corneal melting and supplies various growth factors that may assist in early post-operative healing, however, care must be taken to avoid microbial contamination of serum. The frequency of topical application varies from three to eight times daily, depending on the case. In cases of corneal melting, additional anti-proteolytic effect may be obtained using systemic doxycycline (5 mg/kg PO BID). Systemic antimicrobials are also indicated in cases of full thickness corneal defects or infected wounds. Secondary uveitis is treated with topical atropine applied once or twice daily for its mydriatic and cycloplegic effects. Systemic antiinflammatories, such as nonsteroidal anti-inflammatory drugs are indicated to decrease post-operative discomfort and inflammation. In many cases, a temporary tarsorrhaphy, will help to protect the eye during the initial postoperative period. An Elizabethan collar should be used to prevent self trauma, and exercise should be restricted during the initial two to three weeks of post-operative healing.

Suggested Readings

1. Gelatt KN, Gelatt JP: Surgery of the cornea and sclera In Gelatt KN, ed.: Small Animal Ophthalmic Surgery. Woburn: Butterworth-Heinemann, 2001, p 180.
2. Gilger BC, Whitley RD: Surgery of the cornea and sclera In Gelatt KN, ed.: Veterinary Ophthalmology (ed 3). Philadelphia: Lippincott Williams and Wilkins, 1999, p 675.
3. Herring IP: Corneal surgery: instrumentation, patient considerations, and surgical principles. Clin Tech Small Anim Pract 18:152, 2003.
4. Hollingsworth SR: Corneal surgical techniques. Clin Tech Small Anim Pract 18:161, 2003.
5. Slatter D: Cornea and sclera In Slatter D, ed.: Fundamentals of Veterinary Ophthalmology (ed 3). Philadelphia: Saunders, 2001, p 293.

Introduction

Prolapse of the gland of the third eyelid (also known as “cherry eye”) is a common occurrence in dogs less than 1 year of age. A breed predisposition has been noted in Boston terriers, Cocker spaniels, Bulldogs, and other brachycephalic breeds. Presenting complaints include ocular discharge, conjunctivitis and unacceptable cosmetic appearance due to protrusion of the gland above the third eyelid.

Because of its importance in tear production, replacement of the prolapsed third eyelid (TE) gland to its normal anatomic location is strongly recommended rather than excision of the gland. While numerous surgical techniques have been described for gland replacement, the two most frequently utilized procedures will be described in this chapter. The first technique is creation of a conjunctival pocket which is tried first in all cases. The second technique fixes the gland to orbital periosteum and is used for recurrent gland prolapses or with the pocket technique if the gland is chronically prolapsed and extremely hypertrophied.

Pocket Technique (Morgan Method)

Instrumentation Required

Small Bishop-Harmon forceps with 0.3 mm wide tips, 2 curved mosquito forceps or towel clamps, tenotomy scissors (Stevens or Westcott), an eyelid speculum (Castroviejo or Barraquer), needle holder (Castroviejo or Barraquer), and absorbable 6-0 suture material (polyglactin 910 or polyglycolic acid).

Surgical Procedure

The patient is placed under general anesthesia and positioned in sternal recumbency. The third eyelid surfaces as well as the periocular haired lid surfaces are swabbed three times with dilute (1:50) povidone-iodine solution. The affected eye is draped with either a sterile, disposable drape or with towels. An eyelid speculum is placed to retract the upper and lower eyelids. The leading edge of the TE is grasped with either mosquito forceps or towel clamps placed near the medial and lateral attachments of the TE to the globe. The clamps are used to maneuver the TE by retracting the lid forward and slightly dorsal such that the bulbar aspect of the TE is exposed.

A curvilinear incision is made in the conjunctiva with tenotomy scissors parallel to the base of the TE gland closest to the fornix (Figure 12-17A). The conjunctiva is best handled with small (0.3 mm) Bishop Harmon forceps. A second incision is made 2 to 3 mm from the free margin of the TE parallel to the gland (Figure 12-17B). The length of the incision corresponds to the length of the exposed gland, but usually approaches 1 cm. The incisions should not converge at either end. It is necessary to leave an area at both ends of the gland that is not incised to allow secretions from the gland to exit onto the ocular surface and not cause cyst formation.

The incisions are then closed so that the third eyelid conjunctiva covers the gland. (Figure 12-17C). A knot is tied on the anterior or palpebral surface of the third eyelid and the needle passed through the lid to the posterior or bulbar side near one end of the incision. The incisions are closed in a simple continuous pattern with 6-0 polyglactin 910 or polyglycolic acid. At the far end of the incision, the needle is again passed through the third eyelid and the knot is tied on the palpebral TE surface. This prevents the suture knots from causing corneal irritation or ulceration.

Postoperative Care

Animals are discharged and owners instructed to apply triple antibiotic ophthalmic ointment 3 times daily for 5 days. The TE gland will likely remain swollen for 2 to 3 days postoperatively, sometimes up to 7 to 10 days, and then return to more normal conformation. An Elizabethan collar may be necessary if the animal shows any tendency to traumatize the eye (s).
 

Orbital Tacking (Stanley Modification of the Kaswan Technique)

Instrumentation Required

Bard Parker blade (#11 or #15), small Bishop-Harmon forceps with 0.3 mm wide tips, 2 curved mosquito forceps or towel clamps, tenotomy scissors (Stevens or Westcott), eyelid speculum (Castroviejo or Barraquer), Derf needle holder, and 3-0 nylon on a cutting needle, 6-0 polyglactin 910, needle holder (Castroviejo or Barraquer).

Surgical Procedure

The patient is placed under general anesthesia and positioned in sternal recumbency. The hair ventral to the eye and over the zygomatic arch is clipped. The third eyelid surfaces as well as the clipped site are swabbed three times with dilute (1:50) povidone-iodine solution. The affected eye is then draped with either a sterile, disposable drape or with towels. A 5 mm long skin incision is made with a #11 or #15 Bard Parker blade, parallel to and just ventral to the periorbital rim (Figure 12-18A). An eyelid speculum is placed to retract the upper and lower eyelids. A second incision is made in the center of the ventral conjunctival fornix with tenotomy scissors on the anterior or palpebral side of the third eyelid (Figure 12-18B).

Using nylon suture, the needle is inserted through the skin incision and a portion of periosteum from the ventral orbital rim is engaged. The needle is then directed to exit the incision in the conjunctival fornix. The leading edge of the TE is grasped with either mosquito forceps or towel clamps placed near the medial and lateral attachments of the TE to the globe. The bulbar surface of the TE is then exposed by retracting the TE forward and slightly dorsal.

Suture material is used to penetrate the gland in multiple directions to anchor it to the periosteum. The needle is inserted through the gland toward the leading edge of the TE and then back through the exit hole to cross horizontally or parallel to the leading edge (Figure 12-18C). The needle is passed back through the exit hole and directed towards the ventral fornix so that it emerges from the initial conjunctival incision. All suture should be covered with conjunctiva. The TE is then reflected back to its normal position and the suture needle is passed back beneath the skin to engage the orbital periosteum a second time. The nylon is tied in a secure knot being careful not to place too much tension on the suture and restrict the movement of the third eyelid. The conjunctival incision may be left open or closed with 6-0 polyglactin 910. Similarly, the skin incision may be left open or closed with nylon.

Postoperative Care

Animals are discharged and owners are instructed to apply triple antibiotic ophthalmic ointment 3 times daily for 5 days. An Elizabethan collar should be applied if the animal shows any tendency to traumatize the eye or surgical site. This technique may result in some TE immobilization which is usually not clinically significant.
 

Some ophthalmic diseases or their consequences necessitate enucleation or orbital exenteration. Generally, enucleation refers to removal of the globe, whereas exenteration refers to removal of the globe and all orbital contents. The indications for enucleation and exenteration are different and are discussed in this chapter.

Pre-Operative Preparation and Surgical Positioning

Preoperative preparation of the surgical site is similar for enucleation and exenteration. Clipping the eyelids and liberal clipping of the periocular facial skin is recommended. Surgical scrubs are generally not used on or around the eye ,and although less important when the eye is to be removed, precautions to prevent surgical scrub contact with the contralateral eye are warranted. Dilute povidone-iodine solution (1:10 to 1:50 dilution of a stock 10% solution) is an effective topical antiseptic for surgical preparation and can be safely applied to the eyelids and corneoconjunctival surface. Perioperative intravenous antibiotic administration is also recommended.Surgical positioning is largely a matter of surgeon preference. I generally place dogs in lateral recumbency and rotate the head so that the palpebral fissure is near horizontal.

Enucleation

Indications for enucleation include most causes of a blind and painful eye. Specific diseases that often lead to enucleation in small animals include end-stage uncontrolled glaucoma, septic endophthalmitis, irreparable globe perforation and irreparable globe proptosis. Dogs with chronic glaucomatous eyes are good candidates for implantation of an intrascleral prosthesis, a surgical alternative that should be considered. Intraocular neoplasms constitute an additional indication for enucleation. However, depending upon the specific neoplasm, age of the animal and presence of secondary ocular complications, the necessity of and preferred timing for enucleation is variable. Many intraocular neoplasms follow a benign course with regard to metastasis (e.g. canine anterior uveal melanoma), whereas others commonly metastasize (e.g. feline diffuse iris melanoma). Additionally, some intraocular neoplasms are amenable to surgical resection or treatment by laser ablation. Consultation with and referral to a veterinary ophthalmologist is encouraged with cases of ocular neoplasia.

The two most commonly utilized methods for enucleation in dogs and cats, transconjunctival and transpalpebral will be described. The tissues removed with both approaches are the same and the approach utilized is often a matter of surgeon preference. However, there are specific clinical indications for utilizing the transpalpebral method. The transpalpebral method is indicated in cases where sepsis or neoplasia involves the corneoconjunctival surface, as the closed conjunctival sac formed with this approach serves to prevent orbital contamination during surgery. I prefer the transconjunctival approach in most cases due to improved visualization and less operative hemorrhage than with the transpalpebral technique. With either approach, a minimum of traction should be applied to the globe during surgery. Excessive globe traction or orbital pressure may stimulate an oculocardiac reflex, which causes bradycardia and is occasionally fatal. Additionally, excessive traction may result in trauma to the optic chiasm or contralateral optic nerve, causing vision loss or blindness in the contralateral eye. The latter complication is a particular concern in cats.

Transconjunctival Approach

Preoperative preparation involves periocular hair clipping and aseptic preparation of the eyelids and ocular surface utilizing dilute (1:10-1:50) povidone-iodine solution. Placement of an eyelid speculum improves visualization. Additionally, a lateral canthotomy is often helpful in cats, dogs with tight eyelid apertures and chronic glaucoma cases where severe buphthalmos encumbers globe removal through an intact eyelid opening (Figure 12-19).

Utilizing curved scissors, a 360° incision is made through the conjunctiva and Tenon’s capsule to expose the sclera (Figure 12-20). Placement of this circumferential incision 2-3 mm posterior to the limbus and leaving a small rim of conjunctiva adherent to the eye is useful, as the surgeon can grasp this tissue to fixate the eye during subsequent globe manipulations. Next, the scleral insertions of the rectus and oblique extraocular muscles are identified and transected (Figure 12-21). Muscles can be identified easily by placing one blade of a curved scissor on the posterior surface of the globe and sweeping it anteriorly. The scissor blade will slip underneath the muscle belly and as it is drawn anteriorly will stop at the muscle’s scleral insertion, at which point the scissors are closed to transect the muscle tendon. Muscle transection is performed at the level of scleral insertion rather than mid-body to reduce hemorrhage. The retractor bulbi muscles are then severed by sliding curved, blunt-tipped scissors posteriorly along the scleral surface and gently cutting the muscles at their scleral insertions. After all extraocular muscles have been severed, the globe should rotate rather freely. A curved hemostat is used to clamp the optic nerve and associated vasculature prior to transecting these structures between the clamp and globe using curved scissors (Figure 12-22). The clamp may be left in place for several minutes during subsequent steps of the surgery to maintain hemostasis. Although seldom necessary, absorbable suture can be used to ligate the optic nerve and associated vasculature prior to removing the hemostat. Again, traction on the optic nerve should be minimized. Some surgeons advocate not using a hemostatic clamp at all by simply transecting the optic nerve and achieving hemostasis with gauze packed into the orbit for several minutes following globe removal.
 

After the globe is removed, the nictitating membrane (3rd eyelid) and its associated gland are excised, followed by removal of the remaining conjunctival tissue.(Figures 13-23 and 13-24) The lacrimal gland can be identified in the dorsolateral region of the orbit and excised, although cyst formation seems rare even when the gland is left in situ. Finally, the margins of the eyelids are removed using Mayo scissors. Excision of the eyelid margins must incorporate the meibomian glands which requires removal of approximately 4 mm of marginal eyelid tissue (Figure 12-25). Due to the presence of secretory structures, failure to excise the lacrimal or meibomian glands may lead to intraorbital cyst formation and dehiscence of the surgical closure.

Prior to wound closure, the orbit is flushed copiously with isotonic sterile irrigating solution. A silicone prosthetic sphere can be placed which improves post-operative cosmesis by preventing the sunken appearance associated with the anophthalmic orbit. Closure involves apposition of the deep orbital fascia using 3-0 to 5-0 absorbable suture in a simple continuous pattern. If a silicone sphere is placed, the deep orbital fascia is sutured over the sphere. Subcutaneous closure is performed using 4-0 to 5-0 absorbable suture in a continuous pattern. The skin is closed with 4-0 to 5-0 non-absorbable suture material in a simple interrupted pattern.

As an alternative to placement of a silicone prosthetic sphere, 3-0 to 4-0 non-absorbable suture can be used to span the rostral orbital opening to prevent post-operative sinking of the skin. This suture is anchored in orbital periosteum and run back and forth across the orbital opening to form a tight meshwork of suture. This is performed after closure of the deep orbital fascia and prior to skin closure.
 

Transpalpebral Approach

Presurgical preparation of the surgical site is identical to that described for the transconjunctival approach. The eyelids are apposed and sutured shut using 3-0 nylon in a continuous pattern. An elliptical skin incision is made with a scalpel paralleling and 4-6 mm from the eyelid margins, converging at the medial and lateral canthus (Figure 12-26). The medial and lateral canthal tendons must be severed completely before progress can be made in dissecting down to the sclera. Although not required, Allis tissue forceps can be placed on the apposed eyelid margins to aid in subsequent globe manipulations. A combination of blunt and sharp dissection using Metzenbaum scissors is used to approach the conjunctiva. Care must be taken not to penetrate the conjunctival surface or the aseptic advantage of the transpalpebral technique is lost. If the conjunctiva is inadvertently incised in cases of ocular surface neoplasia or sepsis, the hole in the conjunctiva should be closed before continuing with dissection. Dissection to the scleral surface just posterior to the limbus allows identification of the rectus and oblique extraocular muscles, which are transected at their scleral insertions. The retractor bulbi musculature is then transected at or near their scleral insertions. The optic nerve is then transected after liagation of the nerve and its vasculature with absorbable suture. Depending on the extent of dissection in the dorsolateral aspect of the orbit, the orbital lacrimal gland may or may not be incorporated in the tissues removed. This can be confirmed by careful palpation in the dorsolateral region of the orbit. After the orbit is irrigated copiously with sterile isotonic solution, surgical closure is performed as described for the transconjunctival approach.
 

Exenteration

Exenteration refers to the surgical removal of the eyelids, globe and all orbital contents including the conjunctiva, extraocular muscles, orbital lacrimal gland, nictitating membrane and associated gland, orbital connective tissue and orbital fat. The most common indications for exenteration include extrascleral extension of intraocular neoplasms and primary orbital neoplasms that are not surgically resectable without concurrent removal of the globe. However, if orbital neoplasms have invaded the bony structures of the orbit or extended beyond the confines of the orbit, exenteration would be palliative and more aggressive surgical procedures such as orbitectomy should be considered. Rarely, medically uncontrollable orbital infection may necessitate exenteration.

Exenteration is generally performed in a manner similar to transpalpebral enucleation, with wider excision margins to incorporate removal of the orbital contents, including the globe, extraocular muscles, nictitating membrane and gland, orbital lacrimal gland and orbital fat. Occasionally, removal of periosteum is indicated, as when neoplastic disease abuts this tissue. The eyelids are sutured shut with 3-0 monofilament suture in a continuous pattern. A surgical blade is used to perform an elliptical skin incision outside of the eyelid margins as for transpalpebral enucleation. This incision may be carried further from the eyelid margins, as necessary, to ensure removal of diseased tissue. However, sufficient skin must be left to allow skin closure without tension on the suture line. Following completion of the skin incision, subcutaneous dissection is continued to the bony margin of the orbit, where the orbital septum is incised. Bands of connective tissue that attach the medial and lateral canthus to the orbital wall, the medial and lateral canthal ligaments, must be sharply incised. The goal of the remainder of the surgery is to continue dissection towards the orbital apex, staying outside of the extraocular muscle cone. Blunt dissection is continued with Metzenbaum scissors and should follow the bony wall of the orbit dorsally and medially proceeding towards the orbital apex. The origin of the ventral oblique muscle is encountered ventromedially and is incised. Dorsolaterally, dissection should proceed underneath the orbital ligament, using care not to transect this structure. Ventral dissection should avoid trauma to or excision of the zygomatic salivary gland, unless it is involved in the disease process, in which case it should also be removed. When dissection to the orbital apex is complete, a curved hemostat is placed around the optic nerve and extraocular muscle cone near the posterior wall of the orbit and these structures are transected with curved Metzenbaum scissors near the clamp. A ligature using absorbable suture is placed around the optic nerve and vasculature posterior to the clamp. The orbit is then irrigated with sterile isotonic solution prior to wound closure.

Two layer wound closure is performed as described for enucleation. Since more extensive orbital tissue removal occurs with exenteration, the sunken appearance of the orbit will be greater than occurs with enucleation. Post-operative cosmesis can be improved by the use of non-absorbable suture material to bridge the anterior opening to the orbit prior to skin closure, as described under transconjunctival enucleation closure. Silicone sphere implants can also be used, but the likelihood of dehiscence and sphere extrusion may be increased due to the lack of deep orbital connective tissue to close over the sphere prior to skin closure. If exenteration is performed due to uncontrollable orbital infection, both methods for improving cosmesis are contraindicated.

Post-operative Care

Postoperative considerations include provision of analgesia, prevention of infection and prevention of self-trauma. The use of opiate analgesics in the early post-operative period followed by oral non-steroidal anti-inflammatory medications for a period of 7 days is recommended. An Elizabethan collar may be used to prevent self-trauma of skin sutures. Dogs are more likely than cats to require an Elizabethan collar. Owners should be advised to keep the incision clean to help prevent localized infection. Systemic antibiotics are generally not required beyond the perioperative period, unless pre-existing sepsis is present.

Complications

Operative complications of enucleation and exenteration include hemorrhage and the previously described complications of oculocardiac reflex stimulation and potential damage to the optic chiasm due to excessive globe or optic nerve traction. Postoperative orbital swelling is common and sometimes severe if related to hemorrhage confined to the orbital space. Although not considered a complication, it is also common to note serosaguinous discharge from the ipsilateral nares for a few days post-operatively as fluid passes through the severed nasolacrimal canaliculus to the nasal ostium. Orbital emphysema is occasionally encountered following enucleation, particularly in brachycephalic dogs, presumably due to air being forced up the nasolacrimal duct and accumulating in the closed orbit. Orbital infection, seroma and cyst formation are rare. Cyst formation is more likely to occur when secretory tissues (e.g. nictitans gland, lacrimal gland) are left in the orbital space. When orbital silicone spheres are placed to improve post-operative cosmesis, sphere extrusion is a potential complication that can be minimized by ensuring that adequate deep orbital fascia covers the sphere prior to skin closure. This complication is more common in cats than dogs.

Suggested Readings

1. Ramsey D.T., Fox D.B.: Surgery of the orbit. Vet. Clin. North Am. Small Anim. Pract. 27:1215, 1997.
2. Slatter D., Basher T.: Orbit. In Textbook of Small Animal Surgery. 3rd Ed. Edited by D.H. Slatter. Philadelphia, Saunders, 2003.