Surgery of nasolacrimal apparatus and tear systems

Chapter 6 Surgery of nasolacrimal apparatus and tear systems





Introduction


Diseases of the nasolacrimal and tear systems occur frequently in small animals and, to a lesser extent, horses. They can be grouped into those affecting the drainage apparatus, and those involving the tear-producing lacrimal gland and the superficial gland of the nictitating membrane. The health of the cornea, conjunctiva, and eyelids depends on continuous secretion of tears and removal by the drainage apparatus. Malfunctions by either or both tear-drainage and tear-producing systems can lead to overt acute-to-chronic diseases of the cornea, conjunctiva, and eyelids. Recent advances in the diagnosis and treatment of diseases of the nasolacrimal drainage and tear-producing systems in all animal species have resulted in markedly improved prognosis and successful clinical management of these patients.


For convenience, the surgical procedures of the nasolacrimal and tear systems in this chapter are divided into surgical procedures that improve the drainage of tears, and those that increase or substitute for tear production. Diseases of the nasolacrimal apparatus that require surgical intervention are associated with partial-to-complete obstruction. Diseases of the lacrimal and tear-producing glands that require surgical management are usually associated with reduced levels of aqueous tear formation. With reduced levels of tear formation, disorders of the aqueous portion of the preocular or precorneal film develop, resulting in secondary corneal and conjunctival disease.


Excessive lacrimation is usually secondary to pain, or external and internal ophthalmic diseases. Excessive tear secretion can exceed the normal capacity of the tear drainage system, thereby causing clinical signs of epiphora. Similarly, a drainage system with disease also produces epiphora but tear production is at normal levels. Therapy of tear drainage system diseases is usually a combination of medical and surgical modalities, and re-establishment of patency.



Nasolacrimal apparatus


The nasolacrimal drainage apparatus conveys tears and other debris from the external eye to the nasal cavity. This process appears to be only a passive capillary-like activity in animals, and the valve-like structures within the human nasolacrimal apparatus that prevent reverse flow have not been identified in small animals. The orbicularis oculi muscle may affect the lacrimal sac to create a vacuum and/or pressure that may assist in the movement of tears through the system. The anatomic arrangement of the orbicularis oculi muscle in the medial canthus and near the lacrimal sac also supports a more active process which may be involved in the uptake and movement of tears down the nasolacrimal apparatus.


Two species possess only one lacrimal punctum: 1) the rabbit has a single ventral lacrimal punctum; and 2) the pig has a single upper lacrimal punctum (the ventral punctum and canaliculus are occluded and non-functional).



Nasolacrimal anatomy in dogs and cats


The nasolacrimal apparatus consists of the upper and lower lacrimal puncta, the upper and lower canaliculi, the lacrimal sac, and the long nasolacrimal duct that empties into the rostral nasal cavity (Fig. 6.1). Although there are considerable variations in head shape and size in the different breeds of dogs, the predominant anatomic variation of the nasolacrimal apparatus is the variable length and diameter of the nasolacrimal duct.



In dogs, the upper and lower lacrimal puncta are located in the palpebral conjunctiva just deep to the mucocutaneous junction, about 5 mm from the medial canthus, and appear as slit-like openings. In cats, the lacrimal puncta are more circular and smaller. From both lacrimal puncta the nasolacrimal system continues as two canaliculi that converge beneath the medial canthal ligament at the level of the lacrimal bone and fossa to form a poorly developed nasolacrimal sac. From the ventral portion of the lacrimal sac emerges the nasolacrimal duct to traverse the small intraosseous canal of the maxillary bone to enter the nasal cavity within the maxilloturbinate to the nasal meatus. This intraosseous portion of the nasolacrimal duct appears to have the smallest diameter, and appears to be the area most apt to become obstructed by inflammation and debris.


The variable length of the nasolacrimal duct has a larger diameter, and may also have accessory openings immediately above the root of the upper canine teeth, perhaps just as it enters the nasal cavity. The distal opening of the nasolacrimal duct of both the dog and the cat can be located ventrolateral near the margin of the alar fold. Dilatation of the external nares by speculum assists in locating the distal opening. The distal opening can be cannulated for retrograde lavage of the nasolacrimal system. Because of the difficulty of retrograde nasolacrimal cannulation at the nares in the dog and cat, the convenient and readily accessible upper and lower lacrimal puncta are the usual entry for nasolacrimal flushes and other manipulations.



Nasolacrimal anatomy in large animals


The anatomy of the nasolacrimal system of the horse and cow is very similar to that of the dog and cat, but much larger. In horses, the system starts as two lacrimal puncta, about 2 mm in diameter, located about 8 mm from the medial canthus and inside the lid margins. The two canaliculi or lacrimal canals connect the puncta with the lacrimal sac, which is poorly developed in the horse. The long and tortuous nasolacrimal duct, with a prominent dilatation above the first premolar tooth and about 25–30 cm long, extends from the lacrimal sac to the floor of the mucocutaneous junction of the nostril where its diameter is about 3–4 mm. From its beginning of about 6–7 mm diameter, it extends from the lacrimal sac through the osseous lacrimal canal of the maxillary bone (about 3–4 mm diameter). In mules, the nasolacrimal canal exits on the lateral part of the floor or lateral wall of the nostril. Accessory openings may also occur further caudad. In general, the primary clinical entry into the equine nasolacrimal system is into its distal orifice, at the beginning of the mucosa on the floor of the nostril.


In cattle, the entire length of the nasolacrimal system is about 16–18 cm long. The upper and lower lacrimal puncta are 2–5 mm diameter and connected by the 1–1.5 cm diameter lacrimal canaliculi to the lacrimal sac (about 5–8 mm diameter). The nasolacrimal duct is about 12–15 cm long and straighter than the horse nasolacrimal duct. The distal orifice of cattle, which is not easily accessible clinically, is located near the lateral wall of the nostril on the medial surface of the alar fold of the ventral nasal concha. Hence, for nasolacrimal flushes in cattle, entry is usually through the upper or lower lacrimal punctum.



Clinical diagnostic tests for the nasolacrimal drainage apparatus


The two most useful diagnostic tests for the determination of nasolacrimal apparatus functions in all animal species are: 1) the passage of topical fluorescein; and 2) the nasolacrimal flush and cannulation. The fluorescein test measures both the anatomic and physiologic patency of the nasolacrimal system. Aqueous fluorescein instilled onto the eye will normally enter the lacrimal puncta (mainly the lower punctum), traverse the entire nasolacrimal system, and appear at the external nares in 2–5 min. Fluorescein passage time seems directly related to the length of the entire nasolacrimal system. In brachycephalic breeds of dogs and cats, the nasolacrimal duct is considerably shorter and tortuous, and fluorescein may exit the nasolacrimal duct to enter the nasopharynx rather than the external nares. In any breed of dog, if the dog’s head is restrained upward during the test, the dye can also collect in the nasopharynx.


With a delayed or negative fluorescein test, the entire nasolacrimal system can be flushed. The nasolacrimal flush tests for the anatomic patency of the nasolacrimal system. Under topical anesthesia and with the head of the dog firmly restrained, either the upper or lower lacrimal punctum is located, cannulated with a lacrimal or 20–22 g blunt stainless steel needle, and flushed with 1–3 mL of sterile saline. The saline should exit out of the external nares, unless the head is maintained dorsally, in which case the saline will enter the nasopharynx, and the animal may gag or sneeze.


In the cat, topical anesthesia, sedation, and some magnification are generally necessary for nasolacrimal flushes. The cat’s lacrimal puncta are round rather than oval, and best cannulated with a 25–26 g blunt hypodermic needle or lacrimal cannula.


In horses, the entire nasolacrimal system is flushed from its distal orifice, located on the floor of the nostril at its mucocutaneous junction. An 18 g blunt hypodermic needle connected via tubing and a 10 mL syringe is used to flush the system. Careful observation can usually distinguish the individual patency of the upper and lower lacrimal puncta during the injection of saline or sterile water.


In cattle, nasolacrimal flushes are conducted under topical anesthesia and manual restraint of the animal’s head. Either the upper or lower lacrimal punctum is cannulated with an 18 g blunt hypodermic needle and a 10 mL syringe, and either saline or sterile water is used to flush the entire system.


Visualization of the nasolacrimal system is possible in all animal species with dacryocystorhinography (Fig. 6.2). Observation of the system may be necessary when there is medically non-responsive or recurrent nasolacrimal sac or duct obstructions, or the possibility of nasal cavity masses. For dacryocystorhinography, general anesthesia of the patient and at least two radiographic views of the nasolacrimal system are necessary. A viscid cardiovascular radio-opaque solution (0.2–0.7 mL) is slowly injected into the upper lacrimal punctum in small animals and about 4–6 mL in foals and adult horses; 10–30 s later at least two radiographic views are taken. Dacryocystorhinography can detect irregularities in both the system’s diameter and course, and is generally most useful prior to consideration of surgeries of the lacrimal sac and nasolacrimal duct.




Nasolacrimal catheterization


Nasolacrimal catheterization in the dog, cat, and horse consists of the placement of indwelling sutures or tubing spanning the upper or lower lacrimal punctum to the external nares for several days to a few months to help maintain patency. Nasolacrimal catheterization is indicated in patients with repeated obstructions of the nasolacrimal system (usually the nasolacrimal sac and duct), secondary to nasolacrimal duct atresia in foals, following lacerations of the upper nasolacrimal system (usually the lacrimal puncta and canaliculi), and postoperatively after nasolacrimal system surgery.


With the dog or cat under short-acting general anesthesia, a blunted (smooth melted end) 2-0 to 3-0 monofilament nylon suture is carefully inserted into the upper lacrimal punctum, upper canaliculus, lacrimal sac, and nasolacrimal duct to emerge from the external nares (Fig. 6.3a). The nylon suture can potentially become halted temporarily at the base of the lacrimal sac and at the accessory opening of the nasolacrimal duct immediately above the root of the upper canine tooth. Gentle turning and twisting of the suture can pass these barriers en route to the external nares. Once the nylon suture has traversed the system, PE 90 polyethylene, fine polyvinyl, or silicone tubing is slid over the entire length of the suture if a larger diameter cannula is preferred. The suture is removed leaving the tubing within the nasolacrimal system; both ends are attached by one or two simple interrupted non-absorbable sutures to the skin of the medial canthus and lateral of the external nares (Fig. 6.3b,c). In foals and adult horses, the entire nasolacrimal system from the upper or lower lacrimal punctum to its distal orifice can be easily traversed by a No. 5 French catheter.



In some small animal patients only the nylon suture can be passed through the nasolacrimal system. Perhaps the lumen within the system is too restricted or swollen to permit passage of the larger diameter tubing. In these patients, the presence of the suture can still maintain the patency of the system. If the dog is lightly anesthetized, contact of the catheter in the distal nasolacrimal duct, perhaps at the accessory opening, may initiate sneezing. The system should remain in place for several days to a few weeks. Both topical solutions and systemic medications are usually administered with the nasolacrimal catheter in position.


In general, an E-collar is necessary in small animals, or a face mask and stockinet in horses to prevent the animal from dislodging the ends of the nasolacrimal catheter. For sufficient and complete epithelialization of a new tear bypass, it is necessary for the catheter to remain in position for several weeks.



Surgical procedures for the nasolacrimal apparatus


Surgical procedures for the nasolacrimal apparatus are divided into minor and major procedures. Minor procedures include surgical treatment of the imperforate punctum, displacement of the lower punctum, enlargement of the lower punctum, lacerations of the canaliculi, and dacryocystotomy. The more extensive or major surgical procedures, which construct new avenues for the drainage of tears from the conjunctival fornix, include conjunctivorhinostomy, conjunctivomaxillary sinusotomy, and conjunctivoralostomy (or conjunctivobuccostomy). In the conjunctivorhinostomy technique, a tear drainage bypass is created into the caudal nasal cavity from the medial conjunctival fornix. In the conjunctivobuccostomy procedure, a subcutaneous tear drainage bypass is created from the middle of the ventral conjunctival fornix to terminate in the oral mucosa beneath the upper lip. These surgical procedures are indicated when the nasolacrimal system has been irreversibly damaged by inflammation, trauma, and neoplasia, and restoration of its patency is impossible in all animal species.



Surgery for imperforate lacrimal punctum


Imperforate lacrimal punctum occurs in a number of breeds of dogs, but most frequently in the Toy and Miniature Poodles, Sealyham Terrier, American Cocker Spaniel, Golden Retriever, and Bedlington Terrier. Lower punctum obstructions are commonly presented because of epiphora. However, upper punctum obstructions do not generally produce clinical signs and are only detected as part of an ophthalmic examination.


The imperforate lacrimal punctum should be distinguished from atresia of the puncta. In the imperforate lacrimal punctum, the opening of the punctum is covered by a thin veil of mucosa. Absence of the punctum indicates that the entire punctum is missing; with punctum absence the corresponding canaliculus is also missing. In my experience, imperforate lacrimal puncta are not infrequent in dogs, but atresia of the lacrimal puncta is rare.


With the impaired drainage of tears with lower lacrimal punctum obstruction, excessive moisture and rust-colored staining of the medial canthal skin and hair are usually present (Fig. 6.4). Concurrent conjunctivitis is usually absent, but variable amounts of dermatitis of the eyelids and face may be present.



Close inspection of the medial lower palpebral conjunctiva detects the absence of the lower lacrimal punctum. The topical fluorescein test is usually delayed or negative. The nasolacrimal flush performed through the upper lacrimal punctum exits from the nasolacrimal duct and external nares, but not through the lower punctum. Observation of the medial lower palpebral conjunctiva during the initial injection of saline may reveal a slightly raised or ballooned area during the initial flush that corresponds to the orifice of the lower punctum (Fig. 6.5a).



The mucosa overlying the lower punctum may be excised, leaving an oval to round defect, or a cruciate incision may be performed in the area (Fig. 6.5b). The nasolacrimal flush is again performed to confirm patency. Topical antibiotic/corticosteroid solutions are instilled six to eight times daily for 10–14 days to maintain patency and prevent the orifice wall from healing together. Intracanalicular gelatin implants may also be used to maintain the punctum’s patency.



Enlargement of the lower punctum


Lower lacrimal micropuncta occur occasionally in the dog and result in epiphora. Scarring following conjunctival inflammation and trauma may also reduce the lower lacrimal punctum’s diameter and impair the drainage of tears. The fluorescein test will be delayed or negative. The nasolacrimal flush will indicate patency of the lower lacrimal punctum, but greater resistance to the flush.


Treatment consists of surgical enlargement of the lower punctum. Under short-acting general anesthesia, the opening of the micropunctum is incised with the Bard–Parker No. 11 scalpel or Beaver No. 6500 or 6700 microsurgical blade (Fig. 6.6). The knife blade is slid further into the lower canaliculus, and an additional 3–5 mm of canaliculus wall is incised. Alternatively, the mucosa around the lower punctum is incised into three sections and excised. Postoperative treatment consists of topical antibiotics and corticosteroids administered six to eight times daily to control the healing process and prevent fibrosis.




Displacement of the lower lacrimal punctum


The lower punctum is normally situated 3–5 mm from the medial canthus and 1–2 mm bulbar of the eyelid margin in the palpebral conjunctiva. Displacement of the punctum occurs infrequently in the dog; in these patients the lower punctum is usually displaced several millimeters ventral of its normal position. The condition may be primary or secondary to entropion, ectropion, trauma, and scarring.


Treatment for a displaced lower punctum is influenced by the extent and severity of epiphora, the associated dermatitis, and tear staining. Mild or intermittent epiphora is usually tolerated, and no surgical treatment is attempted. Patients with extensive medial canthal dermatitis and irritation require treatment. The fluorescein passage test is either delayed or negative. The nasolacrimal flush will indicate if the system is patent, but the lower punctum is failing to convey the normal volume of tears into the lower canaliculus. The recommended initial treatment is to dilate the displaced lower punctum and canaliculus to enhance the uptake of the tears. In the event that this fails, the displaced punctum can be relocated to its normal position or a new exit for tear drainage is constructed to the mouth, maxillary sinus, or nasal cavity. Transposition of the lower punctum, although minor surgery, requires magnification and cannulation of the punctum and canaliculus during surgery and for several weeks postoperatively.


After general anesthesia and surgical preparation of the medial canthus, the lower punctum and canaliculus are cannulated with 2-0 to 3-0 monofilament nylon, and PE 90 polyethylene tubing is slid over the suture. The mucosa around the lower punctum is incised with the Beaver No. 64 scalpel blade. By dissection with tenotomy scissors, the lower canaliculus is isolated for approximately 5–8 mm. The lower punctum and canaliculus are moved to a small linear incision in the lower palpebral conjunctival mucosa, 1–2 mm deep in the eyelid margin. The monofilament suture or polyethylene tubing catheter is sutured to the medial lower eyelid and the skin caudal to the nostril. If the transplanted lacrimal punctum and canaliculus have some surrounding mucosa, at least three 6-0 simple interrupted absorbable sutures are placed about the punctum to secure it. If limited mucosa is available, sutures may adversely affect the punctum, and the cannula is critical to maintain the transplanted tissues in position. Topical antibiotics and corticosteroids as well as systemic antibiotics are administered for 7–10 days. The nasolacrimal catheter is removed after 3–4 weeks.



Lacerations of the canaliculi


Most lacerations of the dog’s eyelids involve the lateral aspects; medial eyelid lacerations are infrequent. If the laceration affects the medial canthus, transection of the canaliculus is likely. Lacerations that involve the canaliculi, generally the lower, are usually in the vertical or somewhat angled plane. The torn eyelid is usually highly edematous; debris and hemorrhage may obscure the extent of the injury. Identification of the canaliculus is usually difficult but is enhanced during the injection of air either retrogradely from the nares or from the fellow nasolacrimal punctum. The exit of bubbles from within the lacerated lid can greatly facilitate localization and canalization of the severed canaliculus. Tissue destruction and resultant inflammation can markedly distort the area.


After surgical preparation, the upper lacrimal punctum and canaliculus are cannulated with the gold lacrimal or 22–23 g stainless steel needle, and the system is flushed to locate the lower canaliculus. The distal portion of the lacerated lower canaliculus is usually difficult to locate because of tissue trauma and swelling. If both parts of the canaliculus can be identified and cannulated, the edges of the eyelid laceration are carefully apposed, usually in two layers. The nasolacrimal catheter of PE 50 to 90 polyethylene is manipulated over the suture through the system, tied, and sutured to the skin at the medial canthus and lateral to the nostril.


Postoperative treatment includes topical and systemic antibiotics and corticosteroids. The nasolacrimal catheter is left in situ for 4–6 weeks. Frequency of topical therapy should be about six times daily. After most of the eyelid swelling has decreased, topical therapy is applied three to four times daily until the nasolacrimal catheter is removed.


Oct 14, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Surgery of nasolacrimal apparatus and tear systems
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