How to Manage Excessive Tearing in the Horse

Amber L. Labelle, DVM, MS, Diplomate ACVO

1. Introduction the eye. Immunologic properties of the tear film Tearing is a common sign of ocular disease and is are important for ocular surface defense and health. frequently misdiagnosed by equine practitioners as The old adage, “no foot, no horse,” is certainly true; obstruction of the nasolacrimal system. This re- its ocular equivalent is “no tear film, no eye”! port will focus on the anatomy of the lacrimal sys- The nasolacrimal drainage system is responsible tem, the differential diagnoses of excessive tearing, for removing the tear film from the ocular surface. and treatment of excessive tearing in the horse. The structures involved in the nasolacrimal drainage system include the ocular (proximal) puncta, the 2. Anatomy and Physiology of the Nasolacrimal canaliculi, the lacrimal sac, the nasolacrimal duct, System and the nasal (distal) puncta (Fig. 1). The ocular The primary function of the lacrimal system is to puncta are located in the medial canthus, with one produce and drain the tear film from the surface of punctum located just inside the eyelid margin of the eye. The tear film is composed of three inte- the upper eyelid and one punctum located just inside grated layers: the aqueous, mucus, and lipid lay- the eyelid margin of the lower eyelid. The ocular ers. The aqueous layer is produced by the orbital puncta are difficult to visualize without magnifica- lacrimal gland and gland of the third eyelid and tion. Normal tear film flow through the ocular secreted onto the ocular surface through ductules puncta is facilitated by blinking and by the apposi- that traverse the conjunctiva. The mucus layer is tion between the eyelid and the ocular surface. produced primarily by conjunctival goblet cells and Each punctum is drained by a canaliculus that con- secreted directly onto the ocular surface. The lipid nects to a common lacrimal sac. This lacrimal sac layer is produced by the meibomian glands present is drained by the nasolacrimal duct, which runs at the eyelid margin and is also secreted directly through the skull and empties through the nasal onto the ocular surface. Tear film plays an essen- puncta, located on the ventral floor of the nasal tial role in corneal health; it provides oxygen and passage (Fig. 2). nutrients to the corneal epithelium while removing The nasolacrimal system exists in a balance be- debris and waste products. Tear film also keeps tween tear production and tear drainage by the na- the ocular surface lubricated and plays an important solacrimal drainage system. Normal horses have part in the optics of the eye, allowing light to pass an ocular surface tear volume of approximately uninterrupted from the external environment into 230 ␮L and a tear flow rate of 33.62 ␮L/min, with

NOTES

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Fig. 3. A positive Jones test is demonstrated in this horse with a normal nasolacrimal drainage system. Fluorescein is observed draining freely from the nares.

3. Assessment of the Nasolacrimal System Tear production can be assessed in the horse by the Schirmer tear test (STT). To perform an STT, a folder Schirmer tear strip is placed in the lower Fig. 1. Diagram of the nasolacrimal drainage system in a nor- conjunctival fornix of an unsedated horse for 60 mal horse. Two proximal ocular puncta (dorsal and ventral) are seconds. The STT is useful for diagnosing deficien- each drained by a canaliculus to a common lacrimal sac. The cies of tear production, but is not particularly help- nasolacrimal duct drains the lacrimal sac to the distal nasal ful for diagnosing excessive tear production. The punctum. function of the nasolacrimal drainage system can be assessed several ways, most importantly by per- forming a complete ophthalmic examination on the patient to identify any cause for excessive tearing. the entire volume of the tear film recycled every 1 The function and patency of the nasolacrimal sys- 7 minutes. Any abnormality in the system can tem is assessed by the Jones test, whereas patency result in the tear film overflowing the system and alone can be assessed by lavage of the nasolacrimal draining onto the face. Diseases of the nasolacri- duct. It is important to distinguish the clinical im- mal drainage system can be roughly divided into two plications of the results of these two tests: lavage categories: diseases of excessive tear production of the nasolacrimal system only confirms patency, and diseases of decreased tear drainage. not function. The Jones test is performed by in- stilling a small amount (0.3–0.5 mL) of fluorescein solution onto the ocular surface and observing fluorescein at the nasal puncta within 5 to 20 minutes (Fig. 3). Sedation may facilitate rapid passage of fluorescein by lowering the horse’s head. A negative Jones test is one in which no fluorescein is observed at the nares. Nasolacrimal duct lavage can be performed as retrograde (through the nasal puncta) or normograde (through the ocular puncta). Retrograde lavage is easier to perform because it does not require topical anesthesia or magnification to identify the puncta. When retrograde lavage is unsuccessful, normograde lavage should be performed. A suit- able cannula should be used, which may include a 4F to 6F polyethylene urinary catheter, an open- ended tomcat catheter (best for normograde lav- Fig. 2. The normal nasal puncta can be observed on the ventral age), or a 16-gauge intravenous (IV) catheter with floor of the nares as a pink mucosal oval in otherwise haired skin the stylet removed (best for retrograde lavage). (arrow). To perform retrograde lavage, the patient should be

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Table 1. Possible Causes of Ocular Pain in Horses

Corneal perforation/ Blunt trauma penetrating trauma

Eyelid abrasion/laceration Corneal ulcer Entropion Corneal abrasion Eyelid margin defect Corneal foreign body Eyelid neoplasia Stromal abscess Ocular surface neoplasia (ie, squamous cell Ectopic cilia carcinoma) Conjunctivitis Conjunctival foreign body Uveitis Glaucoma

clinical practice but are useful for localization in cases of nasolacrimal duct obstruction.4,5

4. Diseases of the Nasolacrimal System: Excessive Production The most common cause of excessive tearing in horses is excessive production of tears secondary to an irritating stimulus. A complete ophthalmic examination, including fluorescein staining, tonome- Fig. 4. Retrograde lavage of the nasolacrimal duct. The prac- try, and funduscopy, should be performed on every titioner stands to the side of the horse and uses the far-side hand horse presented with a complaint of tearing. Ex- to place a cannula (in this case, a 16-gauge IV catheter with the cessive tear production is frequently accompanied stylet removed) into the nasal puncta. The near hand then occludes the nasal puncta and secures the cannula while the far by blepharospasm, another indicator of ocular pain. hand injects saline solution through IV extension tubing attached Sign of ocular pain is an important observation for to the cannula. This positioning allows the practitioner to keep differentiating ocular discharge associated with ex- the cannula in a secure position while easily injecting with less cessive production of tears from that associated chance of the patient dislodging the cannula. with decreased drainage of tears. Decreased drainage of tears is not associated with ocular pain and should not be associated with blepharospasm. When blepharospasm and excessive tearing are observed sedated and the cannula gently fed several centime- concurrently, a painful ocular condition is the most ters into the nasal puncta (Fig. 4). The cannula likely cause of the excessive tearing. should be retracted if resistance is encountered be- Possible causes of ocular pain are extensive and cause some horses may have a blind-ended pouch in diverse (Table 1). The astute practitioner will thor- their distal nasolacrimal duct that can be inadver- oughly examine the patient for subtle clinical signs tently cannulated, making lavage more difficult. of ocular disease. Careful attention should be paid Intravenous extension tubing can be attached to the to the intraocular exam. Miosis accompanying cannula to allow the practitioner more freedom to blepharospasm is a sign of intraocular disease and attach a syringe with less risk of dislodging the should prompt further examination. The applica- cannula. Sterile saline (10–12 mL) may then be tion of topical anesthetic to the ocular surface may slowly injected through the cannula and observed to be a useful diagnostic test. If blepharospasm re- drain from the eye. No more resistance should be solves with the application of topical anesthetic, an encountered during injection than is expected with ocular surface disease is the most likely cause of the an IV injection. Gentle pulsing pressure may be excessive tearing and blepharospasm. If blepharo- useful for dislodging obstructions. Normograde la- spasm does not resolve, intraocular disease is the vage is performed similarly, with the exception that most likely cause. a topical anesthetic should be applied to the ocular One important cause of ocular discomfort and ex- surface before cannulation of the ocular puncta. cessive tearing is environmental irritants. These Advanced imaging techniques have been de- may include allergens, particulate matter, wind, scribed for the nasolacrimal duct. Dacryocystorhi- ultraviolet light, or extreme temperatures. This is nography refers to the technique of imaging the a diagnosis of exclusion after eliminating other nasolacrimal drainage system through the use of causes of excessive tearing. Treatment beyond envi- radiopaque contrast agents and can be performed by ronmental modification may not be required for such means of radiography or computed tomography.2,3 cases. A flymask may be useful in decreasing en- Endoscopy of the nasolacrimal duct has also been vironmental irritants. Topical antihistaminesa are reported. These techniques are not widely used in rarely indicated but may be useful in some cases.

AAEP PROCEEDINGS ր Vol. 59 ր 2013 157 HOW-TO SESSION: OPHTHALMOLOGY 5. Diseases of the Nasolacrimal System: ment with broad-spectrum systemic antibiotics and Decreased Drainage anti-inflammatories for 2 to 3 weeks is warranted. A topical antibiotic-corticosteroid solution may also Congenital Malformations be used, provided that the cornea is fluorescein- Congenital abnormalities of the nasolacrimal drain- negative and free of ulceration. When the obstruc- age system are most frequently diagnosed in horses tion is difficult to dislodge or recurrence occurs, Ͻ1 year of age.6–10 Ocular discharge may be se- cannulation of the nasolacrimal duct as is described rous or mucopurulent in nature. The nasal puncta for nasal punctal atresia may be warranted. Any is the most common site of atresia, and diagnosis catheter should be left in place for 4 to 6 weeks, and can be confirmed by visual assessment of the nasal concurrent antibiotic and anti-inflammatory treat- floor. The Jones test and nasolacrimal duct lavage ment should be implemented. Advanced surgical will be negative in cases of nasal punctal atresia. intervention, including creation of alternate tear The nasolacrimal duct itself may also have atresia, flow pathways into the nearby nasal cavity or sinus and dacryocystorhinography may be warranted. (canaliculorhinostomy or conjunctivorhinostomy), Nasal punctal atresia is treated by surgical cre- has been infrequently reported in the horse.9,13 ation of a nasal puncta. The procedure can be performed under general anesthesia or standing sedation Malpositioned Globe with topical and local anesthetic. The upper or Enophthalmos (caudal displacement of the globe lower ocular puncta are cannulated with the use of within the orbit as the result of decreased orbital 5F plastic tubing (such as a urinary catheter) and contents) results in poor apposition of the eyelid advanced distally until the catheter tip can be ob- margin against the globe. This malpositioning of served at the ventral nasal floor. A No. 15 scalpel the globe relative to the eyelids results in decreased blade is used to make a single full-thickness incision tear flow into the ocular puncta and canaliculi. through which the catheter is fed. Hemorrhage as- Enophthalmos is more common in older horses and sociated with this incision may be significant, so a horses in poor body condition caused by atrophy of single decisive incision is recommended. The cath- orbital fat. Treatment includes improving body eter is then sutured at the medial canthal skin and condition where possible and diligent facial hygiene, nares with the use of three to five sutures per site for with special attention to keeping the periocular skin maximum security. After surgery, the patient is clean and dry. treated with a broad-spectrum topical antibiotic solution and systemic nonsteroidal anti-inflammatory Ocular Punctal Occlusion drugs. The catheter is left in place for 4 to 6 weeks as a stent while the newly created puncta heals. Atresia of the ocular puncta is rare, but chronic Patency can be confirmed by the Jones test before conjunctival inflammation may lead to fibrosis and removal of the catheter. Premature dislodging of occlusion of the ocular puncta. Treatment is simi- the catheter can be addressed by replacing the cath- lar to nasal punctal occlusion, although cannulation eter as previously described. Dacryocystitis and of the nasolacrimal duct must be performed in a other complications associated with catheter place- retrograde fashion. ment is uncommon. Other congenital malformations, including anom- References and Footnote 5 alous puncta, have been reported in the horse. 1. Chen T, Ward DA. Tear volume, turnover rate, and flow Surgical repair of such abnormalities require dac- rate in ophthalmologically normal horses. Am J Vet Res ryocystorhinography to ensure that the anatomic 2010;71:671–676. location is identified and that appropriate surgical 2. Latimer CA, Wyman M, Diesem CD, et al. Radiographic and gross anatomy of the nasolacrimal duct of the horse. Am J Vet repair is selected. Res 1984;45:451–458. 3. Nykamp SG, Scrivani PV, Pease AP. Computed tomography Functional Obstruction: Dacryocystitis, Foreign dacryocystography evaluation of the nasolacrimal apparatus. Body, and Dacryolith Vet Radiol Ultrasound 2004;45:23–28. The nasolacrimal drainage system may become in- 4. Latimer CA, Wyman M. Atresia of the nasolacrimal duct in three horses. J Am Vet Med Assoc 1984;184:989–992. flamed or infected (termed dacryocystitis), resulting 5. Gilger BC, Histed J, Pate DO, et al. Anomalous nasolacri- in functional obstruction to outflow. Intraluminal mal openings in a 2-year-old Morgan filly. Vet Ophthalmol foreign bodies are suspected as an occasional cause of 2010;13:339–342. nasolacrimal drainage system obstruction. Dacryo- 6. Hjorth P. Atresia of the naso-lacrimal duct in a horse. liths (mineral concretions within the nasolacrimal Nord Vet Med 1971;23:260–262. 11 7. Lundvall RL, Carter JD. Atresia of the nasolacrimal meatus duct) are rarely reported. External compression in the horse. J Am Vet Med Assoc 1971;159:289–291. from sinonasal disease may also decrease nasolacri- 8. Mason TA. Atresia of the nasolacrimal orifice in two Thor- mal duct flow.12 oughbreds. Equine Vet J 1979;11:19–20. Clinical signs include serous or mucopurulent 9. Theoret CL, Grahn BH, Fretz PB. Incomplete nasomaxil- lary dysplasia in a foal. Can Vet J 1997;38:445–447. discharge. The Jones test is negative, and naso- 10. Grahn BH, Wolfer J, Cullen CL. What is your diagnosis and lacrimal duct lavage should be attempted in all therapeutic plan? Congenital atresia of the left nasolacri- cases. If lavage is successful, post-lavage treat- mal duct. Can Vet J 1999;40:71–72.

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11. Cassotis NJ, Schiffman P. Calciﬁcation associated with the 13. McIlnay TR, Miller SM, Dugan SJ. Use of canaliculorhinos- nasolacrimal system of a horse: case report and mineralogic tomy for repair of nasolacrimal duct obstruction in a horse. composition. Vet Ophthalmol 2006;9:187–190. J Am Vet Med Assoc 2001;218:1323–1324;1271. 12. Carslake HB. Suture exostosis causing obstruction in the nasolacrimal duct in three horses. N Z Vet J 2009;57:229– 234. aOpcon A, Bausch & Lomb, Rochester, NY 14604-2701.

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