Nasolacrimal duct (NLD) obstruction and dacryocystitis are frequently encountered conditions in equine ophthalmology.
Overview and Clinical Importance
Nasolacrimal duct (NLD) obstruction and dacryocystitis are frequently encountered conditions in equine ophthalmology. The nasolacrimal system functions to drain tears from the eye to the nasal cavity, and any obstruction leads to epiphora (overflow of tears), ocular discharge, and secondary infection. These conditions may be congenital or acquired and represent an important differential diagnosis for horses presenting with chronic ocular discharge.
Understanding the anatomy of the equine nasolacrimal system is essential for accurate diagnosis and successful treatment. The equine NLD is approximately 24-30 cm long in adult horses, making it one of the longest nasolacrimal ducts among domestic animals and prone to obstruction at multiple sites along its course.
| Structure |
Clinical Details |
| Lacrimal Puncta |
Two oval openings (approximately 2 mm diameter) located 8-9 mm lateral to the medial canthus on superior and inferior eyelids |
| Lacrimal Canaliculi |
3-4 mm diameter tubes connecting puncta to the lacrimal sac |
| Lacrimal Sac |
Funnel-shaped structure located in the bony fossa of the lacrimal bone; much less developed in horses compared to humans |
| Nasolacrimal Duct |
Total length: 24-30 cm. Three segments: (1) Caudal osseous segment through lacrimal canal (6-7 mm diameter narrowing to 3-4 mm), (2) Middle membranous segment, (3) Rostral cartilaginous segment |
| Nasal Orifice (NLO) |
3-4 mm oval opening on the ventral floor of the nasal vestibule at the mucocutaneous junction; accessory openings common |
Anatomy of the Equine Nasolacrimal System
The equine nasolacrimal system consists of both secretory and excretory components. The lacrimal gland is located at the dorsolateral aspect of the orbit within the lacrimal fossa, beneath the supraorbital process of the frontal bone.
Components of the Excretory System
High-YieldThe primary clinical entry point for nasolacrimal flushing in horses is through the DISTAL nasal orifice (retrograde access), located on the floor of the nasal vestibule. This is the preferred technique because the duct narrows as it courses caudally.
| Condition |
Description |
Clinical Finding |
| Nasal Puncta Atresia |
Imperforate nasal orifice; most common congenital defect |
Visible bulge at distal NLD during normograde flushing; membrane pulsates with flushing |
| Lacrimal Puncta Atresia |
Absence or stenosis of superior/inferior eyelid puncta |
Cannot cannulate punctum; retrograde flush exits at medial canthus without entering duct |
| NLD Agenesis |
Complete or partial absence of duct |
Dacryocystorhinography shows absence of contrast passage; requires surgical bypass |
Etiology and Pathophysiology
Congenital Causes
Congenital abnormalities of the nasolacrimal system are the most common congenital ocular defect in horses. Clinical signs typically appear within the first 3-4 months of life, though may not manifest until 1-2 years of age.
Acquired Causes
Acquired NLD obstruction is usually unilateral and secondary to various pathological processes:
High-YieldMost acquired NLD obstructions in horses are TEMPORARY and can be alleviated with retrograde flushing. Always investigate for underlying dental or sinus disease, especially if obstruction recurs.
| Category |
Causes |
Mechanism |
| Trauma |
Facial/nasal fractures, eyelid lacerations, blunt trauma |
Direct damage or secondary callus formation/suture exostosis causing stenosis |
| Infection |
Sinusitis, dental disease, primary dacryocystitis, EHV, Adenovirus |
Inflammatory debris, mucosal swelling, stenosing adhesions from chronic infection |
| Foreign Bodies |
Plant material, dust, debris, seeds |
Physical obstruction with secondary inflammation |
| Parasitic |
Habronema spp., Thelazia spp. |
Granulomatous inflammation, especially habronemiasis at medial canthus |
| Neoplasia |
Squamous cell carcinoma (most common), sinus tumors |
Mass compression or invasion of duct |
| Dental Disease |
Periapical tooth root abscess of maxillary cheek teeth |
Extension of infection to adjacent NLD; important in donkeys |
Clinical Signs and Presentation
Primary Signs
- Epiphora: Overflow of tears onto the face, initially clear watery discharge
- Mucopurulent discharge: Thick discharge at medial canthus as condition becomes chronic and infected
- Reflux exudation: Discharge refluxes from puncta when pressure is applied to medial eyelid area
- Conjunctival hyperemia: Mild to severe redness of conjunctiva
- Facial hair staining: Chronic tear overflow causes darkening of facial hair below medial canthus
Clinical Differentiation
| Feature |
Congenital |
Acquired |
| Age at presentation |
Usually less than 3-4 months; may be up to 1-2 years |
Any age |
| Laterality |
May be unilateral or bilateral |
Usually unilateral |
| Response to flushing |
Unsuccessful unless membrane opened surgically |
Often responds to repeated flushing |
| Globe involvement |
Globe usually normal unless chronic blepharoconjunctivitis develops |
May have concurrent ocular disease depending on etiology |
Diagnostic Approach
Complete Ophthalmic Examination
A complete ophthalmic examination should be performed including:
- Visual assessment of discharge character and location
- Examination of eyelid puncta for patency and position
- Schirmer tear test to rule out keratoconjunctivitis sicca
- Fluorescein staining to evaluate corneal integrity
- Examination of nasal orifice location and patency
Nasolacrimal Duct Flushing (Jones Test)
The most useful diagnostic test for nasolacrimal system patency:
Technique for Retrograde Flushing (Preferred Method)
- Sedation and auriculopalpebral nerve block recommended
- Locate nasal orifice on floor of nasal vestibule at mucocutaneous junction
- Insert 14-gauge IV catheter, tomcat catheter, or specialized nasolacrimal catheter
- Flush with sterile saline (10-20 mL) in retrograde direction
- Observe for fluid exit from upper and lower lacrimal puncta
Interpretation: Patent duct = fluid exits from both puncta. Obstruction = fluid refluxes from nostril or does not pass. Careful observation distinguishes upper vs. lower canaliculus patency.
NAVLE TipRemember 'R for Retrograde, R for Rostral' - retrograde flushing enters through the ROSTRAL nasal orifice and flushes caudally toward the eye. This is preferred because you enter at the WIDEST part of the duct.
Fluorescein Passage Test (Jones Test)
Topical fluorescein is applied to the eye and observed for passage through the nasolacrimal system:
- Positive test: Fluorescein appears at nasal orifice within 5-15 minutes
- Negative test: No fluorescein passage indicates obstruction
- Note: Test evaluates both anatomic AND physiologic patency
Advanced Diagnostics
| Diagnostic |
Indication |
Findings |
| Dacryocystorhinography |
Recurrent obstruction, suspected structural abnormality, pre-surgical planning |
Iodinated contrast (4-6 mL) injected via punctum; lateral radiographs show duct course, site of obstruction, stenosis, or agenesis |
| CT Dacryocystography |
Facial trauma, suspected neoplasia, complex anatomical abnormalities |
Three-dimensional assessment of duct, surrounding structures, and relationship to dental arcades |
| Nasolacrimal Endoscopy |
Direct visualization needed, foreign body suspected, therapeutic intervention |
Small ureteroscope (8.5 Fr) passed retrograde; visualizes intraluminal pathology, strictures, foreign bodies |
| Bacterial Culture |
Chronic or recurrent dacryocystitis, purulent discharge |
Collect discharge from puncta or flush material; guides antibiotic selection |
Treatment Options
Medical Management
Initial treatment for most cases of dacryocystitis and acquired obstruction:
Nasolacrimal Catheterization (Stenting)
Indwelling catheter placement for chronic or recurrent obstruction:
- Indication: Repeated obstructions, post-surgical to maintain patency, NLD atresia after opening
- Technique: No. 5 French catheter or polyethylene tubing passed from punctum to nasal orifice
- Duration: Maintain for several weeks to months for epithelialization
- Aftercare: Stockinette or hood to protect; suture both ends to skin
Surgical Interventions
Exam Focus: For the NAVLE, remember that MOST acquired obstructions respond to medical management with repeated flushing. Surgery is reserved for congenital atresia and cases refractory to medical treatment. Always address underlying causes (dental disease, sinusitis, neoplasia).
| Treatment |
Protocol |
Notes |
| NLD Flushing |
Sterile saline 10-20 mL retrograde; repeat daily to every few days until patent |
Most acquired obstructions resolve with repeated flushing |
| Topical Antibiotics |
Triple antibiotic (neomycin/polymyxin B/bacitracin) or gentamicin ophthalmic 3-4x daily |
Instilled after flushing; may also flush through catheter directly into duct |
| Topical Corticosteroids |
Dexamethasone or prednisolone ophthalmic (only if no corneal ulcer) |
Reduces mucosal inflammation; instill after flushing |
| Systemic NSAIDs |
Flunixin meglumine 1.1 mg/kg IV or phenylbutazone 2.2-4.4 mg/kg PO |
Reduces inflammation and provides analgesia |
| Systemic Antibiotics |
TMS 15-30 mg/kg PO BID or based on culture results |
Reserved for severe dacryocystitis or concurrent sinusitis/dental disease |
Prognosis
- Acquired obstruction: Generally good with medical management; most resolve with repeated flushing
- Congenital atresia: Good prognosis with surgical correction; highly effective
- Secondary to neoplasia: Guarded to poor; depends on tumor type and extent
- Canaliculosinostomy: Resolves or improves epiphora with good functional and cosmetic outcome
| Procedure |
Indication |
Description |
| Nasal Puncta Opening |
Nasal puncta atresia (imperforate membrane) |
Pulsating membrane visualized with normograde flush; punctured with #15 blade or 14-gauge needle; followed by catheterization |
| Diode Laser Ablation |
Distal NLD atresia |
Can be performed standing under sedation; creates opening with minimal hemorrhage; followed by stent placement |
| Canaliculorhinostomy |
Permanent mid-duct obstruction |
Creates new drainage pathway from canaliculus to nasal cavity; bypasses obstruction site |
| Canaliculosinostomy |
Permanent NLD obstruction |
Diverts lacrimal secretions into maxillary sinus; can be performed standing; good functional and cosmetic outcome |
| Conjunctivorhinostomy |
Complete NLD agenesis, lacrimal puncta atresia |
Creates direct communication between conjunctival sac and nasal cavity; requires general anesthesia |
Memory Aids and Board Tips
NLD Anatomy Mnemonic: 'PCSND'
Puncta (2 mm) → Canaliculi (3-4 mm) → Sac → Nasolacrimal Duct (24-30 cm) → Distal orifice (3-4 mm)
Remember 'RETROGRADE = ROSTRAL'
Enter from the Rostral (nasal) end and flush Retrograde. This is the preferred technique because you enter at the widest point of the duct.
Congenital vs Acquired: 'Age and Side'
Congenital = Young foal (less than 4 months typically), can be bilateral. Acquired = Any age, usually Unilateral.
High-YieldThe equine NLD is approximately 24-30 cm long (nearly a foot!) - one of the longest among domestic animals. Key landmarks: duct passes OVER the roots of the maxillary cheek teeth and has a dilation above the first premolar.