Nasolacrimal Duct Cannulation and Flushing in Rabbits (Disease Investigation & Management - Treatment and Care)

• Nasolacrimal duct flushing
• Irrigation of the nasolacrimal duct
• Lacrimal cannulation

• While most veterinary procedures described for use in domestic rabbits can also be used in wild lagomorphs, it is much more likely that sedation or anaesthesia will be required to carry out such procedures in these animals.

Flushing purulent debris through the nasolacrimal duct will improve the tear drainage and remove infected debris. Flushing is often successful in curing primary bacterial infections and can improve secondary infections of the duct that are caused by underlying dental disease. (B600.11.w11)

Relevant Anatomy

• Lacrimal punctum:
  • The "punctum lacrimale" or "lacrimal punctum" is the opening of the nasolacrimal duct in the conjunctiva. 
  • It can be seen in the lower conjunctiva, near the medial canthus of the eye, by everting the lower eyelid. (J213.9.w1)
  • It is large (two to four millimetres, depending on the size of the rabbits) and may be pigmented. (B602.14.w14)
  • There is no lacrimal punctum in the upper eyelid unlike in cats and dogs. (B600.11.w11)
• Lacrimal sac:
  • "The punctum opens into a short (2 mm) canaliculus that opens into a dilation of the duct or lacrimal sac". (B600.11.w11)
• Nasolacrimal duct:
  • The nasolacrimal duct exits the lacrimal sac via a small hole (lacrimal foramen) in the lacrimal bone into the maxilla where the duct is encased in the bony lacrimal canal and runs rostroventrally and medially until it comes to the root of the primary maxillary incisor. Here it makes an abrupt mediodorsal bend and becomes smaller in diameter (decreases from around 2 mm to 1 mm). The duct is compressed between the nasal cartilage and the alveolar bone that surrounds the root of the primary maxillary incisor and so it can easily be occluded at this point if the root of the incisor becomes elongated. The duct then runs medially alongside the incisor tooth root, emerging at the ventromedial aspect of the alar fold in the nasal cavity just inside the mucocutaneous junction. (B600.11.w11)

Restraint

• Anaesthetise for the initial investigation and flushing
  • "General anaesthesia is always indicated for the initial investigation and irrigation of the nasolacrimal duct and is, in general, preferable for subsequent nasolacrimal duct flushing". (B600.11.w11)
  • The nasal mucosa is sensitive in rabbits and flushing the nasolacrimal duct can be intensely stimulating particularly if the duct has ruptured. This will cause some rabbits to scream even under general anaesthesia. (B600.11.w11)
• Ideally sedate the animal. (B601.2.w2)
• This procedure can be performed in conscious rabbits with topical anaesthetic drops instilled into the eye; however if the patient is under general anaesthesia for another procedure it is less stressful to flush the ducts while the animal is still under anaesthesia. (J213.9.w1)

Technique

• Instil topical anaesthetic drops to the eye (B601.2.w2, J213.9.w1)
  • Such as proparacaine. (B602.14.w14)
• Select an appropriate cannula
  • Plastic irrigation cannula (B600.11.w11)
    • 20 to 27 gauge (B601.2.w2)
  • An intravenous catheter with the stylet removed (B601.2.w2, B602.14.w14)
    • 24 gauge (J213.9.w1)
    • These can be cut to size if necessary; to aid the placement, a slightly bevelled end can be created but extra care must be taken with this sharp tip to avoid iatrogenic damage to the duct. (B601.2.w2)
  • Metal irrigating cannula (B601.2.w2)
    • These may be used in some cases, particularly those where the duct is dilated. However, there is a higher risk of iatrogenic damage to the duct with these catheters. Trauma can lead to the formation of scar tissue and stenosis. (B600.11.w11)
• Fill a small syringe with sterile saline or water (B600.11.w11, B602.14.w14, B606.12.w12)
• Gently evert or pull out the lower eyelid to expose the slit of the lacrimal punctum of the duct that is in the lower conjunctiva near the medial canthus. (B600.11.w11, B601.2.w2)
• Insert the cannula into the nasolacrimal duct in a ventromedial direction. 
  • If the positioning is correct, there should not be much resistance. (B601.2.w2)
  • The cannula can be passed into the duct and into the lacrimal sac. (B600.11.w11)
• Attach the syringe to the cannula and GENTLY flush the duct. (B600.11.w11, B601.2.w2)
  • Only apply gentle pressure during flushing because the lacrimal duct can rupture especially if the duct is blocked. (B600.11.w11)
  • If the duct is patent, the instilled fluid and contents of the duct (e.g. purulent material) should come through at the ipsilateral nostril. (B600.11.w11, B601.2.w2, B606.12.w12)
  • If the duct is very blocked then the initial flushing can result in purulent material pouring from the punctum. (B606.12.w12)
  • In some cases, purulent material can be left in the maxillary section of the duct especially if it has become blocked and dilated. (B600.11.w11)
    • Gentle digital pressure can be applied to the lacrimal punctum during flushing to force fluid down the duct to clear the blockage. (B600.11.w11)
    • Alternatively, a plastic cannula can be gently manipulated and directed through the lacrimal foramen to flush the maxillary section of the duct. This must not be attempted in the conscious animal. Do not use a metal catheter. (B600.11.w11)
  • Bulging of the globe
    • If the procedure leads to bulging of the globe then the duct has ruptured and the saline has leaked into the retrobulbar space; flushing should be abandoned immediately. (B600.11.w11, B601.2.w2, B606.12.w12)
    • This pressure behind the eye is painful and analgesia is necessary. The saline should reabsorb over the following twenty four hours. (B606.12.w12)
  • If flushing is not possible
    • If there is a large amount of purulent material and it is not possible to flush the duct then a solution of trypsin (dissolve one capsule of pancreatic enzyme, for example Tryplase, in five to ten millilitres of saline) can be instilled into the duct to try and break the debris down. Flushing should then be reattempted after forty eight hours. (B606.12.w12)
    • OR Treat the eyes topically with acetylcysteine (Parvolex, UCB Pharma Limited,Slough, UK) (1 mL added added to a 5.0 - 7.5 mL bottle of topical antibiotic eye drops and applied at the frequency indicated for the eye drops), to aid in the dissolution of blockage; re-attempt the flushing after a one week course of treatment. (V.w125)
• Collect any flushed purulent material on a sterile swab
  • This can be used for bacterial culture and sensitivity if required. (B600.11.w11, B606.12.w12)
•  Instill medication via the cannula into the duct if required
  • Once successful flushing has been achieved, medication can be instilled via the cannula into the duct if treatment for an infection is required. (B600.11.w11, B601.2.w2, B606.12.w12)
  • A few drops of eye ointment can be added to a syringe for instillation via the cannula. (B600.11.w11)
• Repeat the procedure as necessary
  • Depending on the severity of the condition, subsequent flushing may be required on a daily or weekly basis. (B606.12.w12)

Dacryocystography

Useful procedure for visualising changes of the nasolacrimal duct radiographically. (B600.11.w11, B601.2.w2)

• Instil one to two millilitres of a contrast medium into the duct via the cannula. (B600.11.w11)
  • Dilute preparations are cheaper and easier to inject than the more concentrated formulations. (B600.11.w11)
    • Sodium/meglumine iothalamate (Conray 280) (B600.11.w11)
  • Concentrated preparations will give a clearer image of the duct and are retained for longer. (B600.11.w11)
• Complications:
  • It is harder to get a clear image of a patent duct than a blocked duct. (B600.11.w11)
  • When contrast medium has passed through a patent duct to the nose, it can be easily inhaled into the nasal passages resulting in superimposition. (B600.11.w11)

Indications

• To determine and restore the patency of the nasolacrimal ducts where there is a suspected blockage or infection. (B601.2.w2, B602.14.w14, J213.9.w1)
  • Obstruction of the duct may be caused by dental disease and infectious agents. (J213.9.w1)
    • A common sequela to pasteurellosis is chronic conjunctivitis. The chronic inflammation involved in this condition can lead to occlusion of the lacrimal puncta with thickened mucosa or purulent debris. Flushing the nasolacrimal duct on a regular basis helps to clear the infection. (B602.14.w14)
• Instillation of topical medication into the nasolacrimal duct. (B601.2.w2)
• Contrast dacryocystography for visualising changes of the nasolacrimal duct radiographically.. (B601.2.w2)

Anaesthesia 

• Ideally, anaesthesia or sedation should be used during this procedure particularly for the initial investigation. (B600.11.w11, B601.2.w2, J213.9.w1)

Retrograde cannulation of the nasolacrimal duct

• Retrograde cannulation via the nares has also been reported. However, this is a challenging procedure especially in small rabbits because the aperture is narrow and difficult to locate. (B600.11.w11, B601.2.w2)

• Lighting
  • Good illumination is necessary for this procedure. (B600.11.w11)
• Radiology
  • Many rabbits with dacryocystitis have major dental problems so radiology prior to flushing the nasolacrimal duct is often very informative and will give an idea of how difficult flushing is likely to be and whether it will be able to effect a cure. (B600.11.w11)

• In wild lagomorphs
  • While most veterinary procedures described for use in domestic rabbits can also be used in wild lagomorphs, it is much more likely that sedation will be required to carry out such procedures in wild lagomorphs.
• Using intravenous catheters
  • To aid the placement of this type of catheter (stylet removed) into the duct, a slightly bevelled end can be created but extra care must be taken with this sharp tip to avoid iatrogenic damage to the duct. (B601.2.w2)
• Using metal catheters
  • There is a higher risk of iatrogenic damage to the duct with these catheters. Trauma can lead to the formation of scar tissue and stenosis. (B600.11.w11)
  • These should not be used when the catheter is to be passed through the lacrimal foramen to specifically flush the maxillary section of the duct. (B600.11.w11)
• Rupture of the duct during flushing
  • Only apply gentle pressure during flushing because the lacrimal duct can rupture especially if the duct is blocked. (B600.11.w11)
  • If the procedure leads to bulging of the globe then the duct has ruptured and the saline has leaked into the retrobulbar space; flushing should be abandoned immediately. (B600.11.w11, B601.2.w2, B606.12.w12)
  • This pressure behind the eye is painful and analgesia is necessary. The saline should reabsorb over the following twenty four hours. (B606.12.w12)
  • The nasal mucosa is sensitive in rabbits and flushing the nasolacrimal duct can be intensely stimulating particularly if the duct has ruptured. This will cause some rabbits to scream even under general anaesthesia. (B600.11.w11)
• Complications of dacryocystography
  • It is harder to get a clear image of a patent duct than a blocked duct. (B600.11.w11)
  • When contrast medium has passed through a patent duct to the nose, it can be easily inhaled into the nasal passages resulting in superimposition. (B600.11.w11)
• The use of anaesthesia or sedation for this procedure
  • Ideally, anaesthesia or sedation should be used during this procedure particularly for the initial investigation. (B600.11.w11, B601.2.w2, J213.9.w1)
  • Passing a plastic cannula through the lacrimal foramen to aid flushing of the maxillary section of the duct should not be attempted in the conscious animal. (B600.11.w11)

• Local anaesthetic drops
  • Such as proparacaine. (B602.14.w14)
• Cannula
  • Plastic irrigating cannula (B600.11.w11)
    • 20 to 27 gauge (B601.2.w2)
  • An intravenous catheter with the stylet removed (B601.2.w2, B602.14.w14)
    • 24 gauge (J213.9.w1)
  • Metal irrigating cannula (B601.2.w2)
• Syringe: 5 -10ml
• Sterile saline or water
• Sterile swab for collection of purulent material for bacterial culture and sensitivity if required.
• If dacryocystography is required:
  • A contrast medium, e.g. sodium/meglumine iothalamate (Conray 280). 
  • Radiography plates and machine.

• Equipment for nasolacrimal duct cannulation and irrigation is relatively inexpensive.
• Cost of equipment for in-house testing.
• Cost of external laboratory fees.
• Cost of radiograph plates for dacryocystography if required.