Joanna Hedley, Victoria Ede and Charlotte Dawson

Dacryocystitis is relatively common in pet rabbits and is often present concurrently with other diseases. However, there are relatively few studies reporting the prevalence of ocular disease – and particularly dacryocystitis.

We recently conducted a study to investigate potential risk factors associated with dacryocystitis in pet rabbits. It was a retrospective review of clinical records from all rabbit cases at the RVC’s first opinion and referral exotics clinic.

Dacryocystitis was identified in 55 of 821 rabbits (6.70%) examined over the study period. Of those rabbits with dacryocystitis, dental disease was found in 24 rabbits (45%), respiratory disease in 20 (38%), aural disease in seven (13%) and concurrent ocular disorders in 15 (23%).

Breed status was found to be a significant risk factor, with Lionhead/Lionhead cross and Dwarf Lop/Dwarf Lop cross rabbits being more likely to have dacryocystitis. The results suggest that a breed predisposition for dacryocystitis may exist, and vets should advise clients accordingly.
Rabbits are thought to be susceptible to dacryocystitis due to the anatomy of their nasolacrimal duct, which can easily become obstructed.

The duct starts at a slit-like opening located in the conjunctiva of the lower lid close to the medial canthus, following a tortuous path to empty into the nares. After the lacrimal sac and canal, the lacrimal duct reduces from 2 to 1 mm in diameter and curves where it passes close to the maxillary incisor root. It is there that blockage usually occurs.

Acute dacryocystitis can occur due to conjunctivitis causing obstruction of the lacrimal sac, impaired drainage and secondary bacterial infection. More typically, chronic dacryocystitis develops secondary to dental disease with elongation of tooth apices and periductal osteomyelitis. Alternatively, infection may ascend from the nasal cavity.

The research

In our study, records of all rabbits evaluated between February 2015 and February 2018 at the first opinion and referral clinic were reviewed retrospectively. Data collected included weight, sex, neuter status, breed and presence of lop ears. A subset of cases was identified for further analysis, based on the presence of the key terms ‘dacryo’, ‘dacro’, ‘naso- lacrimal’, ‘tear duct flush’, ‘isathal’, ‘exocin’, ‘tiacil’, ‘maxitrol’ and ‘chloramphenicol’ in records.

Additional data recorded from the subset included age at onset of clinical signs and the presence of concurrent dental, ear, ocular or respiratory disease. Cases were categorised as having respiratory disease if there was mention of respiratory signs, including nasal discharge and respiratory noise or dyspnoea. Cases were categorised as having dacryocystitis present if it was specified in notes or if there was a description of clinical signs, such as ‘mucopurulent discharge of tear ducts’.

Of the 821 rabbits presented between 2015 and 2018, 305 were male neutered, 140 were male entire, 242 were female neutered and 124 were female entire. The other 10 were of unknown sex. 53 different breeds or breed crosses were recorded. Mini Lop/Mini Lop cross was the most common category (16.93%), followed by Lop/Lop cross (13.89%).

Of the subset of 82 of cases that underwent further analysis, 55 rabbits met the criteria for the presence of dacryocystitis (6.70% of the study population). Those comprised 29 male neutered, four male entire, 17 female neutered and five female entire rabbits.

Fifteen breed categories presented with dacryocystitis. Significantly, Lop/Dwarf Lop cross rabbit having dacryocystitis compared to a crossbreed rabbit were 4.57 times and 4.26 times higher, respectively. Breeds that did not present with dacryocystitis included the English Lop, Holland Lop, Cashmere Lop, Californian, Continental Giant, German Giant, New Zealand White, Beveren cross, Belgian Hare, Dwarf Hotot, Thrianta, Himalayan, American Sable cross, Norwegian Dwarf and Silver Marten.

Brachycephalic rabbit breeds have been suggested to be at higher risk of developing nasolacrimal duct disease. In cats, a study using CT assessed the effects of brachycephalic skulls on nasolacrimal drainage. That study showed that the higher the degree of brachycephaly, the steeper the orientation of the nasolacrimal duct and thus the more likely that drainage is affected. It is therefore possible that, as in cats, a shortened skull leading to a distorted nasolacrimal duct applies to rabbits.

The Netherland Dwarf, Lionhead and some Lop breeds are often seen to exhibit marked brachycephalism, although there is no defined system for the classification of brachycephaly in rabbits to quantify this theory.