Rabbit eye disorders

Eyes diseases: clinical cases

Warning: this page contains pictures that may be distressing for some persons.

Corneal ulcer

Well it looks like an ulcer with purulent inflammatory material at its lower edge doesn't it? But the cornea was fluorescein-negative and here's the other eye! No money for cytology and bacteriology so its on topical antibiotic and NSAID and I'll let you know what happens. Don't always expect me to have the answer straight away!

Cataract

If this were a dog we would say for sure it was a diabetic catarct, given its mature appearance and rapid onset. But in a rabbit things aren't quite so simple; the animal has no other signs of diabetes and most importantly the other eye still has a clear lens! Not all diagnoses are as straight forward as we would like them to be! More importantly the animal is behaviourally unaffected and needs no treatment. It is always possible that Encephalitozoan cuniculi is involved in cataractogenesis here, but here the owner was not concerned enough to warrant serological confirmation of this.

Keratitis and Wessely ring

This white circle with a target lesion centrally in a somewhat oedematous cornea with an inflammatory 'muddy' loss of intraocular detail, is most probably a Wessely ring; that is to say a circle of antibody-antigen complex deposition with the antigen coming most probably from a central traumatic event and the antibody from blood vessels at the limbus. Its the same sort of deposit that gives an immunopreciptate in an agar gel preciptation assay, as here, where antigen is placed in one well and antibody in the other. While this is a classic corneal appearance it is very rare - I've never seen one before apart from in experimentally induced situations in textbooks. Topical anti-inflammatory and antibiotic treatment has been used here with some success but it is a shame that we don't know which antigen(s) are involved. Suttorp-Schulten and colleagues produced a paper documenting the changes that occur in such a lesion: The fate of antigen-antibody complexes in the rabbit cornea. Current Eye Research 1991 10:773-8 and Meyers-Elliott has documented the condition occuring with corneal herpesvirus infection in people: Viral antigens in the immune ring of Herpes simplex stromal keratitis. Arch Ophthalmol. 1980 98:897-904.

Retrobulbar abscess

This is exophthalmos caused by a retrobulbar space occupying mass. It could be a tumour or an abscess, but in a rabbit that latter is far more likely. Here is an MRI of the head, showing pus extending up in the orbit and then down as far as the cervical area. The kindest thing in this case was euthanasia. Less severe lesions could be treated with enucleation and orbital exenteration, but even then the infection almost always recurs at some point.

Dacryocystitis

This is dacryocystitis - inflammation (and in all probability infection) or the nasolacrimal duct. The rabbit has a narrow duct with two points at which the duct bends and narrows. This, together with the likelihood of maxilary bone involvement in nutritional bone disease and dental abnormalities, leads to this build up a pus, shown well here as it leaves the single nasolacrimal punctum. Regular flushing and probably systemic antibiotic therapy too are steps to resolutin of the problem, but the road to a cure, like the nasolacrimal duct iteslf, is long and tortuous!!

Fundus

This is a rabbit's fundus - the question image was from a New Zealand White animal with a non-pigmented eye while this is from a normally pigmented Netherland Dwarf. We call this a merangiotic fundus - the rebbit has a long horizontal visual streak, giving it good vision all along the horizon, from whence might spring a hungrey fox! So it keeps its blood vessels and myelinated nerve fibres (the whiote streaks - but who knows why it has any mylelinated fibres - no other species bothers!) away from this lnie of high photoreceptor density.

Glaucoma

Here the intraocular pressures were 45mmHg in each eye and the condition was glaucoma caused by the bu gene. Other possibilities might include retrobulbar abscessation, although this would be rare bilaterally, and venous congestion causing retrobulbar plexus engorgement, again a very rare condition. The bu gene is common in New Zealand White rabbits like this one, causing a dysplastic iridocorneal angle where drainage is very poor. A useful paper on the condition is Ueno and colleagues report on Histopathological changes in iridocorneal angle of inherited glaucoma in rabbits. Graefes Arch Clin Exp Ophthalmol. 1999;237:654-60

Myxomatosis

While such masses could be inflammation or tumour of many different sorts, the vast majority in domestic rabbits are associated with myxomatosis. The relation between the myxoma virus and the host rabbit is a fascinating story (very well reviewed in Zuniga MC: A pox on thee! Manipulation of the host immune system by myxoma virus and implications for viral-host co-adaptation. Virus Res. 2002 88:17-33) with viral virulence factors and host resistance in a major host-virus battle. This rabbit had been vaccinated and thus was not as severely affected as an unvaccinated animal such as this poor rabbit.

Encephalitozoan-associated uveitis

The dense white mass lesion in the iris with vascularisation is virtually pathognomonic for a lens-induced uveitis associated with Encephalitozoan cuniculi infection. The pathogenesis appears to be that the parasite enters the lens in utero and exits later sometimes giving cataract and sometimes a lens-induced inflammation, characteristically appearing as a variably vascularised white mass. Treatment can be by phacoemulsification of the lens, but a medical therapy if surgery is not possible, involves anti-inflammatory medication with topical steroid or NSAID and anti-parasitic systemic medication such as oral albendazole.

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