35 Rabbit uveitis
Owners will present rabbits with uveitis in one of two ways – either because the eye is red and painful, or because they have noticed a small white lesion within it. There is normally no history of trauma and in most cases the rabbit is systemically well. Younger animals tend to be affected and it is normally just one eye that is involved. It is unusual for the owner to have noticed any visual impairment.
Often there is no prior general or ocular history, although occasionally the rabbit will have suffered from previous problems – urinary infections or dental disease for example. It is unusual for the owner to have tried any treatment before presentation. Normally the owner will have been aware of the ocular changes for days to weeks before presentation – the lack of systemic illness makes it unlikely for them to present the rabbit as an emergency.
The rabbit is normally systemically well but occasionally other systemic signs might be present. These could include weight loss, urine scalding, head tilt, dental disease and so on. Other ophthalmic lesions such as a dacryocystitis or retrobulbar abscess can be present but this is not typical. Normally one eye is completely normal on examination. The affected eye may or may not be visual, demonstrated by normal or absent menace responses, and if blind in one eye the animal is likely to be nervous and ‘jumpy’ when approached on the blind side.
The most obvious lesion is usually a white mass within the anterior chamber, attached to the iris and lens at the pupil margin. The pupil is distorted as a result (dyscoria). Local uveal inflammation with rubeosis iridis will be appreciated in animals with a pale coloured iris (Figure 35.1). The lens is often opaque with total or partial cataract formation. Some episcleral congestion and conjunctival hyperaemia are to be expected but the eye is often non-painful (unless affected with secondary glaucoma). Ulceration is not a feature.
Figure 35.1 Uveitis due to Encephalitozoon cuniculi in a young dwarf rabbit. Note the bulging iris dorsally, with rubeosis iridis, plus the dyscoria and white lesion within the pupil – the lens is cataractous.
A thorough ophthalmic examination should narrow the differential list to either phacoclastic uveitis due to E. cuniculi or an abscess due to a bacterial infection such as Pasteurella multocida or Escherichia coli. General clinical examination should determine whether any systemic involvement is present. A minimal work-up should include serology for E. cuniculi (antibody detection), the results of which need interpreting in conjunction with clinical signs, since a positive titre demonstrates exposure to the organism but not necessarily active infection which can be attributed to the clinical symptoms. The organism is excreted intermittently in urine, but collection is not usually easy from pet rabbits and false negatives can occur if the sample happens to be taken during a period of non-shedding. It is unusual for a more thorough laboratory work-up to be undertaken in pet rabbits – response to treatment is more frequently used to assist with definitive diagnosis.
The general nursing of lagomorphs should be addressed – keeping warm, feeding from appropriate containers, water dispensers with which they are familiar and so on. Topical and systemic medication might both be required, and if anaesthesia is required the specific risks of this in rabbits need considering.