VN August 2022

Vetnews | Augustus 2022 37 ATora-like virus has been isolated fromthe faeces of several affected cats. The prognosis for this condition is good. The diarrhoea and nictitating membrane protrusion are self-limiting, although clinical signs may be long-lasting. Therapy is not indicated, but a topical adrenergic agent may be helpful if the nictitating membrane protrusion is severe. 4] Anisocoria: Anisocoria refers to the presence of unequal pupil sizes. There are many causes of this [to be discussed in detail in a future Vetnews article]. Still, one condition referred to as internal ophthalmoparesis/ophthalmoplegia [IO/O] is characterised by the decreased [ophthalmoparesis] or absent [ophthalmoplegia] motor function of the iris sphincter and ciliary body muscle as a result of loss of the parasympathetic innervation from the oculomotor nerve [CNIII] and seen as areflexive mydriasis of the pupil. Most cases of IO/O reported in the veterinary literature include the cavernous sinus syndrome, which is characterised by IO/O, paresis or plegia of the extra-ocular muscles [known as external O/O] and decreased or absent facial and corneal sensation. The dysfunction is due to several cranial nerves that pass at the level of the middle cranial fossa. The cranial nerves include CNIII [motor and parasympathetic], CN IV [trochlear], CNVI [abducens], the ophthalmic branch of CNV [trigeminal] and postganglionic sympathetic nerve fibres. The maxillary branch of CNV may also be affected as it passes through the round foramen. The general cause of this in cats is intracranial or retrobulbar masses invading the orbital fissure or the middle cranial fossa. The reasons are osteochondromas, lymphoma, squamous cell carcinoma, chondrosarcoma, trauma, orbital abscessation, infectious diseases [FIP/ FeLV and Cryptococcus] and idiopathic. Lesions only affecting CNIII alone and causing internal IO/O are more uncommon. IO/O generally occurs in older cats of all breeds and sexes. When performing the diagnostics of such cases, it is vital to check on the history regarding the use of Atropine drops. The neurological assessment of the anisocoric patient must be done carefully, taking into account the facial sensation [CNV], corneal reflex [touching the cornea with a cotton bud, CN V] and careful assessment of the palpebral reflex [CNV]. There will be reduced menace response with normal vision, poor palpebral reflex, poor corneal reflex and depressed vestibulo-ocular reflexes. Ocular ultrasound and CT /MRI should be performed to confirm a diagnosis. Cats with a systemic disease should have an abdominal ultrasound performed. Poor mental status is often reported in these cats and is most likely related to an intracranial mass causing compression of the forebrain/brainstem. The poor menace response with intact vision may also be associated with this pathology. Provocative testingofmydriasis canbe performedusingPilocarpine 0.1% solution to assess the parasympathetic innervation of the oculomotor nerve to the eye. The results of this, however, are somewhat unreliable. IO/O is a serious condition carrying a very guarded prognosis due to the high prevalence of neoplasia in this population of cats. 5] Feline Leukemia Virus (FeLV) Anisocoria or dyscoria may arise because of the neurological effects of FeLV on the ciliary ganglia and short ciliary nerves of affected cats. Alternatively, dyscoria [irregular pupil shape] may result from lymphocytic infiltration of the ciliary body and iris. In particular, spastic pupil syndrome, involving a static anisocoria during dark adaptation, has been reported in FeLV-positive cats. Anisocoriamay have been noted by the patient’s owner over time, alternating with periods of normal pupil behaviour. Other ophthalmic abnormalities are absent, however, and vision is unaffected. These cats are positive for FeLV but may have no clinical signs other than the anisocoria. It has been found that C-type viral particles have been identified in the ciliary ganglia and short ciliary nerves of these cats, suggesting that the virus has invaded these nerves. The prognosis for long-term survival in these cats is poor. v Regulars I Ophthalmology Column