Monocular Nystagmus Representing Heimann - Bielschowsky Phenomenon in a Dog With Ipsilateral Vision Loss

A 6-year-old female-neutered vaccinated Cocker Spaniel presented for preadoption neurological evaluation due to abnormal left-eye movements that had been noticed since young age. Clinical examination revealed left-eye cataract with a nonvisible left and a normal right retina on ophthalmoscopy. Neurological examination revealed absent left-sided menace response and cataract-related ipsilateral visual impairment, and intermittent left-sided abnormal eye movements consisted of intermittent, slow, coarse, variable amplitude, vertical movements of the eye that they were giving the impression of random movements of the eye within the globe as it was floating ("wandering" eye) interchangeable with periods of rest. Blood and infectious diseases tests were unremarkable. Magnetic resonance imaging of the brain was unremarkable, whilst cerebrospinal fluid analysis revealed mildly inflammatory in the light of blood contamination. A presumptive diagnosis of meningoencephalitis of unknown origin was established and trial with dexamethasone was performed, however nystagmus remained unchanged 2 weeks post-treatment. Therefore, based on the fact that monocular nystagmus existed since youth and remained static, and the dog was otherwise neurological-sign-free regardless the discontinuation of steroids, the diagnosis of meningoencephalitis was considered as unlikely and a presumptive diagnosis of Heimann - Bielschowsky phenomenon of the left eye due to cataract-related ipsilateral visual impairment was established. This vergence eye movement abnormality also known as searching, wandering or amaurotic nystagmus is a constant or intermittent benign eye movement abnormality mostly related with vision impairment due to ophthalmological or neurological disease. Heimann - Bielschowsky phenomenon is an underreported eye abnormality in veterinary medicine. Although the most common type of eye movement abnormalities seen in veterinary practice is the bilateral conjugate jerk nystagmus, monocular nystagmus representing Heimann - Bielschowsky phenomenon exists in animals, it has been related with partial or complete vision impairment and it should be recognised by the clinicians.