Clinical and ocular motor characterisation of infantile and acquired nystagmus using eye movement recordings

Our aim was to characterise the ocular motor abnormalities in infantile (IN) and acquired nystagmus (AN) using eye movement recordings in order to improve diagnosis and understanding of these diseases. The first aim was to compare a genetically homogenous idiopathic IN group (FRMD7-IN) with albinism associated IN. The second aim was to investigate acquired pendular nystagmus (APN) due to MS along with other ocular motor abnormalities, in relation to disease severity and MS subtype. Eye movements were recorded in all IN and AN participants (n=117). Ocular motor characteristics of the nystagmus were analysed. Other clinical features were compared including strabismus, stereopsis and anomalous head posture (AHP) in IN and the disability score and MS subtype in MS. FRMD7-IN contained higher proportions of pendular waveform compared with albinism. Nystagmus frequency was significantly lower in albinism compared with FRMD7-IN. Strabismus and AHP were more frequent in albinism, and stereopsis was worse compared with FRMD7-IN. In MS APN coexisted with various other ocular motor deficits including gaze-evoked nystagmus, internuclear ophthalmoplegia and square wave jerks although the occurrence of these was not related to MS severity or subtype. The APN was dysconjugate mainly due to a difference in amplitude between the two eyes rather than frequency. There was no clear change in APN parameters with MS severity or subtype. We describe for the first time the differences in nystagmus characteristics associated with albinism and FRMD7- IN which may be useful information in the future elucidation of mechanisms underlying the nystagmus and also in diagnosis. In MS we confirm that APN is mainly dysconjugate due to amplitude and can co-exist with various ocular motor abnormalities. Eye movement recordings can assist in differentiating various ocular motor abnormalities in IN and AN that are difficult to characterise on clinical examination.