title: OKN asymmetry in human subjects: a literature review.
abstract: Optokinetic nystagmus (OKN) is a reflex eye movement induced by motion of the whole or a large proportion of the visual field. It can be horizontal, vertical, and torsional in direction and consists of two basic components, a slow tracking movement and a rapid recovery saccade. Two forms of OKN exist: "look" and "stare" OKN. There is strong evidence that horizontal OKN is symmetrical in normal healthy adults and that the OKN gains can be influenced by a variety of different factors including target size, shape, contrast, and velocity. Vertical OKN on the other hand is less well understood, although there is a belief that vertical OKN is asymmetrical with an upward preference. Recent publications contradict this assertion. In this article a comprehensive literature review was carried out to determine whether a vertical OKN asymmetry exists in healthy subjects and to explain any anomalous findings.
authors.affiliation: Department of Ophthalmology, Lincoln County Hospital, Lincolnshire, UK. christopher.knapp@ulh.nhs.uk
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Knapp
authors.forename: Frank A
authors.initials: FA
authors.lastname: Proudlock
authors.forename: Irene
authors.initials: I
authors.lastname: Gottlob
mesh_terms: D006801:Humans; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D009801:Oculomotor Muscles / Q000502:physiology*; D012016:Reference Values; D014794:Visual Fields