title: Comparison of the main sequence of reflexive saccades and the quick phases of optokinetic nystagmus.
abstract: OBJECTIVE
  Abnormalities in the saccadic main sequence are an important finding and may indicate pathology of the ocular motor periphery or central neurological disorders. In young or uncooperative patients it can be difficult eliciting a sufficient number of saccades to measure the main sequence. It is often assumed that the quick phases of optokinetic nystagmus (OKN) are identical to saccades. If this were the case, it would be feasible to use OKN, an involuntary response that is easily evoked, as a simple way of eliciting many saccades. The aim of this study was to determine whether reflexive saccades and the quick phases of OKN are indeed identical, and whether OKN quick phases could have a clinical role in identifying patients with slow saccades.
  
  
  METHODS
  OKN and reflexive saccades were recorded from 10 healthy adults using an infrared limbus eye tracker and bitemporal DC electro-oculography simultaneously. OKN was stimulated by rotating a full field patterned curtain around the subject at 10-50 degrees /s. Reflexive saccades were elicited to red LED targets at 5-20 degrees eccentricity.
  
  
  RESULTS
  OKN quick phases tended to have a longer duration compared to saccades, but these differences were not significant. OKN quick phases had a slightly lower peak velocity compared to saccades, which was statistically significant (p<0.05).
  
  
  CONCLUSIONS
  The main sequence for duration is the same for reflexive saccades and OKN quick phases. The main sequence for peak velocity is slightly faster for reflexive saccades than OKN quick phases, but the difference is unlikely to be of clinical significance. As an illustration of the potential of this technique, the authors demonstrate that OKN quick phases show similar slowness to saccades in a child with brainstem pathology caused by Gaucher disease type III. It is concluded that recording OKN may be a simple clinical means for approximating the main sequence.
authors.affiliation: Department of Ophthalmology, Great Ormond Street Hospital for Children NHS Trust, London and Department of Visual Science, Institute of Child Health, London WC1N 3JH, UK. s.garbutt@ich.ucl.ac.uk
authors.forename: S
authors.initials: S
authors.lastname: Garbutt
authors.forename: M R
authors.initials: MR
authors.lastname: Harwood
authors.forename: C M
authors.initials: CM
authors.lastname: Harris
mesh_terms: D000328:Adult; D004585:Electrooculography; D005776:Gaucher Disease / Q000503:physiopathology; D006801:Humans; D007259:Infrared Rays; D008875:Middle Aged; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D015835:Ocular Motility Disorders / Q000175:diagnosis / Q000503:physiopathology; D012438:Saccades / Q000502:physiology*; D013997:Time Factors