title: Grating visual acuity in infantile nystagmus in the absence of image motion.
abstract: OBJECTIVE
  Infantile nystagmus (IN) consists of largely horizontal oscillations of the eyes that usually begin shortly after birth. The condition is almost always associated with lower-than-normal visual acuity (VA). This is assumed to be at least partially due to motion blur induced by the eye movements. Here, we investigated the effect of image motion on VA.
  
  
  METHODS
  Grating stimuli were presented, illuminated by either multiple tachistoscopic flashes (0.76 ms) to circumvent retinal image motion, or under constant illumination, to subjects with horizontal idiopathic IN and controls. A staircase procedure was used to estimate VA (by judging direction of tilt) under each condition. Orientation-specific effects were investigated by testing gratings oriented about both the horizontal and vertical axes.
  
  
  RESULTS
  Nystagmats had poorer VA than controls under both constant and tachistoscopic illumination. Neither group showed a significant difference in VA between illumination conditions. Nystagmats performed worse for vertically oriented gratings, even under tachistoscopic conditions (P < 0.01), but there was no significant effect of orientation in controls.
  
  
  CONCLUSIONS
  The fact that VA was not significantly affected by either illumination condition strongly suggests that the eye movements themselves do not significantly degrade VA in adults with IN. Treatments and therapies that seek to modify and/or reduce eye movements may therefore be fundamentally limited in any improvement that can be achieved with respect to VA.
authors.affiliation: School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom.
authors.forename: Matt J
authors.initials: MJ
authors.lastname: Dunn
authors.forename: Tom H
authors.initials: TH
authors.lastname: Margrain
authors.forename: J Margaret
authors.initials: JM
authors.lastname: Woodhouse
authors.forename: Fergal A
authors.initials: FA
authors.lastname: Ennis
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Harris
authors.forename: Jonathan T
authors.initials: JT
authors.lastname: Erichsen
mesh_terms: D000328:Adult; D000368:Aged; D005074:Evoked Potentials, Visual; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009038:Motion; D020417:Nystagmus, Congenital / Q000503:physiopathology*; D009887:Ophthalmoscopy; D010775:Photic Stimulation; D014792:Visual Acuity; D055815:Young Adult
keywords: amblyopia; orientation; tachistoscopic