title: Objective concurrent measures of open-loop accommodation and vergence under photopic conditions.
abstract: OBJECTIVE
  To investigate the relationship between photopic open-loop accommodation and vergence and the effect of mental effort on these positions.
  
  
  METHODS
  Twenty subjects (11 men and 9 women) viewed monocularly a photopic (25 cdm-2), high-contrast (90%) Maltese cross-target for 3 minutes, through a 0.5-mm pinhole drilled into an infrared filter. Accommodation was measured objectively at 1-second intervals using a Canon Autoref R-1 infrared optometer, and vergence was recorded continuously and objectively using a differential infrared eye tracking system.
  
  
  RESULTS
  Under passive viewing conditions there was a significant correlation between photopic open-loop accommodation and vergence (R = 0.671, P = 0.0012); for the majority of subjects the imposition of mental effort shifted the passive levels of both open-loop accommodation and vergence, but these shifts were unsystematic and uncorrelated (R = 0.259, P = 0.270). The active open-loop positions of accommodation and vergence were also found to be correlated (R = 0.692, P = 0.0007).
  
  
  CONCLUSIONS
  The influence of proximal stimuli can explain the correlations identified between photopic open-loop positions of accommodation and vergence. The uncorrelated responses of the accommodation and vergence systems to mental effort are likely to reflect interactions between various spatiotopic stimuli including mental effort and perceived proximity.
authors.affiliation: Department of Vision Sciences, Glasgow Caledonian University, United Kingdom.
authors.forename: L S
authors.initials: LS
authors.lastname: Gray
authors.forename: B
authors.initials: B
authors.lastname: Winn
authors.forename: B
authors.initials: B
authors.lastname: Gilmartin
authors.forename: A S
authors.initials: AS
authors.lastname: Eadie
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000328:Adult; D003290:Convergence, Ocular / Q000502:physiology*; D003623:Dark Adaptation; D005260:Female; D005556:Form Perception / Q000502:physiology; D006801:Humans; D008297:Male; D010775:Photic Stimulation