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Fluctuations in both accommodation and fixational eye movements: covariation and effect of viewing distance

Compartir 08/09/2016 Publicaciones Científicas

Josselin Gautier, Carles Otero, Jaume Pujol, Harold E. Bedell

Purpose

Microsaccades and fluctuations of accommodations have been shown separately to be influenced by the stimulus, task and the cognitive load, while to be partially synchronous to heart rate. We study whether they might covariate over time and whether this might be an artefact or a specific function of the visual system during fixation.

Methods

  • Fixational eye movements and accommodative fluctuations were recorded simultaneously on respectively the left and right eye of participants (fluctuations are known to be highly correlated in phase and amplitude on both eyes [2]).
  • A PowerRef II recording at 25 Hz was synchronized to an Eyelink 1000 Plus sampling at 500 Hz.
  • The stimuli were displayed binocularly at three distances (0D, 2D, 5D) along the midline of the two eyes. This is an improvement from a previous monocular experiment varying the peripheral cues and distance.
  • The two instruments were electronically synchronized before each trial (Host PCs’ Parallel port).
  • 11 subjects (normal without glasses, age: 20-28) were asked to fixate during 10s a Maltese cross.

Conclusions

  • While amplitude of fluctuations increase with distance, fixational eye deviations appear to decrease in amplitude.
  • Over time, both horizontal and vertical position appear to covary with spherical refraction either in a correlated or anti-correlated manner.
  • Two exclusive hypothesis can be deduced:
    • a) both eye mechanisms act together during and for visual discrimination
    • b) fluctuation of accommodation is a recording artefact due to fixational eye movements
Fluctuations in both accommodation and fixational eye movements: covariation and effect of viewing distance

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