title: Dynamic visual acuity during walking after long-duration spaceflight.
abstract: BACKGROUND
  Astronauts experience alterations in gaze control as a result of adaptive changes in eye-head coordination produced by microgravity exposure. This may lead to potential changes in postflight visual acuity during head and body motion.
  
  
  METHODS
  We gathered dynamic visual acuity (DVA) data from 14 astronauts and cosmonauts after long-duration (approximately 6 mo) stays in space. Walking was used to induce self-motion and visual acuity was determined by sequentially presenting Landolt ring optotypes on a computer display placed 4 m in front of subjects. Acuity assessments were made while seated (static condition) and walking (dynamic condition) at 6.4 km x h(-1) on a motorized treadmill. In each condition, a psychophysical threshold detection algorithm minimized the required number of optotype presentations by maximizing the amount displayed around the subject's acuity threshold. The difference between static and dynamic acuity measures provided a metric of change in the subjects' ability to maintain gaze fixation on the visual target while walking.
  
  
  RESULTS
  A decrement in postflight visual acuity during walking was found. A mean dynamic acuity decrement of approximately 0.75 eye-chart lines was observed 1 d after returning from space. The population mean showed a consistent improvement in DVA performance during the first postflight week.
  
  
  CONCLUSIONS
  The recovery curves for individual subjects did not necessarily follow a pattern of continuous improvement with each passing day. When adjusted for previous long-duration flight experience, the population mean showed an unexpected DVA reduction in the re-adaptation curve that is similar to recovery patterns observed in prism adaptation studies.
authors.affiliation: Wyle Integrated Science and Engineering Group, 1290 Hercules Drive, Houston, TX 77058, USA. brian.peters-1@nasa.gov
authors.forename: Brian T
authors.initials: BT
authors.lastname: Peters
authors.forename: Chris A
authors.initials: CA
authors.lastname: Miller
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Brady
authors.forename: Jason T
authors.initials: JT
authors.lastname: Richards
authors.forename: Ajitkumar P
authors.initials: AP
authors.lastname: Mulavara
authors.forename: Jacob J
authors.initials: JJ
authors.lastname: Bloomberg
mesh_terms: D000328:Adult; D018480:Astronauts; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012027:Reflex, Vestibulo-Ocular; D013026:Space Flight; D014792:Visual Acuity; D016138:Walking; D014893:Weightlessness