title: Applicability of infrared photorefraction for measurement of accommodation in awake-behaving normal and strabismic monkeys.
abstract: OBJECTIVE
  This study was designed to use infrared photorefraction to measure accommodation in awake-behaving normal and strabismic monkeys and describe properties of photorefraction calibrations in these monkeys.
  
  
  METHODS
  Ophthalmic trial lenses were used to calibrate the slope of pupil vertical pixel intensity profile measurements that were made with a custom-built infrared photorefractor. Day to day variability in photorefraction calibration curves, variability in calibration coefficients due to misalignment of the photorefractor Purkinje image and the center of the pupil, and variability in refractive error due to off-axis measurements were evaluated.
  
  
  RESULTS
  The linear range of calibration of the photorefractor was found for ophthalmic lenses ranging from -1 D to +4 D. Calibration coefficients were different across monkeys tested (two strabismic, one normal) but were similar for each monkey over different experimental days. In both normal and strabismic monkeys, small misalignment of the photorefractor Purkinje image with the center of pupil resulted in only small changes in calibration coefficients, that were not statistically significant (P>0.05). Off-axis measurement of refractive error was also small in the normal and strabismic monkeys (approximately 1 D to 2 D) as long as the magnitude of misalignment was <10 degrees.
  
  
  CONCLUSIONS
  Remote infrared photorefraction is suitable for measuring accommodation in awake, behaving normal, and strabismic monkeys. Specific challenges posed by the strabismic monkeys, such as possible misalignment of the photorefractor Purkinje image and the center of the pupil during either calibration or measurement of accommodation, that may arise due to unsteady fixation or small eye movements including nystagmus, results in small changes in measured refractive error.
authors.affiliation: Division of Sensory-Motor Systems, Yerkes National Primate Research Center, Emory University, Atlanta, GA 30322, USA.
authors.forename: Heather
authors.initials: H
authors.lastname: Bossong
authors.forename: Michelle
authors.initials: M
authors.lastname: Swann
authors.forename: Adrian
authors.initials: A
authors.lastname: Glasser
authors.forename: Vallabh E
authors.initials: VE
authors.lastname: Das
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000818:Animals; D002138:Calibration; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation; D004195:Disease Models, Animal; D005133:Eye Movements / Q000502:physiology; D007259:Infrared Rays; D008253:Macaca mulatta; D012029:Refraction, Ocular; D012030:Refractive Errors / Q000503:physiopathology; D013285:Strabismus / Q000503:physiopathology*; D015348:Vision, Binocular / Q000502:physiology