title: Day to day variability of the dark-adapted pupil diameter.
abstract: OBJECTIVE
  To determine the individual variability of the dark-adapted pupil diameter over 2 testing sessions using a standardized dark-adaptation protocol.
  
  
  METHODS
  Texas Tech University Health Sciences Center, Lubbock, Texas, USA.
  
  
  METHODS
  In this prospective observational cohort study, 40 volunteers with no history of ocular disease, surgery, or injury other than requirement for refractive correction were included. The right eye was tested. A standardized dark-adaptation protocol was used that controlled for accommodation and patient alertness. Infrared, still digital photographs were taken after 5 and 10 minutes of dark adaptation and analyzed independently by 2 investigators using digital-image software. Two test sessions were performed 1 to 7 days apart. Lifestyle factors such as sleep, diet, and exercise were not controlled.
  
  
  RESULTS
  The mean subject age was 31.5 years (range 20 to 49 years). There were 20 men; 27 subjects wore correction for myopia, and 13 wore no correction. The mean interval between test sessions was 2 days (range 1 to 7 days). The mean difference and 95% confidence intervals for pupil diameter difference between sessions were as follows: 5-minute readings, +0.032 mm (-0.030 to +0.094); 10-minute readings, -0.006 mm (-0.059 to +0.047); mean of 5- and 10-minute readings, +0.013 mm (-0.038 to +0.064). Using the paired t test, the pupil diameter did not differ significantly between sessions in 5-minute dark adaptation (P =.2980), 10-minute dark adaptation (P =.8263), or the mean (P =.6049).
  
  
  CONCLUSIONS
  Using a consistent dark-adaptation protocol that controlled for alertness, individuals aged 20 to 49 years showed no significant variation in dark-adapted pupil diameter when tested twice in 1 week.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Texas Tech University Health Sciences Center, Lubbock, TX, USA. Sandra.brown@ttuhsc.edu
authors.forename: Sandra M
authors.initials: SM
authors.lastname: Brown
authors.forename: Arshad M
authors.initials: AM
authors.lastname: Khanani
authors.forename: Ke Tom
authors.initials: KT
authors.lastname: Xu
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology; D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D003623:Dark Adaptation / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010781:Photography; D011446:Prospective Studies; D011680:Pupil / Q000502:physiology*