title: Horizontal versus vertical dark-adapted pupil diameters in normal individuals.
abstract: OBJECTIVE
  To determine the distribution of the difference between the horizontal and vertical dark-adapted entrance pupil diameters (PDs) in normal individuals.
  
  
  METHODS
  Texas Tech University Health Sciences Center, Lubbock, Texas, USA.
  
  
  METHODS
  In this observational cohort study, high-magnification infrared pupil photography was performed of the right eye of 26 normal volunteers from 20 to 47 years of age. The horizontal and vertical PDs were measured using commercially available digital-image software, taking into account the effect of photographic parallax.
  
  
  RESULTS
  In 24 subjects (85%), the vertical PD was larger than the horizontal PD; in 8 subjects (31%), it was 0.30 mm to 0.50 mm larger. In 2 subjects, the horizontal diameter was slightly larger but the difference was <0.10 mm. The mean horizontal to vertical PD ratio was 0.97.
  
  
  CONCLUSIONS
  In this study population, the vertical PD was larger than the horizontal PD in most subjects. Although the difference was a fraction of the total PD, it may be important for laser refractive surgery planning and preoperative risk counseling of some patients.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Texas Tech University Health Sciences Center, Lubbock, Texas, USA.
authors.forename: Arshad M
authors.initials: AM
authors.lastname: Khanani
authors.forename: Steven M
authors.initials: SM
authors.lastname: Archer
authors.forename: Sandra M
authors.initials: SM
authors.lastname: Brown
mesh_terms: D000328:Adult; D001837:Body Weights and Measures; D015331:Cohort Studies; D003623:Dark Adaptation / Q000502:physiology*; D003941:Diagnostic Techniques, Ophthalmological; D006801:Humans; D007498:Iris / Q000033:anatomy & histology*; D008875:Middle Aged; D011680:Pupil / Q000502:physiology*