title: Impact factors on intraocular pressure measurements in healthy subjects.
abstract: OBJECTIVE
  To evaluate whether intraocular pressure (IOP) calculation by applanation tonometry is determined more essentially by the subject's neck position or by neck constriction.
  
  
  METHODS
  23 right eyes of 23 healthy subjects (12 male, 11 female) were included. IOP was measured by applanation tonometry with the TonoPen on sitting participants under four different conditions: with open collar upright (A) or with the head in the headrest of a slit lamp (B), with a tight necktie upright (C) or in slit lamp position (D). All measurements with neck constriction were performed 3 minutes after placing the necktie.
  
  
  RESULTS
  Mean IOP was 16.9 (SD 2.3) mm Hg (range 11-21 mm Hg) (A), 18.1 (SD 2.2) mm Hg (range 14-22 mm Hg) (B), 17.9 (SD 2.9) mm Hg (range 12-25 mm Hg) (C) and 18.7 (SD 2.7) mm Hg (range 13-24 mm Hg) (D). Mean IOP increased by 1.3 (SD 2.6) mm Hg (p = 0.028, paired t test, range +0.2 to +2.4 mm Hg) if subjects changed position from A to B. There was no statistically significant difference between measurements with or without neck constriction.
  
  
  CONCLUSIONS
  Applanation tonometry may be inaccurate if performed in slit lamp position. In contrast, tight neckties do not significantly affect IOP evaluation in healthy subjects.
authors.affiliation: Department of Ophthalmology, University Medical Centre Nijmegen, Philips van Leijdenlaan 15, 6525 EX Nijmegen, Netherlands. t.theelen@ohk.umcn.nl
authors.forename: T
authors.initials: T
authors.lastname: Theelen
authors.forename: C F M
authors.initials: CF
authors.lastname: Meulendijks
authors.forename: D E M
authors.initials: DE
authors.lastname: Geurts
authors.forename: A
authors.initials: A
authors.lastname: van Leeuwen
authors.forename: N B M
authors.initials: NB
authors.lastname: Voet
authors.forename: A F
authors.initials: AF
authors.lastname: Deutman
mesh_terms: D000328:Adult; D003020:Clothing; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D009333:Neck / Q000502:physiology; D011187:Posture; D014065:Tonometry, Ocular / Q000379:methods*