title: The effect of vertical gaze position on ocular tear film stability.
abstract: BACKGROUND
  An enlarged exposed ocular surface area is known to degrade tear film stability. Little is known of how tear film stability alters with vertical gaze and the change of palpebral fissure height.
  
  
  METHODS
  Tear film break-up time (TBUT; fluorescent dye) and palpebral fissure height were measured in three vertical gaze positions (primary position and 20 degrees up and 20 degrees down) on 23 healthy volunteers. The effect of gaze direction on TBUT was analysed by ANOVA.
  
  
  RESULTS
  Gaze had a significant influence on tear film stability [F(2,44)=27.6, p<0.001]. In up-gaze with an enlarged palpebral fissure height (11.1 +/- 1.4 mm), TBUT was degraded (17.3 +/- 12.7 seconds). In down-gaze and decreased palpebral fissure height (6.7 +/- 1.2 mm) TBUT was extended (43.5 +/- 35.4 seconds).
  
  
  CONCLUSIONS
  Ocular tear film stability alters with vertical gaze. Our hypothesis is that the change of the palpebral fissure height and the exposed ocular surface area alters the thickness of the lipid layer and with it tear film evaporation.
authors.affiliation: Unit of Optometry, Section for Eye and Vision, Institution for Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden. tony.pansell@ste.ki.se
authors.forename: Tony
authors.initials: T
authors.lastname: Pansell
authors.forename: Madeleine
authors.initials: M
authors.lastname: Porsblad
authors.forename: Saber
authors.initials: S
authors.lastname: Abdi
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D005123:Eye / Q000378:metabolism*; D005133:Eye Movements / Q000502:physiology; D005143:Eyelids / Q000502:physiology; D005260:Female; D005403:Fixation, Ocular; D006801:Humans; D008297:Male; D012016:Reference Values; D013666:Tears / Q000378:metabolism*; D013997:Time Factors