title: Diurnal variation of central corneal thickness and Goldmann applanation tonometry estimates of intraocular pressure.
abstract: OBJECTIVE
  To determine whether there is a temporal relationship between the diurnal variation of central corneal thickness (CCT) and intraocular pressure (IOP) by Goldmann applanation tonometry in young normal human participants in vivo.
  
  
  METHODS
  Twenty-five eyes of 25 young healthy normal participants were examined in a prospective observational cross-sectional study. IOP, CCT and corneal curvature were measured using standard clinical techniques over a 24-hour period, and the temporal interrelationships between these parameters were examined.
  
  
  RESULTS
  The overnight change in IOP measured by Goldmann tonometry was 3.1+/-2.4 mm Hg (P<0.001), CCT was 20.1+/-10.9 mum (P=0.016), with no statistical change in central corneal curvature (0.05 mm, P=0.477, paired t test with Bonferroni correction). Both IOP and CCT were highest on awakening at 7:00 then dropped rapidly to baseline levels by 9:00 (linear mixed models), and these two parameters were highly correlated (r=0.978, P<0.001). After 9:00, there was no correlation between these parameters (r=-0.453, P=0.260).
  
  
  CONCLUSIONS
  The results of this study have highlighted a potential link between the diurnal variation of CCT and the accuracy of Goldmann tonometry estimates of IOP during the first 2 hours after awakening. Clinicians should be wary of using Goldmann tonometry to estimate IOP until the overnight increase in CCT has resolved.
authors.affiliation: School of Optometry and Vision Science, University of New South Wales, Sydney NSW 2052, Australia.
authors.forename: Kirsten Elizabeth
authors.initials: KE
authors.lastname: Hamilton
authors.forename: David Cecil
authors.initials: DC
authors.lastname: Pye
authors.forename: Shivani
authors.initials: S
authors.lastname: Aggarwala
authors.forename: Sindy
authors.initials: S
authors.lastname: Evian
authors.forename: Joti
authors.initials: J
authors.lastname: Khosla
authors.forename: Rachithri
authors.initials: R
authors.lastname: Perera
mesh_terms: D000293:Adolescent; D000328:Adult; D000886:Anthropometry; D002940:Circadian Rhythm / Q000502:physiology*; D003315:Cornea / Q000033:anatomy & histology*; D003430:Cross-Sectional Studies; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D011446:Prospective Studies; D014065:Tonometry, Ocular