Diurnal variation of central corneal thickness and Goldmann applanation tonometry estimates of intraocular pressure

Purpose: To determine whether there is a temporal relationship between the diurnal variation of central corneal thickness (CCT) and intraocular pressure (10P) 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 im (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.