Diurnal variation of axial length, intraocular pressure, and anterior eye biometrics

PURPOSE. To investigate the diurnal variation in axial length and anterior eye biometrics, while simultaneously measuring intraocular pressure (IOP) with dynamic contour tonometry in human subjects. METHODS. Fifteen young adult near-emmetropic subjects had axial length, anterior eye biometrics (central corneal thickness and anterior chamber dimensions), and IOP measured at six different times across a 24-hour measurement period. Repeated-measures ANOVA and sine curve fitting were used to analyze the diurnal rhythms in each measured parameter. RESULTS. Axial length was found to undergo significant diurnal variation (P = 0.0006). The mean amplitude of axial length change was 0.046 +/- 0.022 mm. The mean peak in axial length was found to occur at 1113. Intraocular pressure and ocular pulse amplitude were also found to undergo significant diurnal change (P < 0.0001 and 0.0006, respectively). The variation in axial length exhibited a significant association with the change in IOP (r = 0.37, P = 0.001). No significant difference was found between the mean peak times of axial length and IOP. Anterior eye biometric measures of central corneal thickness and anterior chamber depth were also found to undergo significant diurnal changes (P < 0.0001 and 0.0368, respectively). CONCLUSIONS. Axial length undergoes significant variation over a 24-hour period. Associations exist between the change in axial length and the change in IOP, as measured by dynamic contour tonometry. These results may have significant implications for the role of ocular diurnal rhythms in emmetropization.