Diurnal Variation of Ocular Hysteresis, Corneal Thickness, and Intraocular Pressure

Purpose. To investigate, in healthy Asian subjects, the diurnal changes of the corneal biomechanical properties of corneal hysteresis (CH) and its relation to fluctuations of intraocular pressure (IOP) and central corneal thickness (CCT) after sleeping. Methods. Forty eyes of 20 healthy Asian Volunteers (4 males and 16 females) with a mean age of 19.7 +/- 1.1 years were measured with a modified retinal optical coherence tomography and an ocular response analyzer (ORA). CH, CCT, Goldmann-equivalent intraocular pressure (IOPg), corneal resistance factor (CRF), and corneal compensated intraocular pressure (IOPcc) were obtained. Repeated measurements were conducted on both eyes during a 24-h period, including immediately before and after sleeping. Results. There were no significant differences in any measured variable between right and left eyes [Repeated measurement analysis of variance (Re-ANOVA), p > 0.05]. Diurnal variations (Re-ANOVA, p = 0.001) of CCT, IOPg, IOPcc, and CRF were found during the 24-h period. Significant increases occurred a few minutes after overnight sleep compared with the baseline values at 10:00 PM before sleep (post hoc tests, p = 0.001). However, there were no differences of CH over time during the Study period (Re-ANOVA, p = 0.11). A few minutes after awakening, the increase of CCT was not related to the changes of CH, IOPg, IOPcc, or CRF. However, the increase of CRF was significantly correlated with the changes of IOPg. Conclusion. Diurnal variation of CH was not detectable in healthy Asian eyes. The diurnal fluctuation of IOP appears not to be associated with CH. However, CRF was increased a few minutes after sleeping, a change that was correlated to the changes of IOPg.