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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.

Purpose: To determine if corneal hysteresis (CH) was associated with increased central corneal thickness (CCT) induced by wearing soft contact lenses during eye closure., Design: A prospective laboratory investigation., Methods: CCT was measured with a modified optical coherence tomography (OCT), and CH was measured with a Reichert Ocular Response Analyzer (ORA) [Reichert Ophthalmic Instruments, Depew, New York, USA]. The ORA also determined values for intraocular pressure (IOP), corneal compensated IOP (IOPcc), and corneal resistance factor (CRF). One randomly selected eye of 20 non-contact lens wearers (four males and 16 females, age 19.7 +/- 1.1 years) was patched during three hours of soft contact lens wear. Measurements were made before lens insertion, immediately upon removal, and every 20 minutes thereafter for 100 minutes., Results: Immediately after contact lens removal, CCT was increased by 13.1 +/- 2.2% (mean +/- SD) compared with baseline (post hoc, P = .001). After 100 minutes, it remained elevated by 2.4 +/- 1.6% (post hoc, P = .001). However, there were no significant differences of CH at any time after lens wear (analysis of variance [ANOVA], P = .9). Immediately after lens removal, there were significant increases in IOP (post hoc, P = .003) and corneal resistance factor (CRF) (post-hoc, P = .015), but not in IOPcc (post hoc, P = .07). After lens wear, there were significant but weak correlations between the percentage change of CCT (CCT%) and IOP (r = 0.32, P = .001) and IOPcc (r = 0.29, P = .001). However, there was no significant correlation between CCT% and CH (r = 0.07, P = .458)., Conclusion: CH as measured by ORA was not associated with corneal swelling induced by soft contact lens wear in this study group.