Diurnal variations in corneal biomechanics in healthy young adults.

Abstract

Purpose: To assess the diurnal changes in corneal biomechanics in healthy young adults.

Methods: At Wenzhou Medical University Eye Hospital in China, a prospective case series. Each healthy subject had six Corvis ST examinations, from 10:00 on a first day to 6:00 on the following day, at 4-hour intervals. The data collected included the biomechanically corrected IOP (bIOP), the central corneal thickness (CCT) and six dynamic corneal response (DCR) parameters, namely deformation amplitude (DA), the ratio between DA values at the apex and 2 mm from the apex (DAR2), integrated inverse radius (IIR), the stiffness parameter at first applanation (SP-A1), Corvis biomechanical index (CBI) and the updated stress-strain index (SSIv2). A multilevel model was used to assess the changes in DCR parameters of patients over time during the examination period.

Results: Sixty-one subjects were included and intra-operator reproducibility was good for most DCR parameters at the 6 time points. DA, DAR2, IIR and CBI showed small fluctuations during the 24-hour cycle with mean values of 0.1, 0.16, 0.34, and 0.04 units, respectively, while SP-A1 showed higher variations averaging 20.57 units and SSIv2 had the least fluctuation within 0.10 units during 24-hour cycle. After correcting for the effects of CCT and bIOP, the diurnal fluctuations in IIR, CBI and SSIv2 were not statistically significant, unlike the fluctuations in DA, DAR2 and SP-A1, which remained significant.

Conclusions: Compared with the DA, DAR2, IIR and CBI, SP-A1 was more affected while SSIv2 was the less affected by the diurnal variations and associated corneal edema.