Diurnal variation of corneal biomechanics and intraocular pressure in normal subjects

To assess and investigate the relationship between diurnal variations in intraocular pressure (IOP) and biomechanical properties of cornea.

Sixty-two healthy volunteers were recruited. Corneal compensated IOP (IOPcc), Goldmann-correlated IOP (IOPg), corneal resistance factor (CRF), and corneal hysteresis (CH) parameters were recorded by the Ocular Response Analyzer (ORA). Central corneal thickness (CCT) was measured using an ultrasonic pachymeter. Three consecutive measurements of IOPcc, IOPg, CRF, CH, and CCT were recorded at 8:00 am, 11:00 am, 2:00 pm, and 5:00 pm. One-way analysis of variance and Pearson correlation tests were used for statistical analysis. Intra device repeatability was evaluated using Scheffe multiple comparison.

IOPcc, IOPg, CRF, CH, and CCT measurements displayed a stable profile during daytime acquisitions and no statistically significant variation was noted (p>0.05). All measurements of IOPcc, IOPg, CRF, and CH recorded by ORA at 8:00 am, 11:00 am, 2:00 pm, and 5:00 pm were all found to be highly repeatable (p>0.05). There was a statistically significant and inverse correlation between IOPcc and CH (p=0.001), and a positive correlation was detected between IOPcc and CRF (p=0.001). CRF and CH were both found to be positively correlated to CCT (p=0.001).

IOPcc readings and recordings of corneal biomechanics were constant throughout the day in healthy eyes. CRF and CH seem to exert different effects on IOPcc as diverse correlations were detected between CRF, CH, and IOPcc. Assessment of IOP and corneal biomechanics using ORA was found to be a highly repeatable.