To analyze the diurnal change in intraocular pressure (IOP) and corneal biomechanical properties measured using the Ocular Response Analyzer (ORA; Reichert Inc., Depew, NY, USA) in Korean patients with normal tension glaucoma (NTG) patients.

Intraocular pressure (Goldmann applanation tonometer IOP [GAT IOP], Goldmann-correlated IOP [IOPg], corneal-compensated IOP [IOPcc]) and corneal hysteresis (CH), corneal resistance factor (CRF) and central corneal thickness (CCT) were measured in 21 eye of NTG patients (12 males, 9 female) at 3 hour intervals for 48 hours using ORA. We recorded the time of each parameter that showed the lowest and the highest values of during the 48 hour testing period (Day 1 and Day 2) and evaluated the change of diurnal variation using Repeated measures analysis of variance (Re-ANOVA).

Peak IOP measured with GAT and ORA occurred at 6 AM-9 AM, 3 PM-6 PM and the trough IOP at 9 PM-12 AM during the 48 hour period. CCT, GAT IOP, IOPcc and IOPg measurements showed statistically significant variations ( p <0.05). CH and CRF variations were not statistically significant ( p >0.05).

In Korean NTG patients, IOP exhibits significant diurnal variation, with higher values during the dawn and afternoon and lower values before retiring. Clinically, measurements of IOP performed in the afternoon could aid in the detection of relatively elevated IOP.