Intraoffice variability of corneal biomechanical parameters and intraocular pressure (IOP).

PURPOSE

To evaluate the intraoffice hour variability of intraocular pressure (IOP) and in vivo biomechanical properties of the cornea, as measured with the Ocular Response Analyzer (ORA).

METHODS

The right eye of each of 58 young healthy subjects (14 men, 44 women) was measured at 1-hour intervals from 9.00 a.m. until 7.00 p.m. with the ORA. Subjects' age ranged from 19 to 45 years (average +/- standard deviation, 25 +/- 6 years).

RESULTS

Average intraoffice hour variability of IOP and corneal biomechanical parameters were not statistically significant, showing a stable profile during the hours of the day studied. An interesting finding was that although there were no significant diurnal variations in any of the parameters, minor changes in corneal-compensated IOP and a Goldmann-equivalent IOP were significantly correlated with the intraoffice hour variability of corneal biomechanical parameters corneal hysteresis (CH) and the corneal resistance factor (CRF). Corneal-compensated IOP changes were the most strongly associated with intraoffice hour variability in CH for all measurement times (r = 0.598; p < 0.001). Changes of Goldmann-equivalent IOP were strongly correlated with intraoffice hour variability of corneal resistance factor (r = 0.849; p < 0.001).

CONCLUSIONS

The present study confirms that intraoffice hour values of CH and corneal resistance factor are quite stable among a population of young healthy adults. However, average changes in these parameters over time correlate well with the changes in IOP values obtained with the same instrument, suggesting that diurnal variations of IOP could be at least in part related with changes in the biomechanical behavior of the cornea against the mechanical stimuli used by current non-contact tonometers. The most stable period to measure IOP and biomechanical parameters with ORA was in the afternoon.