Comparison of current tonometry techniques in measurement of intraocular pressure.

Purpose: To compare four tonometry techniques: Goldmann applanation tonometer (GAT), Dynamic contour tonometer (DCT), Non-contact tonometer (NCT), and Ocular Response Analyzer (ORA) in the measurement of intraocular pressure (IOP) and the impact of some corneal biomechanical factors on their performance.

Methods: In this cross-sectional study, volunteers with normal ophthalmic examination and no history of eye surgery (except for uncomplicated cataract surgery) or trauma were selected. Twenty-five subjects were male, and 21 were female. The mean age was 48 ± 19.2 years. Anterior segment parameters were measured with Scheimpflug imaging. IOP was measured with GAT, DCT, NCT, and ORA in random order. A 95% limit of agreement of IOPs was analyzed. The impact of different parameters on the measured IOP with each device was evaluated by regression analysis.

Results: The average IOP measured with GAT, DCT, NCT, and ORA was 16.4 ± 3.5, 18.1 ± 3.4, 16.2 ± 3.9, and 17.3 ± 3.4 mmHg, respectively. The difference of IOP measured with NCT and GAT was not significant ( = 0.382). Intraocular pressure was significantly different between GAT with DCT and IOP ( < 0.001 and  = 0.022, respectively). The 95% limit of agreement of DCT, NCT, and IOP with GAT was -5.7 to 2.5, -4.1 to 4.7, and -5.3-3.7 mmHg, respectively. Simple regression model corneal resistance factor (CRF) and central corneal thickness (CCT) and multivariate model CRF had a significant relationship with IOP measured with the four devices.

Conclusion: Although the mean difference of measured IOP by NCT, DCT, and ORA with GAT was less than 2 mmHg, the limit of agreement was relatively large. CCT and CRF were important influencing factors in the four types of tonometers.