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 (P = 0.382). Intraocular pressure was significantly different between GAT with DCT and IOPCC (P < 0.001 and P = 0.022, respectively). The 95% limit of agreement of DCT, NCT, and IOPCC 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.