Intraocular pressure measured by dynamic contour tonometer and ocular response analyzer in normal tension glaucoma

To investigate intraocular pressure (IOP) measurement values in normal tension glaucoma (NTG) eyes using two different types of tonometer that are supposed to be little affected by corneal biochemical properties.

This study included 30 normal eyes of 16 healthy subjects and 30 eyes of 16 patients with NTG. IOP was measured with a Goldmann applanation tonometer (GAT), a Pascal dynamic contour tonometer (DCT), and a Reichert ocular response analyzer (ORA) three times each for normal and NTG eyes. The main measures were GAT-IOP, DCT-IOP, corneal-compensated IOP (IOPcc), Goldmann-correlated IOP (IOPg), and central corneal thickness (CCT).

In normal eyes, GAT-IOP was 13.2 +/- 1.4 mmHg; DCT-IOP, 13.0 +/- 1.6 mmHg; IOPcc, 13.6 +/- 2.0 mmHg; and IOPg, 12.4 +/- 2.0 mmHg. Multivariate analysis revealed no significant differences between the four measurements (p = 0.08). CCT was 524.6 +/- 27.3 microns. In NTG eyes, GAT-IOP was 13.1 +/- 1.3 mmHg; DCT-IOP, 13.7 +/- 1.3 mmHg; IOPcc, 15.2 +/- 2.0 mmHg; and IOPg, 12.7 +/- 2.0 mmHg. Multivariate analysis showed significant differences between the four measurements (p < 0.01). Sheffé's test showed that IOPcc was significantly higher than GAT-IOP, DCT-IOP, and IOPg (GAT-IOP vs IOPcc: p < 0.0001; DCT-IOP vs IOPcc: p = 0.01; IOPcc vs IOPg: p < 0.0001). CCT was 515.4 +/- 32.9 microns, with no significant difference between normal and NTG eyes (p = 0.15).

We investigated the values of IOP in NTG eyes as measured by the DCT and ORA. IOPcc was significantly greater than GAT-IOP, DCT-IOP and IOPg in NTG eyes, suggesting the possibility that IOP values may be underestimated.