Goldmann applanation tonometry and dynamic contour tonometry in eyes with elevated intraocular pressure (IOP): comparison in the same eyes after subsequent medical normalization of IOP

Abstract

Although it is widely accepted that the Pascal dynamic contour tonometry (DCT) reading is higher than Goldmann applanation tonometry (GAT) in normal range of intraocular pressure (IOP), it remains unclear whether DCT reading is higher or lower than GAT in an eye with severely elevated IOP. This study aimed to compare the IOP measurements obtained using GAT with DCT in eyes with elevated IOP and to compare the GAT and DCT measurements in the same eyes after subsequent normalization of the IOP with medical therapy. Eyes with IOP greater than 30 mmHg as measured by GAT at the initial examination were enrolled for a prospective study. IOP was measured by GAT and DCT. Central corneal thickness (CCT) was measured using a specular microscope. When the GAT-IOP was reduced to below 21 mmHg with medical therapy, DCT and CCT measurements were taken in the same eyes. Measurements from 27 patients were suitable for statistical analysis. At baseline examination, the mean DCT was significantly lower than their mean GAT (30.0 ± 5.8 mmHg vs 38.7 ± 9.1 mmHg, P < 0.001). After the IOP-lowering medical therapy had been instituted, the mean DCT was significantly higher than the mean GAT (17.9 ± 3.1 mmHg vs 15.6 ± 2.7 mmHg, P < 0.001). The mean post-treatment IOP reduction was 12.1 mmHg (40.3%) by DCT and 23.1 mmHg (59.7%) by GAT. The mean CCT showed no significant difference after the IOP-lowering therapy (537.7 ± 31.4 μm vs 543.1 ± 47.7 μm, P = 0.596). The mean ocular pulse amplitude decreased significantly after the medical treatment (3.16 ± 1.24 mmHg vs 2.07 ± 0.93 mmHg, P < 0.001). DCT-IOP, which is higher than GAT-IOP in normotensive eyes, is lower in eyes with GAT-IOP exceeding 30 mmHg.