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H.–K.V. Ho, S.C. Lin, R.L. Stamper; Dynamic Contour Tonometry and Ophthalmic Pulse Amplitude in Patient With Normal Tension Glaucoma, Pseudo–Exfoliative Glaucoma, and Primary Open–Angle Glaucoma . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4438.
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The ophthalmic pulse amplitude (OPA) is the difference between systolic and diastolic intraocular pressures (IOP) and may be indicative of the intraocular blood flow. Dynamic contour tonometry (DCT) based on the principle of contour matching can be used to measure both IOP and OPA simultaneously. While the accuracy of Goldmann applanation tonometry (GAT) depends on central cornea thickness (CCT), the DCT does not. The goals of this study were  to evaluate OPA using DCT in patients with normal tension glaucoma (NTG), pseudo–exfoliative glaucoma (PXG), and primary open–angle glaucoma (POAG), and  to compare the DCT IOP readings with GAT in these conditions.
A total of 79 patients (50 females and 29 males) were enrolled in this prospective study. Of these patients, 11 had been diagnosed with NTG, 12 with PXG, 38 with POAG, and 18 were non–glaucomatous normal controls (NC). All the glaucomatous eyes were receiving at least one type of glaucoma treatment modality. For all patients, IOP measurement was performed using GAT, CCT was measured using ultrasonic pachymetry, and measurement of IOP and OPA was performed using DCT.
The mean OPAs in the LTG, PXG, POAG, and NC groups were 2.1, 2.3, 2.4, and 2.5 mmHg, respectively. The mean CCT in the NTG group was 517 µm, significantly lower than that of the POAG and NC groups being 547 µm (P = 0.0008) and 551 µm (P = 0.0025), respectively. Similarly, the mean CCT in the PXG group was 512 µm, significantly lower than that of the POAG (P = 0.0010) and NC (P = 0.0009) groups. However, there was no statistically significant difference in CCT between the NTG and PXG groups, or between the POAG and NC groups. The mean variation (DCT–GAT) of the IOPs measured by DCT and GAT in the NTG group was 2.4 mmHg, not significantly different from that of the PXG, POAG, and NC groups being 2.7, 1.4, and 2.1 mmHg, respectively. The mean variation (DCT–GAT) in the PXG group was significantly higher than that of the POAG group (P = 0.0297), but not the NC group. There was no statistically significant difference in the mean variation (DCT–GAT) between the POAG and the NC groups.
The study demonstrated that IOP measurement was often higher with DCT than with GAT. Eyes with NTG and PXG had significantly thinner CCT, and appeared to have reduced OPA and greater variation of IOP readings with DCT than with GAT. The meaning of these findings is unclear but measuring IOP and OPA with DCT in these cases may have some values.
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