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A. Sawada, H. Murase, K. Mochizuki, T. Yamamoto; Effect of Corneal Thickness on Intraocular Pressure Measurements With Three Different Tonometers in Healthy Subjects. Invest. Ophthalmol. Vis. Sci. 2008;49(13):700.
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To compare the intraocular pressures (IOPs) measured by a Goldmann applanation tonometer (GAT), a non-contact tonometer (NCT: NT-2000; Nidek Co., Ltd., Gamagori, Japan), and a newly developed portable non-contact tonometer (PNCT: PT-100; Reichert, Inc., NY; USA) in eyes of normal volunteers, and to determine if a significant correlation exists between the IOP and the central corneal thickness (CCT).
A total of 144 normal participants was randomly assigned into the following two groups. In the first group, IOP was measured with first the NCT and then with the GAT. In the second group, IOP was measured with first the PNCT and then with the GAT. Subsequently, the CCT was measured using an ultrasonic pachymeter.
There was a strong correlation between the IOPs determined by the GAT and the NCT and between the GAT and PNCT (both P<0.001; spearman test). However, a Bland-Altman plots showed that the correlation between the GAT and NCT or PNCT measurements were not significant. With all instruments, the IOP readings revealed statistically significant correlations with CCT (GAT; P=0.028, NCT; P=0.017, PNCT; P=0.006). The mean IOPs obtained with the GAT increased by 0.22 mmHg with a 10 µm increase of the CCT, i.e., 0.22 mmHg/10 µm. The comparable value for the NCT was 0.29 mmHg/10 µm, and for the PNCT was 0.31 mmHg/10 µm.
The GAT is the tonometer least affected by the CCT compared to PNCT and NCT when used to measure IOP in normal eyes. The PNCT is more likely to be affected by variations in the CCT than the GAT.
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