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F.A. Navas, S.P. Azen, M. Lai, R. Varma, LALES Group; Comparison of IOP Measurements Obtained by the Goldmann Tonometer and the Tonopen and their Relationship to Central Corneal Thickness in a Population-based Cohort of Adult Latinos. The Los Angeles Latino Eye Study (LALES) . Invest. Ophthalmol. Vis. Sci. 2003;44(13):796.
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Purpose: To determine the difference between IOP measurements obtained by the Goldmann tonometer and the Tonopen, and explore their relationship with Central Corneal Thickness (CCT) in a population-based cohort of Latinos. Methods: Study participants underwent a complete ophthalmologic examination including 3 measurements of IOP using a Goldmann tonometer and 3 measurements using a Tonopen. Additionally, 3 measurements of CCT were obtained using an ultrasonic pachymeter. Differences between Goldmann and Tonopen readings were compared overall and stratified according to different Goldmann IOP readings. Differences between Goldmann and Tonopen measurements were also stratified by different categories of CCT. Results: The cohort consisted of 2583 participants. Mean (± SD) Goldmann tonometry and Tonopen determinations of IOP were 14.2 (± 3.3) mmHg, and 15.0 (± 3.1) mmHg, respectively. Tonopen readings were lower than Goldmann readings, when Goldmann IOP readings were between 21 to 30 mm Hg (mean difference 2.63 ± 2.78 mmHg) and when Goldmann IOPs were >30 mmHg (mean difference 4.29 ± 2.43 mmHg, p< 0.003). Conversely, Tonopen readings were higher than Goldmann readings when Goldmann IOP ranged from 0-10 mmHg. (2.88 ± 2.31 mmHg), and from 11-20 mmHg (0.74 ± 2.56 mmHg). All differences were significant at the 0.05 level. CCT was thicker in eyes with higher IOPs measured by both the Goldmann tonometer and the Tonopen (p<0.0001). The difference in IOP measurements between the Goldmann tonometer and the Tonopen were smaller in eyes with CCT <526 µm compared to eyes with thicker CCTs (p<0.05). Conclusions: Differences between the Goldmann tonometer and the Tonopen are dependant on the underlying IOP and the CCT. While these differences are quite variable, they are statistically and clinically significant and should be considered when measuring IOP in the clinical setting.
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