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A.G. Boehm, M. Kohlhaas, S. Rose, E. Spoerl, L.E. Pillunat; The Effect of Corneal Thickness, Axial Length and Corneal Curvature on IOP Measurements Taken by Applanation Tonometry, Tonopen and OBF . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4866.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:To examine if there is an influence of corneal thickness, corneal curvature and axial length on tonopen and OBF tonometry in comparison to applanation tonometry. Methods: In a prospective clinical trial 57 eyes of 57 patients undergonig phacoemulsification (19 m and 38 w, mean age 72.8+/–9.6y), with a corneal thickness of 549.3 +/–38.7 µm, with a corneal curvature of K1=43,60±1,62D and K2=42,73±1,62D were examined. Before phacoemulsification the anterior chamber was canulated at the temporal corneal limbus. In a closed system the IOP was adjusted to 20 mmHg by manometric watercolumn. IOP was measured with the Perkins tonometer, tonopen and the ocular blood flow system (OBF). Results: At the IOP level of 20mmHg mean IOP readings were 20.72±2.08mmHg with applanation tonometry (p=0.11), 17.52±3.94mmHg with tonopen (p=0.001) and 15.82±2.67mmHg for OBF (p=0.001). Applantion tonometry readings were positively correlated to corneal thickness (p=0.001), but not to corneal curvature (p=0.468), and axial length (p=0.344). Tonopen readings were not correlated to corneal thickness (p=0.450), corneal curvature (p=0.183) and axial length (p=0.379). OBF readings were correlated to corneal curvature (p=0.008), but not to corneal thickness (p=0.077), and axial length (p=0.170). Conclusions: Applanation tonometry readings are affected by corneal thickness, and OBF readings by corneal curvature. Tonopen measurements are not influenced by corneal thickness, corneal curvature and axial length. Therefore, tonopen seems to be a good alternative for IOP measurements if corneal thickness or curvature needs to be considered.
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