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ET White, P-AA Tonnu, K Sharma, DF Garway-Heath; Objective Tonometry: A Comparison of Three Methods with Goldmann Applanation Tonometry . Invest. Ophthalmol. Vis. Sci. 2002;43(13):278.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare the inter-method agreement in intraocular pressure (IOP) measurements made with the Goldmann Applanation tonometer (GAT), the Tono-pen XL, the Ocular Blood Flow tonograph (OBF) and the Canon TX-10 non-contact tonometer (NCT). To assess whether inter-method differences are related to central corneal thickness (CCT). Methods: IOP was measured in one randomly selected eye in 105 patients with ocular hypertension or glaucoma with the GAT (2 observers), Tono-Pen, OBF and NCT in randomised order. IOP was measured 3 times with each method. CCT was recorded for each eye. GAT inter-observer and inter-method agreement was assessed by the Bland and Altman method of analysis. The relationship between inter-method differences and CCT was explored by linear regression. Results: 95% levels of agreement between observers for GAT were -2.5 to +2.7 mmHg. 95% levels of agreement between GAT and Tonopen, OBF and NCT were 155%, 110% and 82% greater, respectively, than the 95% levels of agreement between observers for GAT. The 95% confidence intervals for intra-session repeated measurement for each method were 1.3 mmHg and 1.5 mmHg for GAT, 2.6 mmHg for Tono-Pen, 2.1 mmHg for OBF and 1.9 mmHg for NCT. IOP measured higher with thicker corneas by all methods of tonometry. The rise in IOP was 2.3 mmHg and 4.5 mmHg per 100 increase in CCT for GAT and NCT, respectively. The difference was statistically different. Conclusion: There was good inter-observer agreement with GAT and moderate agreement between the NCT and GAT. However the inter-method differences between GAT and OBF and Tono-Pen probably preclude the latter instruments from routine clinical use as objective methods to measure IOP in normal adult eyes. IOP measurements by all forms of tonometry are affected by CCT.
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