PURPOSE: The influence of corneal thickness and curvature on the difference between intraocular pressure (IOP) measurements obtained with a non-contact tonometer (NCT) and those with a Goldmann applanation tonometer (GAT) was studied. METHODS: The corneal thickness and curvature were obtained in 230 eyes of 115 subjects. The correlation between them and ratios of measurement with NCT to that with GAT ([NCT/GAT]) were examined. RESULTS: [NCT/GAT] and corneal thickness showed a significant positive correlation (r = 0.556, p < 0.01), but, the correlation between [NCT/GAT] and the radius of corneal curvature was not statistically significant (r = -0.035, p = 0.30). CONCLUSION: The thick cornea has more influence on the measurement with NCT than GAT, because IOP is measured with NCT over a wider applanation area. The corneas with steeper curvature also cause higher corneal rigidity and produce more overestimation of NCT measurement, while they have stronger capillary attraction of the precorneal tear film for the GAT tip and also produce overestimation of GAT measurement. As a result, [NCT/GAT] was believed to be not influenced by the corneal curvature.
PURPOSE: The influence of corneal thickness and curvature on the difference between intraocular pressure (IOP) measurements obtained with a non-contact tonometer (NCT) and those with a Goldmann applanation tonometer (GAT) was studied. METHODS: The corneal thickness and curvature were obtained in 230 eyes of 115 subjects. The correlation between them and ratios of measurement with NCT to that with GAT ([NCT/GAT]) were examined. RESULTS: [NCT/GAT] and corneal thickness showed a significant positive correlation (r = 0.556, p < 0.01), but, the correlation between [NCT/GAT] and the radius of corneal curvature was not statistically significant (r = -0.035, p = 0.30). CONCLUSION: The thick cornea has more influence on the measurement with NCT than GAT, because IOP is measured with NCT over a wider applanation area. The corneas with steeper curvature also cause higher corneal rigidity and produce more overestimation of NCT measurement, while they have stronger capillary attraction of the precorneal tear film for the GAT tip and also produce overestimation of GAT measurement. As a result, [NCT/GAT] was believed to be not influenced by the corneal curvature.
Authors: Milko E Iliev; Alexander Meyenberg; Ernst Buerki; George Shafranov; M Bruce Shields Journal: Br J Ophthalmol Date: 2007-05-10 Impact factor: 4.638