The effect of contact lens induced oedema on the accuracy of Goldmann tonometry in a mature population

Aim: To determine the effect of contact lens induced oedema on the accuracy of Goldmann tonometry measurements of intraocular pressure (IOP) in mature subjects. Methods: 22 healthy subjects aged between 50 and 60 years were recruited. Corneal curvature, IOP, and central corneal thickness (CCT) were measured before and after two hours of monocular closed eye wear of a thick hydroxyethyl methacrylate ( HEMA) contact lens. Measurements were then repeated at 20 minute intervals for one hour after lens removal. Results: Both CCT (+ 54.1 mm) and IOP (+ 2.7 mm Hg) increased significantly after lens wear (p<0.001, paired t test with Bonferroni correction). For the hour following lens removal, the measured IOP was correlated to the increase in CCT (r = 0.84, p<0.001), at a rate of 1.0 mm Hg/10 mu m (95% confidence interval, 0.8 to 1.2 mm Hg/10 mm, linear mixed model analysis). Conclusions: A relatively small increase in CCT from contact lens induced corneal oedema caused an overestimation error in Goldmann tonometry measurements of IOP in healthy mature subjects.