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K.E. Hamilton, D.C. Pye, A. Hali, P. Kam, C. Lin, T. Nguyen; Corneal Oedema Can Cause an Overestimation Error in Goldmann Tonometry . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4856.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Corneal parameters are known to affect the accuracy of Goldmann applanation tonometry (GAT) estimates of intraocular pressure (IOPG), though reports on corneal oedema are scarce. This study sought to determine if corneal oedema, induced by short–term contact lens wear, affects Goldmann applanation tonometer (GAT) estimates of intraocular pressure on human eyes in vivo. Methods: Young normal subjects (n = 25) presented for 3 separate visits where they wore no contact lens, a "thin" hydroxy ethyl methacrylate (HEMA) contact lens (centre thickness (ct) = 0.3mm) and a "thick" HEMA contact lens (ct = 0.7mm) for 2 hours of eye closure on one eye only. The lens wearing eye was chosen at random initially but remained the same for all visits: the non–lens wearing eye acted as the control. Central corneal curvature (CCC), intraocular pressure using Goldmann tonometry (IOPG) and central corneal thickness (CCT) were measured before and after lens wear. Results: No statistical difference was found in CCC, IOPG or CCT on the control day between the control and the lens eye. These baseline parameters did not change over subsequent visits (Friedman related measures test) in the control eye or lens eye. There was no statistical difference in CCC, IOPG or CCT in the control eye before or after lens wear on any visit (two tailed paired t–test). There was a significant increase in IOPG following thin lens wear (2.72 ± 2.25 mmHg, p < 0.001) but not the thick lens (p = 0.063) and in CCT in the lens wearing eye after both lenses (thin 40.0 ± 19.3 µm p < 0.001 , thick 44.5 ± 21.5 µm, p < 0.001) (2–tailed paired t–test). There was no correlation between IOPG or the corrected IOPG with the amount of corneal oedema or the change in corneal thickness for either lens. Conclusions: This study shows that the accuracy of Goldmann applanation is reduced following two hours of hydrogel contact lens wear resulting in an overestimation of IOP. This suggests the need for clinicians to consider corneal properties when interpreting GAT estimates.
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