Varying Effects of Corneal Thickness on Intraocular Pressure Measurements with Different Tonometers

Abstract

Aims To compare the intraocular pressure (IOP) measurements using the Goldmann applanation tonometer (GAT), noncontact tonometer (NCT), and ocular blood flow tonometer (OBFT), and to evaluate the effects of varying central corneal thickness (CCT) on the readings. Methods Ultrasound pachymetry and tonometry were performed on 170 eyes. Using the corrected GAT values that took CCT into account as the standard, we calculated the NCT and OBFT measurement errors related to the CCT variable by a linear regression model. Group comparisons were performed with the v 2 test and one-way ANOVA test. The correlation between the various tonometer measurements was analysed by Pearson's correlation method. Results Both the NCT (r ¼ 0.872, Po0.001) and OBFT measurements (r ¼ 0.861, Po0.001) were highly correlated with the GAT measurements. IOP measurements using the three tonometers were all correlated with CCT (all Po0.001), with the NCT measurements showing the greatest regression coefficient (b ¼ 0.063, r ¼ 0.650) and the GAT measurements the least (b ¼ 0.037, r ¼ 0.496). A linear regression model indicated that a 10 lm change in CCT resulted in a NCT measurement deviation of 0.47-0.98 mmHg and an OBFT measurement deviation of 0.29-0.81 mmHg.Conclusion Pressure readings with the GAT, NCT, and OBFT are all affected by CCT, with the NCT being the one most affected and the GAT the least. Our findings suggest CCT an essential variable to consider in interpreting IOP readings, especially for the NCT measurements.

Clinical evaluation of multiparameter correction equations for Goldmann applanation tonometry

“…As noted by several earlier studies, 3,6,7 there was a significant positive association between CCT and IOPG, with the IOPG on average being greater in individuals with thicker CCT when compared with those with thinner CCT. The CCT accounted for 7.2, 3.6, and 6.6% of the IOP variance in Europeans, Indians, and African Americans, respectively.…”

“…4 Numerous studies have evaluated the factors that affect the accuracy of IOP measurements made by the clinically available tonometers, and in particular the Goldmann applanation tonometer (GAT), the reference standard in tonometry. 5 As identified previously, the IOP measurements obtained using the GAT (IOPG) are known to vary with changes in biomechanical parameters that affect corneal stiffness, predominantly the central corneal thickness (CCT), 6,7 central corneal radius of curvature (R), 8,9 hydration, 10,11 ectasia, 12 and age. 13,14 Recently studies have reported that the 'new age' tonometers like the Pascal dynamic contour tonometer (DCT) 15 and the ocular response analyzer 16 are less affected by the physiological variations in the biomechanical parameters of the cornea.…”

Goldmann applanation tonometry versus non-contact tonometry: a comparative study

“…Many previous studies have also included eyes on anti-glaucoma medications. 1,3,8,10,13 The effect of treatment on the hydration properties of the cornea was overlooked as this was not the aim of the present study.…”

“…1,3,9,13 The shortcomings of present study were dependency bias since both eyes of a subject was included. Also, certain biases like observer bias may creep in, though measures were taken to avoid same by taking average of multiple readings and masking.…”

Surveillance for ocular hypertension: an evidence synthesis and economic evaluation

“…In total, 642 reports were identified from the electronic searches as being possibly relevant. [189][190][191][192] three in each of Saudi Arabia, [193][194][195] India, [196][197][198] Portugal 106,199,200 and Greece [201][202][203] and two in Taiwan, 125,204 Israel, 205,206 the Netherlands, 207,208 Sweden 209,210 and Turkey. 211,212 One study took place in each of Austria, 126 Brazil, 213 France, 123 Ireland, 214 New Zealand, 215 Norway 216 and Denmark.…”