Dynamic Contour Tonometry and Goldmann Applanation Tonometry: Difference of Intraocular Pressure Values Between Eyes with and without Glaucomatous Damage in Thin Corneas

Background: To examine the differences in intraocular pressure (IOP) measurements obtained with Goldmann applanation tonometry (GAT) and Pascal dynamic contour tonometry (DCT) in subjects with thin corneas and to correlate these with structural and functional parameters of glaucoma damage. Patients and Methods: One hundred and thirty participants (130 eyes) with central corneal thickness lower than 500 mu m were included in five groups in this cross-sectional observational study: 52 eyes with primary open angle glaucoma (POAG), 19 eyes with normal tension glaucoma (NTG), 27 eyes with ocular hypertension (OHT), 21 participants suspected of having glaucoma (GS), and 11 healthy subjects. The measurements were obtained with GAT and DCT in a masked fashion. The corrected GAT-IOP for central corneal thickness (CCT), the difference between DCT and GAT (Delta IOP = DCT-GAT) and corrected Delta IOP (corrected Delta IOP = DCT-corrected GAT) were calculated. Age, mean deviation (MD) from the most recent reliable visual field examination, average retinal nerve fibre layer thickness (RNFL), cup-to-disc ratio (CDR), ocular pulse amplitude (OPA), and treatment status were recorded for statistical analysis. Results: In all of the subjects (n = 130), the mean DCT, GAT and corrected GAT values were 17.6 +/- 3.4 mmHg, 13.2 +/- 3.8 mmHg, and 15.5 +/- 2.1 mmHg, respectively. Delta IOP and corrected Delta IOP were 4.4 +/- 2 mmHg and 1.7 +/- 2 mmHg, respectively. Delta IOP was correlated negatively with MD (rs = -0.32, p < 0.0001) and average RNFL thickness (r = -0.46, p < 0.0001) and positively with CDR (rs = 0.50, p < 0.0001). The mean IOP measured by GAT differed statistically significantly between eyes with glaucoma (n = 71, POAG and NTG) and eyes without damage (n = 59; OHT, GS, and healthy) (p < 0.0001), whereas the mean IOP by DCT did not (p = 0.935). The mean Delta IOP values were also statistically significantly higher in the glaucomatous group, with and without correction for CCT (p < 0.001). OPA and glaucoma diagnoses statistically significantly predicted Delta IOP (R-2 = 0.41, F-2.127 = 47.46, p < 0.0001). Conclusion: Greater underestimation of IOP by GAT was observed in the glaucomatous eyes with thin corneas. Performing DCT on patients with thin corneas might be advantageous in establishing the need for more aggressive treatment.