Corneal Biomechanical Properties Affect Goldmann Applanation Tonometry in Primary Open-angle Glaucoma

• Published in: Journal of glaucoma Vol. 23; no. 2; pp. 69 - 74
• Main Authors: Costin, Bryan R, Fleming, Gloria P, Weber, Paul A, Mahmoud, Ashraf M, Roberts, Cynthia J
• Format: Journal Article
• Language: English
• Published: United States by Lippincott Williams & Wilkins 01-02-2014
• Subjects: Biomechanical Phenomena - physiology; Cornea - physiology; Elasticity - physiology; Female; Glaucoma, Open-Angle - physiopathology; Gonioscopy; Humans; Intraocular Pressure - physiology; Male; Middle Aged; Prospective Studies; Tonometry, Ocular; Visual Fields - physiology
• ISSN: 1057-0829; 1536-481X
• DOI: 10.1097/IJG.0b013e318269804b

PURPOSE:To study differences in corneal biomechanical properties between primary open-angle glaucoma (POAG) and central corneal thickness (CCT)-matched control subjects and their effect on intraocular pressure (IOP) measurement.
METHODS:Thirteen eyes of 13 POAG subjects and 15 eyes of 15 normal subjects underwent corneal topography; IOP using Goldmann applanation tonometry (GAT), dynamic contour tonometry (DCT), and corneal compensated IOP (IOPcc) using the Reichert ocular response analyzer (ORA); corneal hysteresis; and CCT. Results from POAG and control eyes were then compared using t tests.
RESULTS:Ages in the POAG group were slightly greater than that in the control group. CCT was closely matched between groups. Significant differences were found between GAT versus DCT and GAT versus IOPcc within both groupsMean GAT IOP was not significantly different between POAG and controls, whereas mean DCT IOP did show a significant difference between groups as did mean IOPcc. The delta differences, GATΔDCT and GATΔIOPcc, were of greater magnitude in POAG subjects when compared with controls. Corneal hysteresis was significantly lower in POAG subjects.
CONCLUSIONS:The delta differences between GAT and newer measures of IOP are greater in magnitude in patients with POAG than in the normal controls, independent of CCT. This is likely due to differences in the corneal biomechanical properties with POAG corneas being softer than healthy corneas, which causes greater underestimation of IOP by GAT in POAG than controls. Underestimation of IOP could affect treatment decisions and outcomes in POAG.