Corneal biomechanical properties in normal-tension glaucoma

Purpose: To investigate the intraocular pressure (IOP) and corneal biomechanical properties of normal and normal-tension glaucoma (NTG) eyes. Methods: This study included 83 normal and 83 NTG eyes. We measured corneal-compensated IOP (IOPcc), Goldmann-correlated IOP (IOPg), corneal resistance factor (CRF), corneal hysteresis (CH) and central corneal thickness (CCT) three times each for normal and NTG eyes using an Ocular Response Analyzer (ORA). Results: No significant difference in CCT was seen between normal eyes (541.4 +/- 26.8 mu m) and NTG eyes (535.4 +/- 24.9 mu m; p = 0.16). IOPcc was significantly higher in NTG eyes (16.1 +/- 2.6 mmHg) than in normal eyes (15.1 +/- 2.9 mmHg; p = 0.01), while IOPg was significantly lower in NTG eyes (14.1 +/- 2.7 mmHg) than in normal eyes (15.1 +/- 3.0 mmHg; p = 0.04). CRF and CH were significantly lower in NTG eyes (CRF, 8.9 +/- 1.5 mmHg; CH, 9.2 +/- 1.3 mmHg) than in normal eyes (CRF, 10.6 +/- 1.4 mmHg; CH, 10.8 +/- 1.3 mmHg; p < 0.0001 each). Conclusion: IOPcc was significantly higher in NTG eyes than in normal eyes. The ORA may be useful for distinguishing between the IOPcc of NTG eyes with normal IOP and that of normal eyes. In addition, the ORA enables CRF and CH to be measured in vivo, and weakness of the lamina cribrosa may be clinically inferred from the fact that CRF and CH were reduced in NTG eyes in our study. Low CRF and CH may be clues to the pathology of NTG.