Comparison of corneal biomechanical properties in normal tension glaucoma patients with different visual field...

To compare the corneal biomechanical properties difference by ocular response analyzer (ORA) in normal tension glaucoma (NTG) patients with different visual field (VF) progression speed.

NTG patients with well-controlled Goldmann applanation tonometer (GAT) who routinely consulted Kitasato University Hospital Glaucoma Department between January 2010 and February 2014 were enrolled. GAT and ORA parameters including corneal compensated intraocular pressure (IOPcc), Goldmann estimated intraocular pressure (IOPg), corneal hysteresis (CH), corneal resistance factor (CRF) were recorded. VF was tested by Swedish interactive threshold algorithm (SITA)-standard 30-2 fields. All patients underwent VF measurement regularly and GAT did not exceed 15 mm Hg at any time during the 3y follow up. Patients were divided into four groups according to VF change over 3y, and ORA findings were compared between the upper 25(th) percentile group (slow progression group) and the lower 25(th) percentile group (rapid progression group).

Eighty-two eyes of 56 patients were studied. There were 21 eyes (21 patients) each in rapid and slow progression groups respectively. GAT, IOPcc, IOPg, CH, CRF were 12.1±1.4 mm Hg, 15.8±1.8 mm Hg, 12.8±2.0 mm Hg, 8.4±1.1 mm Hg, 7.9±1.3 mm Hg respectively in rapid progression group and 11.5±1.3 mm Hg, 13.5±2.1 mm Hg, 11.2±1.6 mm Hg, 9.3±1.1 mm Hg, 8.2±0.9 mm Hg respectively in slow progression group (P=0.214, <0.001, 0.007, 0.017, 0.413, respectively). In bivariate correlation analysis, IOPcc, IOPcc-GAT and CH were significant correlated with mΔMD (r=-0.292, -0.312, 0.228 respectively, P=0.008, 0.004, 0.039 respectively).

Relatively rapid VF progression occurred in NTG patients whose IOPcc are rather high, CH are rather low and the difference between IOPcc and GAT are relatively large. Higher IOPcc and lower CH are associated with VF progression in NTG patients. This study suggests that GAT measures might underestimate the IOP in such patients.