Corneal biomechanics measured with the ocular response analyser in patients with unilateral open-angle glaucoma

Abstract

. Purpose: To evaluate the relationship between biomechanical properties of the cornea and intraocular pressure (IOP) and the role of biomechanical properties in eyes of patients with unilateral primary open‐angle glaucoma (POAG). Methods: The biomechanical properties of corneal hysteresis (CH) and the corneal resistance factor (CRF) were measured with the ocular response analyser (ORA). In an experimental setting, three human donor eyes with Schiotz‐tonometry‐controlled IOP were investigated. In addition, a series of patients with unilateral POAG were evaluated. Main outcome measures were CH, CRF, corneal‐compensated IOP (IOPcc), standard automated perimetry parameters mean defect (MD) and pattern standard deviation, central corneal thickness, Goldmann applanation tonometry (GAT), and cup‐to‐disc ratio. Results: A highly significant linear correlation between CH and the corneal‐compensated IOP (IOPcc, r = −0.926; p < 0.001) was found. The correlation between IOPCC and CRF was not significant (r = 0.335; p = 0.08). In total, 36 eyes of 18 patients with unilateral POAG were examined. Regarding uncorrected CH (mean 7.73 ± 1.46 mmHg glaucomatous eye and 9.28 ± 1.42 mmHg fellow eye), there was a highly significant difference between both eyes. This difference disappears, when CH was corrected for IOP (9.44 ± 3.78 mmHg and 9.97 ± 3.22 mmHg, respectively). Conclusions: Corneal hysteresis but not corneal resistance factor is dependent on IOP. In patients with unilateral POAG, IOP is higher in the affected eye. When CH is corrected for IOP, corneal biomechanical properties do not differ in both eyes of patients with unilateral POAG.

Analyzing biomechanical parameters of the cornea with glaucoma severity in open-angle glaucoma

“…Only these adjusted parameters can be used for the interpretation of biomechanical differences [20][21][22][23][24][25][26][27]. Most of the published studies on ORA measurements do not consider these dependencies in their analysis.…”

Association between Corneal Biomechanical Properties with Ocular Response Analyzer and Also CorvisST Tonometry, and Glaucomatous Visual Field Severity

“…35–39 The reported CH and CRF values varied among these studies. Previous studies have reported that CH was 7.7 to 10.0 and CRF was 7.8 to 11.2 in POAG 36–38 or NTG, 37–39 whereas CH have been reported as between 9.5 to 11.1 and reported CRF values were between 9.2 to 11.0 in normal control.…”

Corneal hysteresis in patients with glaucoma-like optic discs, ocular hypertension and glaucoma

“…Kotecha et al described an IOP-independent corneal factor (corneal constant factor; mm Hg) and demonstrated that this parameter increased with thicker CCT and decreased with age [12]. Other studies have also found an association between greater CH, greater CCT, and lower IOP [6, 13, 14]. One such study looking at 207 normal eyes demonstrated only a moderate correlation between CH and increasing CCT suggesting CH measurements may reflect different aspects of biomechanical rigidity [6].…”

“…One such study looking at 207 normal eyes demonstrated only a moderate correlation between CH and increasing CCT suggesting CH measurements may reflect different aspects of biomechanical rigidity [6]. In contrast, a study on patients with unilateral POAG found that CH but not CRF was significantly correlated with IOP concluding that once CH is corrected for IOP, there is no difference in corneal biomechanical properties between eyes with and without POAG [13]. Due to these findings it is important to take both CH and CRF into consideration.…”