Relationship between corneal stiffness and glaucoma severity: clinical insights from Corvis ST technology

To explore the mechanical indices used for differential diagnosis and to investigate the relationship between ocular biomechanics and glaucoma severity within each group.

This cross-sectional study included 185 eyes from 185 subjects: 62 normal controls, 91 high-tension glaucoma (HTG), and 32 normal-tension glaucoma (NTG) patients. All participants underwent a comprehensive ophthalmic examination that involved ocular biomechanical measurements. Glaucoma severity was assessed using visual field index (VFI), mean deviation (MD), pattern standard deviation (PSD) and retinal nerve fiber layer (RNFL) thickness. Multivariable models were used to compare fifteen biomechanical parameters among the three groups adjusting for age, gender, intraocular pressure (IOP), central corneal thickness (CCT), and axial length (AL). The generalized linear model was utilized for multifactor comparison.

Significant differences in first applanation time (AT1), highest concavity time (HC time), stress strain index (SSI), and HC deflection were found among the three groups (P<0.05). AT1 was significantly higher in the HTG group compared to controls (P<0.05), and SSI was higher in HTG than NTG (P<0.05). HC deflection in the HTG group was significantly smaller than in NTG (P<0.05). Furthermore, AT1 levels were observed to be significantly higher in primary open angle glaucoma (POAG) patients compared to controls (P<0.05). Receiver operating charactristic (ROC) analysis showed HC deflection had an area under the curve (AUC) of 0.802 between HTG and NTG. A negatively significant correlation was observed between SSI and VFI in POAG patients.

Biomechanical analysis reveals that corneas in POAG patients are stiffer than normal controls, with increased corneal stiffness correlating with more severe glaucomatous damage. Interestingly, stiffer corneas in NTG patients appeares protective. In addition, HC deflection may be useful for differentiating HTG and NTG.