Corneal Biomechanical Properties, CCT and IOP Across the Spectrum of Glaucoma
This Indian prospective cross-sectional study evaluated corneal biomechanical properties across the glaucoma spectrum and studied the relationship between these measurements and intraocular pressure (IOP) measured by Goldmann applanation tonometry (GAT-IOP) and central corneal thickness (CCT).
The study, which took place at a tertiary-care teaching institute, included 323 eyes of 323 participants (71 normal, 101 glaucoma suspect [GS], 38 ocular hypertension [OHT], 59 primary angle-closure disease [PACD], 36 primary open-angle glaucoma [POAG], and 18 normal-tension glaucoma [NTG]) who had received no ophthalmic treatment. Corneal hysteresis (CH), corneal resistance factor (CRF), corneal-compensated IOP (IOPcc), and Goldmann-correlated IOP (IOPg) measured by the Ocular Response Analyzer (ORA) were noted and GAT-IOP and CCT were recorded in all subjects. Main outcome measures included regression analysis used to determine the relationship between GAT-IOP, CCT, age, CRF and CH as well as Bland-Altman plots used to assess agreement between IOP measured by GAT and the ORA (IOPg).
It was reported that CH measurements were significantly less in POAG and NTG compared to normal subjects (p = .034 and p = .030 respectively), regardless of the IOP. It was also noted that the CRF was significantly less in NTG and maximum in POAG and OHT and regression analysis with CH as dependant variable showed significant association with GAT-IOP and CRF (p < .001) but not CCT, persisting on multivariate analysis (adjusted R2 = 0.483). Furthermore, GAT-IOP correlated strongly with Goldmann-correlated IOP on the ORA (IOPg) (r = 0.82; p < .001), but limits of agreement between the measurements were poor.
To conclude, CH and CRF may constitute a pressure-independent risk factor for glaucoma. CRF appears to influence GAT-IOP measurements more than simple geometric thickness measured by CCT. However, IOP measurements from the ORA are not interchangeable with, and are unlikely to replace, Goldmann applanation tonometry at the present time.