Corneal Biomechanics in Primary Open Angle Glaucoma and Ocular Hypertension: A Systematic Review and Meta-analysis

Abstract

Précis: Normal tension glaucoma patients had softer corneas than normal controls, whereas high-tension glaucoma and ocular hypertension patients had stiffer corneas.Purpose: To comprehensively identify the corneal biomechanical differences of patients with primary open angle glaucoma (POAG) and ocular hypertension (OHT) using the Ocular Response Analyzer or the Corvis ST. Methods:The electronic databases PubMed, Embase, and Web of Science were comprehensively searched for studies comparing corneal biomechanical differences between POAG and OHT patients with normal controls by Ocular Response Analyzer or Corvis ST. The weighted mean differences and 95% confidence intervals (CIs) were calculated. Subgroup analyses were performed according to the subtypes of POAG, including high-tension glaucoma (HTG) and normal tension glaucoma (NTG).Results: Thirty-one case-control studies were ultimately included, with 2462 POAG patients, 345 OHT patients, and 3281 normal controls. The corneal hysteresis (CH), corneal resistance factor (CRF), and highest concavity time (HC-t) were all lower in POAG patients than in normal controls. The CH, time at the second applanation (A2t), HC-t, highest concavity radius (HC-R), and deformation amplitude at the highest concavity (HC-DA) were lower in OHT patients, while the CRF, time at the first applanation (A1t), and stiffness parameter at the first applanation (SP-A1) were greater in OHT patients than in normal controls. The subgroup analyses showed that the CH, A2t, length at the second applanation (A2L), and HC-DA were lower in HTG, and the CH, CRF, A1t, and HC-t were lower in NTG patients than in normal controls. Conclusion:The corneas of NTG patients are more deformable than normal controls, whereas the corneas of HTG and OHT patients are stiffer.

Comparing corneal biomechanic changes among solo cataract surgery, microhook ab interno trabeculotomy and iStent implantation

“…A lower SSI, a parameter of corneal stiffness independent of IOP 24 , also indicates softer corneas. These results are consistent with the “softer cornea” findings in normal tension glaucoma compared with normal controls that were previously reported 32 . Indeed, preoperative IOP was relatively low in the iStent group; this was similar to the solo cataract group while contrasting with the µLOT group.…”

“…Recently, Liu et al conducted a meta-analysis of 15 case‒control studies, including the studies described above, reporting severe heterogeneities between the studies. They found lower A2 time and HC deformation amplitude suggestive of stiffer cornea in high-tension glaucoma (untreated IOP of more than 21 mmHg), whereas lower A1 time, HC time, and higher peak distance, suggestive of softer corneas, were observed in normal tension glaucoma than in normal controls 32 . In the current population at baseline, eyes in the µLOT group exhibited a significantly longer A1 time, shorter A2 time, smaller magnitude of A1 and A2 velocity, and deflection amplitude max than eyes in the solo cataract group, which are in agreement with the “stiffer cornea” findings in previous studies.…”

“…Many studies have compared the biomechanical properties measured with Corvis ST between OAG eyes and normal eyes, providing different or partially contradictory results 26 – 32 . Many studies have found a longer A1/HC time, shorter A2 time, smaller magnitude of A1/A2 velocity, and smaller deformation amplitude (nearly equal to the deflection amplitude max plus posterior displacement of the whole eye) in POAG eyes than in normal eyes 26 , 27 , 31 .…”

Predictive Value of Dynamic Corneal Response Parameters Evaluated with Scheimpflug High-Speed Video (Corvis ST) on the Visual Field Progression in Prostaglandin Treated Ocular Hypertension and Open-Angle Glaucoma Patients

“…A thin central corneal thickness (CCT) is recognized as a risk factor for glaucoma, both due to the noise it brings to the measurement of IOP, but also because it may act as a surrogate of the biomechanical susceptibility to suffer ONH damage in glaucomatous eyes [ 3 – 6 ]. However, other factors beyond CCT are also regarded as important, and cornea biomechanics seem to play a role in the pathogenesis of glaucoma subtypes [ 7 ].…”