Abstract
Purpose :
Low corneal hysteresis (CH) is a risk factor for glaucoma progression, as well as a combination of thin, stiff corneas. This study investigates viscoelastic and elastic metrics from air puff deformation in Normal (NL) and Primary Open Angle Glaucoma (POAG).
Methods :
A prospective study of 107 subjects was done with 110 eyes of 55 NL subjects, age>50 years, 104 eyes of 52 POAG subjects. Viscoelastic response was evaluated with CH from the Ocular Response Analyzer; elastic response was evaluated with Corvis ST corneal metrics: Stress Strain Index (SSI) and stiffness parameter at first applanation (SP-A1). Scleral stiffness at highest concavity (SP-HC) and central corneal thickness (CCT) were included. Ganglion Cell Complex (GCC) from Optovue OCT was acquired. ANOVA was performed for age, CCT and IOPcc, while ANCOVA was used with IOPcc and CCT as co-variates for GCC, CH, SP-A1, and SP-HC. Regressions were performed between viscoelastic and elastic metrics, as well as between GCC and biomechanical metrics. Stepwise regressions with 0.15 entry/exit criteria were performed to predict GCC as a function of biomechanical metrics, and to predict CH as a function of elastic metrics. Statistical analysis was performed using SAS with significance threshold at p<0.05.
Results :
No difference in age was found. CCT was thinner and IOPcc higher in POAG. GCC was thinner in POAG (p < 0.0001), with CH, SP-A1 and SP-HC not different when controlling for CCT and IOPcc. CH was significantly associated with CCT, SP-A1, SP-HC, and IOPcc in both groups. GCC was significantly positively associated with CH and CCT, only in POAG, but not with SP-A1, SP-HC or IOPcc in either group. GCC was predicted in POAG inversely by SSI, and directly by CH and SP-HC. In NL, GCC was predicted by SSI, CCT and IOPcc. CH was predicted in POAG directly by SP-HC, and inversely by corneal stiffness metrics and IOPcc. CH was predicted in NL by SP-HC, corneal stiffness metrics, IOPcc and CCT.
Conclusions :
In POAG, thinner GCC was associated with lower CH and greater corneal stiffness, consistent with the literature on risk factors, as well as low scleral stiffness. Although greater cornea or sclera stiffness were associated independently with greater CH in POAG, when all elastic parameters were included in a predictive model, low CH was predicted by a combination of greater corneal stiffness, higher IOP, and lower scleral stiffness.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.