Abstract
Purpose :
This study investigates the relationship between viscoelastic and elastic metrics from air puff deformation in subjects with ocular hypertension (OHT) and normal controls (NL).
Methods :
A prospective study of 100 subjects was done with 110 eyes of 55 NL subjects, age>50 years, and 85 eyes of 45 OHT subjects. Viscoelastic response was evaluated with CH from the Ocular Response Analyzer, along with Corneal Compensated intraocular pressure (IOPcc); elastic response was evaluated with Corvis ST biomechanical metrics with stiffness parameter at first applanation (SP-A1) representing corneal stiffness and stiffness parameter at highest concavity (SP-HC) representing scleral stiffness. Central corneal thickness (CCT) was included. ANOVA was performed for age, CCT, IOPcc, CH, SP-A1, and SP-HC, followed by ANCOVA for CH, SP-A1, and SP-HC with CCT and IOPcc as co-variates. Regressions were performed between viscoelastic and elastic metrics. Statistical analysis was performed using SAS with significance threshold, p<0.05.
Results :
No difference was found in age (OHT; 61±17yrs, NL; 58 ± 5 yrs). CCT was thicker (OHT; 578 ± 46µ, NL; 556 ± 34µ; p=0.0002) and IOPcc higher (OHT; 21.0 ± 4.6mmHg, NL;15.5 ± 3.4mmHg; p< 0.0001) in OHT than NL. CH was significantly associated with CCT, SP-A1, and IOPcc in both groups, and with SP-HC in NL. Although CH was quite close in magnitude (OHT; 10.3 ± 2.0mmHg, NL;10.3 ± 1.5mmHg), the difference was ultimately significant (p=0.0002) in the ANCOVA when controlling for CCT and IOPcc, with the adjusted mean for OHT (10.8mmHg) greater than NL (10.0mmHg). SP-A1 was significantly different only in the ANOVA, but lost significance in the ANCOVA (OHT; 142 ± 17mmHg/mm, NL;126 ± 18mmHg/mm), while SP-HC was significantly greater in OHT in both the ANOVA and ANCOVA (OHT; 23 ± 6.9mmHg/mm, NL;15 ± 4 mmHg/mm p < 0.0001).
Conclusions :
Greater corneal stiffness in OHT is driven by higher IOP and thicker corneas. However, greater scleral stiffness in OHT is persistent, even after controlling for IOP and CCT. Although low CH is a risk factor for conversion from OHT to glaucoma, the combination of IOP and CH should be considered in evaluating risk, since the negative relationship between CH and IOP is well known, and our results show that similar values of CH become significantly different, if IOP is taken into account.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.