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Cynthia J Roberts, Ashraf Mahmoud, Gloria Fleming, Matthew Ohr, Paul Weber; Comparisons of Novel Stress-Strain Index and Other Clinical Measures of Corneal and Ocular Stiffness in Normal and Pathologic Cohorts. Invest. Ophthalmol. Vis. Sci. 2020;61(7):5213.
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© ARVO (1962-2015); The Authors (2016-present)
To compare multiple measures of corneal/ocular stiffness from air puff induced deformation in Normal (NL), Primary Open Angle Glaucoma (POAG), Ocular Hypertension (OHT), Diabetic without retinopathy (DIA), Diabetic Retinopathy (DR), and Keratoconus (KC) subjects.
A total of 301 subjects: 278 eyes of 140 NL, 53 eyes of 28 POAG, 32 eyes of 16 OHT, 88 eyes of 44 DIA, 72 eyes of 37 DR, and 59 eyes of 36 KC subjects. Data were acquired on multiple ophthalmic diagnostic devices, including the Corvis ST, reported here. HbA1C was also recorded in DIA and DR. Parameters include a novel corneal stress-strain index (SSI) and two stiffness parameters (SP) calculated as load over displacement, from undeformed state to first applanation (SP-A1) for cornea, and from applanation to highest concavity (SP-HC) for sclera. MANCOVA was performed to compare groups with IOP from Dynamic Contour Tonometry (DCT) as well as pachymetry and age as covariates. Statistical significance threshold was set to p<0.05. HbA1C was compared between DIA and DR using a t-test, and linear regression was performed with the combined DIA and DR cohorts.
For SP-A1 and SSI: KC is significantly less stiff (p<0.0001) than all other cohorts, and for SP-A1 only, no other cohort was different from another. For SSI, OHT is significantly stiffer (p<0.0001) than all other groups, and DR is significantly stiffer than DIA (p=0.0004) and NL (p < 0.0001) which are not different than each other. Also, POAG is stiffer than NL (p=0.0061). For SP-HC, OHT has a significantly stiffer response (p < 0.0001) than all other cohorts, and DR has a significantly stiffer response (p<0.0003) than all other cohorts except OHT. No other cohorts are different. HbA1C was significantly greater (p=0.0112) in DR than DIA (8.1±1.6 vs 7.4±1.8, respectively). No relationship was found between any measure of cornea or scleral stiffness and HbA1C in DIA and DR.
DR shows a stiffer corneal response by SSI and stiffer scleral response by SP-HC, than both DIA and NL with no differences between DIA and NL. Since HbA1C is not correlated to level of increased stiffness in DR, it is proposed that the stiffer scleral response is due to an increase in basement membrane associated with retinopathy, rather than glucose. OHT has a stiffer corneal response by SSI and a stiffer scleral response by SP-HC than both POAG and NL.
This is a 2020 ARVO Annual Meeting abstract.
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