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Cynthia J Roberts, Ashraf M Mahmoud, Gloria Fleming, Matthew Ohr, Paul A Weber; Preliminary Comparisons of Clinical Measures of Corneal and Ocular Stiffness in Normal and Pathologic Cohorts. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4780.
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© ARVO (1962-2015); The Authors (2016-present)
To compare multiple measures of stiffness from air puff induced deformation in 6 cohorts: Normal (NL), Primary Open Angle Glaucoma (POAG), Ocular Hypertension (OHT), Diabetic without retinopathy (DIA), Diabetic Retinopathy (DR), and Keratoconus (KC).
A total of 142 subjects were recruited with 104 eyes of 52 NL, 28 eyes of 14 POAG, 20 eyes of 10 OHT, 65 eyes of 33 DIA, 33 eyes of 18 DR, and 29 eyes of 15 KC subjects. Data were acquired on multiple ophthalmic diagnostic devices, including the Corvis ST, which will be the subject of the current report. Two stiffness parameters (SP) were calculated as load over displacement, the first based on displacement from undeformed state to first applanation (SP-A1), and the second based on displacement from applanation to highest concavity (SP-HC), along with Integrated Inverse Radius (IntInvRad) and Deformation Amplitude Ratio at 2mm (DARatio2mm). For SP-A1 and SP-HC, a larger value indicates a stiffer response. For DARatio2mm and IntInvRad, a smaller value indicates a stiffer response. MANCOVA was performed to compare groups with intraocular pressure (IOP) from Dynamic Contour Tonometry (DCT) as well as pachymetry as covariates. Statistical significance threshold was set to p < 0.05.
For SP-A1: OHT > NL (p = 0.0116) and POAG > NL (p=.0149) with no difference between OHT and POAG (p=.6059), while for SP-HC: OHT > NL (p < 0.001), OHT > POAG (p < .0001) and POAG > NL (p < .0001). KC was lowest of all groups (p < .0001) for SP-A1, but only lower than POAG and OHT for SP-HC. For SP-A1, both DIA and DR were not different from each other (p = 0.5122) and neither was different from NL (p = .7900 and 0.3751, respectively). However, for SP- HC: DR > DIA (p=.0105), DR > NL (p = .0071), and DIA was not different from NL (p=.9813). For both DARatio2mm, and IntInvRad, only KC was significantly greater than all other groups (p < 0.0001) and no other groups were different from each other.
SP-HC has been shown to be sensitive to scleral stiffness, which may be important to separate Diabetic and Normal subjects from those with Diabetic Retinopathy, as well as OHT from POAG in this preliminary report. SP-A1, DARatio2mm, and IntInv Rad have been shown to be sensitive to corneal stiffness, which is important in separating keratoconus from normal and other pathologic groups.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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