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Cynthia Roberts, Ashraf Mahmoud, Richard Lembach, Thomas Mauger; Corneal Deformation Characteristics and IOP before and after Collagen Crosslinking. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5272. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate in vivo corneal deformation characteristics and measures of intraocular pressure (IOP) before and after corneal collagen crosslinking (CXL).
26 eyes of 26 subjects with keratoconus or post-refractive surgery ectasia had CXL treatment (Tx), and had pre and 6 month post CXL data from Goldmann Applanation Tonometry (GAT), PASCAL Dynamic Contour Tonometry (DCT), Ocularl Response Analyzer (ORA) for Goldman-correlated IOPg, corneal compensated IOPcc, corneal hysteresis, CH and corneal resistance factor, CRF, as well as CorVis ST, for inward (T1) and outward (T2) applanation times, pachymetry (pach), and inward (Vin) velocity. 16 fellow eyes who had data from the same devices at the same times were controls (C). Custom software for ORA produced pressures at inward (P1) and outward (P2) applanations, applanation times (Time1,Time2), maximum pressure, (Pmax) and time, (Tpmax). Custom software for CorVis image edges produced radius of curvature at highest concavity, (rad-curveHC) and time, (TimeHC). Data were compared with t-tests.
Significant differences between Tx and C groups were found in IOPg (Tx: +1.2±2.2mmHg; C: -1.1±1.4mmHg; p=.0004), IOPcc (Tx: +1.4±3.5mmHg; C: -1.3±1.9mmHg; p=.0020), P1(Tx: +7.5±17.3mmHg; C: -5.8±15.3mmHg; p=.0155), P2(Tx: +10.8±20.7mmHg; C: -8.3±10.9mmHg; p=.0003), Pmax (Tx: +25.4±59.6mmHg; C: -8.6±24.2mmHg.0138; p=), Tpmax (Tx: +.24±.74ms; C: -.11±.29ms.0375; ), Time1(Tx: +.17±.36ms; C: -.13±1.9ms; p=.0085), Pach(Tx: -71±52µ; C: -21±44µ; p=.0029), and Vin(Tx: -.005±.063ms; C: +.035±.039ms; p=.0301). In the ORA, the difference in pre to post-CXL Time2 minus Time1 was significant in C (+.21±.32ms; p=.0161), but not in Tx. In the CorVis, the difference in pre to post-CXL T2-T1, was significant in Tx(-1.11±.99ms; p<.0001), but not in C. Significant post minus pre-cxl differences were found in C but NOT in Tx for rad-curveHC (C: +.43±.70mm; p = .0261), as well as in Tx but NOT in C for TimeHC (-.89±1.3ms; p=0021). No differences were found in CH, CRF, GAT, or DCT.
Differences were consistent with corneal stiffening after CXL: longer time to applanate, slower velocity, shorter time between applanation points and shorter time to greatest concavity. Fellow untreated eyes showed opposite behavior consistent with softening: shorter time to applanate, faster velocity, longer time between applanation points and steepening at greatest concavity.
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