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J. C. Ramos-Esteban, W. J. Dupps, Jr.; IOP Changes Affect Corneal Hysteresis and Corneal Resistance Factor. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1855. doi: https://doi.org/.
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To determine whether serial increments in intraocular pressure (IOP) lead to changes in the corneal biomechanical properties measured by the Ocular Response Analyzer (ORA).
Six phakic de-epithelialized eye-bank globes were thinned to physiologic central corneal thickness (CCT) with 15% dextran solution. Vitreous infusion of Lactate-Ringer’s solution and continuous digital monitoring were used to maintain a constant intraocular pressure (IOP). Four replicate ORA measurements were performed on each globe at the following IOP levels: 5, 10, 15, 20 and 30 mmHg. CCT was returned to initial values prior to ORA measurements at each step by controlling surface hydration. The effect of serial IOP changes on corneal viscoelastic properties (Corneal Hysteresis (CH) and Corneal Resistance Factor (CRF)) was studied using linear regression analysis.
Mean pachymetry measurements at each step remained between 509 to 514 um throughout the experiments. CH was inversely correlated to IOP (R2 = 0.72, p = 0.07) and CRF was positively correlated to IOP (R2 = 0.87, p = 0.02). Between the lowest and highest IOP values, CH decreased significantly from CH = 13.64±1.94 to 10.64±1.79 (p=0.009). Over the same IOP interval, CRF increased from 8.47±1.94 to 13.05±1.72 (p < 0.001).
Some clinical studies have suggested that CH is a biomechanical property that is independent of IOP. These experiments show that, while directly manipulating IOP and controlling CCT, both standard biomechanical properties measured by the ORA are affected by IOP changes. Corneal Hysteresis and Corneal Resistance Factor respond in opposite ways to changes in IOP in the same eyes.
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