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J.P. Sanderson, M.A. Qazi, C.J. Roberts, J.S. Pepose; IOP and Corneal Biomechanical Metrics in Eyes With Keratoconus and Fuchs’ Dystrophy Compared to Pachymetry–Matched Controls . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2267.
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© ARVO (1962-2015); The Authors (2016-present)
To compare intraocular pressure (IOP) and corneal biomechanical parameters in eyes with keratoconus (KCN) and Fuchs’ corneal dystrophy (FCD) with pachymetry–matched normal control eyes using Goldmann applanation tonometry (GAT), the Ocular Response Analyzer (ORA, Reichert), and the Pascal Dynamic Contour Tonometer (PDCT, Ziemer).
Slit–scanning videokeratography, ultrasound pachymetry, and IOP measurements using 3 tonometry techniques were obtained for study eyes (KCN and FCD) and compared to measurements from 2 control groups matched for central corneal thickness (CCT ≤ 510 µm for KCN eyes; CCT ≥ 600 µm for FCD eyes). IOP and markers for corneal biomechanical properties (CCT, ORA corneal hysteresis (CH), ORA corneal resistance factor (CRF), and PDCT ocular pulse amplitude (OPA)) were recorded. Differences were statistically analyzed and correlations were made to normal controls.
Mean CCT in KCN (488.8±80.2 µm) and FCD (605±27.7 µm) were not statistically different from respective sets of control eyes (495.6±10.5 µm, p=0.87; 617.5±12.7 µm, p=0.44). PDCT IOP and ORA IOP for both KCN and FCD groups were statistically not different from IOP measurements from corresponding control eyes (p>0.10). Corneal hysteresis was reduced in KCN eyes (7.0±1.4 mm Hg vs. 8.8±1.2 mm Hg for controls, p=0.04) and FDC eyes (8.2±2.8 mm Hg vs. 12.1±1.7 mm Hg for controls, p=0.05). Similarly, mean CRF was lower in KCN and FDC than in control eyes. OPA was higher in KCN (3.54±1.3 mm Hg) than in matched controls (2.36±0.3 mm Hg, p=0.08).
Keratoconus and Fuchs’ dystrophy are 2 conditions with disparate mean corneal thickness, but corneal biomechanical metrics both showing reduced rigidity compared to control corneas of similar thickness. This demonstrates that metrics of corneal rigidity may not correlate with central corneal thickness, and that corneal biomechanics reflect more than central corneal pachymetry alone. These findings highlight the inherent flaws of algorithms that attempt "linear correction’ of Goldmann IOP based solely upon central corneal pachymetry, as such corrections would be in the wrong direction in Fuchs’ dystrophy.
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