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M. Del Buey, J. Cristobal, L. Lavilla, C. Palomino, E. Lanchares; The Use of the Reichert Ocular Response Analyser to Establish the Relationship Between Biomechanical Properties and Ocular Pathology. Invest. Ophthalmol. Vis. Sci. 2008;49(13):653.
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© ARVO (1962-2015); The Authors (2016-present)
To measure corneal hysteresis (CH) and corneal resistance factor (CRF) on different ocular pathologies, by means of the Ocular Response Analyser (ORA) establishing a relationship between pathologies and the range of values for each parameter and the graphics obtained.
ORA is an instrument to measure the intraocular pressure of the eye and biomechanical properties of the cornea like CH (a measure of viscous damping in the cornea) and CRF (indicator of the overall resistance of the cornea).Patients with different pathologies like keratoconus (25 patients), corneal transplant (40 patients), glaucoma (50 patients) and corneal dystrophies (9 patients) were tested and different groups of signals (related to each pathology) and values for the parameters were obtained.
Pathologies like advanced keratoconus and some corneal transplant often give significant changes in applanation signal morphology. The results indicate that corneas with keratoconus, Fuchs’ dystrophy and corneal transplant show a general decrease in CH compared to normal eyes, independent of the Goldman's intraocular pressure. The mean hysteresis was 11.1 mm Hg (SD 1.9, range 7.1-16.7) in normal eyes compared with 8.7 mm Hg (SD 2,1, range 3.9-13.9) in Keratoconic eyes,10.4 mm Hg (SD 2.0, range 6.9-15.7) in glaucomatous population, and 8.8 mm Hg (SD 2.5, range 6.1-14.7) in patients with Fuchs' endothelial dystrophy. In most of the analysed ocular pathologies, the CH causes a change in the measured intraocular pressure, which is different to the Goldman's intraocular pressure. In addition to simple differences in the corneal hysteresis measurement values, significant differences are observable in the morphology of the measurement-signal waveform.
The biomechanical properties of the cornea change according to the pathology. Therefore, parameters like CH and CRF are distorted, which means that measured values of Goldman’s intraocular pressure can be incorrect. So it is necessary to considerate the value of IOPCC given by ORA. Hysteresis was significantly higher in normal than keratoconic, Fuchs’ dystrophy, and some corneal transplant eyes. While at present we are only utilizing the corneal hysteresis measurement, it is possible that after further investigation we may be able to gain additional information from other elements of the signal wavwform.
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