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D. Luce; Air–Jet Temporal and Spatial Pressure Properties of the Reichert Ocular Response Analyzer (ORA) . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5009.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The Reichert ORA uses air puff technology similar to that used in conventional air puff tonometers to measure both IOP and corneal biomechanical properties. Special measurement devices have been designed and used to determine spatial and temporal characteristics of the air–jet employed in the ORA to assist in quantifying the corneal biomechanical properties and their influence on IOP measurements. Detailed analysis of corneal deformation during Goldmann applanation tonometry has been reported, but not for deformation during air puff tonometry, presumably because detailed properties of air–jets employed in these devices have not been determined. Corneal deformation analysis is needed to understand observed ORA signal differences between normal and keratoconic corneas, and the differences between pre and post LASIK corneas. Methods: The vertical/horizontal spatial pressure profile of the air–jet of the ORA (at nominal operating distance) was determined employing a micro–aperture (0.25 mm) fast response (200 usec) pressure sensor positioned sequentially over a precise vertical/horizontal grid spacing of 0.125 mm, overall radial diameter, 6 mm. A complete pressure versus time signal (500 data points) was recorded at each grid point. Absolute pressure response of the sensor was derived from a reference standard. Results: The radial pressure distribution is a remarkably constant width (3%) Gaussian with a half pressure full diameter of 2.9 mm over the intraocular pressure measurement range of 5 to 60 mmHg. Repeatability of the average pressure over the 3 mm central optical observation zone is better than 2%. The averaged absolute pressure over the 3mm central zone agrees within 5% of the nominal IOP derived from Goldmann clinical comparison. Conclusions: Non–contact tonometer air puff technology employed in the Reichert ORA provides a precise, repeatable pressure profile versus time to the eye during measurement of IOP and corneal biomechanical properties. The profile data provides a basis for detailed modeling of the air puff driven corneal deformation using finite element analysis methods.
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