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E.J. Sarver, R.A. Applegate; Multiple Resolution Target for Resolving Double Reflections in Corneal Topography of Surfaces . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2872.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:To develop a corneal topography reflection target and image processing algorithms capable of detecting and resolving double reflections from surfaces as can occur in highly aberrated corneas. Methods:We developed a color multiple resolution reflection target which has a low frequency sinusoidal profile for the red component, medium frequency for the blue component, and high frequency for the green component. A prototype optical system utilizing a color camera and the color reflection target was constructed. Calibrated spherical and bicurve surfaces designed to give double reflections were used in testing. Results:For spherical surfaces, the acquired image was a warped (one–to–one) version of the reflection target. For the bicurve surfaces, the acquired image exhibited some target points which were imaged once by the central region and again by the peripheral region as can occur in highly aberrated corneas (double reflection). By comparing higher resolution peaks to the lowest resolution peaks, the occurrences of these double reflections were detected. Applying a modified arc–step reconstruction algorithm to the resulting features yielded a good representation of the surface with maximum errors significantly less than reported for similar surfaces measured by four commercial corneal topographers. For the three bicurves tested, our average maximum surface error was 11 microns compared to 55, 60, 121, and 163 microns for the commercial corneal topographers. This in an improvement in surface measurement error in the range of 5:1 to 15:1. Conclusion:The multiple resolution target and processing increase the reliability of corneal topography exams for bicurve surface profiles. We are in the process designing and testing more complicated surfaces representative of clinical eyes.
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