3433 Precision of the ultrasound biomicroscope (34 mhz) in measurement of corneal curvatures

Purpose. To develop a mathematical tool for decomposition of comeal topographic data into comprehensive optical components. Methods. The polar data values arising from each mire of the TM>1 cornea1 topographer were separated into spherical (average power), regdar astigmatic (2’ harmonic), and non-regular astigmatic components (l’, 3’, and higher harmonics) by Fourier series analysis. Averages of these optical components were calculated for groups of normal, keratoconic, and transplanted eyes, and the best sphere-cylindrically conwted visual acuity was compared with the amount of non-regular astigmatism. Changes in topographic refractive components were compared with subjective refractive changes in eyes that had undergone myopic-astigmatic excimer laser ablation. Resulk. The topography of keratoconic and transplanted corneas were characterized by high amounts of non-regular astigmatic components, which correlated inversely and significantly with the best spherocylindrically corrected visual acuity. Fourier series analysis was found superior to conventional keratometry in predicting spherical and regular astigmatic changes in subjective refraction after myopicastigmatic excimer laser ablation. Conclusions. Fourier series analysis is a powerful tool to decompose the information of complex topographic comeal images into comprehensive optical components. Furthermore, Fourier series analysis results in a ZO-fold reduction in the data necessary for analysis and re-construction of colotir-coded topographic images.