Table 2 Demographic and Refractive Data for 130 Eyes Measured for

PURPOSE: With the aberrometer based on Tscherning's principle, measurements of wavefront aberrations of human eyes with high accuracy and reproducibility are available for standard diagnostic investigations. METHODS: During investigational and clinical trials, wavefront-aberrations of about 300 human eyes were measured and evaluated within the last few years. RESULTS: measurements are presented in terms of Zernike coefficients and as height maps that can be converted directly to ablation profiles for wave-front-guided laser treatments. CONCLUSION: The Tscherning aberrometer is a simple optical device with high accuracy appropriate for routine clinical investigations on optical aberrations of the human eye. B ased on the principle of Tscherning aberrom-etry (well known since the end of the 19th century 1), Mierdel 2 and Mrochen 3 described an objective method of this aberrometer developed and used in Dresden, Germany. The goal of this paper is to describe the measurement procedure under clinical conditions and to summarize the results of some clinical trials with this new diagnostic tool. Clinical Measurements The measurement procedure with the Tscherning Aberrometer is subdivided into five single steps: (1) grabbing of the retinal images, (2) image enhancement, (3) detection of the retinal spot positions, (4) calculation of the wavefront aberration , and (5) presentation of the results. After the aberrometer was correctly centered on the line of sight of the patients eye, approximately five to ten retinal images were grabbed by means of a CCD camera and a standard personal computer (PC). From these images it was possible to determine the geometrical mass centers of each of the retinal spots. The next step was to calculate the shift of each retinal spot from its ideal position. An ideal, distortion free grid in the retinal plane was reconstructed by means of a grid spacing calculated from the length of Gullstrand's eye model and the position of the CCD camera in the aberrometer (depended on the ametropy of the investigated eye). From these deviations it was possible to determine the slope of the wavefront aberration. Some mathematical algorithms were needed to calculate the actual wave-front aberration in terms of Zernike polynomials from these slopes (two-dimensional least-square fit). The result of the whole procedure is a set of polynomial coefficients that describe the wavefront aberration of the investigated eye in terms of standard optical errors like astigmatism, coma, or spherical aberration (Table 1). Finally, the measured wavefront-aberration was presented as a height map with a diameter …