Fourier transformation of corneal topography data

The clinical interpretation of corneal topography power maps has progressed through the development of both qualitative pattern classification systems and a range of quantitative descriptors. Although a number of different indices have been described, they do not all possess obvious clinical utility.

Fourier series analysis decomposes any circumferential fluctuations in corneal power into various components that have direct clinical correlates. The zero frequency and two-cycle components, which represent spherical equivalent and regular astigmatism, respectively, are analogous to keratometric spherical (equivalent) and astigmatic powers. The other Fourier components have no keratometric equivalent but have distinct clinical value. Decentration is a tilt of the cornea with respect to the videokeratoscope axis and irregular astigmatism is the sinusoidal variation in power that cannot be corrected with conventional lenses.

The present paper demonstrates the application of Fourier series analysis to corneal topography data.