Progression of keratoconus assessed by fourier analysis of videokeratography data

Objective: To quantitatively document changes in corneal refractive parameters in relation to the progression of keratoconus over years. Design: Retrospective observational case series. Participants: Eighty-five eyes of 64 patients with keratoconus who had undergone videokeratography examinations at least twice with an interval of 1 year or longer between each examination. Methods: By means of Fourier series harmonic analysis, topography data were decomposed into spherical component, regular astigmatism, decentration component, and higher order irregularity. Main Outcome Measures: Change rate of each parameter per year was calculated by use of the least squares method. Results: All four refractive parameters were significantly larger in the keratoconic eyes than in the age-matched normal controls (P < 0.001, Student's t test). The yearly rate of change was significantly positive for spherical component (P = 0.008) and higher order irregular astigmatism (P = 0.015) but not for the regular astigmatism and decentration component. In eyes that showed apparent progression on color-coded maps, spherical component showed a significantly positive change rate per year (P = 0.002), but other parameters did not. In eyes without apparent progression, the yearly change rate of higher order irregular astigmatism was significantly larger than zero (P = 0.049). Conclusions: Keratoconus, progression over years was quantitatively described, It was indicated that spherical equivalent is a manifest indicator for the apparent progression of keratoconus, and irregular astigmatism increases along with the natural course of the disease. (C) 2002 by the American Academy of Ophthalmology.