Cone dimensions in keratoconus using Zernike polynomials

Purpose. To determine the physical dimensions and location of the cone in keratoconic corneas from videokeratoscopic height data. Methods. Corneal height data from keratoconus patients are obtained with a commercial videokeratoscope and decomposed into the set of orthogonal Zernike polynomials. The low-order Zernike terms are removed from the height data to expose the cone. The location of the peak of the cone and the cone's height and lateral dimensions are measured from the residual height data. This technique is compared to previous dioptric power-based methods of locating the cone. Results. The corneal protrusion due to keratoconus takes on a variety of shapes and locations. These dimensions are easily measured with the Zernike decomposition technique and provide more detailed and accurate information regarding the cone than dioptric power data. Conclusions. The proposed method for quantifying cone dimensions and locale in keratoconic corneas provides practical and detailed information which may be useful in tracking the progression of the disease, contact lens fitting, and surgical planning.