3-D corneal modeling system

Abstract

New surgical procedures have been introduced recently that provide refractive correction to replace the use of eyeglasses or contact lenses. The procedures involve reshaping the cornea to compensate for the optical anomalies of astigmatism and nearsightedness. Although thousands of operations are currently performed in the U.S., there are no instruments available for monitoring the results. Thus, a critical need has arisen to inspect and measure the cornea's surface both before and after surgery. In this paper an instrument is presented which provides a detailed topographical model of an individual's cornea. The method uses a novel structured light source. The cornea is modeled as a convex mirror which forms a virtual image of the structured light source. A single image is recorded from the patient's cornea. The depth is obtained from triangulation between the acquired image and a reference image of a sphere. The reconstruction of the depth map is complicated by the fact that the magnification used in recording the image varies with the radius of curvature of the cornea. An iterative method is presented which solves for the radius of curvature despite the variation in magnification. The virtual image is digitized and the instantaneous curvature of the cornea is obtained. The instantaneous curvature is displayed in units of optical power (diopters). This display provides the ophthalmologist or optometrist with the essential optical properties of the cornea.