DEVELOPMENT OF A WIDE-FIELD HEIGHT EYE TOPOGRAPHER - VALIDATION ON MODELS OF THE ANTERIOR EYE SURFACE

Purpose. The aim of this research was to develop a corneal topographer that determines the shape of the entire anterior surface of an eye wi thout assumptions, and with uniformly high accuracy in the center and periphery. Methods. Based upon a double projection of two sine wave gr atings and analysis of the distortion of the sine wave gratings due to the corneal-scleral shape, point-by-point measurements of surface ele vation were obtained with a sample density equal to the pixel density of the CCD-detector. Using this principle, a prototype topographer, ca lled the Maastricht Shape Topographer (MST), was developed. The accura cy and reproducibility of the instrument were evaluated using bispheri c models of the anterior surface of the eye. Results. The average accu racy of height measurements was +/-0.55 mu m in the 10-mm central area and +/-22.50 mu m in the periphery (14 to 19 mm). Reconstruction accu racy of the radius of curvature was +/-0.0155 mm (+/-0.08 D) in the ce nter and +/-0.0313 mm in the periphery (sclera). Average height reprod ucibility standard error was 0.0282 mu m in the center and 2.6156 mu m in the periphery, Conclusions. With the MST, unambiguous shape measur ements of the entire anterior surface of the eye are possible, with ac curacy up to clinically accepted standards. MST is able to measure hei ght over a wide area of 20 mm, with a 6-mm depth of field. The tested prototype of the device can be further improved by the use of custom-m ade optics in order to increase signal to noise ratio in the periphery of the image. This height topographer could offer a reliable method i n cases where shape is of paramount importance, e.g., in (scleral) con tact lens fitting and refractive surgery.