an ophthalmic pachymeter which is highly effective in aiding in the determination of thickness and the optical density of the cornea of an eye on a real - time basis . the pachymeter therefore lends itself to effective employment in aiding in radial keratotomy and other surgical procedures with respect to the eye . the ophthalmic pachymeter of the invention has three major subsystems which include a television camera , a multiple slit projector and an associated processing and display system . in a broad form , the invention comprises illuminating a selected portion of the cornea , moving a slit across the cornea and generating tyndall image ray paths for enabling analysis of the optical density of the cornea and the thickness of the cornea . this is accomplished through a series of digitally - encoded television images of the optical section of the cornea produced by a multiple slit projector and which images are then subjected to digital analysis . a locus of each of the significant elements of the reflected image of the anterior portion of the eye is defined . in this way , the optical character of the cornea / air interface is compared with the corrected reflectance of the stroma and the endothelium , in order to determine relative transparency . a density map may be constructed in parallel slices for display as a three - dimensional plot of the frontal surface shape of the cornea and for defining and displaying the local thickness , the posterior surface contour , and the optical density of the cornea .