Fig. 16. A. The soft lens produces a diffuse area of corneal edema that does not alter the radius of curvature of the cornea and does not cause spectacle blur. B. The rigid lens produces a discrete type of edema, confined to the corneal cap, which does cause spectacle blur because it produces a radical steepening of the corneal curvature. (Stein HA, Slatt BJ: Fitting Guide for Rigid and Soft Contact Lenses: A Practical Approach, 2nd ed. St. Louis, CV Mosby, 1984)