A graphical representation of the front surface power as a function of total lens power in best-form lenses. There are two possible solutions: (1) Those lenses which are the least curved and represented by the lower portion of the Tscherning ellipse. This portion is called the Oswalt branch of the ellipse. (2) Those lenses which are most curved and represented by the upper portion of the ellipse. This latter portion is called the Wollaston branch of the ellipse. See best-form lens.