Fig. 11. Scleral rigidity from Friedenwald nomogram. Solid line (A) joins Po (determined by applanation tonometry) and Pt1 (Schiøtz scale reading with 5.5-g weight). Theoretically, the same line could be obtained by joining scale readings with any two Schiøtz weights indicated by dots. Slope of line is scleral rigidity, which can be obtained directly from nomogram by drawing parallel line through 20 on the pressure scale (dotted line B to scleral rigidity scale on top of nomogram). In this case, scleral rigidity is 0.022.