Experimentally determined dn/dc values for lens proteins from different organisms. A. HEWL (control), B. γM8b-crystallin, C. γM8c-crystallin, D. γM8dcrystallin, E. γS1-crystallin, F. γS2-crystallin, G. J2-crystallin, H. human γS-crystallin, I. tunicate βγ-crystallin. Hen egg white lysozyme was measured as a control protein that has not been selected for high refractivity.