Fig. 9. Diagram of two types of corneal nipples, with parabolic and sinusoidal cross-section. The corneal nipples are spaced at a distance of d=220 nm, and they have a height h=250 nm. The paraboloid is chosen so that the area at its base equals the area of the unit lattice cell, and has at the base a radius . The radius of the sinusoid at the base is r₀=d/2=110 nm.