For example, to change refraction by 4 diopters with an optical zone of 3 mm would require ablation of 12 μm.
As the depth of ablation is proportional to the square of the optical zone, changing the refraction by 4 diopters but with an optical zone of 6 mm would require a much deeper ablation of approximately 48 μm.
The actual ablation depth and surface shape will be slightly different from the theoretical Munnerlyn formula.
The sex, age, and race of the patient, and such things as the barometric pressure and ambient humidity will change slightly the required ablation.
The formula was derived based on creating a theoretical lenticular surface in a polymethylmethacrylate (PMMA) model, and modified by testing on in vivo animal tissue.