Math of the Eye

*Corneal radius: r = 337.5/K

*The SRK formula is calculated easily by hand as P = A - 0.9 K - 2.5 L, where P is the IOL power to be used for emmetropia, A is the IOL specific A constant, K is the average corneal refractive power (diopters), and L is the length of the eye (mm). The SRK II formula adjusts the A constant utilized depending on the axial length: increasing the A constant for short eyes and decreasing the A constant for long eyes.

https://en.wikipedia.org/wiki/Intraocular_lens_power_calculation