This calculator app consists of two parts.
The first part is used to calculate the intraocular lens power using Sanders-Retzlaff-Kraff formula (SRK II)
The second part is used to calculate surgically induced astigmatism.

The user need to enter pre-operative Kh and Kv values in the first part in addition to specified A-constant and axial length. On clicking the find IOL power button, we are able to calculate the desired intraocular lens power in Diopters.

In the second section of this calculator, user need to enter only post-operative Kh and Kv values for calculating surgically induced astigmatism (SIA). The user is then clicks the find SIA vector magnitude button and then SIA vector axis button that readily calculates the resultant SIA vector.

The SIA calculations utilizes Pythagorean concept for calculating the vector on applying keratometric horizontal and vertical curvatures representing the adjacent and opposite sides of a right angle triangle. And then the hypotenuse is calculated that represents the SIA magnitude. On subtracting the post-operative SIA vector magnitude from pre-operative vector magnitude, we derive at resultant SIA vector magnitude.

Similarly, the axis of astigmatism is calculated namely pre-operative SIA axis and post-operative SIA axis, on subtracting one from the other, we derive the resultant SIA vector axis on using tan inverse function.