An iterative method applied to enhance the proton radiation tolerance and the responsivity of PIN photodiodes was developed. The method allows to calculate optimal values of the intrinsic layer thickness and the incident light wavelength, in function of the light intensity and the maximum proton fluence to be supported by the device. These results minimize the effects of radiation on the total reverse current of the photodiode and maximize its response to light. The implementation of the method is useful in the design of devices that will not suffer variations from its operation point due to radiation.