A method that measures the stimulus accommodative convergence/accommodation (AC/A) ratio where the changes in deviation in prism diopters are divided by the change in lens power. It calculates accommodative convergence by getting the accommodation ratio divided by lens power. The method measures the amount of accommodation by using either minus lenses at distance fixation or plus lenses at near fixation. For esotropia, a positive value is inputted, while a negative value is inputted for exotropia.