a method for calculating the required cylindrical power of a toric implant by using both the measured pre - operative corneal / ocular astigmatism and the predicted surgically - induced astigmatism . the post - operative corneal / ocular astigmatism is predicted using power vector analysis of the surgical technique employed by the surgeon . such a method provides a more accurate method of calculating the required spherocylindrical refractive power of the implant . the method can be implemented manually , but preferably is automated by implementation on a computer through appropriate software .