We compared several mathematical methods for the calculation of surgically induced astigmatism, including Jaffe's horizontal component, Jaffe's vector, Cravy's axis-based cylinder, and Holladay's with-the-wound cylinder. Computer stimulation indicated that Jaffe's vector and Holladay's with-the-wound cylinder methods correctly calculate the surgically induced astigmatism regardless of the direction of wounds. The remaining two methods, however, were found to give erroneous values when the wound is constructed off the x-y axis. Holladay's parameter was least affected by the deviation of the surgical axis. When pre- and postsurgical data of eyes undergoing cataract surgery were analyzed (55 eyes were operated on with a 5.5 mm incision located superiorly, 35 eyes with a 5.5 mm incision located supratemporally, and 40 eyes with a superiorly located 3.2 mm incision), only the Holladay's with-the-wound cylinder method could calculate the actual amount of with-and/or against-the-wound changes.