Was Vitruvius right when he stated that the optical corrections of the Doric temple were meant to counteract optical distortions that would make the temple look faulty? The corrections were certainly used by the architects designing these temples to achieve a certain aesthetic goal; they were tools to help the architects to achieve the result that they felt to be correct. In this sense, taken strictly literally, we can say that Vitruvius was actually right; the corrections were indeed used to avoid some negative impression that was felt to be unacceptable. However, when we go a bit deeper and analyze his whole approach to the question, it appears in somewhat different light.
Vitruvius was a typical Hellenistic pedant collecting and classifying ancient knowledge; understanding it properly was not always the prime goal. There is no reason to doubt that he had, indeed, been acquainted with the book written by Ictinus about the design of the Parthenon, and in this sense, he was most likely repeating Ictinus’ words. He lived, however, half a millennium after the flourishing of Doric temple architecture in an entirely different world with different values and ideals, and therefore these words became to mean different things to him. Vitruvius’ well known suggestion to solve the so called “corner conflict” of the Doric order actually proves beyond any doubt that he didn’t understand at all what the corrections were about. His corner solution with the half metope in the corner would turn the temple into a mechanical collection of an amount of similar columns; it would deprive of the temple its most important quality, which is unity in plurality; i.e. a unity although it was composed of many equal members (Doric columns). However, this ideal was the very reason for the invention of the corrections in the first place, and therefore the “solution” of Vitruvius would destroy the very essence of the Doric temple entirely.