Im not so sure. At first I thought it was just a metaphor, but if you watch episode 13 when Itachi and Kakashi are having their little chat, at around the 9:55 mark Kakashi asks him "how bad has your eyesight become" and Itachi says "kakashi, you couldnt have...".

If Itachi were thinking that Kakashi "couldn't have" achieved the Mangyekou, then this implies that Kakashi was correct in describing the consequences of using the technique. But this is in the anime, so Im not sure its completely legit. Just my 2 cents