It's too early to say that what happened to Sasuke is actually the permanent loss of sight caused by Mangekyou. Since it's so hard on the eyes, he could have simply used them too much in one day, and moreover, too many powerful techniques in one day, resulting in so severe exhaustion he couldn't keep it up anymore and it affected his normal vision as well, for the time being. It would seem more logical than hitting the hard limit so soon. While it's true Itachi managed to do with much less due to keeping his head cool and being overall better ninja, he should have still used Mangekyou every now and then over the years.