Originally Posted by apacolypz
Well technically Zetsu was the one who brought it to his attention...and that was the reason why Madara gave his response...
Remember Obito couldn't use both RG eyes. Madara told him to use his SG with the RG to be able to control the bijuu and use the jutsus. Obito's stamina could take using both a full pair of RG eyes. Madara got his original eyes back. His own stamina is outrageous. As he said if he uses the RG's power it will make his own skills look more polished and refined. This is what a youthful Madara looks like fighting with full power and some. Madara didn't need a break...once he got one of his eye back he got focused on the battle at hand rather than going all out. Again he still has sage chakra activated and now he is using the statue which was said already possesses huge amounts of power.
As Kael mentioned Kishi made Madara too powerful and he hasn't even explained why he was able to use dojutsu when he was blind.
(totally hypothetical )
Maybe Madara could use his dojutsu because he already developed the special chakra in his brain. Since he awakened his eyes early on in his life, maybe his brain got use to the special chakra that was being absorbed via optic nerve. The nerves probably grew thicker over time due to the alignment with Madara's dark emotions. Like a pseudo effect his brain may think his eyes are still connected. The darker ones emotional state goes the more stronger his potential in using the SG becomes.
My opinion on why Madara could still use his dojutsu is because even though the eyes are the visible signs of it and actually hold and execute most of the powers, the spiritual energy is still being supplies by the Uchiha body, the spirit and genetics of which comes from the 1st Sage. Susanno is an Uchiha's spirit protecting them and fighting for them, which is why it hurt Sasuke to his cells, or something like that, he said. Kakashi could never use the Sharingan to the extent of an Uchiha because his body and spirit is not that of an Uchiha.
I believe that Sasuke, in his fight at the Kage summit, surrounded himself with his black flames without even looking directly at where the flames appeared all around him. His spiritual energy produces these black flames, just as it does susanoo. Madara, as a genius Uchiha who lived to an old age, does not surprise me by using any Uchiha dojutsu while blind. However, I might not agree so much with him using any genjutsu dojutsu byjust looking, eyeless, at someone without first using some handsigns or touching them.