Sasuke went blind fast because he was overusing his Sharingan.
Amaterasu burns anything, endlessly tearing away at its target until its completely destroyed. He gave Sasuke Amaterasu before he died, setting a trap for when Madara would try to contact him. Sasuke got Amaterasu from his brother Itachi. The Eternal Mangekyou Sharingan is activated when a Mangekyou Sharingan user transplants eyes with a fellow Mangekyou Sharingan user. Sasuke got the Eternal Mangekyou Sharingan when Itachi’s eyes were given in a transplant. How Did Sasuke Get Eternal Mangekyou Sharingan? He used them to awaken the Eternal Mangekyou Sharingan, since the eye combination with his own would create the upgraded Sharingan. It’s exclusive to the Uchiha clan and one of the three main Dojutsu eye-abilities alongside the Byakugan and the Rinnegan. The Mangekyou Sharingan is activated under moments of intense emotional distress. The eyes are a next level form of the Sharingan only wielded by a few Uchiha. He did not kill Itachi, but the experience was still intense enough to give Sasuke the Mangekyou Sharingan. Sasuke got the Mangekyou Sharingan after witnessing his brother’s death. Sasuke gets the Mangekyou Sharingan in episode #141, titled “Truth.” It takes place during the “Fated Battle Between Brothers” arc and features manga chapters #400-402.
