Over time, use of the Mangekyō Sharingan's techniques deteriorates the user's eyesight to the point of blindness. Only by taking and transplanting the eyes of another Uchiha clan member can the vision be restored, a process that results in the creation of an Eternal Mangekyō Sharingan (永遠の万華鏡写輪眼, Eien no Mangekyō Sharingan). The tighter the blood ties are between the "donor" and the receiver, the better it is for compatibility, siblings for example. The time from fusing the donor's Mangekyō with the receiver's Mangekyō to the point of full recovery is at least several days in the case of Sasuke. Not only does this process permanently restore one's eyesight, but it also gives the person even greater power. The Eternal Mangekyō Sharingan also changes form from the original, with what appears to be a fusion of the current owner's Mangekyō with the previous owner's.