Sense manipulation

Blindness is the ability to blur, reduce or to blind the optimal vision of people, generally by magic.

Magic

 * Catherine Madison made that Cordelia Chase become blind during the cheerleading squad session.
 * Willow Rosenberg cast a spell to have her will done in an attempt to get over the pain of Oz's departure, but the exact wording she used caused anything she said to come true, though only when she did so inadvertently. With this ability, she rendered Giles completely blind.
 * Tara Maclay cast a defensive spell which fended off The Monster by conjuring a magical "fog of protection" who disorient his vision.

Demon

 * Destroy or to burst the eyes of a demon is sometimes the only way to kill it. It is proved when Buffy faces Der Kindestod, Ovu Mabani or Gnarl.