Blindness

This is a percentile value that determines the actor's disability to see the Player while hiding (sneaking without moving).

0 is the default value, meaning that only the player's skill will affect whether sneaking is successful or not.

100 means that the player can hide right in front of the affected NPC.

This does not make the NPC blind (or he'll make up for his blindness with an excellent hearing if you like) As long as you're not sneaking or moving while you sneak, the NPC will see you. But once you stand still he'll forget that you were there.