Restraints On Spellcasting
The more powerful a magical spell is, the more gesturing and chanting must be done to achieve the results. If the magic wielder is prevented from completing his gestures or chants, it may stop the spell from being completed. If a magic wielder is somehow blinded, certain spells may not be used as the target cannot be seen.
Bound, Gag, and Blind Effects: If a magic wielding character is bound (hands tied securely behind his back), he may not use any universal spells. If a magic wielding character is bound and gagged (prevented from speaking clearly), he cannot use any dimensional spells. A successful Hold when Grappling effectively binds a character.
Unless a magical item is used to bind and gag a character and is specifically described as negating all of the victim's magical spells, a character can always use any personal spells he may have though bound and gagged.
If a magic wielding character is blinded (deprived of sight by a blindfold, intense light or darkness, sand thrown in the eyes, etc.), he cannot use any spell which requires sight such as targeted attacks, Bands, Sensing - Clairvoyance, Postcognition, and so on.