An excellent vision activity is to get someone to wear a pair of glasses with strong prisms in them. The prisms displace everything that the person sees to one side, which means that many of their actions are way off-target. For example, if they try to throw a ball to someone, they will often miss by a large margin. They also make errors when catching the ball. However, quite soon they adapt to the prisms and stop making errors. But now when the prisms are removed, they start misjudging things again! People (audience and participants) usually find this very funny.
However, glass or plastic prisms are bulky and heavy, give a small field of view, and suffer badly from chromatic aberration. For the Where's your head at? show that I developed, I made some much lighter prism glasses using stick-on fresnel prisms obtained from a local optician. They were about £15 each (2004), but, in return for an acknowledgment, Eye2Eye opticians in Glasgow provided them free.
The prisms I used had a strength of 25 prism dioptres, which gives a displacement of the field of view of just over 14 degrees. This proved very satisfactory. I mounted the prisms on a pair of safety spectacles. The prisms are easily cut to shape and very easy to fix to the glasses - they can also be removed and refitted if you don't get them positioned right first time.
The best effect is had if the wearer of the spectacles can't see their own arms and hands. To achieve this we blanked off the lower half of the spectacles with self-adhesive metal foil. This worked very nicely and gave the specs a great sci-fi look. Thanks to Gillian Lang for suggesting this modification.