Reversible Prism Glasses
These right angle prism glasses have two settings to help people confined to one position for a long period of time. In one setting, a person can lie down on a bed, and easily view the television without lifting their head. Change the prism setting, and a standing person who is unable to lift their head can see straight in front of them.
Changing the setting requires removing a small hand screw and resetting.
More information: http://www.lssproducts.com/product/reversible-prism-glasses/household-items