I have just been told that I need a prism in one of my lenses. What does this mean?
Prism lenses are used to prevent double vision occurring as a result of a muscle imbalance, such as a squint.
They work by moving the image of the object. The image will move either vertically or horizontally depending on the direction of the prism and the power of the lens.
People who experience eye strain and headaches may in fact require prism lenses in order to resolve their symptoms.