what is a prism used for
The simple definition of a prism is a solid object that has the same cross-section along the entire length of its shape. When you cut straight across an object, the cut portion is called a cross-section. Draw any shape using straight lines. Now use your imagination to see it extend upward and that is a prism. In eyeglasses, prisms are used primarily for double vision, positional correction, or convergence correction. Double vision (diplopia) is when a viewer sees two individual images using both eyes, instead of the one most people see, merged together by the brain.