Prism eyeglasses are prescription glasses that have a prism in the lens. The prism can be ground into the lens, or it can be a sticker stuck to the lens. The primary use of prisms in eyeglasses is for positional correction, convergence correction and double vision correction.
Diplopia, or double vision, occurs when a person sees an image for each eye, rather than a merged image. Prism eyeglasses assist in the positioning of the eyes so that each image will merge properly to give the viewer a single focused image.
Wearing glasses can cause diplopia in some people. However, adding a prism to the lenses can correct this.