This is an adhesive prism that is stuck onto your glasses as a temporary method of fixing double vision. Prism glasses can be very effective for correcting alignment problems (diplopia). However, prism glasses are expensive and notoriously difficult to get made correctly. In some cases, I’ll prescribe a temporary “stick-on” prism. It is a clear sticker, similar to a fresnel lens, that is cut out to the size of your glasses and adhered to the surface of the lens. This is cheaper then getting new glasses and allows you to see if you will tolerate the prism correction before more expensive prism glasses are made. The stick-on prism is somewhat unsightly, however, and not as clear as “normal glass” so is not a long-term solution.