Prism glasses are prescription eyeglasses with special lenses for correcting double vision (also known as diplopia) . They are used to correct eye alignment or movement issues, not refractive errors. A prism added to eyeglasses bends light before it travels through the eye, and the light is redirected to the proper place on the retina of each eye. This helps the eyes to perceive images in a way that single vision can be achieved, improving binocular vision, and reducing double vision, headaches, reading difficulties, and more. Prism glasses can be effectively used to treat vision conditions, such as double vision and other binocular vision difficulties. Prism lenses are special lenses that are prescribed by eye doctors and infused into regular lens prescriptions. They do not contain any focusing power, and therefore cannot correct any refractive errors. Prism glasses may only be a temporary solution for double vision, and they are not helpful for all types of double vision. A temporary Fresnel prism (a thin press-on vinyl sticker) can be fitted over the front or back of eyeglasses to test drive a prism and see how it works. If prism correction is needed for a longer period, it can be ground into (made part of) the lens of eyeglasses. Eyeglasses with a prism look like any other glasses without a prism, although the lens on one side may be thicker and more noticeable.