Double vision is caused by light entering the eyes at the wrong angle, which sends two different images to the brain. Eyeglasses with prism lenses eliminate double vision.
How do prism eyeglasses work?
A prism is a shape with flat, transparent surfaces that bends light. Some people suffer from double vision caused by their eyes not focusing on the same location. Adding a prism shape to eyeglass lenses bends light travelling into the eye in such a way that it aligns what each eye is seeing, eliminating the double image interpreted by the brain.
If you need prism correction, you will have a separate set of numbers on your prescription that indicate the vertical and/or horizontal angle needed to correct double vision.