A fresnel lens is a magnifying lens that is built into a flat piece of plastic. You may have seen fresnel magnifiers in a bookstore … they look like a clear, flexible sheet of plastic with tiny ridges along the surface. They are commonly used in overhead projectors and rear projection screen televisions. Fresnel lenses can be made very flat. Because of the many “ridge lines,” they are not as clear as a normal lens, so they have limited use in eye care. The one exception is that a type of fresnel lens is used in multifocal implants like the Restor lens. This is a premium implant used in cataract surgery that has a bifocal built in. The implant has concentric rings built into its surface, with half the rings focused at distance and the other half focused for near. This technology can get people out of reading glasses after cataract surgery, though the fresnel effect can create visual side effects like ring halos and some loss of clarity.