These lenses come with computer-generated lens designs. The best brands are even customized to suit the shape of your optical frame shape, the distance from your eyes, your lens power, the tilt of your lenses, and your individual visual needs. These lenses differ from conventional lenses which grind the surface of the lens for large areas resulting in distortion in the periphery, particularly in progressive lenses, and high-prescription lenses. Digitally surfaced or freeform lenses have the curves mathematically computed at multiple points over the lens and are manipulated to contrast the front and back of the lens to minimize distortions caused by the physics of a conventional lens. They also push any remaining distortion away from where the patient would typically look through the lens.