What is the process of removing plastic from the bottom of a contact to produce a flat edge to control rotation called?

The process of removing plastic from the bottom of a contact lens to create a flat edge, thereby controlling the lens's rotation on the eye, is known as truncation. This technique is especially useful for stabilizing lenses that are specifically designed for astigmatism or other conditions that require precise lens positioning. Truncation leads to a distinct edge profile, which helps keep the lens in place by providing a fit that can counteract any natural tendencies of the lens to rotate due to eyelid movements or other factors.

In contrast, the other options relate to different concepts in contact lens design. Blending refers to the smoothing of lens surfaces or transitions within lens designs rather than the creation of flat edges. Ballast describes a method of adding weight to the bottom portion of the lens to stabilize it, typically used in designs without truncation. Toric relates to lenses designed to correct astigmatism, often incorporating various stabilizing features, including truncation, but it does not specifically refer to the process of creating flat edges.