The term "minus cylinder" design in lenses refers to what aspect of manufacturing?

The term "minus cylinder" design in lenses specifically relates to the way the lens is shaped to correct for astigmatism. In a minus cylindrical lens, the curvature that changes the light refraction is actually created on the back surface of the lens. This is crucial because the back surface grinding shapes how lightwaves come into focus, allowing for the proper correction of vision.

When lenses are manufactured for astigmatic correction, the cylindrical component is typically ground on the back surface. This ground surface is where the specific curvature needed to correct the vision is formed, influencing how light bends as it passes through the lens. This design helps ensure that the lens provides accurate visual correction tailored to the individual's optical needs.

The other options relate to aspects of lens manufacturing but do not specifically pertain to the "minus cylinder" design as it works through the back surface grinding to achieve the required optical effects.