During the manufacture of a contact lens using a lathe, what should be avoided to prevent distortion?

In the context of contact lens manufacturing, particularly when using a lathe, avoiding unwanted prism is crucial to prevent distortion of the lens. Prism in optics refers to a variation in thickness across the lens surface, which can lead to improper light refraction. This distortion can cause visual discomfort or incorrect vision correction outcomes for the patient. Ensuring that any unintended prism is eliminated during fabrication helps maintain the intended optical properties and ensures proper lens performance.

The other factors, while important in their own right, do not relate directly to the distortion of the lens's optical properties in the same way. Surface scratches can affect the lens's clarity and surface integrity, but they do not inherently introduce prism distortion. An incorrect diameter may lead to fitting issues, and curvature deviation affects the surface shape, but neither directly addresses the optical distortion caused by prism. Hence, focusing on prism during the manufacturing process is key for maintaining the lens's efficacy and comfort for the wearer.