Aspheric curves can be placed on which surfaces now?

• A. Front surface only
• B. Back surface only
• C. One surface
• D. One or both surfaces

Answer: (C)

Aspheric curves are used to reduce aberrations and improve image quality, and in modern spectacle lenses the practical approach is to place the aspheric profile on a single surface. This gives most of the desired optical improvement while keeping manufacturing simpler and less costly. The front surface is typically chosen because it directly shapes the incoming light and is easier to polish and measure, while keeping the back surface spherical helps preserve lens strength and thickness. While some designs do use back-surface or dual-surface aspherics for specific goals, the common, straightforward implementation is one surface carrying the aspheric curve.