During the creation of an aspheric lens, what happens to the back surface?

• A. It moves backward, increasing center thickness
• B. It moves forward, decreasing center thickness
• C. It remains stationary
• D. It becomes steeper

Answer: (B)

Aspheric shaping is achieved by altering the back surface to follow a non-spherical contour while the front surface largely sets the power. Advancing the back surface toward the eye creates that gradual departure from a sphere. This forward movement reduces the distance between front and back at the center, thinning the center of the lens. In other words, the center becomes thinner to allow the back surface to curve more gradually toward the edges, producing the desired aspheric profile without changing the overall power. Moving the back surface backward would increase center thickness and wouldn’t produce the same non-spherical form, and simply steepening or keeping the back surface stationary wouldn’t create the required aspheric transition.