What are atorics?

• A. Aspheric lenses that have a different rate of flattening in each meridian that's independent of the other meridian's flattening
• B. Spheric lenses with cylindrical power only
• C. Lenses with identical flattening in all meridians
• D. Spherical lenses with no astigmatism

Answer: (B)

Atorics are best described as a spherical base lens with cylindrical power only. The essential idea is that the underlying surface is spherical (same curvature in all meridians), and astigmatic correction is achieved solely by adding cylindrical power in one meridian. There isn’t a meridian-by-meridian change in the surface’s flattening beyond that cylinder.

This distinguishes them from lenses that rely on more complex surface shapes (aspheric or true toric surfaces) where the curvature or rate of flattening varies between meridians in a way that isn’t captured by a simple cylinder. It also explains why a lens with no astigmatism or with identical flattening in all meridians wouldn’t be an atoric.