Why are atorics used instead of standard aspheric lenses?

• A. Because aspherics are heavier and more expensive.
• B. Because aspherics require special frame materials.
• C. Because aspheric lenses still can't completely correct for cylinder power.
• D. Because atorics are more aesthetically pleasing.

Answer: (C)

The main idea is that correcting astigmatism needs different focusing power in two perpendicular directions, not just a single, uniform power. Standard aspheric lenses are great for reducing spherical aberration and making edges thinner, but they keep the same refractive power in all meridians, so they can’t fully correct cylinder (astigmatism). Atoric lenses, on the other hand, are designed with two different curvatures along orthogonal meridians, allowing independent adjustment of spherical and cylindrical powers. This lets the lens precisely correct astigmatism and provide sharper, more accurate vision for eyes with cylindrical error.