Which of the following is NOT reduced by choosing the correct base curve?

• A. Radial Astigmatism
• B. Curvature of Field
• C. Longitudinal
• D. Distortion

Answer: (C)

Choosing the base curve mainly changes how the lens back surface sits on the cornea and how optical power is distributed across the pupil, especially away from the center. When the base curve matches corneal curvature well, off-axis rays are bent in a way that reduces angular errors across the retina, which lowers radial (or oblique) astigmatism and helps keep the image plane closer to flat. That better match also decreases curvature of field, because the eye’s retina sits on a more optimally curved imaging surface, so the periphery doesn’t come to focus too far in front of or behind the center. Distortion improves as magnification becomes more uniform across the lens optic zone with a compatible back surface.

Longitudinal chromatic aberration, on the other hand, is dictated by the material’s dispersion—the way refractive index changes with wavelength. That effect shifts focal length differently for red and blue light, and this shift isn’t altered by changing the lens’s base curve shape.