Which of the following is not used on a contact lens prescription?

• A. Pupillary distance
• B. Frame size
• C. Base curve
• D. Diameter

Answer: (A)

Pupillary distance isn’t used on a contact lens prescription because contact lenses sit directly on the cornea and move with the eye, so there's no eyewear frame to align to. The measurements that matter for contacts are those that describe how the lens fits the eye: the base curve, which matches the corneal curvature for a comfortable, stable fit, and the diameter, which ensures the lens covers the necessary area without causing lid interaction or movement issues. Frame size is a term tied to glasses rather than contacts, since the prescription for contact lenses focuses on how the lens sits on the eye rather than how a frame sits in front of it.