What is a practical reason to match frame PD to patient PD when prescribing aspheric lenses?

• A. Ensures proper centration of the lens optics
• B. Reduces cost
• C. Improves frame aesthetics
• D. Eliminates need for monocular PDs

Answer: (D)

Aspheric lenses prize accurate centering because their non-spherical surface design distributes power differently across the lens. If the lens centers are decentered relative to the pupil, you get unintended prismatic effects and peripheral image distortion, which can negate the benefits of the aspheric design.

Matching the frame PD to the patient’s PD helps the optical centers of the lenses align with each pupil when the person looks straight ahead. This alignment reduces decentration errors and, in practice, minimizes the need to rely on separate monocular PD measurements to fine‑tune centering. It’s a practical way to ensure the designed aspheric power profile is delivered consistently, especially during mounting and initial fitting.