Which of the following is a reason why a lens power produced via an empirical fit vs a diagnostic fit would not be the same?

• A. lens flexure
• B. inaccurate refraction
• C. inaccurate Ks
• D. inaccurate BCR

Answer: (B)

The key idea is how GP lens power is determined in different fitting approaches. An empirical power is estimated from corneal measurements and fitting relationships, without on-eye refraction testing. A diagnostic fit, however, relies on refraction with a trial lens worn on the eye to pinpoint the exact power that best corrects vision. If that refraction is inaccurate, the final power prescribed from the diagnostic process will differ from the empirically estimated power. So the mismatch comes from errors in the refraction measurement during the diagnostic step, not from the theoretical basis used to choose the empirical power. While factors like lens flexure or keratometry values can influence fit, they are not as direct a cause of this specific discrepancy as an inaccurate refraction.