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

Answer: (B)

The main idea is that the empirical power is derived from the patient’s refraction, so errors in that refraction directly lead to the predicted power being off. When you fit empirically, you rely on the refractive measurement to estimate what lens power will correct vision. If that refraction is inaccurate, the calculated power won’t match what a diagnostic trial with real lenses on the eye shows as optimal. The diagnostic fit relies on actual on-eye performance and subjective feedback, so it can reveal the true needed power regardless of initial refraction accuracy. Other factors like back vertex distance or keratometry can influence calculations, but the most direct reason they wouldn’t match is an inaccurate refraction.