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. lens decentration
• C. inaccurate BCR
• D. inaccurate Ks

Answer: (B)

Power from a gas permeable lens is most affected by where the optic center sits on the eye. An empirical fit predicts the lens power assuming the lens remains centered on the visual axis, so the intended correction is delivered. A diagnostic fit uses actual trial lenses on the eye, and if the lens decentrates, the pupil views the corrective surface off-axis. That off-center position changes how light is bent through the lens and alters the effective power at the eye, so the on-eye power can differ from the empirically predicted value. While lens flexure or errors in base curve radius or corneal K can influence fit and refractive outcome, decentration specifically explains why the power from an empirical estimate may not match what’s measured with a diagnostic, on-eye lens.