True or False: Theoretically, the lens power produced via an empirical fit vs a diagnostic fit should be the same.

• A. True
• B. False
• C. Cannot be determined
• D. Depends on the device used

Answer: (A)

The main idea is that the goal of a gas-permeable lens fit is to deliver the same refractive correction for the eye, regardless of whether you estimated the lens power empirically or confirmed it with a diagnostic trial. If you’re aiming to neutralize the patient’s ametropia, the back-vertex power needed to achieve that correction should be the same in theory. The empirical method uses keratometry, refraction, and nomograms to predict the appropriate back surface power and fit, while the diagnostic approach tests actual trial lenses on the eye and adjusts until the desired visual outcome is reached. When all factors are ideal—readings are accurate, the tear layer is accounted for, the lens sits correctly, and you convert refraction to the proper back-vertex power—the resulting lens power should converge to the same value.

In real life, small differences can creep in due to practical factors like tear-film variability under the lens, slight changes in lens位置, measurements, or manufacturing tolerances, but these are deviations from the ideal.