Comparison of modulation transfer function and through focus response with monofocal and bifocal IOLs.

We analyzed modulation transfer function (MTF) and through focus response (TFR) of the TRUE VISTA bifocal IOL and monofocal IOLs and compared the experimental and clinical data. MTF and TFR were measured at different pupil sizes (2, 3, 4 mm), base powers (14, 21, 27 D), add powers (2, 3, 4 D), and distance zone diameters (1.25, 1.5, 1.75 mm). Standards were established to correlate MTF and contrast sensitivity, as well as TFR and the defocus curve measured clinically. MTF of TRUE VISTA decreased with increasing pupil size and base power. A near add of 4 D showed the best MTF at distant and near focus. MTF of TRUE VISTA at near focus was lower than at distant focus and MTF at distant focus was lower than MTF of monofocal IOLs. TFR and the defocus curve correlated closely. MTF and contrast sensitivity of TRUE VISTA at far and near focus also correlated closely. MTF and contrast sensitivity of monofocal IOLs and TRUE VISTA at distant focus did not correlate. MTF was considerably better with monofocal IOLs while contrast sensitivity was slightly better only at low contrast. However, MTF of monofocal IOLs was much higher than MTF of a normal eye while MTF of TRUE VISTA at distant focus was only slightly lower than the MTF of a normal eye. Using MTF of a normal eye as a threshold, our results demonstrated a close correlation between experimental and clinical findings. MTF and TFR may therefore reliably predict the performance of bifocal IOLs.