Minimum resolution specification of intraocular lens implantsusing the modulation transfer function.

We investigated the use of modulation transfer function (MTF) measurements to provide a standard test of minimum optical quality of intraocular lenses. We used a water cell with plane entrance and exit windows. This geometry is independent of lens material but relatively simple to implement. We investigated the choice of aperture stop, and 3.0 mm was deemed a suitable choice of stop diameter. Minimum acceptable performance must be specified if this technique is to be adopted as a standard method. The MTF of an ideal lens defocused 1/2 wave is suggested as a possible reference. Strehl ratios, although desirable because they can be measured directly without determining MTF's, were found to be unsuitable. These ratios tend to emphasize the high-frequency response, and the observed ratios are typically too low to provide assurance that the low-frequency response is as high as desired. MTF integrals or contrast at spatial frequencies of particular interest were found to be useful benchmarks of acceptable optical quality.