MINIMUM RESOLUTION SPECIFICATION OF INTRAOCULAR-LENS IMPLANTS USING THE MODULATION TRANSFER-FUNCTION

We investigated the use of modulation transfer function (MTF) measurem ents to provide a standard test of minimum optical quality of intraocu lar lenses. We used a water cell with plane entrance and exit windows. This geometry is independent of lens material but relatively simple t o implement. We investigated the choice of aperture stop, and 3.0 mm w as deemed a suitable choice of stop diameter. Minimum acceptable perfo rmance must be specified if this technique is to be adopted as a stand ard method. The MTF of an ideal lens defocused 1/2 wave is suggested a s 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 t hat 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.