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A recent paper by Eppig et al. (2008) evaluates the optical properties of diffractive multifocal intraocular lenses (IOLs). The theoretical background to the measurement of the Modulation Transfer Function (MTF) using a point source is discussed, and experimental MTF results are given. MTF measurement using a point source can work acceptably for monofocal lenses, but unfortunately it has drawbacks for the measurement of multifocal IOLs because the image of a point source is a bright spot surrounded by an extremely faint halo. In practice, it is difficult to accurately capture the light in the halo, and the use of a point source can lead to errors. Difficulties that are probably due to this cause are visible in Figures 3 and 4, where the MTF plots for a 3 mm pupil have characteristics that are more similar to monofocal lenses than to multifocal lenses. The MTF values in these plots are much higher than would be expected from the designs of the lenses for a 3 mm pupil. A more robust method for measuring the MTF of multifocal IOLs is to use the line spread function (LSF) (Simpson, 1992). This has a distinct benefit for accurate measurement because the LSF represents an optical integral across the PSF. Rather than recording the extremely faint optical signal at each point in the halo of the PSF, the total energy across the halo is combined into a single LSF point, resulting in a greatly increased signal-to-noise ratio. The MTF is only given in one direction, but measurements can be made in different orientations by rotating the system or the lens. Despite the benefits provided by the LSF measurement method, the accuracy of the measurement is also affected by various other parameters such as the choice of the dark background level, stray light, detector noise, and detector width. A practical system has to deal with the effects of all these variables, and it has been found that excellent results can be achieved for IOL measurements using a cooled scientific-grade 12-bit camera with approximately 1024 · 1024 detector pixels for the typical range of IOL test conditions. The most important parameter for multifocal IOL measurements is the choice of background level, because a small change can significantly affect the contribution of the halo to the MTF. One practical method for setting this is to average pixels at the edges of the detector array where the LSF image is very dark outside the primary halo. This method provides automatic compensation for any light that might reach the detector due to scattering from optical surfaces in the system, and it is a method originally used for monofocal lens measurements in the Ealing EROS MTF Measurement system a few years ago. Attention must also be given to whether the data should be windowed , so that very faint regions of the LSF that may be noisy are not included in the calculation. With a cooled detector, and correct choice of background level, the entire LSF can usually be used to calculate the MTF for a multifocal IOL, though this would not necessarily be appropriate for a monofocal IOL where only the central focused region of the LSF would be used. The usual corrections for the finite source and finite detector pixel widths must also be made.