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J. Schwiegerling; Connecting MTF Measurements of Multifocal IOLs to Clinical Measures of Visual Acuity. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5619.
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To assess the Modulation Transfer Function (MTF) of multifocal IOLs and relate these contrast values to clinical measures of visual acuity.
We recently introduced the polychromatic Defocus Transfer Function (DTF) as a means for rapidly calculating the through-focus MTF of rotationally symmetric optical elements. We apply these techniques to multifocal IOLs to determine the amount of contrast these lenses provide as a function of object vergence. In general, multifocal IOLs exhibit strong peaks in contrast relating to distance vision and again to their near add power. To these functions, we overlay clinical measures of visual acuity with the same lens. In this manner, we can connect the amount of contrast the lens provides with their clincal performance.
The figure illustrates the photopically weighted polychromatic DTF of a diffractive multifocal IOL with a +4 D add. Vertical cross-sections through this plot correspond to the through-focus MTF of the lens. The horizontal band is the contrast associated with the distance portion of the lens, while the downward sloping band in related to the +4 D add. Plotted over the DTF is the clinical measure of visual acuity for this lens converted to its fundamental spatial frequency. Comparing the contrast of the DTF with the visual acuity points shows that 16.6% contrast is needed for 20/20 vision, 5% contrast is needed for 20/32 vision and 1% contrast is needed for 20/40 vision.
The DTF is a useful means for evaluating the performance of multifocal IOLs. By connecting clinical measures of visual acuity with the DTF, threshold requirements for visual performance can be defined. Using these thresholds, future IOL designs can be evaluated and likely clinical performance predicted.
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