THE APPEARANCE OF IMAGES THROUGH A MULTIFOCAL IOL

Abstract

Multifocal intra-ocular lenses (IOL) of various designs are now used to replace the eye’s crystalline lens in cataract surgery. To replace accommodation the multifocal IOL simultaneously images near and far points on the retina. Thus, at every viewing distance an out-of-focus image is superimposed over the clear in-focus image. The optical transfer functions (OTF) of eyes with such multifocal lenses have been measured and computed (Holladay et al, 1990, Navarro et al, 1993). The appearance of images to patients with such IOLs has not been determined yet, though it is generally believed that the OTF provides all the information needed for such determination. While the OTF should be sufficient to determine the retinal image accurately, the OTF can not predict perception directly, because of the nonlinear nature of the visual system (threshold response) (Peli, 1990). However, when comparing the image appearance between two eyes of the same person, one equipped with a monofocal IOL and one with a multifocal IOL, the between eyes’ OTF ratio will properly describe the difference between the retinal image in the multifocal IOL lens and the retinal image in the monofocal IOL. Thus the image appearance based on the OTF can be tested directly in such patients and be used to verify the OTF.