Study of the AMO ARRAY silicone lens and a monofocal IOL

Abstract

Steinert et al (Ophthalmology 1999;106:1243–55) found the results are better for bilateral multifocal intraocular lens (IOL) when compared with one eye multifocal–other eye unifocal IOLs. However, the article does not discuss the explanation for this disparity in detail. Various studies have shown that the patients with multifocal IOLs achieve a satisfactory level of unaided distance and near visual acuity, yet patients complain of general blur and overall reduction in clarity of vision and dissatisfaction. Early in our series of bilateral multifocal vs. one eye multifocal–one eye monofocal IOLs, we are finding such complaints are minimal and that satisfaction is significantly improved in the bilateral multifocal IOL group. We suggest a psychophysical explanation for these results. As shown by Steinert et al, only 50% of available light is used for distance, 37% for near, and 13% for intermediate focus, reducing the overall luminace and contrast of retinal images. Binocular perception of the visual space requires cortical processing of the retinal images from the foveae and peripheral retinal points of two eyes and fusion of these images. Although mild retinal disparity is essential for fusion and stereopsis, the range of fusion is influenced by the spatial, temporal, and luminance characteristics of the retinal images and is very small in terms of the dissimilarity of monocular pattern as shown by Schor, Wood and Ogawa.1Schor C. Wood I. Ogawa J. Binocular sensory fusion is limited by spatial resolution.Vision Res. 1984; 24: 661-665Crossref PubMed Scopus (183) Google Scholar Another factor is cortical processing of different sized images in the periphery in a patient with one eye multifocal and one eye monofocal IOL. As shown by Marr and Poggio,2Marr D. Poggio T. Cooperative computation of stereo disparity.Science. 1976; 194: 283-287Crossref PubMed Scopus (1016) Google Scholar retinal images with different sizes are processed by different mechanisms. For patients with one eye multifocal and one eye monofocal IOL, there is disparity in contrast for the foveal images and disparity of contrast and size for the peripheral retinal images. This may cause difficulty in cortical processing and fusion and lead to an overall confused visual perception. Patients with bilateral multifocal IOLs need to adjust to changed levels of luminance, but changes in retinal images in the two eyes are similar. Therefore, acceptance and satisfaction is better. We agree with the result of better patient satisfaction in the bilateral multifocal IOL group.