Basic Optics Underlying Current Intraocular Lenses.

As surgeries using multifocal intraocular lenses (IOLs) to correct both cataracts and presbyopia have become common, it has become essential for clinicians to understand their basic optical characteristics to select the optimal lens for their patients. However, there are relatively few review articles on optics that are directly useful to clinicians who perform surgery on patients. In this paper, we systematically review fundamental concepts, from the basic properties of light, geometric optics, and Gaussian approximation to lens performance metrics like the point spread function and modulation transfer function (MTF), and the clinical implications of spherical and chromatic aberrations. Based on these principles, the mechanisms of major multifocal technologies are explained. We also explore the refractive extended depth of focus lenses, which expand the range of focus by precisely controlling higher-order spherical aberrations. In contrast, diffractive lenses use diffractive kinoforms to split light into multiple foci, and they may also leverage higher diffraction orders to correct chromatic aberration. However, this multifocality involves an optical compromise, often resulting in a reduced overall MTF compared to monofocal IOLs and photic phenomena such as glare and halo. In conclusion, while multifocal IOLs are groundbreaking technology that significantly enhances quality of life by reducing spectacle dependence, this comes at the cost of sacrificing optimal image quality. Therefore, a thorough understanding of these optical principles by ophthalmologists is crucial for selecting the optimal lens according to each patient's ocular condition and for managing postoperative outcomes.