To investigate the effect of illumination on visual acuity and visual field in eyes with multifocal intraocular lens (IOL), the near and far visual acuity of the eyes with multifocal implants were compared to those of the eyes with monofocal implants in the diminished illumination, and the visual fields of two groups were also compared by the different target size and intensity. The near and far visual acuity of the eyes with multifocal implants were significantly decreased as compared to those of the eyes with monofocal implants under diminished illumination, and the visual field of the multifocal implanted eyes also significantly decreased as compared to that of the monofocal implanted eyes by the reduction of spot size and intensity. From the above results, it is assumed that the bifocal separation of incident light to two simultaneous focal points in the multifocal implants causes more decreased visual acuity and narrower visual field in the diminished illumination as compared to that of the eyes with monofocal implants.