Effect of the eye pupil diameter and the phase shift in the diffraction structure on bifocal properties of diffractive-refractive intraocular lenses

Abstract

As the eye pupil decreases, the bifocal properties of the intraocular lens (IOL), which is an artificial eye lens, can be violated. To avoid it, a phase shift is introduced into the structure of the IOL diffractive component. Results of an analytical study of the light intensity distribution on the axis of a bifocal IOL for different values of the eye pupil and phase shift in the diffractive component with a focal power of 4.2 D (diopters) are presented. Because of broadening and asymmetry of the intensity distribution function arising at small pupil diameters, the foci of orders 0 (far vision) and +1 (near vision) of the bifocal IOL are demonstrated to affect each other: they come closer or farther, become separated or overlapped. The total intensity distribution may be continuous or have a dip whose magnitude depends on the pupil diameter and phase shift. It is noted that the optimal phase shift at which separation of the foci (bifocality) begins from the pupil diameter of ∼0.9 mm and is not violated with further pupil expansion is 180° (π radian).