Design of double-zone aspheric diffractive intraocular lens with extended depth of focus
Design methods of intraocular lens with extended depth of focus for pseudophakic presbyopia.
The accommodation amplitude of the human eye usually decreases to less than 1 D after 50 years old, resulting in the inability of eyes to focus near object accurately. This dysfunction is called presbyopia, which makes it impossible for human eyes to obtain clear vision over a continuous object range. Achieving a continuous clear vision is of great importance for pseudophakic presbyopia to improve their living quality. The implantation of intraocular lens (IOL) to replace the crystalline lens is a mature method in clinical practice.
Many attempts of special designed IOLs have been made in this research area to obtain clear vision over a range of object distance. The bifocal IOLs are attempted to provide clear vision in both far and near distance, leaving the intermediate vision uncorrected. The multifocal IOLs are attempted to correct far, near, and intermediate vision simultaneously, yet it fails to provide a continuous clear vision. The accommodative IOLs aims to overcome the defects of bifocal and multifocal IOLs by the axial movements of the special designed haptics or the use of special materials. Unfortunately, it can only provide very limited accommodation.
To regain a continuous range of clear vision for pseudophakic presbyopia, the research group of Yongji Liu from Nankai University proposed a double-zone aspheric diffractive IOL with an extended depth of focus (DOF) of 1.5 D. The modulation transfer function at 50 cycle/mm remained above 0.29 within ± 5° field of view for object distance ranging from 6 m to 0.66 m in photopic vision. In addition, the imaging qualities are robust for pupil changes, different corneal asphericities and polychromatic light, which makes it valuable for real clinical application. The designed IOL was manufactured and the optical performance was evaluated in a continuous range of object distance. The manufactured IOL exhibits the ability to extend DOF. This work has been published in Chinese Optics Letters, Volume 16, No. 9, 2018 (Yayan Bian et al., Design of double-zone aspheric diffractive intraocular lens with extended depth of focus).
"The goal for presbyopia correction is to obtain a continuous clear vision as younger eyes do." says the corresponding author Yongji Liu, "The proposed IOL gives a new possible way to achieve this ultimate goal."
Further work will focus on achieving an IOL with larger range of DOF, good image quality over this distance and easy to be manufactured, because such characters are of great value for clinical practice.