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.

扩展焦深的双区域非球面衍射型人工晶体的设计

人工晶体整体图和显示微结构图

人眼的调节能力在50岁之后通常不足1 D，从而导致人眼无法准确地聚焦近处物体。这种视功能障碍被称为老视眼，它使得人眼不能在连续范围内清晰视物。实现连续范围内的清晰视物对提高植入人工晶体的老视患者的生活质量极为重要。现今植入人工晶体替代人眼的自然晶状体是临床上治疗白内障的一种成熟方法。

为了在一段物距内获得清晰的视力，不同设计的人工晶体相继被提出。双焦点人工晶体的出现使得患者能看清远距离和近距离处的物体，但无法看清中间距离的物体。多焦点人工晶体的设计克服了单焦点和双焦点人工晶体的缺点，使得患者能看清远距离、近距离以及中间距离的物体。但它并没有实现连续物距范围内的清晰视物。具有可调节性的人工晶体旨在克服双焦点、多焦点人工晶体的缺点，通过特殊设计的人工晶体攀或特殊材料的使用，使得人工晶体的轴向移动成为可能，但其提供的调节范围十分有限，不能满足实际需要。

南开大学刘永基课题组提出了一种具有1.5 D焦深的双区域非球面衍射型人工晶状体的设计，可以使得植入人工晶体的老视人眼重新获得连续清晰的视力。理论分析结果表明此款人工晶体在明视觉（3 mm瞳孔）环境下，当物距在0.66～6 m范围内变化时，空间频率为50 cycle/mm处的调制传递函数（MTF）值在±5°视场范围内均高于0.29。在实际临床应用中，大焦深人工晶体的成像性能应尽可能不受人眼瞳孔大小变化、角膜非球面度的影响，同时在白光下成像性能良好。而此款人工晶体均满足以上要求，具有临床应用的价值。该研究团队还对所设计的人工晶体进行了加工检测，测试了此款人工晶体在连续焦深范围内的成像质量。实验结果表明此款人工晶体具有良好的扩展焦深性能。相关研究结果发表于Chinese Optics Letters 2018年第16卷第9期（Yayan Bian et al., Design of double-zone aspheric diffractive intraocular lens with extended depth of focus)。

该研究团队的刘永基副研究员指出："实现类似于年轻人的连续成像范围，是老视矫正追求的最终目标，而此款大焦深人工晶体的设计则为实现上述目标提供了一个可能的途径。"

今后的研究工作将会进一步提高人工晶体的焦深范围，且在焦深范围内能够提供良好的成像性能。同时，为了实现临床应用，所设计的人工晶体应具备易于加工的特点。