Lenses with tunable focal length play important roles in nature by helping species avoid predators and capture prey. Many practical devices mimic lens concept for imaging, sensing, and detection. This review covers fundamental optics of lenses and its extension to lenses made of liquid crystals (LCs). Three main types of LC lenses are described, namely, lenses with curved surfaces, flat gradient-index lenses and composite lenses. The review discusses advantages of LC lenses over their isotropic counterparts, challenges in their fabrication and control, as well as a variety of potential applications. We also discuss the current challenges associated with nematic LC lenses and their solutions. LC lenses are already having significant impacts on optics and optometry, and these impacts will grow with discovering new LC materials and new lens designs.

具有可调节焦距的镜头通过帮助物种避免掠食者和捕获猎物而在自然界中发挥重要作用。许多实用设备都模仿镜头的成像，传感和检测概念。这篇综述涵盖了镜片的基本光学原理及其对液晶（LC）镜片的扩展。描述了三种主要类型的LC透镜，即具有曲面的透镜，平梯度折射率透镜和复合透镜。这篇综述讨论了液晶透镜相对于各向同性透镜的优势，其制造和控制方面的挑战以及各种潜在的应用。我们还将讨论与向列液晶透镜相关的当前挑战及其解决方案。LC透镜已经对光学和验光产生重大影响，随着发现新的LC材料和新透镜设计，这些影响将越来越大。