State-of-the-art in smart contact lenses for human-machine interaction

Contact lenses have traditionally been used for vision correction applications. Recent advances in microelectronics and nanofabrication on flexible substrates have now enabled sensors, circuits, and other essential components to be integrated on a small contact lens platform. This has opened up the possibility of using contact lenses for a range of human–machine interaction (HMI) applications, including vision assistance, eye tracking, displays, and healthcare. In this article, we systematically review the range of smart contact lens materials, device architectures, and components that facilitate this interaction for different applications. In fact, evidence from our systematic review demonstrates that these lenses can be used to display information, detect eye movements, restore vision, and detect certain biomarkers in tear fluid. Consequently, whereas previous state-of the-art reviews in contact lenses focused exclusively on biosensing, our systematic review covers a wider range of smart contact lens applications in HMI. Moreover, we present a new method of classifying the literature on smart contact lenses according to their six constituent building blocks, which are the sensing, energy management, driver electronics, communications, substrate, and the input/output interfacing modules. Based on recent developments in each of these categories, we speculate the challenges and opportunities of smart contact lenses for HMI. Moreover, based on our analysis of the state-of-the-art, we develop guidelines for the future design of a self-powered smart contact lens concept with integrated energy harvesters, sensors, and communications modules. Therefore, our review is a critical evaluation of current data and is presented with the aim of guiding researchers to new research directions in smart contact lenses.