Contact Lenses Get Smarter

Smart contact lenses have long been a fixture of science fiction, but they have not yet fully arrived in the real world. These futuristic devices are often depicted in movies and literature as offering capabilities such as enhanced vision, real-time information display, and health monitoring, all through a seemingly ordinary lens. Present technological limitations have greatly limited what real smart contact lenses are capable of, however.

One area in which these devices are rapidly advancing, which has many practical applications, is eye tracking. In augmented and virtual reality, for example, eye tracking in smart contact lenses could enhance user experience by enabling more natural and intuitive interactions. Instead of relying on handheld controllers or external sensors, users could navigate menus, select objects, and interact with virtual environments simply by moving their eyes. This technology also has the potential to diagnose and monitor a number of neurological conditions, or improve accessibility for individuals with disabilities.

Unfortunately, existing approaches have some drawbacks that have limited their widespread adoption. The commonly used pupil center corneal reflection technique relies on near-infrared light for operation and is highly susceptible to interference from ambient light sources. Electrooculography, on the other hand, utilizes electrodes placed on the skin, but accuracy can be reduced by interference from electrical signals coming from non-target muscles, and it also has the potential to pose health risks.

Fresh thinking on the topic has led to the development of a new contact lens-based eye tracking system that is accurate, safe for human use, and resistant to external interference. A team led by researchers at Nanjing University have leveraged radio frequency signals to make this possible. In this way, the lenses were made to be devoid of batteries or any other active electronic components that could cause harm or otherwise limit practicality.

To produce the lenses, a set of four flexible RFID tags were embedded into a medical-grade silicone elastomer. Regular contact lenses are also made from silicone, so biocompatibility is assured. A portable sweeping frequency reader is then used to both power the RFID tags, and measure the signals that they produce. As the eye moves, the signals are altered in predictable ways that can be translated into gazing directions. This translation is highly accurate — an angular accuracy of less than 0.5 degrees was observed.

A series of experiments demonstrated the utility of the smart contact lenses in a variety of applications. It was shown that the lenses could be used to control a video game, or browse the web. In another test, it was shown that a remote control vehicle can be controlled by eye movements. It was even suggested that the ability of the lenses to monitor rapid eye movement could be used to monitor and diagnose sleep disorders.

These lenses do have one glaring limitation at present — the RFID tags are not transparent, so they will, to some extent, limit vision while in use. The researchers do plan to address this issue in the future, however, by exploring the possibility of using highly-conductive transparent electrodes, perhaps made of AgNF/AgNW hybrid networks. Such an enhancement would go a long way towards making smart contact lenses a practical reality.