Over the past few years, teams of engineers around the world have been trying to build contact lenses that function as wearable displays. While American and European militaries have been honing Head-Up Display (HUD) technologies for use in aviation since the 1960s, and the U.S. military already employs wearable displays called wearable glass, the innovation to build augmented reality into a contact lens is only a few years old . Currently, wearable glass, such as Google Glass, consists of a lightweight pair of glasses with a side-mounted processor and ‘pico-projector.��” This device can be linked to wi-fi or a mobile device by Bluetooth. When a user is wearing the glasses, a small virtual screen appears in the upper right corner of the person’s field of vision .
The history of augmented vision technologies dates back several decades. The Head-Up Displays of the mid-1970s, comprised of a display unit, a combiner, and a computer, were created to enable pilots to operate aircraft with increased accuracy by placing critical information within their normal field of vision . By relieving pilots of the need to look down at panels of instruments, HUDs increased both precision and safety, even under low-visibility conditions . The systems were so effective that they have been incorporated into commercial aircraft as well. Nonetheless, HUDs and wearable glass have presented a variety of persistent engineering challenges, from the presence of distracting reflections to the bulky inconvenience of the headgear. Wearable lenses overcome such limitations.
Innovations in wearable glass have made this technology considerably more lightweight and comfortable. However, wearable glass is still bulkier and more cumbersome than wearable lenses, which, like other contact lenses, rest directly on the user’s cornea . Currently, there are a variety of functional features of wearable glass for which engineers are developing wearable lens analogs. Today, wearable glass includes hardware such as touch buttons and cameras as well as wireless functionality and communication with other devices  . Wearable contact lenses will experience great leaps in usability if engineers can incorporate hardware, wireless, and communication capabilities (Fig. 1).
The concept components of a wearable lens that may become a viable reality in the near future are depicted in Fig. 1. A semi-transparent display and micro lens array rests directly over the center of the user’s cornea. A display control circuit determines the content of the display. For functions that require biometric information from the user, a biosensor module can gather data on metrics including heart rate, blood pressure, and eye pressure. The biometric data may then be interpreted and displayed by the sensor readout and control circuit. To enable wireless and communication capabilities, the lens will need to be equipped with a telecommunication and power reception antenna. The concept sketch in Fig. 1 shows an example of a solar powered wearable lens. Accordingly, both a solar cell module to collect solar energy as well as an energy storage module are built into the lens. Finally, the radio and power conversion circuit and the energy interconnects operate as translators between the input signals and the other components of the device.
A major challenge in designing wearable glass has been the limited ability of the human eye to focus on objects that are very near . Wearable contact lenses utilize a “display architecture that is based on enhancing the human eye’s normal vision capabilities” by sharpening one’s real-world vision and also allowing the wearer to detect details in objects placed at “the usual distance between traditional eyewear and the eye.” This approach permits users to simultaneously detect real-world and augmented visual stimuli. These special lenses permit light from the surrounding environment to enter through the outer portion of the pupil and light from the display to enter through the center . The sets of light rays are superimposed upon one another to create a single image. If the wearer requires a prescription for normal vision, this may be incorporated into the lens too . In order to achieve this technology, it will be necessary for engineers to develop an electrode that is both transparent and flexible.
Numerous researchers are collaborating and competing to make advancements in this active field of technology development. Engineers at many different commercial, scientific, and academic institutions are contributing to this research, including Randall Sprague of Innovega, Babak Parviz at the University of Washington, Jang-Ung Park at the Ulsan National Institute of Science and Technology, and Sung-Woo Nam at the University of Illinois at Urbana-Champaign  . These engineers are using nanomaterials to troubleshoot the transition from glass to lens. Recent breakthroughs have come in the solution to the problem of how to create an electrode that is both transparent and flexible. Transparency is the easier issue to address, as transparent electrodes are already in use in solar cells, flat screen TVs, and touch screens . In these conventional rigid electronic devices, the electrodes are made of indium tin oxide (ITO). Unfortunately, ITO is brittle; if flexed, it cracks and loses functionality . Moreover, ITO is also incompatible with contact lenses because it degrades over time and must be deposited at temperatures that would melt an ordinary contact lens . Finally, because indium metal is rare in nature and only exists in limited quantities, ITO is prohibitively expensive . On the other hand, while graphene and silver nanowires are sufficiently flexible and transparent, they are not conductive enough .
A collaboration between Jang-Ung Park and Sung-Woo Nam would solve the problem of creating a material that had all the needed properties: transparent, flexible, and conductive . They determined that arranging silver nanowires between graphene sheets created a composite material that had considerably lower electrical resistance than either material alone . On their own, silver nanowires have high resistance, as they exist in a random orientation, “like a jumble of toothpicks facing in different directions.” Graphene is also a popular candidate for creating transparent electrodes as it has high mechanical flexibility and other special properties . However, when graphene is mass produced for commercial purposes, the quality declines, and its electrical resistance increases .
This technology could revolutionize daily experience in fields from navigation to medicine to entertainment (Fig. 3). For example, drivers today must take their eyes off the road to consult maps and directions. Navigational tools built into wearable contact lenses could overlay driving directions and other useful information such as speed and road conditions to reduce accidents and traffic congestion. These lenses are already demonstrating important medical applications: Swiss researchers have created an electronic lens that continuously monitors eye pressure for glaucoma patients . People who wish to monitor their daily health and fitness activities could use the contact lenses during workouts to detect heart rate and blood pressure, distance traveled and/or number of steps taken, and perhaps even calories burned. Wearable lenses have obvious social networking applications too, such as syncing with other devices to allow users to check email and text messages. Entertainment like films, gaming, and music will be made more realistic and immersive through the use of wearable lenses. There are limitless possibilities when it comes to where and how this technology can be used (Fig. 3).
Currently, the functionality of wearable contacts has a long way to go, primarily due to the limitations of the components. Engineers are currently at work creating ways to incorporate the vast functionality of wearable glass into wearable lenses. Development is also focused on how to supply power to these devices and how to make the displays more flexible, conductive, and transparent. These innovations are not far off though, and when wearable lenses become widely available to the general public, they are likely to change a great deal about how we live and work from day to day.
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