HEALTH


GOOGLE LENS


Public interest in smart contact lenses was first triggered back in early 2014 when Google announced it was testing lens technology to measure glucose levels in tears. Later that year, Novartis announced that it would license the technology from Google. Its eye care unit, Alcon, set up a collaboration with Verily Life Sciences, Google’s life science division, created in in 2015. But the promised clinical trials have


stalled. According to its website, Verily is still working with Alcon on a glucose-sensing lens and an accommodating contact lens for people with age-related far-sightedness. Verily is responsible for the integrated


rabbit did not show any abnormal behaviour when wearing the lens.


Autofocus lens Another area of research of interest are lenses that focus themselves within milliseconds. These could be life-changing for people with presbyopia or age-related far- sightedness, in which the eye’s lens gets stiffer so making it difficult to focus on close objects. Presbyopia affects more than


1bn people worldwide, half of whom do not have adequate correction, says Hongrui Jiang of the University of Wisconsin, Madison, US. And while glasses, conventional contact lenses and surgery provide some improvement, these options all involve the loss of contrast and sensitivity, as well as difficulty with night vision. Jiang wants to design contacts that continuously adjust along with a person’s own cornea and lens to restore better vision. The project requires overcoming


several engineering challenges. These include designing the lens, algorithm- driven sensors and miniature electronic circuits that adjust the shape of the lens, plus creating a power source. All of these then need to be embedded in a soft, flexible material that fits over the eye. In its latest study, Jiang’s team has


been investigating image sensors.4 ‘The sensors must be extremely small and capable of acquiring images under low-light conditions, so they need to be exquisitely sensitive to light,’ he says. The team took its inspiration from the retina of elephant nose fish,


circuits, sensors and wireless communication, and has been working on ‘the technical challenges of significant miniaturisation for autonomous sensing systems and dramatic reduction of power consumption to permit tiny batteries’. Alcon’s focus is biocompatible materials, optics and clinical development. In November 2016, Novartis said it was abandoning a goal to start clinical trials of the autofocus lens in that year. Alcon’s spokeswoman says the glucose-sensing lens is in early clinical development with clinical trials planned in the near future, but there isn’t a definitive timeline. She adds that they are pleased with the steady progress, and are


moving at a pace expected in the proof-of- concept development phase. Oregon State University’s Gregory Herman


says the Verily/Alcon prototype sensor is not fully transparent. ‘It’s an amperometric sensor [based on electrochemistry rather than a field effect] and you can see the chips. That means it has to be off to the side of the contact lens,’ he explains. ‘Another issue is the signal is dependent on the size of the sensor and you can only make it so small or you won’t be able to get a usable signal. With an FET [Field-effect transistor] sensor, you can actually make it smaller and enhance the output signal by doing this.’


each liquid differently, resulting in forces that squeeze the droplet into different focal lengths. The team reported that the lens is able to focus on objects as small as 20µm, roughly the width of the thinnest human hair. In another approach, the team has


which live in dark, muddy rivers. The fish can spot predators even in murky waters because of their uniquely shaped retina, which comprises a series of parabolic or cup-like structures with reflective sidewalls that help gather light and intensify the particular wavelengths needed for the fish to see. The researchers created a device with thousands of very small light collectors; shaped like fingers, the insides of these glass collectors are lined with deep cups coated with reflective aluminum. Incoming light hits the fingers and then is focused by the reflective sidewalls. Jiang’s team tested the device’s ability to enhance images using a lab-designed mechanical eye model. They found it enhanced image intensity without consuming power. In separate studies, the


researchers have designed and lab-tested a couple of different approaches for the contact lens material. For one approach, they formed a liquid lens from a droplet of silicone oil and water. The droplet sits in a chamber on top of a flexible platform. A pair of electrodes produces an electric field that modifies the surface tension of


>1bn


Number of people worldwide affected by presbyopia, half of whom do not have adequate correction. Autofocus contact lenses that self-focus in milliseconds could be life-changing for people with this age-related far-sightedness


Glucose concentrations in the eye are much lower than in blood or interstitial fluid under skin so lens biosensors have to be much more sensitive.


tried to mimic the compound eyes of insects, which contain thousands of individual microlenses. Each micolens points in a different direction to capture a specific part of a scene. Jiang’s team developed a flexible array of artificial microlenses. ‘Each microlens is made out of a forest of silicon nanowires,’ Jiang explains. ‘Together, the microlenses provide even greater resolution than the liquid lens.’ In order to change focus, the


contact lens will also need to be equipped with an extremely small, thin power source. Jiang’s working solution is a solar cell that converts solar energy into electricity, and also stores energy within a network of nanostructures. It works much in the way a


References 1 G. Herman et al, Nanoscale, 2016, 8, 18469.


2 G. Herman et al, ACS Appl. Mater. Interfaces, 2016, 8, 7631.


3 Jang-Ung Park et al, Nature Communications; DOI: 10.1038/ncomms14997.


4 H. Jiang et al, PNAS; DOI: 10.1073/pnas.1517953113.


conventional solar panel does, but the addition of storage capability within a single device is novel, according to Jiang. The device still needs tweaking, but the team is optimistic that it will be powerful enough to drive the lens yet small enough to fit the space available. A prototype for clinical testing


may still be five to ten years off, Jiang says. Once it’s available, however, it may not cost much more than conventional contact lenses. ‘There’s a huge market for this and with mass production, the cost is not likely to be a barrier,’ he believes.


08 | 2017 21


ULSAN NATIONAL INSTITUTE OF SCIENCE AND TECHNOLOGY (UNIST)


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