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EETE APR 2014

OPTOELECTRONICS Haptic lens converts light into touch By Julien Happich A lot of research goes into bringing back some level of sight to visually impaired people. Often, researchers look into ways to connect artificial photoreceptors to retinal or optical nerves, bypassing the faulty retina through surgically implanted devices and microelectrodes. But in the vast majority of people suffering from untreatable blindness, the cornea remains unaffected by diseaserelated retinal dis-functions, observes Prof. Zeev Zalevsky, a proponent of less intrusive solutions. And according to anatomical studies, cornea is one of the most sensitive tissues of the body, densely innervated (distinctly from optic nerves which only transmit vision signals), with a density 300 to 600 times that of skin. The nerves in question are sensory, producing touch, thermal and chemical sensations that drive the blink reflex Fig. 1: The haptic lens concept with micro actuators or micro-electrodes featured as pixels. necessary to preserve the integrity of the ocular surface, notes Zalevsky in a 2013 paper discussing the use of tactile corneal stimulation through Braille-like pressure points. In recent research, Zalevsky has also demonstrated through human trials that the cornea’s sensing capacity to discriminate between two points is around 1mm, which in theory could allow the cornea to identify simple spatial shapes and images using adequate stimulation. The Head of the Electro-Optics study program at Bar-Ilan Universitys’ Faculty of Engineering (Israel) and director of the Nano Photonics Center at the Institute of Nanotechnology and Advanced Materials (BINA), Zalevsky together with Prof. Michael Belkin from Tel-Aviv University are now launching a startup called I C Touch with the goal to design a wearable haptic lens together with a dedicated image processing chip that would parse the input from a video camera into a timemultiplexed matrix of surface electrodes or micro-actuators embedded into the lens. Although the initial clinical trials were done using hardwired tubing and air pressure (using micro-channels to stimulate the cornea across discrete points for the patient to recognize basic shapes), the ultimate goal would be to power and control such a lens wirelessly, using an embedded antenna coil and RF energy harvesting to drive surface electrodes. “We started with pressure stimulation in order to prove our basic claim: that cornea has two points discrimination capability and can sense spatial shapes. This is novel to the world of medicine and was never examined before” clarified Zalevsky in an email exchange with EE Times Europe. “Another reason was that for pressure stimulation it is much simpler to get clinical approval for experiments. The third reason is that as in any R&D process there always many non-anticipated difficulties. So our aim is to do electrical stimulation which is simpler from the system point of view but it might not perform as well as expected so we have our fold back path of doing the pressure based stimulation which can also be realized in practice”. Currently Zalevsky’s research team is experimenting with prototypes assembled manually from printed electronic circuits inserted between two soft lenses. The current design includes pixels with a pitch of around 1mm, and the distance between the electrode and the cornea surface is around 50 microns. Although the initial proof of concept was done using pressure stimulation, the team has to figure out what would be the right comfort zone for electrical stimulations to properly define the voltage level at which the stimulation would be felt without being disturbing to the user. So what sort of practical information does the wearer get from such a haptic lens since we humans are not accustomed to make any sense of tactile feedback on the cornea? Zalevsky describes a feeling similar to what someone would get when touching Braille writing with his/her fingertips. “It is a feeling one can train to recognize similarly to how a blind person learns how to recognize the Braille alphabet through touch”, explains Zalevsky. And indeed, during preliminary trials, the researcher confirms that various transmitted shapes (lines, crosses, squares etc…) were recognized by the subjects about 9 times out of ten after only 2 minutes of training. It only took a few minutes for the subjects to learn and distinguish between 10 to 20 different shapes, but that could vary with the pixel density. The current prototypes include electrodes which are like small antennas. The transmitted image induces voltages in them and the voltages do electrical stimulation of the cornea. Fig. 2: The full concept from image acquisition and processing (A) and (B) to the haptic lens (C). 38 Electronic Engineering Times Europe April 2014 www.electronics-eetimes.com


EETE APR 2014
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