Bionic eye

Editor's Notes

• #5: Vision can be affected in a number of ways. Some structures within the eye may not be ideally formed, or may have been damaged, impeding their function.Corrective eyewear and laser eye surgery can address some problems with the light-focussing functions of the eye (such as cataracts, astigmatism and myopia). These problems are usually a result of structural abnormalities within the eye and its component parts.Problems with the light-processing functions of the eye are usually caused by abnormalities of the retina and macula such as retinitis pigmentosa and age-related macular degeneration. They cannot be addressed with corrective eyewear or laser eye surgery and it is these problems that we are seeking to address with the bionic eye. 
• #7: Developed by Second Sight
• #8: The device allows people with a certain type of blindness to detect crosswalks on the street, the presence of people or cars and, sometimes, even large numbers or letters.The artificial retina is a sheet of electrodes implanted in the eye. The patient is also given glasses with an attached camera and a portable video processor. This system, called Argus II, allows visual signals to bypass the damaged portion of the retina and be transmitted to the brain.The Argus II eyeglass camera captures images, which the video processor translates into pixelised patterns of light and dark, and transmits them to the electrodes, which then send them to the brain.With the artificial retina or retinal prosthesis, a blind person cannot see in the conventional sense, but can identify outlines and boundaries of objects, especially when there is contrast between light and dark - fireworks against a night sky or black socks mixed with white ones.It restores a type of vision which is probably going to be black and white, but it gives patients who are severely visually impaired mobility
• #17: The image (nature) contains much more details than an array can projectStep 1: simplify camera image => making just black and whiteStep 2: reduce that image to the number of electrode availableIf an electrode is > than half white => onotherwise => offIf electrode is on => user perceive a white spotA bit more processing to improve quality
• #19: Tests showed that the animals were able to discern facial features and track images with their eyes.A reconstruction based on electrical signals from the implant showed recognisable features of a baby’s face.In contrast, a standard retinal implant without the new encoder produced a confused pattern of bright and dark spots.“In sum, our results show that incorporating the code dramatically increases prosthetic capabilities. Although increasing resolution also improves performance, there is an inherent ceiling on the quality of image this can produce; adding the code breaks through this barrier. The coded output combined with high-resolution stimulation makes natural vision restoration possible” - US team led by Dr Sheila Nirenberg, from Cornell University in New York“Our results show that incorporation of the code dramatically increases prosthetic performance, well beyond what can be achieved just by increasing resolution. Moreover, they show that the combination of the code and high-resolution stimulation is able to bring prosthetic capabilities up to the level of normal or near-normal image presentation.” - US team led by Dr Sheila Nirenberg, from Cornell University in New Yorkhttp://www.telegraph.co.uk/science/science-news/9473387/Scientists-develop-bionic-eye-which-could-restore-sight-to-the-blind.htmlArticle of aug 2012
• #27: he fabrication process of the parylene-C flexible circuit board, i.e., parylene flex, started with a 5μm parylene-C deposition on HMDS treated silicon wafers, which will help the parylene flex to be released from DI water in the last step, as shown in Figure 2. The parylenedeposition was followed by a Ti/Au (~0.3μm) metal lift-off process to provide electrical connection. A second and the top thick parylene-C (~40μm) was then deposited to complete the parylene-metal–parylene sandwich skin structure. Aluminum (0.25μm) was deposited as the parylene-C etching mask to etch through thick parylene-C interfaces. Finally, electrode sites and the device contour were then defined by a two-step O2 plasma etchinB. HIGH-DENSITY MULTI-CHANNEL CHIP INTEGRATION A previously developed high yield and high-density multi-channel chip connection technique [9, 10] was used to make connection of this work. The parylene flex was first aligned with IC chips under microscope. An alignment accuracy of around 10 μm was achieved. A conductive epoxy squeegee technique, as shown in Figure 3, was then applied to make electrical and mechanical connections for the epiretinal prosthesis integration. A commercially available conductive epoxy (MG Chemicals) was first mixed and applied on the surface of the edge of the parylene flex. The parylene flex has holes and wells that were etched during the fabrication process which acted as the screen for this squeegee process. A rubber squeegee was then used to push the epoxy across surface so the epoxy filled the wells in the parylene flex, and electrically connected the electrical traces that were embedded inside the parylene flex and the bonding pads on the chips together.
• #28: 3-COIL WIRELESS POWER TRANSFER AND DATA COIL INTERFERENCE A. 3-COIL WIRELESS POWER TRANSFER To wirelessly power the whole epiretinal system, a 3-coil wireless power transfer system is used as shown in Figure 4. The flexible and foldable MEMS intraocular foil receiver coil, L3 in Figure 4, features a Q factor of 24 (at the operating frequency of 10MHz), a diameter of 10mm and a weight of 10mg in saline [11]. This coil is placed inside the lens capsule. The intermediate coil, L2, is a hand-wounded Litz buffer coil to enhance coupling coefficients κ12 and κ23 due to its high Q factor and close proximity to receiver coil. Because of the additional intermediate coil, the overall power transfer efficiency of the design was measured to be as high as 36.5% with one inch separation between the primary transmitter coil, L1, and the intraocular receiver coil, L3. B. SIMULATION OF INTERFERENCE BETWEEN COILS For surgical and placement consideration, it is the best to have the power and data coils in a co-planar fashion. However, the co-planar placement has the largest interference issue between the power and data coils. To analyze the interference between power and data coils, a model of the coil system was built using high frequency structural simulator (HFSS), as shown in Figure 5. Coil 1 is defined as the receiver coil of the data coil, with 3mm, 5mm, and 7mm inner diameter; coil 2 is defined as the receiver coil of the intraocular power coil, with 10mm inner diameter; coil 3 is defined as the transmitting data coil, with 20mm in diameter; coil 4 is defined as the transmitting power coil, with 42mm in diameter. The thickness of the coils is 2mm and the separation between the receiving and transmitting coils is set to be one inch.
• #29: parameters (S-parameters), describing the electrical behavior of linear electrical networks, from coil 4 to coil 1 and from coil 3 to coil 1 were simulated for us to estimate the interference between power and data coils. The resonating capacitors are 30pF for coil 1, 700pF for coil 2 and coil 3, and 600pF for coil 4. At the frequency of 160MHz where the data coil operates, an interference signal at 10MHz coming from the power coil will cause a 20dB higher coupling compared to the data coilin order to reduce interference from the power coil to the data coil, two notch filters, were added to the circuit. The notch filters, built by RLC circuits, can decrease the coupling in the data path. They reduce the coupling at 10MHz (i.e., the power transfer frequency), making possible to demodulate data at 160MHz. It is also possible to tune the resonant frequency to increase the gain at 160MHz which will be better for data transfer. The only drawback is that 6 more extra discrete components will be added to the whole system. However, our surgical design can tolerate this issue so that not too much volume will be added to the device.
• #30: In order to reduce interference from the power coil to the data coil, two notch filters, as shown in Figure 7, were added to the circuit. The notch filters, built by RLC circuits, can decrease the coupling in the data path. They reduce the coupling at 10MHz (i.e., the power transfer frequency), making possible to demodulate data at 160MHz. It is also possible to tune the resonant frequency to increase the gain at 160MHz which will be better for data transfer. The only drawback is that 6 more extra discrete components will be added to the whole system. However, our surgical design can tolerate this issue so that not too much volume will be added to the device. f the implant is very important. To this end, a paryleneflex mechanical model was designed and fabricated, as shown in Figure 8, to be packaged with silicon chips, discrete components (including capacitors, inductors, and resistors), and coils. A mold was designed to house the silicon chips for one-time conductive epoxy squeegee connection process to increase the connection yield. All the discrete components were placed on a parylene flex tail. A single retinal tack hole (100μm in diameter) and two suture holes (2mm in diameter) were also designed for the implant to be fixed on designated tissues inside eyeball. Biocompatible silicone was used for further protection after all the process [12]. Based on the high flexibility of the parylene flex implant and low interference between power and data coils with notch filters, the parylene tail can be wrapped around the chips and the coils can be put together in a co-planar fashion, which will be beneficial for surgical insertion and placement. The packaging shown here is based on a two-chip master/slave architecture with two notch filters (built by 6 discrete components), and 17 discrete components. However, the final goal of on-going chip development is to have only one single IC chip and fewer discrete components.
• #41: The minimal threshold voltage and current both decrease with radius of electrode if it becomes much smaller than the cell, the electric field will be concentrated in a small area in the proximity of the electrode, while the rest of the cell membrane will not be affected
• #42: the lowest current (2 μA) is required with the smallest electrode size (ro=5μm) when the 10 μm cell is in contact with its surface, but it increases by an order of magnitude when cell is separated from this electrode by just 25μm. The larger electrodes require higher threshold current, but are more tolerant to changes in the separation distance, i.e. the threshold potential does not rise as rapidly with distance as for smaller electrodes.
• #46: Examples of pixelated vision. Lower resolution may allow crude shape recognition, but increasing resolution can lead to (A–C) reading letters on an eye chart and (D–F) face recognition (rectangle added on last image to protect identity). (Face image courtesy of: http://cs www.essex.ac.uk/mv/allfaces/index.html.)Cost Current cost is about US$ 150,000 (S$185,300) , excluding surgery and trainingNext milestone is to make affordable to the mass patientsSurgery durationTakes about 4 hoursNext milestone is to shorten the duration VisionCurrent vision is black and white.Next milestone is colour vision – sensor & encoder chipsVisual acuityPoor relative to normal visionNext milestone improve visual acuity to enable face recognition and large font reading (600 -1000 individual pixels) – increasing number of electrodes , higher resolutionOther Vision Impairment ConditionsCurrently effective on retinitis pigmentosa and age-related macular degenerationNext milestone is to restore useful vision for blind people
• #48: McKinnon, B. J. (2013), Cochlear implant programs: Balancing clinical and financial sustainability. The Laryngoscope, 123: 233–238. doi: 10.1002/lary.23651