ARTIFICIAL RETINA USING THIN-FILM TRANSISTORS DRIVEN BY

WIRELESS POWER SUPPLY

PRESENTED BY B.MANIROOP 15345A0428

ABSTRACT

We have evaluated an artificial retina using thin-film transistors driven by wireless power supply. It is found that the illumination profile can be correctly detected as the output voltage profile even if it is driven using unstable power source generated by inductive coupling, diode bridge, and Zener diodes.This means the feasibility to implant the artificial retina into human eyeballs.

INTRODUCTION• Artificial retinas have been ardently desired to recover the

sight sense for sight-handicapped people. Recently, artificial retinas using external cameras, stimulus electrodes, and three-dimensional large scale integrations (LSIs) have been actively developed for patients suffering from retinitis pigmentosa and age-related macular degeneration.

• In these cases, electronic photo devices and circuits substitute for deteriorated photoreceptor cells.

• The implant methods can be classified to four types: epiretinal implant, subretinal implant, suprachoroidal stimulation, and transretinal stimulation

• Among these implant methods, the epiretinal implant has features that the image resolution can be high because the stimulus signal can be directly conducted to neuron cells and that living retinas are not seriously damaged.

• In our research, we have proposed an artificial retina using thin-film transistors , which can be fabricated on transparent and flexible substrates.

• Electronic photo devices and circuits are integrated on the artificial retina, which is implanted on the inside surface of the living retina at the back part of the human eye balls .Since the irradiated light comes from one side of the artificial retina and the stimulus signal goes out of the other side, the transparent substrate is preferable.

LITERATURE SURVEY

• Takashi Tokuda, Member, IEEE, Kohei Hiyama, Shigeki Sawamura, Kiyotaka Sasagawa, Member, IEEE, Yasuo Terasawa, Kentaro Nishida, Yoshiyuki Kitaguchi, Takashi Fujikado, Yasuo Tano, and Jun Ohta, Member, IEEE

• We propose and characterize a CMOS LSI-based neural stimulator for retinal prosthesis technology. The stimulator is based upon a multichip architecture in which small-sized CMOS stimulators named “unit chips” are organized on a flexible substrate. We designed a unit chip with an on-chip stimulator and light-sensing circuitry. We verified that all the functions implemented on the unit chip worked correctly and that an organized unit chip can be used as a retinal stimulator with multisite image-based patterned stimulation. We also demonstrated light controlled retinal stimulation for the first time in an in vivo animal experiment on a rabbit’s retina.

REFERENCES1. Tomohisa Hachida received the B.E. degree in electronics and

informatics from Ryukoku University, Otsu, Japan, in 2009. He had been working on research and development of artificial retinas using thin-film transistors(TFTs). He is currently a graduate student at Nara Institute of Science and Technology, Ikoma, Japan

2. Yuta Miura received the B.E. degree in electronics and informatics from Ryukoku University, Otsu, Japan, in 2010. He had been working on research and development of artificial retinas using thin-film transistors(TFTs). He is currently a graduate student at Nara Institute of Science and Technology, Ikoma, Japan.

METHODOLOGY• The artificial retina using TFTs is fabricated using the same

fabrication processes as conventional poly-Si TFTs and encapsulated using SiO2 in order to perform in corrosive environments. Although the artificial retina is fabricated on the glass substrate here to confirm the elementary functions, it can be fabricated on the plastic substrate. The retina array includes matrix-like multiple retina pixels.

• Although large contact pads are located for fundamental evaluation, a principal part is 27300 microsquare metre , which corresponds to 154 ppi.

Implants are being researched as a viable way to restore vision in patients suffering from retinal pigmentosa as well as macular degeneration. The epiretinal implants typically work in a two component system that consists of an extraocular and intraocular part. The extraocular part contains an image sensor that is responsible for catching visual images, an artificial neural net which can imitate the functions of different layers of the retina, and a transmitter. The neural net transform the visual images control signals that the electrodes pick up and become stimulated. The signal is passed on to the internal eye and then is picked up by the intraocular part of the implant. The intraocular component consists of a receiver for the relayed signals and also power for the implant. Radiofrequency links are being used currently and optical links may be used in the future. There is an integrated circuitry component that decodes the signals for the electrodes and controls the stimulation array to produce action potentials in the upper ganglion cell layers to cause visual sensations.

EPIRETINAL IMPLANT

• The device works by receiving two types of input; information of the visual scene known as the visual signal as well as power and data to work the electronics and stimulate the retina to generate the matching visual image. This is carried out by wireless communication and radiofrequency transmission which is attached to a transmitting coil on the arm of special glasses which transmits the data and power to the coils located on the prosthesis .

The Retinal Prosthesis Project is based on designing an epiretinal implant that consists of two different components, the retina encoder and the retina stimulator. The retina encoder transforms a visual scene into nerve signals like the retina does. The implant is calibrated to meet each individual’s needs in order to produce optimal results. The encoder works with a photo sensor array for pattern reception and transmission to transmit signals and energy which are found in the glasses.

WIRELESS POWER SUPPLY USING INDUCTIVE COUPLING

• The power transmitter consists of an ac voltage source and induction coil. The Vpp of the ac voltage source is 10V, and the frequency is 34kHz, which is a resonance frequency of this system.

• The material of the induction coil is an enameled copper wire, the diameter is 1.8cm, and the winding number is 370 times.

• The power receiver also consists of an induction coil, which is the same as the power transmitter and located face to face. The diode bridge rectifies the ac voltage to the dc voltage, and the Zener diodes regulate the voltage value. The diode bridge and Zener diodes are discrete devices and encapsulated in epoxy resin.

SUBRETINAL IMPLANTSubretinal implants sit on the outer surface of the retina, between the photoreceptor layer and the retinal pigment epithelium, directly stimulating retinal cells and relying on the normal processing of the inner and middle retinal layers. Adhering a subretinal implant in place is relatively simple, as the implant is mechanically constrained by the minimal distance between the outer retina and the retinal pigment epithelium. A subretinal implant consists of a silicon wafer containing light sensitive micro photodiodes, which generate signals directly from the incoming light. Incident light passing through the retina generates currents within the micro photodiodes, which directly inject the resultant current into the underlying retinal cells via arrays of microelectrodes. The pattern of micro photodiodes activated by incident light therefore stimulates a pattern of bipolar, horizontal, amacrine, and ganglion cells, leading to a visual perception representative of the original incident image. In principle, subretinal implants do not require any external hardware beyond the implanted micro photodiodes array. However, some subretinal implants require power from external circuitry to enhance the image signal.

The arrays can be manufactured by various silicon manufacturing procedures. MPD arrays are manufactured consistently with measurements of each stimulating unit as 20 µm X 20 µm, and adjacent units separated as 10 µm. The elements are produced to be responsive to light corresponding to the visible spectrum (400-700 nm).

Several thousands of the devices can be placed on a single structure of diameter of 3 mm, thickness of 100 µm and with a density same as the replacing RPE cells. These devices have demonstrates the same electrophysiological behaviors as the healthy RPE cells. The MPDA has to be very thin and flexible enough in order to be able to fit to the curvature of the eye ball.

The Retina Implant device contains 1500 micro photodiodes, allowing for increased spatial resolution, but requires an external power source

The single MPD is not enough to stimulate enough current. So a subretinal implant is supported by an external energy source, such as transpupillary infrared illumination of receivers close to the chip or electromagnetic transfer, is currently under progress

OCCIPITAL LOBE• The occipital lobe is one of the

four major lobes of the cerebral cortex in the brain of mammals

• The occipital lobe is the visual processing centre of the mammalian brain.

• It is sub divided into striate cortex and extrastriate cortex.There are many extrastriate regions, and these are specialized for different visual tasks, such as :-1.visuospatial processing2.color differentiation and 3.motion perception.

• Brain consists of micro cells called neurons.• There 100 billion neurons in brain approximately. It takes

3000 years to count the total number of neurons.• The voltage generated from each neuron is of 70 millivolts.• The sensory nerves transmits sensations at a speed of 150

miles (approx 241 kmph) from the tip of the bare foot to the spinal cord and brain.

• When we see , hear ,walk, laugh several neurons get activated . Because electric charge is generated and chemical reaction takes place in our brain

• In our day to day life we learn new things at that time the structure of the brain changes .

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