Artificial Eye

Abstract:- :-

   In the current scenario, where over millions of people are affected by visual anomalities, it was with a challenge that this project came into being. It aims at restoring vision to the blind.

    Today, high-tech resources in microelectronics, Optoelectronic, computer science, biomedical engineering and also in vitreo retinal surgery are working together to realize a device for the electrical stimulation of the visual system.

     Artificial Eye, which works through retinal implants, could restore sight to millions of people around the world who suffer from degenerative eye diseases. This technology is still in its infancy, but has progressed to human trials. This report aims to present a brief overview about the basic aspects of this technology and where it’s headed.

Visual System

       The human visual system is remarkable instrument. It features two mobile acquisition units each has formidable preprocessing circuitry placed at a remote location from the central processing system (brain). Its primary task include transmitting images with a viewing angle of at least 140deg  and resolution of 1 arc min over a limited capacity carrier, the million or so fibers in each optic nerve through these fibers the signals are passed to the so called higher visual cortex of the brain.

          The nerve system can achieve this type of high volume data transfer by confining such capability to just part of the retina surface, whereas the center of the retina has a 1:1 ration between the photoreceptors and the transmitting elements, the far periphery has a ratio of 300:1. This results in gradual shift in resolution and other system parameters.

       At the brain’s highest level the visual cortex an impressive array of feature extraction mechanisms can rapidly adjust the eye’s position to sudden movements in the peripherals filed of objects too small to se when stationary. The visual system can resolve spatial depth differences by combining signals from both eyes with a precision less than one tenth the size of a single photoreceptor.

 

Electrical Signals From The Brain - Vep 

    A special part of the brain, the visual cortex, is believed to be the entrance structure to visual perception and cognition Activity of nerve cells within the brain's surface (the cortex) produce electrical fields that can be picked up at some distance with electrodes (like ceiling microphones pick up sound from instruments in an orchestra during a concert). In humans these electrodes are simply "glued" on the scalp with a sticky paste on the back of the head. In the pig model special arrays of electrodes fixed on a silicone-carrier are placed under the scull bone above the duration by neurosurgeons and can be left there for several months. 

Structure And Working Of Asr

      The ASR microchip is a silicon chip 2mm in diameter and 25 microns thick, less than the thickness of a human hair. It contains approximately 5,000 microscopic solar cells called “microphoto diodes,” each with its own stimulating electrode. These microphoto diodes are designed to convert the light energy from images into electrical chemical impulses that stimulate the remaining functional cells of the retina in patients and rp type or devices.

    The ASR microchip is powered solely by incident light and does not require the use of external wires or batteries. When surgically implanted under the retina—in a location known as the “subretinal space”—the ASR chip is designed to produce visual signals similar to those produced by the photoreceptor layer. From their sub retinal location, these artificial “photoelectric” signals from the ASR microchip are in a position to induce biological visual signals in the remaining functional retinal cells which may be processed and sent via the optic nerve to the brain.

Implant Design And Fabrication

   The current micro photodiode array (MPA) is comprised of a regular array of individual photodiode subunits, each approximately 20×20-µm square and separated by 10-µm channel stops. Across the different generations examined, the implants have decreased in thickness, from ~250 µm for the earlier devices, to approximately 50 µm for the devices that are currently being used. Because implants are designed to be powered solely by incident light, there are no connections to an external power supply or other device. In their final form, devices generate current in response to a wavelength range of 500 to 1100 nm.

Cortical Implants

    Scientists have created a device that allows them to communicate directly with large numbers of individual nerve cells in the visual part of the brain. The device is a silicon electrode array may provide a means through which a limited but useful visual sense may be restored to profoundly blind individuals.

       This shows the development of the first visual prosthesis providing useful "artificial vision" to a blind volunteer by connecting a digital video camera, computer, and associated electronics to the visual cortex of his brain. This device has been the objective of a development effort begun by our group in 1968 and represents realization of the prediction of an artificial vision system made by Benjamin Franklin in his report on the "kite and key" experiment.

    This new visual prosthesis produces black and white display of visual cortex "phosphenes" analogous to the images projected on the light bulb arrays of some sports stadium scoreboards. The system was primarily designed to promote independent mobility, not reading. It has a battery powered, electronic interface that is RF isolated from line currents for safety. This interface can replace the camera, permitting the volunteer to directly watch television and use a computer, including access to the Internet. Because of their potential importance for education, and to help integrate blind people into the workforce, such television, computer, and Internet capabilities may prove even more valuable in the future than independent mobility.