| For the last decade, groups of cell biologists, | | | | chip. The function of this chip/implant is the same |
| chemists and physicists all over the world have | | | | as the retinal photoreceptor cells which are |
| been focusing their motivation of research for the | | | | connected with the bipolar cells and ganglions and |
| improvement of human life. Biological backgrounds | | | | transmitting the photo signal to the respective |
| interpreted with the chemical understandings of a | | | | part of the optic nerve [Ref. 4]. It is not easy to |
| living cell have led physicists to fabricate "Intelligent | | | | explicate the phenomena for the transmission of |
| Devices" sensing alternative to those organs | | | | the sensed sketch produced in the chip of |
| which are naturally integrated in the human body. | | | | photoreceptor diodes to the grown cells of the |
| Broadly speaking these built-in or integrated | | | | retina, and from them to the optic nerve. |
| organs (eye, nose, skin, ear, tong, heart, lungs, | | | | Biologists and chemistry people are trying to |
| etc) in the human body are the devices which | | | | resolve these phenomenons into a simple, |
| provide a man "a signal" of an image, touch, taste, | | | | explainable and electronically feasible for the best |
| hearing, smell. These impulsive signals are then | | | | possible performance of the retinal implants. |
| transmitted through the tissue to the respective | | | | Conclusion and Future work |
| part of the central processing unit, the brain. The | | | | There are certain flaws for the In-vivo application |
| theme of the today's research is to imply this | | | | of retinal implants. Bio-compatibility, one of the |
| simple natural process, design and fabricate a | | | | first main issue, of an Implants means especially |
| substitute to these sensors when the built-in | | | | the metal electrodes and the whole chip (the |
| sensor does not work for certain reasons. These | | | | electronics) must be able to resist the body |
| substituted devices are called Implants. An | | | | environment. The electrolytic properties of the |
| example of such an implant is the Retinal Implant. | | | | blood, pH and ionic behavior of the In-vivo |
| The Retinal Implant | | | | environment are some crucial parameters, |
| An eye is a precious part of a human which plays | | | | nowadays faced by the scientists. The compatible |
| an integral sensory role for the visual capability of | | | | implants should also be longtime susceptible to the |
| the vision. Because of many factors this part | | | | animals as well as to the human beings. |
| may come to loose its visionary sensing power in | | | | Similarly, the diffusion of liquids through the sealing |
| some human beings. For example, Age-Related | | | | and packed retinal implant is also a great challenge |
| Macular Degeneration (ARMD) is a progressive | | | | that limits the working period (life) of an implant. |
| disease of the retina wherein the light-sensing cells | | | | For the commercial available synthetic materials, |
| in the central area of vision (the macula) stop | | | | (plastic foils, etc) the permeability rate of water |
| working and eventually die Ref [1]. By replacing | | | | vapors is 5*10-3 g/m2/day. Scientists are seeking |
| the dead part of retina with the retinal implants, | | | | the best possible material with the least |
| theoretically and practically, the diseases related | | | | permeation which would in turn enhance the life |
| with retina can hopefully be controlled. | | | | time stability and bio compatibility of the implant in |
| The principle and working of an Eye | | | | the body. |
| The construction of the Eye is similar to that of a | | | | Besides the state-of-the-art device fabrication |
| camera. In principle, the visible light is focused by a | | | | improvements, a visual prosthesis must receive |
| lens on a screen called the retina and the image is | | | | two types of inputs, information about the visual |
| realized. Fig.1 (please find at shows a cross-section | | | | signal from the retinal implant and the power to |
| of human eye ball with its different parts. The | | | | run this whole electronic assembly. It is |
| Retina, being the most significant in the functioning | | | | detrimental for the purposes of long-term |
| of the eye, is composed of layers with different | | | | implantation to have wires penetrating the body |
| cells as shown in Fig. 2 (please find at [ ) | | | | or imbedded batteries that could corrode and |
| The light first enters the Nerve Fiber Layer and | | | | have to be replaced if not properly sealed as |
| the Ganglion Cell Layer, under which most of the | | | | mentioned above. Alternatively, one can send the |
| nourishing and aiding blood vessels of the retina | | | | visual signal and power to the implant without the |
| are located. This is where the nerve begins, | | | | use of wires. Wireless communication can be |
| picking up the impulses of the acquired image | | | | accomplished with laser light or radiofrequency |
| from the retina and transmitting them to the | | | | transmission. |
| brain. The light is received by the Photoreceptor | | | | Before performing experiments on the human |
| cells called Rods and the Cones. These cells | | | | eye, it is necessary to perform laboratory |
| convert light into nerve impulses, which are then | | | | experiments to determine safe methods of |
| processed by the retina and sent though nerve | | | | device implantation and electrical stimulation of the |
| fibers to the brain. The nerve fibers exit the | | | | retina. These studies are performed in vitro (i.e. |
| eyeball at the Blind spot and reach the brain | | | | outside the animal; using tissue preparations) and |
| through the Optic nerve. The further anatomical | | | | in vivo (i.e. in the living body). In order to carry out |
| details can be found elsewhere. Ref. [2] | | | | such experiments, approval must be obtained and |
| The Retinal Implant Functionality | | | | granted from committees that monitor |
| To help visually impaired patients, a visual | | | | experimentation with animals and humans from all |
| prosthesis could be designed to be placed in the | | | | the over the world. |
| eye, either under or on the retinal surface, sub | | | | Ref: |
| retinal areas, etc, in the optic nerve, or in the | | | | |
| visual cortex of the brain. Each approach has | | | | 1: Age Related Macular Degeneration, Jennifer I |
| certain advantages and disadvantages. [Ref. 3] | | | | Lim, ISBN 082470682X |
| Based on the above principal idea, the light is | | | | 2: An Introduction to the Biology of Vision, James |
| sensed by a large assembly of photo-receptor | | | | T Mcllwain, ISBN 0521498902 |
| diodes integrated on a Chip connected with the | | | | 3: Neuroprosthetics: Theory and Practice, Kenneth |
| electrodes for the electrical power. This chip | | | | W. Horch, ISBN 9812380221 |
| collects the information of the sketched image fall | | | | 4: Electrical multisite stimulation of the isolated |
| on it and triggers the family of cells grown on this | | | | chicken retina, et. A. |