Artificial Vision

Blindness, the most severe form of visual impairment, deprives people the ability to move about unaided. It is the most feared ailment in the present world. The leading causes of chronic blindness include cataract, glaucoma, age-related macular degeneration, corneal opacities, diabetic retinopathy, trachoma, and eye conditions in children (e.g. caused by vitamin A deficiency). Artificial vision has been a challenging task for the opto bionics. But now, a limited form of artificial vision is a reality. In this paper we present the various forms of artificial vision available for the blind in detail.

INTRODUCTION:
The Biomedical Instrumentation is the field in which various solutions for the medical problems is served. Linking electronics and biotechnology, the scientists has made the commitment to the development of technology that will provide or restore vision for the visually impaired around the world. Several investigations are being carried out on electronic-based strategies designed to bypass various defects or missing links along the brain’s image processing pathway and provide some form of artificial sight. We will discuss about the various development of artificial vision system, the concepts of artificial silicon retina, MARC (multiple artificial silicon retina chipset),and finally advancements and scope of this in future. ORIGIN OF ARTIFICIAL VISION:

Artificial-vision researchers has taken inspiration from another device, the cochlear implant, which has successfully restored hearing to thousands of deaf people and smart pacemakers which keeps heart beat rhythm normal. The eye is one of the most amazing organs in the body. Before we understand how artificial vision is created, it’s important to know about the important role that the retina plays in how we see.

RETINA:
The retina is complex in itself. This thin membrane at the back of the eye is a vital part of our ability to see. Its main function is to receive and transmit images to the brain. These are the three main types of cells in the eye that help perform this function: Rods, Cones and Ganglion Cells. The information received by the rods and cones are transmitted to the nearly 1 million ganglion cells in the retina, which interpret the message and send it to the brain through the optic nerve where images are formed, so with out them we are blind . There are a number of retinal diseases that attack these cells, which can lead to blindness. The most notable of these diseases are retinitis pigmentosa and age-related macular degeneration. Both of these diseases attack the retina, rendering the rods and cones inoperative, causing either loss of peripheral vision or total blindness. RETINITIS PIGMENTOSA

MACULAR DEGENERATION
However, it’s been found that neither of these retinal diseases affects the ganglion cells or the optic nerve. This means that if scientists can develop artificial cones and rods, information could still be sent to the brain for interpretation. This TYPES OF ARTIFICIAL VISION:

The current path that scientists are taking to create artificial vision received a jolt in 1988, when Dr. Mark Humayun demonstrated that a blind person could be made to see light by stimulating the nerve ganglia behind the retina with an electrical pulses that could restore vision. Today, such a device is very close to be available to the millions of people who have lost their vision to retinal disease. There are mainly two types of artificial vision systems available at present, 1. ARTIFICIAL SILICON RETINA (ASR).

2. MULTIPLE UNIT ARTIFICIAL SILICON RETINA CHIPSET (MARC). ARTIFICIAL SILICON RETINA:
CONSTRUCTION:
The ASR is an extremely tiny device. It is a silicon chip 2mm diameter and 25 microns thick, less than the thickness of a hair. It contains around 5000 microscopic solar cells called ‘micro photodiodes’ each will have its own stimulatory electrodes. These micro photodiodes converts light energy from the images into electro-chemical impulses that stimulate the remaining functional retinal cells of the eye. IMPLANTATION :

Coming to the implantation of ASR, it is implanted into the eye by a microsurgical procedure that lasts about 2 hours. To implant this device into the eye, surgeons make three tiny incisions no larger than the diameter of a needle in the white part of the eye. Through these incisions, the surgeons introduce a miniature cutting and vacuuming device that removes the gel in the middle of the eye and replaces it with saline. Next, a pinpoint opening is made in the retina through which they inject fluid to lift up a portion of the retina from the back of the eye, which creates a small pocket in the subretinal space for the device to fit in. The retina is then resealed over the ASR. In the days following the procedure, the air bubble and the saline solution are replaced by the fluids produced by the eye. WORKING :

For any microchip to work it needs power and the amazing thing about the ASR is that it receives all of its needed power from the light entering the eye. This means that with the ASR implant in place behind the retina, receives all the light that is directed to the retina. This solar energy eliminates the need for any wires, batteries or other secondary devices to supply power. This makes it more advantageous than any other device. Another microchip device that would restore partial vision is currently in research is Artificial Retina Component Chip (ARCC), this device is quite similar to the ASR, but the main difference is that Unlike the ASR, which is placed between layers of retinal tissue, the ARCC is placed on top of the retina and also a secondary device attached to a pair of eyeglasses directs a laser at the chip’s solar cells to provide power.

The microchip (ASR) is wireless and inert. It is just 2 millimeters in diameter and 23 micrometers thick, and consists of an array of about 5,000 microphotodiodes. Because each of these microscopic cells is powered by the energy contained in the incident light which lands upon it, the implant does not require batteries. The microphotodiode array constitutes an artificial retina – it is designed to perform the function that would normally be carried out by the photoreceptor cells. Each one is sensitive to light, and has an electrode attached to it, so that, when struck by light, it generates an electrical impulse which is transmitted to the retina. These impulses were taken to the brain where the information is processed in usual manner.

Groups of researchers have found that blind people can see spots of light when electrical currents stimulate cells, following the experimental insertion of an electrode device near or into their retina. Some patients even saw crude shapes in the form of these light spots. This indicates that despite damage to cells in the retina, electronic techniques can transmit signals to the next step in the pathway and provide some form of visual sensation. RESULTS:

The ASR is still in the experimental stages, but has been implanted into about 30 people. In January 2000, the U.S. Food and Drug Administration (FDA) authorised the use of the ASR chip in clinical trials involving up to 10 patients with retinitis pigmentosa. None of the 10 patients who participated in the trials showed any signs of inflammation or rejection of the implant by the immune system. The ASR device therefore seems to be safe, and can feasibly be used to develop treatments for various ocular diseases in which photoreceptor degeneration occurs. By electrically stimulating slightly damaged photoreceptors, the ASR may also prove to be effective in slowing the progression of degenerative eye diseases.

2. MULTIPLE UNIT ARTIFICIAL SILICON RETINA CHIPSET (MARC):
It is another type of artificial system used in curing blindness. CONSTRUCTION:
The main parts of this system are miniature video camera, a signal processor, and the brain implants. The patient should wear sunglasses with a tiny pinhole camera mounted on one lens and an ultrasonic range finder on the other. Both devices communicate with a small computer carried on his hip, which highlights the edges between light and dark areas in the camera image. It then tells an adjacent computer to send appropriate signals to an array of small electrodes on the surface of patient’s brain, through wires entering his skull. The electrodes stimulate certain brain cells, making the person perceive the specks of light. The shifting patterns as scans across a scene tells him where light areas meet dark ones, The tiny pinhole camera, mounted on a pair of [pic] eyeglasses, captures the scene in front of the wearer and sends it to a small computer on the patient’s belt. . The processor translates the image into a series of signals that the brain can understand, and then sends the information to the brain implant that is placed in patient’s visual cortex. And, if everything goes according to plan, the brain will “see” the image. WORKING:

Light enters the camera, which then sends the image to a wireless wallet-sized computer for processing. The computer transmits this information to an infrared LED screen on the goggles. The goggles reflect an infrared image into the eye and on to the retinal chip, stimulating photodiodes on the chip. The photodiodes mimic the retinal cells by converting light into electrical signals, which are then transmitted by cells in the inner retina via nerve pulses to the brain. The goggles are transparent so if the user still has some vision, they can match that with the new information. The device would cover about 10° of the wearer’s field of vision. The device provides a sort of tunnel vision, reading an area about the size of a card 2 inches wide and 8 inches tall, held at arm’s length.

RESULT:
Many people have shown positive response for this system. They are able to recognize faces and also able to read to some extent. The images appear in an field vision of 10°.

CASE STUDY :
|ARTIFICIAL SILICON RETINA (ASR). |MULTIPLE UNIT ARTIFICIAL SILICON RETINA CHIPSET (MARC). | |1. A chip made of silicon is implanted into the retina, no |1. An external device is required to capture and process the | |external device is required. |image. | |2. The chip mimics the function of retina. |2. A camera captures the image and is processed by a signal | | |processor. | |3. It is a simple mechanism, with basic blueprint being the human|3. It is a complex mechanism when compared to ASR. | |eye. |4. Implantation is comparatively easier as it involves mostly | |4. Implantation of the ASR is quite complicated. |external devices. |

The bionic devices tested so far include both those attached to the back of the eye itself and those implanted directly in the brain. Patients with both types of implants describe seeing multiple points of light and, in some cases, crude outlines of objects. Placing electrodes in the eye has proved easier.

BOTTLENECKS OF THE SYSTEM:
Even though the artificial vision system has made the impossible, possible, it is not affordable by a common man. The entire operation, equipment and necessary training cost $70,000 per patient. And also may be much higher depending upon the context and severity.

Since these devices take advantage of surviving parts of the eye they will help only the subset of blind people whose blindness is due to retinal disease, by some estimates about 30% of the blind. Moreover, scientists don’t believe any implant could help those blind since birth, because their brains never have learned to recognize vision. Also for people who were blinded by serious brain damage, or who have chronic infections, etc. this system won’t work out.

Even after years of research, the first wave will most likely provide only crude images, such as the outline of a kitchen doorway. It does not function as well as the real eye, and does not have crystal-clear vision (as it is only a camera).The device is a very limited navigational aid, and it’s a far from the visual experience normal people enjoy. ADVANCEMENTS:

Although the ASR is highly advantageous and effective, the silicon used in it is highly reactive as it cannot merge easily with the eye fluids and may damage the living cells in the eye. To overcome this, recently ceramic based retina chips are being developed which are proved to be neutral and hence doesn’t effect the eye tissues.

In MARC system, the field of vision which is pertained only to 10°, can be improved further. CONCLUSION:
The artificial vision system is the latest development in technological field aimed at helping millions of blind and visually impaired people. Although the images produced by the artificial eye were far from perfect, they could be clear enough to allow someone who is otherwise blind to recognize faces. Besides all this, still lot of research has to be done in developing the perception of the vision so that the images produced will be similar to that of a normal human being.