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Spring 2013 Undergraduate Problems ECE 491.016 Final Report

Eye:Evolution, Structure and Prosthesis

Juan J Faria Briceno

Center for High Technology Materials

The University of New Mexico

Advisor: Dr. Marek Osinski

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February 25, 2013

Table of Contents

1 Introduction............................................................................................................................................1

2 Evolution of the Eye..............................................................................................................................1

3 Human Eye Structure.............................................................................................................................5

3.1 Retina.............................................................................................................................................53.1.1 Photoreceptors, Fovea, Blind Spot.........................................................................................6

4 Birds Eye Structure................................................................................................................................7

5 Electronic Configuration Retina-Human Eye........................................................................................85.1 An Analog Silicon Retina Multichip Configuration......................................................................95.2 Virtual Retina...............................................................................................................................10

6 Retinal Prosthesis.................................................................................................................................116.1 Argus II........................................................................................................................................11

7 Conclusions..........................................................................................................................................13

8 Personal Comments.............................................................................................................................14

9 Cited Page............................................................................................................................................16

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1-IntroductionThis problem report will describe the investigation done during fall 2013 semester on the Eye. A deep understanding on anatomical terminology and electrical engineering devices is required to understand the topic researched. Evolution and structure requires knowledge of biological terminology; while electronic simulation and retinal prosthesis require an electrical engineering background. Most of my research was done through books and journals published between 1995 and 2012.

A review of evolution as it affects the eye was also part of my research. Living species have used the eye since the Paleozoic era as a mechanism to survive. In order to understand the modern eye, it is important to know the evolution process. As a result, this report includes an explanation of the ancient eye and vision, distribution and diversity of the eye, and improvement and obstacles of the eye as sub topic of the evolutionary process.

Biologically, the eye is a complex structure. Multiples components of the eye create the vision perception and the image processing; however, the retina is the main component in processing of the image. Photoreceptor and other important parts of the retina will be briefly describes in this report.

Many species use the eye as an organ to survive. Therefore, multiple structures have developed depending on the needs of the host. Multiple animals’ eyes will be described in this bulletin.

Electronic configurations and prosthesis of the retinal will be explained. For example, an Analog Silicon retina with Multichip configuration and a virtual biological retina will be explained while different retinal prostheses will be addressed as part of the problem report.

2- Evolution of the EyeThe book The Human Eye Structure and Function by Clyde W. Oyster was used to provide facts about the evolution of the eye. The Human Eye Structure and Function was published by Sinauer Associates, Inc at the University of Alabama at Birmingham on 1999. Oyster is a Professor in the Department of Physiological Optics of the School of Optometry at the University of Alabama, Birmingham, USA.

According to Charles Darwin, who established The origin of Species, “The eyes are organs of Extreme Perfection and Complication” (Oyster 1). Darwin is cited multiples times in Oyster book. Another quotes cited by Darwin in The Human Eye Structure and Function is, “The eye to this day gives me a cold shudder, but when I think of the known fine gradations, my reason tells me I ought to conquer the cold shudder” (Oyster 2). Darwin, according to oyster, was scared that the eye could have collapsed his theory on The Origin of Species. Obviously, eyes’ evolution is a complicated subject.

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This process of evolution depends on natural selection. All animal developed different eyes condition costume to their life conditions. What it is for sure is that the eye is older than what we imagine.

One reason why the eye’ evolution is hard to track is because they are made of H2O, bicarbonates, lactic acid, ascorbic acid, glucose and other chemical component that dissolve easily thru the years. Oyster said, “Soft tissues rarely fossilize, and we will never have a fossil record of the eye’s evolution” (3). However, there are other ways to proof the human eye evolution.

The first method used by Oyster to analyze the eye evolution is estimating the age of the earliest appearance of the eye. Second, Oyster explains the different ways that the eye appears in the animal kingdom tree to identify the ancient eye. Third and last, Oyster differences the eye surrounded by different species to identify its evolutionary problems.

Oyster estimated the age of the eye by evaluating different proteins. One protein on the eye that creates the process of the light-vision is opsin. Opsin is a protein can vary its structure; however, its three structures are always found to be the same. Oyster found in different structures of eye that this protein has been an important element on the eye evolution; therefore, opsin has been for more than 500 million years old in the evolution of the eye. Oyster also mentioned that all animals in the animal kingdom have conserved the molecule opsin.

Oyster not just proved in his book the origin of the eye in the animal kingdom but he also found the origin of the eye in multicellular animals. As he defined the eye, “An eye is a collection of cells specialized for light detection by containing photosensitive pigment along with a means of limiting the direction of incident light that will strike the photosensitive cell. This definition says nothing about image formation, lenses, eye movements, or any of the other features we associate with our own eyes […]” (Oyster 5). Oyster infers that eye is mainly an organ to detect light. Therefore, multicellular animals must have had it.

One multicellular animal mentioned in The Human Eye Structure and Function is Protozoan Euglena. This multicellular animal has an eye spot that detect the light. Also, according to Oyster, all the animals come from these multicellular animals. This multicellular animal called Protozoan Euglena is from the era Precambrian. Moreover, he mentioned that animal explosion occurred in an interval of 50 million years called Cambrian Explosion. As a result multiple animals have been identified.

Representation of the Protozoan Euglena Picture taken from LeydenScience.org

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According to Oyster, “[…] 530 million years old, a time shortly after Cambrian explosion; they were found on a mountainside in British Columbia in a deposit known as the Burgess Shale” (Oyster 6). These creatures who bellow to the animal kingdom are soft-bodied, lacking shells animals. The incredible thing about these animals is that some of them had eye which they can be considered the first formation of an eye in animal of the animal Kingdom. Oyster compares the eyes of Burgess Shale with the eyes of living crustaceans like crabs and shrimp. However, Burgess Shale is known as arthropods. Arthropods eyes are completely different from vertebrates’ eyes. By using this information we can infer that vertebrates’ eyes have been created later.

Eyes have arisen multiple times in different animals group. The diversity of the evolution of the eye is huge. Multiple structures have been created after the first design of the eye. Oyster explains this phenomenon with the animal kingdom tree. However, some of them do not have the same eye structure than generations before. One example to this fact is the arthropods eyes. They have been for more than 500 million years since the first animal took place in this world. Vertebrates’ eyes have a different configuration. This proves that the eye has been developed multiple times. Another example explained by Oyster is how two branches from the tree differ with their eye condition. Cnidaria and Ctenophora are two branches that come from the Radiata, but the Cnidaria, which example are jellyfish, have eyes. On the other hand, Ctenophora, which example is sea squirts, do not have eyes. Yet there is a big difference between Ctenophora and Cnidaria, one is a motile animal and the other is a non-mobile animal.

Why jellyfish has developed eyes and sea squirt not can be explained because their mobility necessities. Oyster explains that many animals do not develop the sign of vision because they do not live in condition of moving. For example, anemones which live in shallow water o coral reefs, however they develop other senses like taste and tactile.

Sensing of the incident of light was the first approach to the retina. Retina sends the first image processing to the brain. Retina will be well covered in the next subtopic. However, the first image processing is done by the Photoreceptors. They are photosensitive elements that are arranged differently as the direction of the incident light. Different retina configuration were developed through the years until now days.

Now, more than 3 different types of eyes can be distinguished (simple, compound, and optical superposition eyes), however we will focus in simple eye structure. Simple eyes have just one optical system and might have multiple photoreceptors. Simple eyes have 4 different sub configurations- pinhole, refracting terrestrial, refracting aquatic and reflecting. Oyster quote, “Vertebrates always have simple eyes […]” (13).

Vertebrates’ eyes are better depending on their size and their photoreceptors. How do we determine the size of the eye? The eye’ size depends on the size of the animal; As a matter of fact, the biggest eye in vertebrates is the baleen whale’ eye. Even though baleen whale has the biggest eye size, they don’t have the best vision. Actually, a bigger size of the eye has a bigger lens which will increase the capture of more light, but what it gives the best accuracy is the

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photoreceptors. Therefore, size of photoreceptors and size of the eye depend directly to each other for a better vision.

Evolution of the vertebrate’s eye has developed the number of photoreceptor and the size of the eye. Vertebrates rudimentary’ eyes were not capable of a detail full image. Therefore, the first step to increase the vision was by decreasing the receptor diameter and by increasing the receptor density. After a better picture was taken by the eye, the size of the eye increased. This increase helps to catch larger imaging in the retina. Also, small creatures can have good vision too.

Small in size animals have smaller eyes, however their eye’ size is larger relative to their body weight. Small size animals can have better vision than big mammals. The evolution of each animal depends on their own living conditions, so motility can be the key why some of them have improved better eyes vision.

Humans come from the order of primates which class is Mammalia. Our deep root in the animal kingdom tree is Chordata. As evolution said, humans come from the primates. Oyster mentioned, “[…] human eye and those of our closest relative (chimpanzees and gorilla) are almost negligible” (50). Human ancestors are around 30 million years old; Primates have lived for around 60 million years, so we can infer that the creation of the human eye is between 35 and 50 million years old. According to Oyster, “the first primates were small and nocturnal, and they began to flourish after the dinosaurs” (51). Nocturnal animals have more black and white vision photoreceptors (rods) than daylight photoreceptor (cones). This fact can explain why the humans have 95% more rods than cones in the retina.

Cones process daylight color vision. Cones are the photoreceptors in charge of the image processing during the day. However, how did humans improve color vision and high accuracy? Humans are diurnal animals. This can proved that humans come from the branch of diurnal primates. “Many primate species are still largely fruit eaters, and the basic idea is similar to the coevolution of flower and bees” (Oyster 51). The environment color were primates come from are likely to the three color cones that humans have (green, red and blue). The ability of recognizing fruits, trees and seed were the reason how humans have developed most likely those color.

The lens of the eye is in charge of the eye’s focusing. According to The Human Eye, “Fish deal with changer in object distance by moving the lens forward and backward along the eye’s optic axis, […] while our lens remains stationary” (Oyster 51). Obviously under the water objects are moving, so fish focus need to be moving in order to capture the world. While primates lived in condition that moving fast in a stationary frame is important.

Humans’ eyes are part of our fast mental, cultural, and physical evolution. Humans’ eyes are one of the weakest eyes in the all animal kingdom; however they are the reason why humans have developed fast. We are creature that have improved abilities to thing, reason, decide, react and create faster than any other animal in the kingdom. The combination of our eyes and brain has been the best design that has developed the ability of reasoning. Even though humans’ eyes are behind other eyes structure, humans have the ability to generate, create, and make different strategies to rich to the problem and solve it.

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3- Human Eye StructureVertebrates have eyes which are in charge of the light imaging process to create the sense of vision. Eyes have been an important organ in order to evolve. Including humans and any other motile animal are needed of having eyes in order to survive. The retina and any other information in this chapter will be cover by citing the book The Human Eye Structure and Function by Clyde W. Oyster, the Article Image modeling of the Eye by Acharya U. Rajendra, the article Projection of Rod and Cones Within Human Visual Cortex by Nouchine Hadjikhani and roger B. Tootell, and other credible sources.

The Eye’s components are cornea, sclera, limbus, anterior chamber, iris, pupil, choroid, lens, vitreous, and retina. All these components have an important role in order to have the final image that goes to the brain. However, the most important part of the eye that does imaging processing is called the retina.

Representation of the Eye Components Picture taken from LeydenScience.org

3.1- Retina

Retina is defined by Rajendra as “A thin layer of neural cells that lines the back of the eyeball of vertebrates and some cephalopods” (5). Its role is “detects light and tell the brain aspects of light that are related to objects in the world” (Oyster 545). Retina is a complex part of the eye that is in charge of converting light into neural signals. According to Rajendra, the retina can be denoted as a part of the central nervous system.

The retina has three main types of cells- photoreceptor, bipolar, and Ganglion Cells. These three main cells are in charge of most of the work done in the retina. Photoreceptors process the photons of the light. Then photoreceptors send that information to the bipolar cell. Bipolar cell and ganglion cell create a synapsis of the data that later is send to the brain thru the optic nerve.

Amacrine and bipolar are other cell in the retina. These cells are part of the image processing too. However, they depend of the three main cells to have action in the process.

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3.1.1-Photoreceptors, Fovea, and Blind spot

Photoreceptors are cells in the retina that are in charge of the first process of light. Oyster said, “The human retina is a thin sheet of tissue containing photo pigments […]” (549). These photo pigments are in charge of absorbing energy from photons. Oyster explains that the transfer of energy from photons to photo pigments is significant for vision. Photoreceptors contain this photo pigments. These photoreceptors are located in the most outer part of the retina. There are a proximally 105 millions of photoreceptors and they are divided in two kind rods and cones.

Rods process light in no color while cones process light in color. Rods are photoreceptors in charge of processing light during light during night. The reason why they are called rod is because of their structure. In the other hand, cones are photoreceptors that are in charge to process color light. They are mainly used during the day. Humans have three different cones photoreceptors- red, green, and blue.

Humans can identify the gamma color. Starting from 430nm the color purple can be identified by humans. The maximum wave form that human can detect is around 630-650 nm which can be consider Red. Some animals have other cones that can identify other range including Ultra violet and infrared colors.

Fovea is a small part of the retina where the distribution of photoreceptor varies. Fovea is a small spot in the retina that have a high density of cones and low density of rods. This spot of the retina is the place where the imaging process is mostly accurate. Fovea is “a pit that is the most sensitive to light and is responsible for our sharp central vision” (Rajendra 7). Fovea has a radius of 0.6° and has a diameter of 1.5 nm.

Distribution of cones and rod on the Retina, Picture taken from Projection of Rods and Cones Within Human Visual Cortex by Hadjikhani

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Visual Representation of the fovea inthe retina, Picture taken from The HumanEye Structure and Function by Oyster

The blind spot is a part of the retina where is lacking of photoreceptor. This part of the retina is also called optic nerve head. As shown in the graph the blind spot is place where there is not vision.

4-Birds Eye Structure

After learning the human eye, I have research other eyes structures. Many animals in the animal kingdom tree have developed different eyes structures. Some of them have improved better vision than humans. Birds are one of those groups of animals that have better vision. Likewise, bird of prey has developed an incredible eye structure.

Many characteristics make birds’ eyes better than humans. For example ratio cranium- eyes, frequency, number of photoreceptor, range of vision, numbers of fovea, and other features creates birds eyes better than humans’ eyes.

According to Jerry A. Waldvogel, who published The Bird’s Eye View, birds’ eyes can do other tasks. For instance, detecting the polarization and watching the flicker of a fluorescent lamp. In this following paragraph, I will explain why birds are considered better when vision is the topic.

Human eyes are small in ratio with the human cranium; while birds’ eyes are big in ratio with their cranium. Birds can have big eyes in comparison of their cranium size. According to Waldvogel, “[…] consuming a significantly greater fraction of cranial volume than the eyes of other vertebrates. In many birds the eyes appear small, but this is an illusion created by the fact that only a small portion of the corneal surface is exposed” (345). The ratio of the eyes-cranium makes a unique structure that allows them to have a better range of vision.

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Birds have a larger range of vision. Due to the fact that their eyes are big, birds have their eyes in the two sides of their cranium which open a big range of vision. This is why birds do not move their head and they still can look at you. This range is between -135° to +135°. Also, birds have two foveas on their retina.

As mentioned, fovea is the place on the retina where the image is more precise and clear in any structure of eyes and birds have two. Some birds’ retina is designed to have two foveas. According to Waldvogel, “Dual foveas in each eye allow the barn swallow to see clearly along more than one vision axis […] The additional foveas provide good monocular acuity at angles where human eyes offers only vague peripheral vision” (348). Birds can be looking straight to any subject and capture on the horizon any movement perfectly. This reason and more and unique photoreceptors on the retina are reasons why birds have better vision.

Some birds have two types of cones, one type of rod and higher density of retina cells. These two types of cones are single and double cones. Double cones capture higher range of color which allows them to have a better range on the color range. Also they have better density of retinal cells. Waldvogel mentioned in his article, “[…] almost all birds have a greater density of retinal cells than people do” (348). This fact of better density means of a better number of cells in the imaging processing which in the end translate as a better vision. By having more retinal cells, birds can see faster and slower movements.

Birds can see in higher frequency range than humans. Human can see at 60 Hz of frequency; while birds can see at frequencies higher than 60 Hz. Also, some birds can see movements at frequency higher than 100Hz. According to Waldvogel, “They can easily individual flashes of a fluorescent light bulb oscillating at 60 Hz. This sensitivity to motion is crucial for rapid flight, where miscalculation can be lethal” (349). Also, birds can see in slow motion. Also, “they are able to see the sun moving through its arc or the constellation rotating around the pole star” (Waldvogel 349).

All and all, birds have developed over the years a better eye structure. They are able to see well than other animals including humans.

5-Electronic Configuration Retina-Human Eye

As we mentioned in the evolution section, the eye is one of the hardest, confusing, and perfect organ of the human body. Many universities, researcher, and investigators have tried to simulate it. In this section, I will mention some electronic configuration done of the retina.

5.1 An Analog Silicon Retina with Multichip Configuration

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This publication was done by the IEEE on January 2006. The authors are named Seiji Kameda and Tetsuya Yagi. Both of them PHD, Kameda on computer science and system engineering from the Kyushu Institute of Technology, Japan and Yagi in Medical science from Nagoya University, Japan.

Kameda and Yagi simulated an analog retina by using multichip, transfer busses, sub tractor, and an FPGA board. The two chips (P-chip and H-chip) used in this simulation are based on the Retina components: photoreceptors layer and horizontal cells layer.

The first chip (P-chip) is integrated by three parts: active pixel sensor (APS), Resistive network (P-net) and wide range of amplifier and capacitors (Nbuf1).

Each of these three parts has their own tasks. The APS is in charge of processing the first image, “APS has a high sensitivity to light, by accumulating the photoelectron in the parasitic capacitor of the photo-diode” (Kameda and Yagi 198). Then the P-net is formed by MOS (Metal Oxide Semiconductor) resistors that smoothed the image. The MOS resistors can be controlled by external voltages. The range of the resistance is controlled by the ratio Width/ Large which will determine the number of pixels. Nbur1 is made to minimize the noise from the chip.

The second chip is integrated by three parts: The Analog Memory (AMem), a resistive Network chip (H net), and wide range of amplifier and capacitors (Nbuf2).

The Analog memory is in charge of storing the input of the P-chip. This memory is conformed to of “a capacitor and a voltage follower with a trans conductance amplifier” (Kameda 198). The current applied to the Memory is 0.45 µA. Then the voltage that is store is transferred through the H net of CMOS resistors; where the resistors are control by external voltages. The H-net and the Nbuf2 are the same of the P-chip.

These two chips connect by using parallel method, where parallel busses of 70 parallel lines transferred the output to the input of the next chip. The outputs and the inputs have buffer that helps to get rid of the noise. The buffers are supplied with currents of 50 µA. Transfer time between the chips oscillates between 0 and 100 µs. According to Kameda at all, “The Image processing can be carried out with externally applied controls signals- in this case, generated by the FPGA board” (199), this is the last stage of the processing image.

The P-chip and the H-chip are connected to a vertical shift register (VSR) and a horizontal shift register (HSR). “Each row of the output selected by the VSR of the P chip is transferred to a corresponding row of the H chip pixel array through the parallel bus. Outputs of the P and the H chips are read, pixel by pixel, by the VSR, and HSR” (Kameda 199).

This analog simulation of the retina was “implemented with a 0.6µm, double-poly, three-metal, standard CMOS technology and these die sizes were 8.9* 8.9mm2. The P and H chips have 70*80 pixels. The pixel area of these chips was 103.5*89.6µm. The photo diode area was 647.4-

µm2 (Kameda 201). The power that the P and H chips consume is 220mW at 3.3 V power supply. Kameda also mentioned, “The read time using a parallel method took only 91µs” (202).

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This Analog Silicon Retina can be used in different areas on research. Kameda said, “The advantage of the present multichip silicon retina is not limited to the improvement of pixel resolution. […] functions can be achieved with the multichip system by changing the control signal and the chip configuration” (205).

5.2 Virtual Retina: A biological retina Model and simulator, with contrast gain Control

This publication was dieone Adrien Wohrer and Pierre Kornprobst. Both of them are researcher from the Odyssee Project Team (INRIA/ENPC/ENS), INRIA-France. This project consists in the simulation of software called Virtual retina.

Wohrer and Kornprobst worked in the software that will simulate the Retina process by using videos. The software will transform a video into spike trains. The main purpose of this research was to simulate the retina recognition in a scale of 100,000 neurons processing.

As they mentioned in the document, “ More generally, the model keeps an architecture strongly related to retinal physiology, in a desire to reproduce specific effects which are functionally important, and often discarded by large scale models […]” (Wohrer 219). Models which are Non-separability, contrast gain control, adaptable band-pass, spike generation mechanism. However all of these models don’t represent all the cells simulation in the Retina.

The three main stages of this document are:

1- Linear Filter that reproduces the center surrounds architecture that take place in the processing of light between the photoreceptors and the horizontal cells.

2- This stage is the contrast gain control which is done by the bipolar cells in the retina.

3- The last stage is in charge of providing additional temporal shaping of the signal, and generates the process of the video.

In the first stage they assigned a scale from 0 to 255 of intensity that will help them to identify color received like the photoreceptors. The second stage, according to Wohrer, “ is an instantaneous, nonlinear contrast gain control through a variable feedback shunt conductance Ga(x,y,z), applied on bipolar cells” (221). The third stage model the signal as a simulation of the ganglion cells.

All this processing going from the incoming light, passing thru the photoreceptors and horizontal cells (Outer Plexiform Layer), then going thru the Contrast gain control, biologically bipolar cells; and finally being process in the ganglion cells will end into an output spikes which are going to create an image simulating the retinal process of imaging vision.

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The output signal gotten from this article is clearly effective. They separated the input signal, receptors, and horizontal cells, bipolar and on and off ganglion cells as different picture to compare how each of them creates an image.

6-Retinal ProsthesisThe eye, one of the most complex organs used by animals and humans, has been investigated for many years. Not just understanding the eye configuration, but creating a retinal prosthesis has been a hard task for scientist. Multiple universities around the world have tried to develop the closest prosthesis; however they are still far away of creating a similar simulation of the real Retina. For example, The Institute Dobelle at Columbia University is trying to develop artificial vision for blind people by connecting a camera to the visual cortex. Another group from China is trying to develop C-sight visual prostheses connected to the Optic Nerve with penetrating electrode array. Yet, the only world approved retina device is called Argus II.

Argus II Retinal Prosthesis System

As we mentioned in previous chapters, the first image processing is done in the retina specifically in the photoreceptors; place were the photons of light are convert to electrical impulses that connect with the optic nerve to the brain to create the vision. Retinitis pigmentosa is the disability of photoreceptors by processing photons of light. Argus two is used to help people that suffer from retinitis pigmentosa. If the patient suffers of another visual sickness, there is not a prosthesis that can help this situation yet.

All the information used in this sub chapter of the final report is supported by Second Sight Argus II Retinal Prosthesis System Patient Manual. Also, it was used to provide information An Integrated 256-Channel Epiretinal Prosthesis by Kuanfu Chen at all. The last article used to provide information is Reading Visual Braille with a Retinal Prosthesis by Thomas Z. Lauritzen at all.

Argus II is an epiretinal implant prosthesis that is implanted on the eye. The Argus II is divided in two main parts: internal and external. Internally, the Argus II is integrated by the electronics case, electrode array, and antenna. Externally, it is formed by VPU, camera, glasses, and

transmitter.

Visual representation of the Argus II internally. Picture taken from 2-sight.eu

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Visual representation of the Argus II, transmitter, glasses and antenna. Picture taken from 2-sight.eu

VPU is an external video processing unit that digitizes the signal from the mini camera located on the glasses. The VPU creates a series of stimulus pulses on a pixel gray scale. The pattern is later send through the antenna to the internal part of the Argus II. Glasses are used in other to hold the mini camera. The glasses also have the transmitter. The transmitter and the VPU are connected by using wires. After the VPU creates a series of stimulus pulses, that stimulus is sent to the transmitter which it is in charge, by wireless, to send the pattern to the antenna located internally in the eye.

The Antenna internally is connected to the electrode array by a bus. The bus is in charge of transmitting the signal to the electrode array which turn on by this pattern; representing the final image that the patient will identify as vision. The electrode array excites the other cell of the retina sending the message to the brain. The electrode array is connected by a metalized polymer cable that penetrates the sclera all the way to the retina where the array is located. A sclera band around the eye is what sustained the antenna and array.

The array of leds is located in the fovea, place where the eyes concentrate the best quality of picture, in order to provide to the patients a better image processing.

According to the business wire company, the results of the Argus II in 2011 were excellent. “96% of subjects improved in object localization […] 57% of subjects improved in motion discrimination […] 23% of the subject improved in the discrimination of oriented grating” (Second Sight 1).

Some of the objects that patients can recognize with the Argus II are letters, door, and simple symbols. However in other to be able to read long paragraphs and identify faces, it is necessary to use an array of 256 channels.

The Internal part of the Argus is provided by power through the transmitter. The transmitter which is located externally, send two different signals. The first signal is by coil induction between the VPU and the data receiver. The second one is the power transmitter which is in charge to provide enough power to keep the device working internally. By coin induction, the power transmitter can send signal of 100mW at 2 MHz frequency and up to 12Voltage DC. The Antenna internally controls by diodes the power supply depending of the task that is doing in the moment the device. All these specification can change according to the number of pixel used in the array.

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Many requirements and problems limited the Argus II of being perfect. The requirements for patients in other to get the Argus –

25 years or older

No vision or bare light perception on both eyes

Had the ability of see shapes before

Willing to be expose to surgery

Other regulations are mandatory in order to use the Argus II. The Argus II works uses coil induction to connect between the transmitter and the antenna; therefore, patients cannot be exposing to short wave or microwaves, MR, medical monitoring, monopolar electrosurgical equipment, high output ultra sound and others.

The surgery of the implant also can result-

Chest pain or heart attack

Respiratory failure

Infections

Urinary retention

Damage to the eye muscles

And other that can be fatal for the patient.

Argus II has been an innovation of technology for semi blind or blind people. However it still has a long path to develop better generation of prosthesis.

7-ConclusionsFrom evolution until the Argus II, one can realize how complicated the human eye is. As mentioned in this report initially, the eye is an organ hard to investigate. Obviously, the eye is probably one of the fewer organs in the body that haven’t been replaced. This is because its complicated evolution, structure and function.

The eye evolution is complicated. Especially because of its chemical components that disappear easily through time. However, by knowing the evolutionary process of the human eye multiples ideas can be used in order to know what could be the first step of designing the vision process in humans.

Moreover, the structure of the eye is necessary for any researcher or investigator in order to work in a device that will simulate the image processing of humans. Eye as organ is a complicated part of our body that is formed with the Retina. Place where the first photon of light is

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process/converted to an electrical signal to the brain. The information provided in this report can give an initial idea to work in a project related with it.

All types of animals in the tree differ in eyes structures. Some have better or worst vision; some might have bigger or smaller ball size. The important thing, information provided in the report, is to know why and how other creatures can see well. By using that data we can improve vision conditions in any electronically device of a retina.

Then the electronic simulations and prosthesis are helpful for us to connect what has been done on the field. By understanding what type of electronica simulations, we can determine how to improve it. As a result of this, in the next topic of this report, I will provide personal opinions of how can we create an electronic simulation of the eye.

8-Personal Comments Personally, Human eye has a lot of application in the future. Even though one needs a lot of knowledge to create or design real eye prosthesis, it is easy to come with multiple ideas of what kind of project can end in a successful project in bio-engineering.

If one do deep research of the difference of connection between the all the cell of the retina, and identifying the way that they interact to each other would be the first step. After being involved with the human eye for this semester, I can infer that some of the Cells won’t be part of a final result in prosthesis.

For instance, the human eye used the horizontal cell to identify a surrounded area that is not in the focus and horizontal cell highlighted during night, so one can have an idea of the shape of a object without focusing the a accurate picture of the object. Therefore, this would not be the first task that I would address as researcher.

I would focus more on the fovea which is fully made of cones and rods. I would concentrate in the rods and by creating a picture that can adapt to the specification of the human eye vision processing, we can end having a way of connecting the eye prosthesis and a human life.

Also ganglion cells are so complex that would be impossible to simulate them. Center surrounded on and off is one of the way how the retinal in this places process light. It would be impossible to create two different circuits that can connect to each other if initially we will concentrate on the fovea. When the image is coming from the fovea, the surrounded center of the ganglion cells is off which would be the first task that I would address.

One of the biggest challenges of creating prosthesis for humans is the acceptation of the human body in such a sensible place like the eye. So the materials that are going to be used in the elaboration of eye prosthesis have to be approved to be used in the human body. This task makes the all prosthesis as a really hard project to finish, however not impossible.

Moreover, this is all connected to the brain which creates small synapsis bonds between neurons that are in such small scale in the voltages. Creating a device, or a imaging processing of

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software would require busses of high transfer capacities which can complicate the size problem of creating a human eye prosthesis.

In the end, cameras have been so improved that challenging them would be a waste of time. As a result I would try to create a new device that will use Memristors in order to create a new device that will open new doors of super camera. As we know, Memristors can simulate neurotransmission data because of their analog characteristics.

Concluding that, the eye could have been an organ that evolves in a wrong way, so I would not worry about simulating the all image processing of the eye. I would concentrate on a device that can have similarities with the human eye and them connecting then in way that electronics and neurons can transfer image to the brain and people will have the ability to see.

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Human Brain Mapping, p. 55-63, Wiley, 2000.

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3. Oyster W, Clyde. The Human Eye Structure and Function. Sunderland, MA, USA: Sinauer Associates, Inc., 1999.

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