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Contact us at email@example.com Image Analysis for Automatically-Driven Bionic Eye F. Robert-Inacio1,2, E. Kussener1,2, G. Oudinet2 and G. Durandau2 1Institut Materiaux Microelectronique et Nanosciences de Provence, (IM2NP, UMR 6242) 2Institut Superieur de l’Electronique et du Numerique (ISEN-Toulon) France
1. Introduction In many ﬁelds such as health or robotics industry, reproducing the human visual system (HVS) behavior is a widely sought aim. Actually a system able to reproduce even partially the HVS could be very helpful, on the one hand, for people with vision diseases, and, on the other hand, for autonomous robots.
Historically, the earliest reports of artiﬁcially induced phosphenes were associated with direct cortical stimulation Tong (2003). Since then devices have been developed that target ùany different sites along the visual pathway Troyk (2003).These devices can be categorized according to the site of action along the visual pathway into cortical, sub-cortical, optic nerve ane retinal prostheses. Although the earliest reports involved cortical stimulation, with the advancements in surgical techniques and bioengineering, the retinal prosthesis or artiﬁcial retina has become the most advanced visual prosthesis Wyatt (2011).
In this chapter, both applications will be presented after the theoretical context, the state of the art and motivations. Furthermore, a full system will be described including a servo-motorized camera (acquisition), speciﬁc image processing software and artiﬁcial intelligence software for exploration of complex scenes. This chapter also deals with image analysis and interpretation.
1.1 Human visual sytem The human visual system is made of different parts: eyes, nerves and brain. In a coarse way, eyes achieve image acquisition, nerves data transmission and brain data processing (Fig. 1).
The eye (Fig. 2) acquires images through the pupil and visual information is processed by retina photoreceptors. There exist two kinds of photoreceptors: rods and cones. Rods are dedicated to light intensity acquisition. They are efﬁcient in scotopic and mesopic conditions. Cones are speciﬁcally sensitive to colors and require a minimal light level (photopic and mesopic conditions). There are three different types of cones sensitive for different wavelengths.
Fig. 3a shows the photoreceptors responses and Fig. 3b their distribution accross the retina from the foveal area (at the center of gaze) to the peripheral area. At the top of Fig. 3b, small parts of retina are presented with cones in green and rods in pink. This outlines that the repartition of cones and rods varies on the retina surface according to the distance to the
Fig. 1. Human visual system Fig. 2. Human eye center of gaze. Most of the cones are located in the fovea (retina center) and rods are essentially present in periphery. Then light energy data are turned into electrochemical energy data to be carried to the visual cortex through the optic nerves. The two optic nerves converge at a point called optic chiasm (Fig. 4), where ﬁbers of the nasal side cross to the other brain side, whereas ﬁbers of the temporal side do not. Then the optic nerves become the optic tracts. The optic tracts reach the lateral geniculate nucleus (LGN). Here begins the processing of visual data with back and forth between the LGN and the visual cortex.
1.2 Why a bionic eye?
Blindness affects over 40 millions people around the world. In the medical ﬁeld, providing a prosthesis to blind or quasi-blind people is an ambitious task that requires a huge sum of
Fig. 3. Rods and cones features knowledge in different ﬁelds such as microelectronics, computer vision and image processing and analysis, but also in the medical ﬁeld: ophtalmology and neurosciences. Cognitive studies determining the human behavior when facing a new scene are lead in parallel in order to validate methods by comparing them to a human observer’s abilities. Several solutions are offered to plug an electronic device to the visual system (Fig. 4). First of all, retina implants can
Fig. 4. Human visual system and solutions for electronic device plugins be plugged either to the retina or to the optic nerve. Such a solution requires image processing in order to integrate data and make them understandable by the brain. No image analysis is necessary as data will be processed by the visual cortex itself. But the patient must be free of pathology at least at the optic nerve, so that data transmission to the brain can be achieved. In another way, retina implants can directly stimulate the retina photoreceptors. That means that the retina too must be in working order. Secondly, when either the retina or the optic nerve is damaged, only cerebral implants can be considered, as they directly stimulate neurons. In this context, image analysis is required in order to mimick at least the LGN behavior.
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1.3 Why now?
The development of biological implantable devices incorporating microelectronic circuitry requires advanced fabrication techniques which are now possible. The importance of device stability stems from the fact that the microelectronics have to function properly within the relatively harsh environment of the human body. This represents a major challenge in developing implantable devices with long-term system performance while reducing their overall size.
Biomedical systems are one example of ultra low power electronics is paramount for multiple reasons [Sarpeshkar (2010)]. For example, these systems are implanted within the body and need to be small, light-weighted with minimal dissipation in the tissue that surrounds them.
In order to obtain implantable device, some constraints have to be taken into account such as:
• The size of the device
• The type of the technology (ﬂexible or not) in order to be accepted by the human body
• The circuit consumption in order to optimize the battery life
• The performance circuit The low power hand reminds us that the power consumption of a system is always deﬁned
by ﬁve considerations as shown on Fig.5:
Fig. 5. Low power Hand for low power applications
2. State of the art: Overview Supplying visual information to blind people is a goal that can be reached in several ways by more or less efﬁcient means. Classically blind people can use a white cane, a guide-dog or more sophisticated means. The white cane is perceived as a symbol that warns other people and make them more careful to blind people. It is also very useful in obstacle detection. A guide-dog is also of a great help, as it interprets at a dog level the context scene. The dog
is trained to guide the person in an outdoor environment. It can inform the blind person and advise of danger through its reactions. In the very last decades, electronics has come to reinforce the environment perception. On the one hand, several non-invasive systems have been set up such as GPS for visually impaired [Hub (2006)] that can assist blind people with orientation and navigation, talking equipment that provides an audio description in a basic way for thermometers, clocks or calcultors or in a more accurate way for audio-description that gives a narration of visual aspects of television movies or theater plays, electronic white canes [Faria (2010)], etc. On the other hand, biomedical devices can be implanted in an invasive way, that requires surgery and clinical trials. As presented in Fig. 4, such devices can be plugged at different spots along the visual data processing path. In a general way the principle is the same for retinal and cerebral implants. Two subsystems are linked, achieving data acquisition and processing for the ﬁrst one and electrostimulation for the second one.
A camera (or two for stereovision) is used to acquire visual data. These data are processed by the acquisition processing box in order to obtain data that are transmitted to the image processing box via a wired or wireless connection (Fig. 6). Then impulses stimulate cells where the implant is connected.
Fig. 6. General principle of an implant
2.1 Retina implant For retinal implants, there exist two different ways to connect the electronic device: directly to the retina (epiretinal implant) or behind the retina (subretinal implant). Several research
teams work on this subject worldwide. The target diseases mainly are:
• retinitis pigmentosa, which is the leading cause of inherited blindness in the world,
• age-related macular degeneration, which is the leading cause of blindness in the industrialized world.
2.1.1 Epiretinal implants The development of an epiretinal prosthesis (Argus Retinal Prosthesis) has been initiated in the early 1990s at the Doheny Eye Institute and the University of California (USA)[Horsager (2010)Parikh (2010)]. This prosthesis was implanted in patients at John Hopkins University www.intechopen.com Image Analysis for Automatically-Driven Bionic Eye Image Analysis for Automatically-Driven Bionic Eye 7 in order to demonstrate proof of principle. The company Second Sight1 was then created in the late 1990s to develop this prosthesis. The ﬁrst generation (Argus I) has 16 electrodes and was implanted in 6 patients between 2002 and 2004. The second generation (Argus II) has 60 electrodes and clinical trials have been planned since 2007. Argus III is still in process and will have 240 electrodes.
VisionCare Ophtalmic Technologies and the CentralSight Treatment Program [Chun (2005)Lane (2004)Lane (2006)] has created an implantable miniature telescope in order to provide central vision to people having degenerated macula diseases. This telescope is implanted inside the eye behind the iris and projects magniﬁed images on healthy areas of the central retina.
2.1.2 Subretinal implants At University of Louvain, a subretinal implant (MIVIP: Microsystem-based Visual Prosthesis) made of a single electrode has been developped [Archambeau (2004)]. The optic nerve is directly stimulated by this electrode from electric signals received from an external camera.
In the late 1980s, Dr. Joseph Rizzo and Professor John Wyatt performed a number of proof-of-concept epiretinal stimulation trials on blind volunteers before developing a subretinal stimulator. They co-founded the Boston Retinal Implant Project (BRIP). The collaboration was initiated between the Massachusetts Eye and Ear Inﬁrmary, Harvard Medical School and the Massachusetts Institute of Technology. The mission of the Boston Retinal Implant Project is to develop novel engineering solutions to restore vision and improve the quality-of-life for patients who are blind from degenerative disease of the retina, for which there is currently no cure. Early results are actually a reference for this solution. The core strategy of the Boston Retinal Implant Project 2 is to create novel engineering solutions to treat blinding diseases that elude other forms of treatment. The speciﬁc goal of this study is to develop an implantable microelectronic prosthesis to restore vision to patients with certain forms of retinal blindness. The proposed solution provides a special opportunity for visual rehabilitation with a prosthesis, which can deliver direct electrical stimulation to those cells that carry visual information.
The Artiﬁcial Silicon Retina (ASR)3 is a microchip containing 3500 photodiodes, developed by Alan and Vincent Chow. Each photodiode detects light and transforms it into electrical impulses stimulating retinal ganglion cells (Fig. 8).
In France, at the Institut de la Vision, the team of Pr Picaud has developed a subretinal implant [Djilas (2011)]. They have also set up clinical trials.
As well, in Germany [Zrenner (2008)], a subretinal prosthesis has been developed. A microphotodiode array (MPDA) acquires incident light information and send it to the chip located behind the retina. The chip transforms data into electrical signal stimulating the retinal ganglion cells.
In Japan [Yagi (2005)], a subretinal implant has been designed at Yagi Laboratory4.
Experiments are mainly directed to obtain new biohybrid micro-electrode arrays.
1 2-sight.eu/ 2 http://www.bostonretinalimplant.org 3 http://optobionics.com/asrdevice.shtml 4 http://www.io.mei.titech.ac.jp/research/retina/
Fig. 7. BRIP Solution Fig. 8. ASR device implanted in the retina At Stanford University, a visual prosthesis5 (Fig. 9) has been developed [Loudin (2007)].
It includes an optoelectronic system composed of a subretinal photodiode array and an infrared image projection system. A video camera acquires visual data that are processed and displayed on video goggles as IR images. Photodiodes in the subretinal implant are activated when the IR image arrives on retina through natural eye optics. Electric pulses stimulate the retina cells.
In Australia, the Bionic Vision system6 consists of a camera, attached to a pair of glasses, which transmits high-frequency radio signals to a microchip implanted in the retina. Electrical impulses stimulate retinal cells connected to the optic nerve. Such an implant improves the perception of light.